AAMD 41st Annual Meeting

Poster Abstracts

Analysis of inhomogeneous dose distribution using Volumetric Modulated Arc Therapy (VMAT) for prostate, GBM, and lung patients and the effect on organs at risk
Stacy Peterson

The University of Texas MD Anderson Cancer Center

Abstract:
Analysis of inhomogeneous dose distribution using Volumetric Modulated Arc Therapy (VMAT) for prostate, GBM, and lung patients and the effect on organs at risk

Stacy Peterson, Pasquale Montanaro, M.S., DABR

Purpose: The following study provides an analysis on the difference in dose to normal tissue and organs at risk when limits on dose homogeneity in the target volume are changed.

Methods and Materials: The study used the Pinnacle planning system and VMAT to plan four separate plans for each disease site: prostate, GBM, and lung, each to the prescribed dose. The prescribed dose for each prostate plan was 79.2 Gy/44 fractions. The planning target volume was created by adding a margin of 5 mm to the gross tumor volume. The GTV received 100% of the prescribed dose and the PTV received 98% of the prescribed dose in each plan. The prescribed dose for each GBM plan was 60 Gy/30 fractions. The GTV received 100% of the prescribed dose, the CTV received 98% of the prescribed dose, and the PTV received 95% of the prescribed dose in each plan. The prescribed dose for each lung plan was 63Gy/35 fractions and the planning target volumes varied for each patient. Each plan was examined after the maximum dose allowed was escalated from approximately 105% to 120% of the prescribed dose while maintaining equivalent coverage of the tumor volume for each plan. The maximum dose constraint was then relaxed and priority was given to lowering the dose to normal tissue. The critical structures for each plan were analyzed using data from the dose volume histograms. Metrics used in the evaluation of stereotactic planning will were used for the evaluation of the resulting dose distributions. These include R100 and R50, which are the ratio of the 100% isodose line and 50% isodose line to the planning target volume respectively.

Results: The data for each of the nine plans indicated that as the maximum dose constraint was relaxed the R50 (50% isodose line to the planning target volume) increased, and as a result dose to critical structures and normal tissue decreased. The structures that are pertinent for analysis for the prostate plans are the rectum, urethra, bladder, and femoral heads. The structures that will be analyzed for the GBM plans include the spinal cord, brainstem, right and left orbits, right and left optic nerves, cochlea, optic chiasm, and right and left lenses. The structures that will be analyzed for the lung plans include the heart, both lungs, spinal cord, and esophagus.

Conclusion: When the maximum dose constraint within the PTV was relaxed, the resulting dose distribution exhibited lower doses to the contoured organs at risk, and to normal tissue in general.

Keyword(s): VMAT, Inhomogeneous, Prostate, Glioblastoma, GBM, Lung, Organs at risk

The reader should describe the effect on critical structures when limits on dose homogeneity in the target volume are changed.

The reader should describe how metrics used in the evaluation of stereotactic planning can also be used in the evaluation of resulting dose distributions in VMAT planning.

The reader should describe the effects of the 50% isodose line to the planning target volume escalating in dose as the maximum dose constraint is relaxed.


Efficient delivery of MLC-based grid therapy using a flattening filter free beam
Christopher Beyer
Certified Medical Dosimetrist
Henry Ford Health System

Abstract:

Purpose: To compare and improve upon the efficiency of multi-leaf collimator (MLC) based grid therapy using a flattening filter free (FFF) beam versus a traditional flattened beam. Grid therapy has been proven to be a simple yet effective treatment for bulky tumors but the extended treatment times have a greater risk for intrafraction motion. This study aimed to reduce the treatment time by utilizing a high dose rate FFF beam on the Varian TrueBeam treatment machine, while maintaining comparable plan quality with the regular MLC based grid therapy.

Methods: Five patients were included in this study. Two MLC based grid therapy treatment plans were created for each patients: a FFF 10x treatment plan manually flattened with a field in field technique (FinF) and a flattened 10x treatment plan. The grid sizes were 1cm by 1cm with 1 cm spacing. The dose rates were 2400 MU/min for the FFF beam and 600 MU/min for the flattened beam. Treatment plans were created for treatment sites including head and neck, breast, and extremity.  All treatment plans were created in the commercial Treatment Planning System and delivered on a Varian TrueBeam System with Millennium 120 MLC. Treatment plans were prescribed 15 Gy at depth of 2.0cm in one fraction.

Results: Preliminary data from the 5 cases revealed that the FFF plans were more efficient at delivering MLC-based grid therapy.  Although as a result of FinF, the FFF plans yielded about 36%±22% higher amount of MU, due to the high dose rate of 10xFFF beam, the average beam-on time was significantly reduced by 200%±60% (7.9±3.6 minutes vs. 2.82±1.49 minutes, p<0.01). The FFF plans showed a slightly higher global maximum dose of 1.08±0.91Gy. The valley to peak ratio was 11% and 15% for the FFF plans and flat beam plans respectively.

Conclusion: The preliminary results showed that the treatment time can be significantly reduced in MLC-based grid therapy using FFF beams.  More efficient treatment delivery can potentially reduce the risk of intrafraction motion and increase patient satisfaction.

  1. FFF mode provides much greater efficiency over traditional beam for Grid Therapy
  2. FFF plans can achieve the same plan quality as traditional beam Grid Therapy plans
  3. An increase in MU's does not necessarily equate to longer beam on time

Single-Fraction versus Multi-Fraction Radiotherapy in Palliative Bony Metastasis Patients: Comparison of Primary Malignancy and Demographic Factors
Kristen Vu
Educational Coordinator
Grand Valley State University

Abstract:
Introduction

The intent of this study is to analyze Medicare billing data to discover the differences in patients that are treated with single-fraction and those treated with multi-fraction treatments for the treatment of bony metastases. The factors investigated are the overall number of single versus multiple fraction treatments, primary malignancy, age, gender, race and region in which patients live. The key issues studied are the Radiation Oncologists patterns of utilization of single or multi-fraction treatment.

