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Title: SU-F-T-58: Dosimetric Evaluation of Breast Tissue Composition for Electronic Brachytherapy (BET) Source In High Dose Rate Accelerated Partial Breast (APBI) Irradiation

Abstract

Purpose: To quantitatively evaluate the dosimetric impact of differing breast tissue compositions for electronic brachytherapy source for high dose rate accelerated partial breast irradiation. Methods: A series of Monte Carlo Simulation were created using the GEANT4 toolkit (version 10.0). The breast phantom was modeled as a semi-circle with a radius of 5.0 cm. A water balloon with a radius of 1.5 cm was located in the phantom with the Xoft AxxentTM EBT source placed at center as a point source. A mixed of two tissue types (adipose and glandular tissue) was assigned as the materials for the breast phantom with different weight ratios. The proportionality of glandular and adipose tissue was simulated in four different fashions, 80/20, 70/30, 50/50 and 30/70 respectively. The custom energy spectrum for the 50 kVp XOFT source was provided via the manufacturer and used to generate incident photons. The dose distributions were recorded using a parallel three dimensional mesh with a size of 30 × 30 × 30 cm3 with 1 × 1 × 1 mm3 voxels. The simulated doses absorbed along the transverse axis were normalized at the distance of 1 cm and then compared with the calculations using standard TG-43 formalism. Results: Allmore » simulations showed underestimation of dose beyond balloon surface compared to standard TG-43 calculations. The maximum percentage differences within 2 cm distance from balloon surface were found to be 18%, 11%, 10% and 8% for the fat breast (30/70), standard breast (50/50), dense breast (70/30 and 80/20), respectively. Conclusion: The accuracy of dose calculations for low energy EBT source was limited when considering tissue heterogeneous composition. The impact of atomic number on photo-electric effect for lower energy Brachytherapy source is not accounted for and resulting in significant errors in dose calculation.« less

Authors:
; ; ;  [1]
  1. University of Oklahoma Health Sciences Center, Oklahoma City, OK (United States)
Publication Date:
OSTI Identifier:
22642306
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; 61 RADIATION PROTECTION AND DOSIMETRY; ACCURACY; ADIPOSE TISSUE; BRACHYTHERAPY; COMPUTERIZED SIMULATION; DOSE RATES; ENERGY SPECTRA; IRRADIATION; MAMMARY GLANDS; MONTE CARLO METHOD; PHANTOMS; POINT SOURCES; RADIATION DOSE DISTRIBUTIONS; RADIATION DOSES

