skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: SU-F-T-132: Variable RBE Models Predict Possible Underestimation of Vaginal Dose for Anal Cancer Patients Treated Using Single-Field Proton Treatments

Abstract

Purpose: Anal cancer patients treated using a posterior proton beam may be at risk of vaginal wall injury due to the increased linear energy transfer (LET) and relative biological effectiveness (RBE) at the beam distal edge. We investigate the vaginal dose received. Methods: Five patients treated for anal cancer with proton pencil beam scanning were considered, all treated to a prescription dose of 54 Gy(RBE) over 28–30 fractions. Dose and LET distributions were calculated using the Monte Carlo simulation toolkit TOPAS. In addition to the standard assumption of a fixed RBE of 1.1, variable RBE was considered via the application of published models. Dose volume histograms (DVHs) were extracted for the planning treatment volume (PTV) and vagina, the latter being used to calculate the vaginal normal tissue complication probability (NTCP). Results: Compared to the assumption of a fixed RBE of 1.1, the variable RBE model predicts a dose increase of approximately 3.3 ± 1.7 Gy at the end of beam range. NTCP parameters for the vagina are incomplete in the current literature, however, inferring value ranges from the existing data we use D{sub 50} = 50 Gy and LKB model parameters a=1–2 and m=0.2–0.4. We estimate the NTCP for themore » vagina to be 37–48% and 42–47% for the fixed and variable RBE cases, respectively. Additionally, a difference in the dose distribution was observed between the analytical calculation and Monte Carlo methods. We find that the target dose is overestimated on average by approximately 1–2%. Conclusion: For patients treated with posterior beams, the vaginal wall may coincide with the distal end of the proton beam and may receive a substantial increase in dose if variable RBE models are applied compared to using the current clinical standard of RBE equal to 1.1. This could potentially lead to underestimating toxicities when treating with protons.« less

Authors:
; ; ;  [1]
  1. Massachusetts General Hospital & Harvard Medical School, Boston, MA (United States)
Publication Date:
OSTI Identifier:
22642373
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; COMPUTERIZED SIMULATION; FEMALE GENITALS; MONTE CARLO METHOD; NEOPLASMS; PATIENTS; PROTON BEAMS; RADIATION DOSE DISTRIBUTIONS; RBE