Methods and Materials

Radiation therapy treatment billing claims for bony metastasis from Medicare beneficiaries in 2014 were analyzed. Beneficiary inclusion criteria included ICD-9 code 198.5 (Secondary Neoplasm of Bone Metastases) and a radiation treatment delivery code 77401-77416. The delivery codes were counted for frequency on consecutive days (one per day and with no more than 3 days off in-between) to determine the total number of days treated. Descriptive statistics were used to summarize and describe the data found.

  1. The reader should be able to describe the three standard dose fractionations of palliative bony metastases most commonly prescribed.
  2. The reader should be able to describe what patient population most commonly receives the single-fraction prescription.
  3. The reader should be able to describe why single-fraction treatment is recommended by ASTRO for most patients.

The dosimetric benefits of voluntary deep inspiration breath hold, V-DIBH, treatments for left breast irradiation
Jamie Christ
Student Dosimetrist
Southern Illinois University Medical Dosimetry Program/Rush University Medical Center

Abstract:

Background: Adjuvant radiation therapy is the standard of care for women following breast-conserving surgery for breast cancer.  Whole breast radiation therapy is typically delivered using two opposed tangential beams. To deliver adequate dose to the breast tissue, portions of the cardiac structures and left lung also receive low doses of radiation due to their proximity to the chest wall. V-DIBH treatment is a technique in which patients hold their breath on inspiration during beam delivery. V-DIBH can be used to reduce dose to the cardiac structures, such as the cardiac ventricles and whole heart. During deep inspiration, the heart is pushed posteriorly and inferiorly from the chest wall, increasing its distance to the radiation fields. The goal of this study is to determine the dosimetric benefits of V-DIBH, expressed as the reduction in dose to the cardiac ventricles, heart, and left lung in comparison to the dose that would be received if the patient were to be treated utilizing standard free breathing (FB) technique.

Methods and Materials: 14 left-sided breast cancer patients that have undergone tangent beam radiation to the whole breast using v-DIBH were retrospectively selected. Each patient had undergone an initial CT simulation. During the simulation, the patient was scanned once using a FB pattern and again using V-DIBH technique. Plans were developed on the V-DIBH scan. These optimized plans used to treat with V-DIBH were transferred and registered to the FB image set. A visual inspection was performed for each case and the dose distribution on the FB scan was considered clinically acceptable. The DVHs for the heart, cardiac ventricles and left lung were extracted for both breathing modalities and processed outside of the treatment planning system. Average, minimum and maximum DVHs were generated for each modality and organ at risk.  Mean heart dose, the volume of the left lung receiving 20Gy (V20) the mean dose to the cardiac ventricles and the volume cardiac ventricles receiving 25Gy (V25) and 35Gy (V35) respectively were tabulated for each modality. The samples were compared using a t-test: two-sample assuming unequal variances statistical analysis.

Results: The composite average DVHs for the cardiac ventricles, heart and left lung shows significantly lower dose using V-DIBH treatment modality compared with FB. Compared with FB plans the V-DIBH plans show a reduction of the mean dose to the cardiac ventricles of 212 cGy (207cGy versus 419 cGy). The statistical analysis shows the following results: the average dose to the cardiac ventricles is reduced by about 130 cGy (p=0.045), V25 by 2.5% (p=0.038), and V35 by 1.5% (p=0.048). For the heart, the mean dose was reduced by 70 cGy (p=0.049) while for the left lung the dose was reduced by 7% (p=0.032).

Conclusions: The benefits of using V-DIBH technique translate into statistically significant dosimetric and theoretical clinical benefits for the cardiac structures as well as the ipsilateral lung.

  1. The reader should be able to answer what effect voluntary deep inspiration breath hold, V-DIBH, technique has on the position of the heart in relation to the treatment beams.
  2. The reader should be able to describe the effect of V-DIBH versus free breathing technique on the mean dose to the cardiac ventricles.
  3. The reader should be able to describe the effect of V-DIBH versus free breathing technique on the mean dose to the heart.

Auto-Planning: A Dosimetric comparison of Phillips Pinnacle Auto-planning tool for Lung, Brain, Abdomen, Head and Neck, and Prostate treatment sites.
Hasti Hesami

University of Texas MD Anderson Cancer Center

Abstract:
Auto-Planning: A Dosimetric comparison of Phillips Pinnacle Auto-planning tool for Lung, Brain, Abdomen, Head and Neck, and Prostate treatment sites.

Hasti Hesami, Amalia Flores, Sanya Makahani, Ancy Mathew, Elizabeth Medrano, Hirra Siddiqui, Peter Balter, PhD, Jordan Sutton, CMD

Medical Dosimetry Program, School of Health Professions, The University of Texas, M,D, Anderson Cancer Center, Houston, Texas, USA.

ABSTRACT

The purpose of this study is to evaluate the dosimetric differences between Phillips Auto-planning tool and the clinically approved and treated Volumetric Modulated Arc Therapy (VMAT) plans for multiple treatment sites. A total of thirty patients, six from each site, are re-optimized using identical plan parameters as the previously treated physician approved plans. The Auto-plans are generated by inserting the dose and normal tissue constraints as requested per physician’s planning directive for each patient. The Auto-plan trials are optimized once and the plan differences are evaluated by comparing the target volumes, organs at risk (OARs), monitor units (MU), and dose conformality to determine overall plan quality. Our results indicate that Auto-planning can generate a clinically acceptable treatment plan based on the parameters that are initially set. The target coverage and organs at risk are achieved in most cases. A greater difference is noticed for more complex treatment sites, such as head and neck and lung. High isodose conformality is reduced compared to clinically approved plans in these cases. On average, the trials created for Auto-planning show less monitor units as opposed to the clinically approved plan. Initial plan creation by Philips Auto-planning tool is shown to produce clinically treatable plans, however further optimization would be advantageous.

Keywords: Phillips Pinnacle, Auto-planning, VMAT

  1. The reader should compare the target coverage, OAR dose, integral dose, and monitor units (MUs) for Volumetric Arc Therapy (VMAT)-Auto-plans to already treated and approved clinical VMAT plans.
  2. The reader will be able to conclude that Auto-planning is an acceptable starting point for further optimization and will save planning time.
  3. The reader will find that the auto-planning tool can
  4. decrease (MUs) by decreasing the possible over-optimization that can occur by the planner.