Citation Formats

Taylor, W, Johnson, D, Ahmad, S, and Chen, Y. SU-F-T-58: Dosimetric Evaluation of Breast Tissue Composition for Electronic Brachytherapy (BET) Source In High Dose Rate Accelerated Partial Breast (APBI) Irradiation. United States: N. p., 2016. Web. doi:10.1118/1.4956193.
Taylor, W, Johnson, D, Ahmad, S, & Chen, Y. SU-F-T-58: Dosimetric Evaluation of Breast Tissue Composition for Electronic Brachytherapy (BET) Source In High Dose Rate Accelerated Partial Breast (APBI) Irradiation. United States. doi:10.1118/1.4956193.
Taylor, W, Johnson, D, Ahmad, S, and Chen, Y. 2016. "SU-F-T-58: Dosimetric Evaluation of Breast Tissue Composition for Electronic Brachytherapy (BET) Source In High Dose Rate Accelerated Partial Breast (APBI) Irradiation". United States. doi:10.1118/1.4956193.
@article{osti_22642306,
title = {SU-F-T-58: Dosimetric Evaluation of Breast Tissue Composition for Electronic Brachytherapy (BET) Source In High Dose Rate Accelerated Partial Breast (APBI) Irradiation},
author = {Taylor, W and Johnson, D and Ahmad, S and Chen, Y},
abstractNote = {Purpose: To quantitatively evaluate the dosimetric impact of differing breast tissue compositions for electronic brachytherapy source for high dose rate accelerated partial breast irradiation. Methods: A series of Monte Carlo Simulation were created using the GEANT4 toolkit (version 10.0). The breast phantom was modeled as a semi-circle with a radius of 5.0 cm. A water balloon with a radius of 1.5 cm was located in the phantom with the Xoft AxxentTM EBT source placed at center as a point source. A mixed of two tissue types (adipose and glandular tissue) was assigned as the materials for the breast phantom with different weight ratios. The proportionality of glandular and adipose tissue was simulated in four different fashions, 80/20, 70/30, 50/50 and 30/70 respectively. The custom energy spectrum for the 50 kVp XOFT source was provided via the manufacturer and used to generate incident photons. The dose distributions were recorded using a parallel three dimensional mesh with a size of 30 × 30 × 30 cm3 with 1 × 1 × 1 mm3 voxels. The simulated doses absorbed along the transverse axis were normalized at the distance of 1 cm and then compared with the calculations using standard TG-43 formalism. Results: All simulations showed underestimation of dose beyond balloon surface compared to standard TG-43 calculations. The maximum percentage differences within 2 cm distance from balloon surface were found to be 18%, 11%, 10% and 8% for the fat breast (30/70), standard breast (50/50), dense breast (70/30 and 80/20), respectively. Conclusion: The accuracy of dose calculations for low energy EBT source was limited when considering tissue heterogeneous composition. The impact of atomic number on photo-electric effect for lower energy Brachytherapy source is not accounted for and resulting in significant errors in dose calculation.},
doi = {10.1118/1.4956193},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • Purpose: To objectively evaluate the radiation dermatitis caused by accelerated partial breast irradiation (APBI) using high-dose-rate interstitial brachytherapy. Patients and Methods: The skin color and moisture changes were examined using a newly installed spectrophotometer and corneometer in 22 patients who had undergone APBI using open cavity implant high-dose-rate interstitial brachytherapy (36 Gy in six fractions) and compared with the corresponding values for 44 patients in an external beam radiotherapy (EBRT) control group (50-60 Gy in 25-30 fractions within 5-6 weeks) after breast conserving surgery. Results: All values changed significantly as a result of APBI. The extent of elevation in amore » Asterisk-Operator (reddish) and reduction in L Asterisk-Operator (black) values caused by APBI were similar to those for EBRT, with slightly delayed recovery for 6-12 months after treatment owing to the surgical procedure. In contrast, only APBI caused a change in the b Asterisk-Operator values, and EBRT did not, demonstrating that the reduction in b Asterisk-Operator values (yellowish) depends largely on the surgical procedure. The changes in moisture were less severe after APBI than after EBRT, and the recovery was more rapid. The toxicity assessment using the Common Toxicity Criteria, version 3, showed that all dermatitis caused by APBI was Grade 2 or less. Conclusion: An objective analysis can quantify the effects of APBI procedures on color and moisture cosmesis. The radiation dermatitis caused by APBI using the present schedule showed an equivalent effect on skin color and a less severe effect on moisture than the effects caused by standard EBRT.« less
  • Purpose: Accelerated partial breast irradiation (APBI) is an effective treatment for early stage breast-cancer. Irradiation in a prone position can mitigate breast motion and spare heart and lung. In this study, a comprehensive study is performed to evaluate various treatment techniques for prone APBI treatment including: 3D-CRT, IMRT, co-planar and non-coplanar partial arcs treatment. Methods: In this treatment planning study, a left breast patient treated in prone position in our clinic was imported into Varian Eclipse TPS. Six beams tangential to chest wall were used in both 3D-CRT and IMRT plans. These six beams were coplanar in a transactional planemore » achieved by both gantry and couch rotation. A 60-beam IMRT plan was also created to explore the maximum benefit of co-planar IMRT. Within deliverable couch rotation range (±30°), partial arc treatment plans with one and up to ten couch positions were generated for comparison. For each plan, 30Gy in 6 fractions was prescribed to 95% PTV volume. Critical dosimetric parameters, such as conformity index, mean, maximum, and volume dose of organ at risk, are evaluated. Results: The conformity indexes (CI) are 3.53, 3.17, 2.21 and 1.08 respectively to 3D-CRT, 6-beam IMRT, 60-beam IMRT, and two-partial-arcs coplanar plans. However, arc plans increase heart dose. CI for non-coplanar arc plans decreases from 1.19 to 1.10 when increases couch positions. Maximum dose in ipsilateral lung (1.98 to 1.13 Gy), and heart (0.62 to 0.43 Gy) are steadily decreased with the increased number of non-coplanar arcs. Conclusions: The dosimetric evaluation results show that partial arc plans have improved CIs compared to conventional 3D-CRT and IMRT plans. Increasing number of partial arcs decreases lung and heart dose. The dosimetric benefit obtained from non-coplanar arcs should be considered with treatment delivery time.« less