Citation Formats

McNamara, A, Underwood, T, Wo, J, and Paganetti, H. SU-F-T-132: Variable RBE Models Predict Possible Underestimation of Vaginal Dose for Anal Cancer Patients Treated Using Single-Field Proton Treatments. United States: N. p., 2016. Web. doi:10.1118/1.4956268.
McNamara, A, Underwood, T, Wo, J, & Paganetti, H. SU-F-T-132: Variable RBE Models Predict Possible Underestimation of Vaginal Dose for Anal Cancer Patients Treated Using Single-Field Proton Treatments. United States. doi:10.1118/1.4956268.
McNamara, A, Underwood, T, Wo, J, and Paganetti, H. Wed . "SU-F-T-132: Variable RBE Models Predict Possible Underestimation of Vaginal Dose for Anal Cancer Patients Treated Using Single-Field Proton Treatments". United States. doi:10.1118/1.4956268.
@article{osti_22642373,
title = {SU-F-T-132: Variable RBE Models Predict Possible Underestimation of Vaginal Dose for Anal Cancer Patients Treated Using Single-Field Proton Treatments},
author = {McNamara, A and Underwood, T and Wo, J and Paganetti, H},
abstractNote = {Purpose: Anal cancer patients treated using a posterior proton beam may be at risk of vaginal wall injury due to the increased linear energy transfer (LET) and relative biological effectiveness (RBE) at the beam distal edge. We investigate the vaginal dose received. Methods: Five patients treated for anal cancer with proton pencil beam scanning were considered, all treated to a prescription dose of 54 Gy(RBE) over 28–30 fractions. Dose and LET distributions were calculated using the Monte Carlo simulation toolkit TOPAS. In addition to the standard assumption of a fixed RBE of 1.1, variable RBE was considered via the application of published models. Dose volume histograms (DVHs) were extracted for the planning treatment volume (PTV) and vagina, the latter being used to calculate the vaginal normal tissue complication probability (NTCP). Results: Compared to the assumption of a fixed RBE of 1.1, the variable RBE model predicts a dose increase of approximately 3.3 ± 1.7 Gy at the end of beam range. NTCP parameters for the vagina are incomplete in the current literature, however, inferring value ranges from the existing data we use D{sub 50} = 50 Gy and LKB model parameters a=1–2 and m=0.2–0.4. We estimate the NTCP for the vagina to be 37–48% and 42–47% for the fixed and variable RBE cases, respectively. Additionally, a difference in the dose distribution was observed between the analytical calculation and Monte Carlo methods. We find that the target dose is overestimated on average by approximately 1–2%. Conclusion: For patients treated with posterior beams, the vaginal wall may coincide with the distal end of the proton beam and may receive a substantial increase in dose if variable RBE models are applied compared to using the current clinical standard of RBE equal to 1.1. This could potentially lead to underestimating toxicities when treating with protons.},
doi = {10.1118/1.4956268},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = {Wed Jun 15 00:00:00 EDT 2016},
month = {Wed Jun 15 00:00:00 EDT 2016}
}
  • Purpose: To examine how much lifetime attributable risk (LAR) as an in silico surrogate marker of radiation-induced secondary cancer would be lowered by using proton beam therapy (PBT) in place of intensity modulated x-ray therapy (IMXT) in pediatric patients. Methods: From 242 pediatric patients with cancers who were treated with PBT, 26 patients were selected by random sampling after stratification into four categories: a) brain, head, and neck, b) thoracic, c) abdominal, and d) whole craniospinal (WCNS) irradiation. IMXT was re-planned using the same computed tomography and region of interest. Using dose volume histogram (DVH) of PBT and IMXT, themore » LAR of Schneider et al. was calculated for the same patient. The published four dose-response models for carcinoma induction: i) full model, ii) bell-shaped model, iii) plateau model, and ix) linear model were tested for organs at risk. In the case that more than one dose-response model was available, the LAR for this patient was calculated by averaging LAR for each dose-response model. Results: Calculation of the LARs of PBT and IMXT based on DVH was feasible for all patients. The mean±standard deviation of the cumulative LAR difference between PBT and IMXT for the four categories was a) 0.77±0.44% (n=7, p=0.0037), b) 23.1±17.2%,(n=8, p=0.0067), c) 16.4±19.8% (n=8, p=0.0525), and d) 49.9±21.2% (n=3, p=0.0275, one tailed t-test), respectively. The LAR was significantly lower by PBT than IMXT for the the brain, head, and neck region, thoracic region, and whole craniospinal irradiation. Conclusion: In pediatric patients who had undergone PBT, the LAR of PBT was significantly lower than the LAR of IMXT estimated by in silico modeling. This method was suggested to be useful as an in silico surrogate marker of secondary cancer induced by different radiotherapy techniques. This research was supported by the Translational Research Network Program, JSPS KAKENHI Grant No. 15H04768 and the Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, founded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.« less
  • Purpose: RapidPlan uses a library consisting of expert plans from different patients to create a model that can predict achievable dose-volume histograms (DVHs) for new patients. The goal of this study is to investigate the impacts of model library population (plan numbers) on the DVH prediction for rectal cancer patients treated with volumetric-modulated radiotherapy (VMAT) Methods: Ninety clinically accepted rectal cancer patients’ VMAT plans were selected to establish 3 models, named as Model30, Model60 and Model90, with 30,60, and 90 plans in the model training. All plans had sufficient target coverage and bladder and femora sparings. Additional 10 patients weremore » enrolled to test the DVH prediction differences with these 3 models. The predicted DVHs from these 3 models were compared and analyzed. Results: Predicted V40 (Vx, percent of volume that received x Gy for the organs at risk) and Dmean (mean dose, cGy) of the bladder were 39.84±13.38 and 2029.4±141.6 for the Model30,37.52±16.00 and 2012.5±152.2 for the Model60, and 36.33±18.35 and 2066.5±174.3 for the Model90. Predicted V30 and Dmean of the left femur were 23.33±9.96 and 1443.3±114.5 for the Model30, 21.83±5.75 and 1436.6±61.9 for the Model60, and 20.31±4.6 and 1415.0±52.4 for the Model90.There were no significant differences among the 3 models for the bladder and left femur predictions. Predicted V40 and Dmean of the right femur were 19.86±10.00 and 1403.6±115.6 (Model30),18.97±6.19 and 1401.9±68.78 (Model60), and 21.08±7.82 and 1424.0±85.3 (Model90). Although a slight lower DVH prediction of the right femur was found on the Model60, the mean differences for V30 and mean dose were less than 2% and 1%, respectively. Conclusion: There were no significant differences among Model30, Model60 and Model90 for predicting DVHs on rectal patients treated with VMAT. The impact of plan numbers for model library might be limited for cancers with similar target shape.« less