Preservation of normal brain tissue in patients with multiple metastatic lesions using gamma knife radiosurgery
Marissa Tranquilli
Student
Roswell Park Cancer Institute

Abstract:

Traditionally, patients with metastatic brain lesions have been treated using whole brain radiotherapy (WBRT).   More recently, studies have suggested that treatment with stereotactic radiosurgery (SRS) alone may result in preservation of neurocognition, with no change in overall survival.  The total volume of brain treated may be directly linked to neurocognitive decline, therefore SRS may help preserve patient quality of life by sparing as much normal tissue as possible.  Standard practice has been to favor WBRT if more than four metastatic lesions are present; however, in recent years SRS has been safely used for patients with 10 or more lesions.    Here, we analyze the volume of normal brain tissue treated using gamma knife radiosurgery in patients with varying numbers of brain metastases (from one to twenty nine).   The purpose of the study is to re-evaluate the appropriate number of brain lesions for which SRS may be useful in terms of sparing normal brain tissue, and therefore potentially improving patient quality of life.

Materials and Methods

Approximately 500 patients with brain metastases (of any primary) treated with gamma knife radiosurgery at a single institution were identified using a database search.  Using the patient’s pre-gamma knife MRIs, brain tissue was segmented as accurately as possible using Eclipse software and then exported into the Gamma Knife planning system.   For each plan, the following data points were recorded: total brain volume, number of lesions treated, volume of brain receiving 8 Gy (V8), V10, V12, and V15.  Volume of brain treated was analyzed as a function of number of lesions, as well as total lesion volume.

Results

Using the V12 data set as indicative of the overall results, the volume of brain treated did not correlate with number of lesions treated.  Similar statistics existed for the V8, V10, and V15 data sets. The volume of brain treated did correspond, however, with the total volume of the brain metastases. These relationships are clearly demonstrated through the graphical data representations.

Conclusions

The number of metastatic brain lesions does not correlate with total brain volume treated when using stereotactic radiosurgery (SRS).  Although standard practice has favored using WBRT in patients with greater than 4 lesions, a significant amount of normal brain tissue may be spared by treating these patients with SRS.   This may translate into preservation of neurocognition and quality of life.  SRS should be carefully considered in patients with multiple brain lesions as an alternative to WBRT, with the emphasis on total brain volume involved rather than the number of lesions.

  1. The reader should be able to identify and describe previous WBRT and SRS brain treatment paradigms.
  2. The reader should understand the correlation between number of metastases treated and the volume of brain treated.
  3. The reader should be able to discuss which situations would show preference to SRS  over WBRT.

Dosimetric Comparison Between Pinnacle3 Auto-Planning and Manual Planning for Lung SBRT Treatments
Aaron Bishop

University Texas Health Science Center San Antonio

Abstract:
Introduction:  Stereotactic body radiation therapy (SBRT) has become an effective treatment option for early stage and small metastatic lung tumors. Due to plan complexity with SBRT, traditional, inverse optimized IMRT planning may be time consuming and the quality of plans is likely to vary with the skill and experience of the planner. Auto-Planning, a new functionality developed by Pinnacle3, has been made commercially available with Version 9.10. Auto-Planning is a tool that automates and facilitates inverse optimization of treatment plans. Benefits of Auto-Planning are based on planning efficiency improvements and standardization of plan quality. The aim of this study is to dosimetrically compare the treatment plan quality of Auto-Planning against previously approved clinical plans.

Methods and Materials:  Nine (n=9) lung SBRT patients previously treated using a non-coplanar, 6 MV fix-field IMRT technique with a 120 HDMLC Novalis Tx were replanned in Pinnacle3 (v9.10) with Auto-Planning. Patient plans were normalized to 5000 cGy in 5 fractions such that at least 98% of the PTV received 100% of the prescription dose. The same beam geometries were used for Auto-Planning as the clinical plan. An Auto-Planning template, derived from previously treated patients, was developed based on optimized planning objectives and TG101 dose tolerances to critical structures. The template was applied to all patients. Metrics used for comparison were the dose fall-off (RX = VX%/Vptv) at the 70%, 50%, and 30% isodose lines, conformation number (CN), and homogeneity index (HI = D0.2cc / D98%).  Statistical differences were evaluated using a paired sample Wilcoxon signed rank test with significance level of 0.05.

Results: For the dose fall-off of parameters, a mean percentage difference improvement of 1.6%, 0.4% and 2.9% was found for the R70, R50 and R30, respectively, using Auto-Planning—however no statistically significant difference was noted. The conformation number and homogeneity index showed a mean percentage difference of 2.73% and 4.73%, respectively—no statistically significant difference was noted between Auto-Planning and clinical plans.  Additionally, Auto-Planning did show an increase, on average, of 7.94% (p<0.05) in total monitor units over clinical plans.

Conclusions:  Based on the comparison metrics evaluated, Auto-Planning appears to generate SBRT treatment plans for lung lesions of similar treatment plan quality to the manually optimized, clinical plans. No statistically significant differences were note for the majority of the target dosimetric parameters. Statistically significant differences were only noted in the total treatment plan monitor units. 

  1. To study Pinnacle's Auto-Planning System.
  2. To study planning for Lung SBRT.
  3. To compare Auto-Planning with manual treatment planning.

Evaluating Treatment Plan Quality between Manual Planning and Auto-Planning in Patients with Prostate and Seminal Vesicle Irradiation
Tyler Marston
Student
Department of Radiation Oncology, The University of Texas Health Science Center at San Antonio

Abstract:
Evaluating Treatment Plan Quality between Manual Planning and Auto-Planning in Patients with Prostate and Seminal Vesicle Irradiation                           

T Marston, B.Sc., TY Eng, M.D., D Baacke, B.Sc., N Kirby, Ph.D., N Papanikolaou, Ph.D., AN Gutierrez, Ph.D.          

Department of Radiation Oncology, University of Texas Health Science Center San Antonio, San Antonio TX

INTRODUCTION: Auto-Planning is a tool that automates and facilitates inverse optimization of treatment plans. Benefits of Auto-Planning are based on planning efficiency improvements and standardization of plan quality. With this in mind, the purpose of this treatment planning study is to dosimetrically assess the quality of Auto-Planning plans generated for patients receiving treatment of the prostate and seminal vesicles for low-/intermediate-risk prostate cancer. The primary objective is to compare the quality of Auto-Planning treatment plans against previously approved clinical treatment plans.

METHODS AND MATERIALS: Fifteen (n=15) patients previously treated to the prostate and seminal vesicles using a VMAT technique were replanned with Auto-Planning. All patients were planned in Pinnacle3 (Version 9.10) using single or dual SmartArc plans with either 6 or 10 MV photon energies. Plan settings were equivalent for each patient for both clinical and Auto-Planning. Plans were prescribed to 7920cGy and normalized such that 95% of the PTV received at least 100% of the prescription dose. A template for Auto-Planning was initially developed using the dose constraints to critical structures from QUANTEC. A final template was adjusted based on the preliminary test results of six patients. Patients were evaluated for PTV and organ at risk (OAR) parameters for the bladder, rectum, sigmoid, penile bulb, and femoral heads. Metrics used for PTV comparison were D2cc, homogeneity (HI = D2cc / DRx), conformity (CN), and dose fall-off (Rx = Vx% / VPTV) for the 70%, 50%, and 30% isodose lines. OAR metrics included D2cc and DMEAN along with specific volume based constraints for the bladder and rectum per QUANTEC.

RESULTS: For the PTV, a decrease in the mean percentage difference of 1.7% (p<0.05) was noted in the CN as well as an increase in HI of 1.4% (p<0.05) and total plan MUs of 20.6% (p<0.05) for Auto-Planning. No statistically significant differences were noted for the other PTV parameters. For OARs, statistically significant reductions in the DMEAN of all structures, decrease in the D2CC of the sigmoid of 18.1% (p<0.05), and decrease in the V65Gy of 4.7% (p<0.05) and V50Gy of 11.4% (p<0.05) for the rectum were noted with Auto-Planning. Statistically significant increases in the mean percentage difference in the D2cc of 1.7% (p<0.05) and V80Gy of 21.8% (p<0.05) for the bladder, and D2cc increase of 1.4% (p<0.05) for the rectum was shown.

CONCLUSIONS: The study showed that Auto-Planning produces plans of comparable quality to clinical plans based on the evaluated metrics for the sample of patients studied. Clinical plans showed better homogeneity and less total plan MUs. Auto-Planning had lower average doses (DMEAN) for all critical structures.

  1. To improve IMRT planning efficiency
  2. To standardize treatment plan quality
  3. To test Pinnacle's new Auto-Planning feature

Investigating the Dosimetric Differences between Manual Planning and Auto-Planning in Patients with Prostate and Pelvic Lymph Nodes Irradiation
Aziz Lirani
UTHSCSA

Abstract:

INTRODUCTION: Volumetric modulated arc therapy (VMAT) is now a common technique used in irradiating cancer of the prostate and pelvic lymph nodes due to its improved delivery efficiency over conventional IMRT. However, VMAT planning requires a consistent, proficient, and time-consuming effort from the planner to obtain an optimal plan. Auto-Planning, a new functionality developed by Pinnacle3, has been made commercially available with Version 9.10. Auto-Planning is a tool that automates and facilitates inverse optimization of treatment plans. Benefits of Auto-Planning are based on planning efficiency improvements and standardization of plan quality. The aim of this study is to dosimetrically compare the treatment plan quality of Auto-Planning against previously delivered clinical plans.

METHODS AND MATERIALS: Ten patients (n=10) who were previously treated with a dual or triple arc, 6 MV VMAT technique to the prostate and pelvic lymph nodes were re-planned using Auto-Planning in Pinnacle3 (v9.10). Auto-Planning plans were created with the same beam geometry, isocenter, and dose grid as the clinical plan. An Auto-Planning template was created and utilized for all of the plans. Plans were subsequently modified with a maximum of three warm-starts to further enhance the plan. Both clinical and Auto-Planning plans were normalized such that 95% of the PTV received at least 100% of the prescription dose. Patients were evaluated for PTV and organ at risk (OAR) parameters for the rectum, bladder, sigmoid, small bowel, penile bulb, and the right and left femoral heads. Metrics used for comparison were Dmean, D2cc, homogeneity (HI), conformity (CN), dose fall-off (R50), and total monitor units (MUs) for the PTV, and Dmean, D2cc, V80%, V60%, V40%, and V20% for the OARs. Statistical differences were evaluated with a paired-sample Wilcoxon signed rank test with a significance level of 0.05.

RESULTS:

For the PTV, statistically significant improvements in the median percentage difference of 2.0% were noted for both D2cc and HI for Auto-Planning plans. An increase in the median percentage difference of R50 of 6.5% (p<0.05) was noted for Auto-Planning. With regards to the OARs, all structures except the penile bulb, had a statistically significant reduction in Dmean. The bladder and femoral heads showed an improvement in D2cc. The rectum, bladder, sigmoid, and small bowel all showed improvement in the V40%.

CONCLUSIONS:

Auto-Planning generates similar, if not better, treatment plan quality as compared to previously delivered clinical plans for VMAT based pelvic irradiation based on the metrics evaluated in this study. Auto-Planning appears to facilitate the treatment optimization process all the while making the overall planning process less laborious and time consuming.

  1. To collect and organize clinical data
  2. To become familiar with the Auto-Planning technique
  3. To evaluate the research critically and compare new data with prior findings

Evaluation of Quality and Delivery of Head and Neck treatment plans created with Pinnacle Auto-Plan technique
Kalpana Vaidya
Senior Dosimetrist
Northwell Health system

Abstract:
Evaluation of Quality and Delivery of Head and Neck treatment plans created with Pinnacle Auto-Plan technique

Purpose: This study is to assess the quality and feasibility of selected head and neck treatment plans generated with the Auto-planning module in Pinnacle treatment planning system. The dosimetry and delivery of the Auto-plan VMAT and IMRT after initial optimization were retrospectively compared with previously treated plans.