  • Purpose: To evaluate the point dose variations between Ir-192 HDR treatments on two consecutive days using a single tandem-ovoid insertion without replanning in cervical cancer patients. Methods: This study includes eleven cervical cancer patients undergoing HDR brachytherapy with a prescribed dose of 28 Gy in 4 fractions. Each patient had two tandemovoid insertions one week apart. Each insertion was treated on consecutive days with rescanning and replanning prior to each treatment. To study the effect of no replanning for day 2 treatments, the day 1 plan dwell position and dwell time with decay were applied to the day 2 CTmore » dataset. The point dose variations on the prescription point H (defined according to American Brachytherapy Society), and normal tissue doses at point B, bladder, rectum and vaginal mucosa (based on ICRU Report 38) were obtained. Results: Without replanning, the mean point H dose variation was 4.6 ± 10.7% on the left; 2.3 ± 2.9% on the right. The mean B point variation was 3.8 ± 4.9% on the left; 3.6 ± 4.7% on the right. The variation in the left vaginal mucosal point was 12.2 ± 10.7%; 9.5 ± 12.5% on the right; the bladder point 5.5 ± 7.4%; and the rectal point 7.9 ± 9.1%. Conclusion: Without replanning, there are variations both in the prescription point and the normal tissue point doses. The latter can vary as much as 10% or more. This is likely due to the steep dose gradient from brachytherapy compounded by shifts in the positions of the applicator in relationship to the patients anatomy. Imaging prior to each treatment and replanning ensure effective and safe brachytherapy are recommended.« less
  • Purpose: Hypofractionated partial breast irradiation (HPBI) is being used at our clinic to treat inoperable breast cancer patients who have advanced disease. We are investigating how these patients could benefit from being treated in an MRI-linac, where real-time daily MRI tumor imaging and plan adaptation would be possible. As a first step, this study evaluates the dosimetric impact of the magnetic field for different radiation beam geometries on relevant OARs. Methods: Five patients previously treated using HPBI were selected. Six treatment plans were generated for each patient, evaluating three beam geometries (VMAT, IMRT, 3DCRT) with and without B{sub 0}=1.5 T.more » The Monaco TPS was used with the Elekta MRI-Linac beam model, where the magnetic field is orthogonal to the radiation beam. All plans were re-scaled to the same isocoverage with a prescription of 40Gy/5 to the PTV. Plans were evaluated for the effect of the magnetic field and beam modality on skin V{sub 3} {sub 0}, lung V{sub 2} {sub 0} and mean heart dose. Results: Averaged over all patients, skin V{sub 3} {sub 0}for 3DCRT was higher than VMAT and IMRT (by +22% and +21%, with B{sub 0}-ON). The magnetic field caused larger increases in skin V{sub 3} {sub 0}for 3DCRT (+8%) than VMAT (+3%) and IMRT (+4%) compared with B{sub 0}-OFF. With B{sub 0}-ON, 3DCRT had a markedly lower mean heart dose than VMAT (by 538cGy) and IMRT (by 562cGy); for lung V{sub 2} {sub 0}, 3DCRT had a marginally lower dose than VMAT (by −2.2%) and IMRT (also −2.2%). The magnetic field had minimal effect on the mean heart dose and lung V{sub 2} {sub 0} for all geometries. Conclusion: The decreased skin dose in VMAT and IMRT can potentially mitigate the effects of skin reactions for HPBI in an MRI-linac. This study illustrated that more beam angles may result in lower skin toxicity and better tumor conformality, with the trade-off of elevated heart and lung doses. We are receiving funding support from Elekta.« less
  • Purpose: To investigate the plan quality and feasibility of a hybrid plan utilizing proton and photon fields for superior coverage in the internal mammary (IM) and supraclavicular (S/C) regions while minimizing heart and contralateral breast dose for the left-sided whole breast cancer patient treatment. Methods: This preliminary study carried out on single left-sided intact breast patient involved IM and S/C nodes. The IM and S/C node fields of the 5-Field 3DCRT photon-electron base plan were replaced by two proton fields. These two along with two Field-in-Field tangential photon fields were optimized for comparable dose coverage. The treatment plans were donemore » using Eclipse TPS for the total dose of 46Gy in 23 fractions with 95% of the prescription dose covering 95% of the RTOG PTV. The 3DCRT photon-electron and 4-Field photon-proton hybrid plans were compared for the PTV dose coverage as well as dose to OARs. Results: The overall RTOG PTV coverage for proton-hybrid and 3DCRT plan was comparable (95% of prescription dose covers 95% PTV volume). In proton-hybrid plan, 99% of IM volume received 100% dose whereas in 3DCRT only 77% received 100% dose. For S/C regions, 97% and 77% volume received 100% prescription dose in proton-hybrid and 3DCRT plans, respectively. The heart mean dose, V3Gy(%), and V5Gy(%) was 2.2Gy, 14.4%, 9.8% for proton-hybrid vs. 4.20 Gy, 21.5%, and 39% for 3DCRT plan, respectively. The maximum dose to the contralateral breast was 39.75Gy for proton-hybrid while 56.87Gy for 3DCRT plan. The mean total lung dose, V20Gy(%), and V30Gy(%) was 5.68Gy, 11.3%, 10.5% for proton-hybrid vs. 5.90Gy, 9.8%, 7.2% for 3DCRT, respectively. Conclusion: The protonhybrid plan can offer better dose coverage to the involved lymphatic tissues while lower doses to the heart and contralateral breast. More treatment plans are currently in progress before being implemented clinically.« less