Materials and Methods: 10 patients with oropharyngeal or hypopharyngeal cancers were reviewed to test the consistency of the Pinnacle auto planning function.  Pinnacle v9.10 auto-plan module was used to generate VMAT (2 Arcs) and IMRT (9 fields) head and neck plans based on the adapted RTOG protocol dosimetric requirements  for target coverage as well as organ at risk (OAR) sparing. Treatment planning CTs were taken with Siemens Somatom AS CT scanner in supine, head-first position using a custom aquaplast immobilization mask. Alignment tattoos were given at the time of simulation. CT images had slice spacing of 3 mm. All the plans were constructed with concurrent boost technique of 3 dose levels of 70, 63, and 58/54Gy corresponding to average volumes of 125, 510 and 256cc respectively. All plans were calculated with grid size of 4mm. These plans were compared with dosimetrist generated plans for dose distribution and delivery assessment.

Results and Discussion: The auto-plans were performed with minimal manual interaction. The planning time required for initial optimizing iteration for each VMAT Auto-plan was between 110 to 120 minutes, each IMRT Auto-plan required 30 to 60 minutes. The delivery time and monitor units decreased for VMAT Auto-plan and increased for IMRT Auto-plan compared with plans constructed manually. The following criteria was used to assess dose distribution: 95% of target volume achieves greater than 95% of prescribed dose and  mean dose to larynx and  both parotids  as well as spinal cord max dose.  VMAT and IMRT dosimetry was verified using a 2D chamber array (PTW-Octavius1500), with a 3mm, 3% distance to agreement passing criteria, which indicated the plans were deliverable clinically. There was consistent coverage of the PTV and not a significant difference or improvement in the sparing of critical structures like the parotids or larynx when Auto-plan VMAT and IMRT was compared to previously treated IMRT plans for the oropharynx and hypopharynx.

Conclusion: Auto-plan function was demonstrated to be consistent and feasible for producing clinically acceptable plans. One benefit offered by auto planning is time saving in user’s initial preparation of optimization process by creating structures which otherwise proved to be time consuming if done manually. Auto-plan’s initial optimization achieved an equivalent outcome for beginner or advanced skilled dosimetrists which can help an institution’s standardization process. For complex head and neck cases, clinical adoption of the Auto-plan may require more iterations by dosimetrists, may increase in monitor units and delivery to obtain optimal results. In conclusion, Auto-plan is a reasonable method for the initial optimization of cancers of the oropharynx and hypopharynx.

  1. Describe the importance, purpose and process of utilizing Pinnacle Auto-plan module in Radiation Medicine treatment planning.
  2. Appreciate the importance of standardization amongst multi-skilled dosimetrists.
  3. Save time for dosimetrists initial preparation of VMAT or IMRT treatment plans.

Tradeoffs for setting up isocenter at the time of simulation versus during treatment planning for LINAC-based isocentric radiotherapy
Jayesh Mistry
CERTIFIED DOSIMETRIST
John Theurer Cancer Center at Hackensack University Medical Center

Abstract:
Tradeoffs for setting up isocenter at the time of simulation versus during treatment planning for LINAC-based isocentric radiotherapy

Purpose

Treatment plan isocenter can be setup during simulation (SIM-Iso). No shifts are needed on the day of treatment, however this requires physician’s presence. Another approach utilizes a pre-mark set while the isocenter is setup at the time of planning with known shifts from the pre-mark (PLAN-Iso). For this approach physician presence is not required.. There are pros and cons to using either approach but one way of comparing these two is to evaluate which leads to a better setup on the day of treatment. This was the purpose of our work.

Methods

This was a retrospective study based on two sets of previously treated patients, one with isocenter based on SIM-Iso and the other based on PLAN-Iso. For each patient, we analyzed the first port films acquired after the therapists’s setup. By comparing the port films with the expected reference DRR, we calculated the residual setup error based on each technique.  

Results

A total of 12 treatment deliveries were analyzed, 6 for each technique. For the SIM-iso category, the average residual setup error was 0.18 ± 0.16cm, range (0.00 – .40cm) in SI, 0.20 ± 0.21cm, range (0.00 – 0.50cm) in AP, and 0.17 ± 0.15cm, range (0.00 – 0.40cm) in LR direction. The corresponding average residual setup error for the PLAN-iso category were 0.18 ±0.20cm, range (0.00 – 0.50cm) in SI, 0.17 ± 0.17cm, range (0.00 – 0.40cm) in AP, and 0.17 ± 0.15cm, range (0.00 – 0.40cm) in LR direction.  

Conclusions

The study shows that the residual errors in both techniques are very comparable. This means that one could take advantage of the PLAN-iso approach that does not require physician’s presence with the satisfaction that the shift information would be correctly interpreted and implemented during delivery. This is only a preliminary study. More patients need to be analyzed before any final conclusions can be made.

  1. 1. An opportunity to learn about the pros and cons of   SIM-iso versus PLAN-iso technique.
  2. Provide the Physician with an assessment to guide them towards choosing the appropriate technique.
  3. Introduces the audience to different techniques of isocenter placement.

Evaluating Treatment Plan Quality and the Dosimetric Differences between Pinnacle3 Auto-Planning and Manual Treatment Planning in Brain Cancer Patients
Brianna Zehren
Dosimetry Student
Department of Radiation Oncology, University of Texas Health Science Center at San Antonio

Abstract:
Introduction: Treatment plans for brain cancer patients tend to be complex in nature. There are many organs at risk (OAR) that can have significant consequences if over-irradiated.  Additionally, the Planning Treatment Volume (PTV) could be wrapped around more than one OAR, thus making it difficult to maintain coverage of the PTV while sparing healthy tissue. The Pinnacle3 Auto-Planning feature allows for PTV coverage while minimizing the dose to OARs. The purpose of this study was to compare and evaluate the quality of treatment plans for brain tumors using Pinnacle3 Auto-planning versus manual treatment planning.  

Methods and Materials: Eight patients (n=8), with varying types of brain tumors, were previously planned using a dual arc 6MV VMAT technique in Pinnacle3 TPS (Version. 9.10, Philips Medical, Fitchburg WI). The patients were replanned using the Pinnacle3 Auto-Planning feature with two SmartArc beams utilizing a full arc. An Auto-Planning template was created with the same beam geometry, isocenter, and dose grid as the clinical plan.  This method created Planning Risk Volumes (PRVs), which are 3mm expansions of the OAR. Dose parameters used were in accordance with QUANTEC dose constraints. All plans were normalized so that 95% of the PTV received 100% of the prescription dose. Patients were evaluated for PTV and OAR parameters for the brain, brain stem, optic chiasm, right eye, left eye, right optic nerve, left optic nerve, right and left cochleas. Metrics for comparison used were D2%, D98%, homogeneity index (HI = D2% - D98% / Dmean), conformity index (CN), and fall-off (R25 = PIV25%/PTV, where PIV25% = isodose volume of 25% prescription dose) for the PTV and Dmax (0.03cc) and Dmean for OARs. Statistical differences were evaluated with a paired-sample Wilcoxon signed rank test with a significance level of 0.05.

Results: For the PTV, there was no statistically significant differences in the HI or the R25 fall-off, but the CN showed an improvement of 7.44% (p<0.05) with the Auto-Plan over the manual plan. For the OARs, Dmax to the brain stem was 7.02% lower with the manual plan (p<0.05), Dmean to the right optic nerve was on average 33.51% (p<0.05) lower with the auto-plan, Dmax and Dmean to the left optic nerve was 45.24% (p<0.05) and 28.79% (p<0.05) lower with the auto-plan. The Dmax to the right cochlea and the spinal cord were also lower for the auto-plan by 26.54% (p<0.05) and 18.21% (p<0.05).  There were no significant findings concerning the brain, brainstem, optic chiasm, the left cochlea or eyes.

Conclusions: Treatment planning employing auto-planning produces similar, if not better plan quality as compared to previously delivered clinical plans for VMAT based pelvic irradiation based on the metrics evaluated in this study.  The use of auto-planning makes the planning process less time consuming and less planner dependent.

  1. Learning to do research and statistical analysis on data
  2. Evaluation of the capabilities of Pinnacle3 Auto-planning feature
  3. Improving research presentation skills

A Dosimetric Comparison of 3D-CRT, ECOMP, and Hybrid IMRT Plans for Prone Whole Breast Irradiation
Haley Lowe

Roswell Park Cancer Institute

Abstract:
A Dosimetric Comparison of 3D-CRT, ECOMP, and Hybrid IMRT Plans for Prone Whole Breast Irradiation

Haley Lowe, Rachel Hackett, C.M.D., Kilian Salerno, M.D., Iris Wang, Ph.D.

Abstract

Purpose: To evaluate and compare 3D-CRT, electronic tissue compensation (ECOMP), and hybrid IMRT plans for prone whole breast irradiation in the treatment of early-stage breast cancer.  Literature describes 3D-CRT and hybrid IMRT planning for prone whole breast irradiation, but the use of ECOMP has not been reported on. 

Materials and Methods: Plans from patients who had undergone breast conservation surgery and adjuvant radiation in the prone position were eligible for comparison. Patients were simulated on a specialized prone breast board and computed tomography imaging obtained.  Treatment plans were generated in Varian Eclipse 11 for each patient. The original ECOMP plan was compared to a new 3D-CRT plan using wedges, and hybrid IMRT plans (using a technique where 2/3 of the daily dose would be delivered via 3D-CRT with wedges, and the remaining 1/3 dose with forward planned IMRT). Prescription dose was 40 Gy in 15 fractions to the whole breast.  Dose constraints for the IMRT component were:  >95% and <107% of dose to the 90% isodose line from the 3D plan, maximum <100% to the ipsilateral lung, and a maximum <7.5% dose to <10% of the heart volume. The whole breast was to be covered by the 95% isodose line. All plans were designed to achieve a low maximum dose while maintaining dose homogeneity.  Target and normal tissue dose constraints were compared. The DVH of each plan was analyzed and used to determine maximum breast dose, V20 of the ipsilateral lung, and mean heart dose.  Three comparison plans were designed and evaluated for 20 patients, 10 right sided and 10 left sided. 

Results: Evaluation of comparison plans found, the global maximum dose for all patients was reduced while maintaining dose homogeneity using both ECOMP and hybrid IMRT when compared to 3D-CRT.  The maximum dose reduction using hybrid IMRT averaged a 1.3 Gy dose reduction compared to 3D-CRT planning (Figure 1).  No difference in ipsilateral lung V20 was seen between the different planning techniques (Figure 2).   Mean heart dose was reduced in the ECOMP and hybrid IMRT plans compared to the 3D-CRT plans. Mean heart dose was significantly reduced using ECOMP (Figure 3).  There was no correlation found between the breast volume and maximum dose, ipsilateral lung V20, or mean heart dose (Figure 4). 

Conclusion: Use of prone position for whole breast radiotherapy may achieve a significant reduction in lung and heart radiation dose when compared to traditional treatment in the supine position.  Treatment delivery with ECOMP or a hybrid IMRT technique can further reduce heart and lung dose compared to 3D-CRT with wedges.  Additionally, hybrid IMRT provides a significant reduction in maximum breast dose.   However, planning ECOMP further decreases the mean heart dose while maintaining a relatively low maximum dose. 

  1. Describe three different treatment planning techniques for prone whole breast irradiations. 
  2. Enumerate the benefits and drawbacks of prone whole breast irradiation treatment plans using 3D-CRT vs. ECOMP vs. hybrid IMRT techniques.   
  3. Compare the different modalities when creating a plan for the left vs. right breast using prone whole breast radiation. 

Rationale and technique for dose escalation around prostate fiducial markers to compensate for dose shadowing using pencil beam scanning proton therapy.
Joseph Simmons

Provision Center for Proton Therapy

Abstract:
Purpose/Objective: In the treatment of prostate cancer, high-density fiducials are commonly utilized to visualize and align the prostate during image guided radiation therapy. Studies have shown that, in proton therapy, these high-density fiducials can cause dose shadowing. The purpose of this abstract is to explain the rationale used for dose escalation using proton therapy around prostate fiducials and demonstrate a technique with pencil beam scanning. Methods: For treatment of the prostate gland, our clinic utilizes three Gold Anchor 0.4x10mm fiducials, implanted into the gland at 3 strategic positions. Care is taken at the time of fiducial placement to implant the fiducials at least 1cm away from the prostate capsule/rectal interface. With respect to proton beam dosimetry, the Gold Anchors are optimally implanted if they are in a straight line, perpendicular to the incident proton treatment beam. The fiducial placement is evaluated on the AP and lateral scout views from the CT simulation, and linear measurements are taken of each fiducial in the superior to inferior directions. If the measured fiducial is less than 6mm in length, then it is considered to be in a semi crumpled/folded position and dose escalation in the direction of the proton beam is warranted to mitigate a potential cold dose shadow. During the optimization process, this expanded volume around the fiducial is prescribed 5% higher dose than the prescription, generating an escalated dose around the fiducial.

Results: Using the described technique, we are able to generate treatment plans that meet all of the clinical goals for the target and organs at risk. We are able to compensate for dose shadowing around the fiducial by escalating the dose around the fiducial that is implanted in a crumpled/folded position. Because the fiducials are implanted at least 1cm from the prostate/rectal interface, the subsequent escalated dose does not add additional rectal dose compared to not escalating the dose around the fiducials.

Conclusions: For prostate gland treatments utilizing high-density fiducials implanted in a crumpled/folded position, pencil beam scanning proton therapy gives us the opportunity to optimize treatment plans and compensate for potential dose shadowing by escalating the dose to a focal point around the fiducial. In principle, a similar technique could be used in other areas of the body, if there is concern of dose shadowing.

  1. Learn background of fiducial  based prostate proton therapy.
  2. Learn impact of fiducial perturbation on proton dose distribution.
  3. Learn technique of mitigation of fiducial perturbation on proton dose distribution.

Correlation of Transmission Penetration Depth with varying gradient of the breast when using Irregular Surface Compensators
Luxshan Shanmugarajah
Roswell Park Cancer Institute

Abstract:
Introduction: The purpose of this study is to determine the correlation of transmission penetration depth with varying gradient of the breast contour in 3-D.  Irregular surface compensation is a planning technique available on the Eclipse treatment planning system where it utilizes dynamic multileaf collimators to compensate for irregular body surfaces, a technique useful for breast radiotherapy.  These dynamic multileaf collimators create a fluence which can be modified to a deliver a homogeneous dose distribution.  In determining the depth of compensation, a transmission penetration depth (TPD) is chosen by the user.  Some institutions may use a standard TPD for every breast plan, while others may measure maximum breast size to determining the appropriate TPD.  To choose the optimal TPD the whole breast must be taken into account, including the variation of the breast anatomy in 3-D.

Methods/Materials: In this retrospective study, ten breast patients treated with two tangential fields were analyzed to see the effects of the gradient changes in the breast anatomy along the superior-inferior direction.  First part of the study involved the creation of triangular water phantoms with varying contained angles (10°-65°) to simulate varying slopes of the breast anatomy.  6 MV tangential fields were optimized based on Homogeniety index (HI) and maximum hot spot within the phantoms to determine the optimal TPD value.    As the contained angle of the triangular phantom decreased the TPD increased.  A graph was generated with the values found from the phantoms and points in between were interpolated.  The following trend was used as a guideline to choose the TPD for the ten breast patients.  A standard TPD, chosen by best overall distribution, was used to compare with the angle based TPD.  Contained angles were measured for each of the tangential fields (medial and lateral) for each patient to determine the optimal TPD value at the superior, middle, and inferior sections. 

Results: The maximum dose for each section, dose mean and homogeneity index within the irradiated breast volume were analyzed.  For the ten patients studied, the angle based TPD technique yielded a lower average dose maximum of 103.6% within the irradiated volume than the standard TPD technique, which gave an average dose maximum of 105.2%.  The clinical target volume (CTV) received an average minimum and a mean dose of 95.8% and 101% respectively with the angles based technique, where as the standard technique yielded a minimum and a mean dose of 95.7% and 100.9% respectively.  The angled based technique also yielded lower HI value of 7.6 than the standard technique (HI value of 9.5), indicating that the angle based technique provided better homogeneous plans than the standard technique. 

Discussion/Conclusion: From studying the trend generated from the phantoms, a clear correlation can be noted between the TPD and the breast angle/slope.  For shallower breast angles, a greater TPD showed to have a better dose distribution.  For all patients both the superior and inferior chest wall coverage improved.  This trend can be used as a guideline during planning to get a better dose distribution.

  1. The reader should be able to identify an optimal TPD based on the angle measured from the chest wall to apex of breast when using irregular surface compensators.
  2. The reader should be able to assess breast anatomy by looking at each field (medial and lateral) independently rather than as a whole.
  3. The reader should be able to compare different methods of selecting optimal TPD (standard TPD, measuring breast separation, measuring angle) and particularly evaluate overall chest wall coverage for superior and inferior.

Impact on Lung Dose in Left Breast Radiotherapy Patients with Deep Inspiration Breath Hold vs. Free Breathing Technique
Lili Vijeh
Northwell Health

Abstract:
Purpose/Objectives:

This study evaluates lung dose for deep inspiration breath hold (DIBH) vs. free breathing (FB) technique in patients with left-sided breast cancer.

Materials/Methods:

This is a retrospective study of 20 patients with left-sided breast cancer who underwent radiation therapy to evaluate for ipsilateral lung dose between the use of DIBH technique and FB. At the simulation, CT images were acquired with DIBH as well as FB, in two separate scans. The variation of chest motion was assessed by image fusion and overlay of the image data sets. This identified whether the patient would be benefited with DIBH technique. The treatment plans were constructed using forward planning for tangential field setup for both CT image sets. The coverage of PTV and dose to ipsilateral lung were evaluated and compared. A comparison of the ipsilateral lung volume receiving 20% of prescription dose (V20) was used to show if there were any dosimetric advantages using the DIBH technique.

Results:

Upon comparing the two CT simulated images, the difference in the height of vertical distance yielded a range from 0.3 to 1.9 cm. This measurement corresponded to the change of the vertical (anterior-posterior) distance at the medial border between DIBH and FB images. The results indicated that V20 of the ipsilateral lung in patients with a vertical distance range of 1.9 cm to 0.8 cm was 9% to 36% lower for the DIBH plans compared to the FB plans. For patients with a vertical distance range of 0.8 cm to 0.3 cm, the difference between DIBH and FB plans was less significant, as expected. The V20 of the ipsilateral lung DIBH plans were 0 to 22% lower in comparison to the FB plans.

Conclusions:

These results indicate that treating left-sided breast cancer patients with DIBH technique yields dosimetric advantages. With a deeper inspiration, which yields a greater difference in the height of the vertical distance, the dose to the ipsilateral lung can be reduced significantly. Hence, in order to reduce lung dose further, patients should be instructed to attempt deeper inhalation.

Key Words: Deep inspiration breath hold, Free breathing, Lung

  1. The reader should describe the dosimetric advantages of using deep inspiration breath hold technique vs. free breathing.
  2. The reader should describe the process of how to measure the variation in chest motion between deep inspiration breath hold and free breathing scans.
  3. The reader should describe how larger vertical chest motion distance increases lung volume, and thereby reduces ipsilateral lung dose.  

Quantification of Interfractional Motion of Organs at Risk in Liver Stereotactic Body Radiation Therapy
Gwendolyn Deger

Massachusetts General Hospital

Abstract:
Background: Previous studies have addressed the respiratory effects on motion of patients receiving Stereotactic Body Radiation Therapy (SBRT) to liver targets (see sources 1-2 supporting documentation). We sought to quantify the additional impact of interfractional motion caused by gastrointestinal processes (sources 3-4).

Methods: Liver SBRT at Massachusetts General Hospital begins with a two-day radiation mapping session yielding two consecutive days of CT scans. Only the CT scan taken on the second day of mapping, called the primary scan, is used to develop the final radiation plan. Our target liver SBRT population consisted of 6 patients with two consecutive days of CTs, and one patient with two months between CT scans. Effects of motion on non-involved organs at risk (OARs) were measured. The primary scan was utilized to determine Planning Risk Volume (PRV) expansions of the stomach, duodenum, small bowel, and hepatic flexure. At Massachusetts General Hospital, a 0.5 cm PRV expansion is used for gastrointestinal OARs in Liver SBRT cases. The efficacy of an isotropic PRV expansion of 0.5 cm was tested using the secondary CT scan (the first day of CT scans) as a sample for range of motion for OARs during the standard five fractions of liver SBRT. Following contouring and treatment planning, fiducials near the target were used to guide fusions of the primary and secondary scans. The centroid of the portion of the secondary OAR outside the PRV is compared to the centroid of the target to indicate if the non-accounted for volume is near the high dose region.  The dose delivered to each OAR was compared between scans as a ratio of secondary scan metric value for a relevant constraint to primary scan metric value for the same constraint (secondary:primary). For RTOG Protocol constraint objectives, see Table 2 in the Data Sheet Supplement.

Results: For the stomach and hepatic flexure, the secondary constraint value was 10% and 21% less than the primary constraint value. In contrast, for the small bowel and duodenum, the secondary constraint value was 11% and 138% greater than the primary constraint value.

Conclusions: For the duodenum and small bowel, an isotropic 0.5 cm PRV may not be sufficient. Daily dose variability along specific OAR borders can potentially be minimized by using a variable PRV expansion or other planning tools. For liver SBRT patients with multiple suitable CT simulations, minimum necessary patient-specific abdominal organ PRVs can be calculated using organ border information.  Analyzing a larger cohort of patients may yield a generally applicable PRV expansion that better represents interfraction gastric organ motion.

  1. The reader should have an awareness of possible non-respiratory abdominal organ motion.
  2. The reader should understand that gastrointestinal processes can affect abdominal setup and interfractional dose delivery.
  3. The reader should understand the advantages and disadvantages of using a standard isotropic planning risk volume compared with patient-specific planning risk volume based on multiple days of imaging information.

Evaluation of Minimum Aperture Segment Size vs Plan Quality in IMRT Treatment Planning
Marissa Garza

University of Texas MD Anderson Cancer Center-School of Health Professions

Abstract:
The influence of aperture segment sizes on Intensity Modulated Radiation Therapy (IMRT) treatment planning quality are significant from both a treatment delivery and a maintenance standpoint. Smaller sized apertures used in IMRT planning are known to be difficult to maintain due to the dependence on the accuracy of the small mechanical features in the treatment unit. Smaller multi-leaf collimators (MLCs) require a large quantity of intricate machinery to operate effectively. This study aims to measure the accuracy and validity of using larger IMRT segments, which could lead to machine development with larger MLC widths. The project involves five unilateral head and neck and five prostate IMRT treatment plans. The head and neck cases will be treated to 60 Gy in 33 fractions and optimized using 2, 4, 6, and 8 cm² minimum aperture segment sizes. The prostate IMRT treatment plans will be treated to 78 Gy in 39 fractions and optimized using 4, 6, 8, and 10 cm² minimum aperture segment sizes. These two sites were selected for their differences in field size and complexity. Pinnacle 9.10v will be used for all planning purposes. The head and neck cases will be evaluated using the 2cm² minimum segment area as the benchmark plan, while a 4cm² minimum segment area will serve as the benchmark plan for the prostate cases. Data will be collected for critical structures and target areas for all cases and their aperture sizes. The results show the use of larger aperture segment sizes may lead to less machine usage and possible future machine development using larger MLCs with a continued adherence to quality.

  1. The reader will be able to explain how increasing the segment size area in IMRT can affect the accuracy of target coverage and sparing of critical structures.
  2. The reader will able to describe how changing the segment size area in IMRT affects plan conformality.
  3. The reader should describe how treating with an increased segment size area will aid in reducing treatment cost.