  • Purpose: The current standard TG-43 dose calculation method for SAVI-based Accelerated Partial Breast Irradiation (APBI) assumes an ideal geometry of infinite homogeneous water. However, in SAVI treatments, the air cavity inside the device and the short source-to-skin distance raise concerns about the dose accuracy of the TG-43 method. This study is to evaluate TG-43 dose calculation accuracy in SAVI treatments using Monte Carlo (MC) simulations. Methods: We recalculated the dose distributions of 15 APBI patients treated with SAVI devices, including five cases with a size of 6–1, five with 8−1 and five with 10−1, using our in-house developed fast MCmore » dose package for HDR brachytherapy (gBMC). A phase-space file was used to model the Ir-192 HDR source. For each case, the patient CT was converted into a voxelized phantom and the dwell positions and times were extracted from treatment plans for MC dose calculations. Clinically relevant dosimetric parameters of the recalculated dose were compared to those computed via the TG-43 approach. Results: A systematic overestimation of doses was found for the 15 cases in TG-43 results, with D90, V150, and V200 for PTV-eval 2.8±1.8%, 2.0±2.2%, and 1.8±3.5% higher than MC results. TG-43 also overestimated the dose to skin with the maximum dose 4.4±8.4% higher on average. The relatively large standard deviation seen in the difference of maximum skin dose is partially ascribed to the statistical uncertainty of MC simulations when computing the maximum dose. It took gBMC ∼1 minute to compute dose for a SAVI plan. Conclusion: The high efficiency of our gBMC package facilitated the studies with a relatively large number of cases. An overestimation of TG-43 doses was found when using this MC package to recompute doses in SAVI cases. Clinical utilization of TG-43 dose calculation method in this scenario should be aware of this fact.« less
  • Purpose: To perform a detailed analysis of variables associated with late tissue effects of high-dose-rate (HDR) interstitial brachytherapy accelerated partial breast irradiation (APBI) in a large cohort of patients with prolonged follow-up. Methods and Materials: Beginning in 1995, 75 women with Stage I/II breast cancer were enrolled in identical institutional trials evaluating APBI as monotherapy after lumpectomy. Patients eligible included those with T1-2, N0-1 ({<=}3 nodes positive), M0 tumors of nonlobular histology with negative surgical margins, no extracapsular nodal extension, and negative results on postexcision mammogram. All patients underwent surgical excision and postoperative irradiation with HDR interstitial brachytherapy. The planningmore » target volume was defined as the excision cavity plus a 2-cm margin. Treatment was delivered with a high-activity Ir-192 source at 3.4 Gy per fraction twice daily for 5 days to a total dose of 34 Gy. Dosimetric analyses were performed with three-dimensional postimplant dose and volume reconstructions. All patients were evaluated at 3-6-month intervals and assessed with a standardized cosmetic rating scale and according to Radiation Therapy Oncology Group late normal tissue toxicity scoring criteria. Clinical and therapy-related features were analyzed for their relationship to cosmetic outcome and toxicity rating. Clinical features analyzed included age, volume of resection, history of diabetes or hypertension, extent of axillary surgery, and systemic therapies. Therapy-related features analyzed included volume of tissue encompassed by the 100%, 150%, and 200% isodose lines (V100, V150, and V200, respectively), the dose homogeneity index (DHI), number of source dwell positions, and planar separation. Results: The median follow-up of all patients was 73 months (range, 43-118 months). The cosmetic outcome at last follow-up was rated as excellent, good, and fair/poor in 67%, 24%, and 9% of patients, respectively. Suboptimal cosmetic outcome was significantly associated with the number of source dwell positions, V150, and V200 and inversely associated with DHI (0.77 vs. 0.73; p = 0.05). Late skin toxicity was rated as Grade 0, 1, or 2 in 77%, 19%, and 4% of patients, respectively. The risk of Grade 1/2 skin toxicity was significantly associated with V150 and V200 and inversely associated with DHI (0.77 vs. 0.71; p = 0.009). Late subcutaneous toxicity was rated as Grade 0, 1, 2, 3, or 4 in 55%, 15%, 12%, 5%, and 13% of patients, respectively. The risk of Grade 0/1 vs. Grade 2-4 subcutaneous toxicity was significantly associated only with a lower value of DHI (0.77 vs. 0.73; p = 0.02). To further explore factors that might contribute to the risk of fat necrosis (symptomatic or asymptomatic), a separate analysis showed that only dose hotspots as reflected in V150 and V200 were significantly associated with elevated risk. The use of adriamycin-based chemotherapy after APBI was found to be associated with a significant increase in the incidence of higher-grade skin toxicity and a higher risk of fat necrosis and suboptimal cosmetic outcome. Patient age, volume of resection, extent of axillary surgery, a history of diabetes or hypertension, and the use of tamoxifen were not found to be significantly associated with cosmetic outcome or late normal tissue complications. Conclusions: Long-term cosmetic results and the risk of late skin and subcutaneous toxicity after APBI with interstitial HDR brachytherapy can be correlated with specific treatment-related variables. These data provide dosimetric parameters that might be used to minimize the risk of normal tissue injury after APBI interstitial brachytherapy.« less
  • Purpose: The purpose of this analysis was to evaluate dose-volume relationships associated with a higher probability for developing chest wall toxicity (pain) after accelerated partial breast irradiation (APBI) by using both single-lumen and multilumen brachytherapy. Methods and Materials: Rib dose data were available for 89 patients treated with APBI and were correlated with the development of chest wall/rib pain at any point after treatment. Ribs were contoured on computed tomography planning scans, and rib dose-volume histograms (DVH) along with histograms for other structures were constructed. Rib DVH data for all patients were sampled at all volumes {>=}0.008 cubic centimeter (cc)more » (for maximum dose related to pain) and at volumes of 0.5, 1, 2, and 3 cc for analysis. Rib pain was evaluated at each follow-up visit. Patient responses were marked as yes or no. No attempt was made to grade responses. Eighty-nine responses were available for this analysis. Results: Nineteen patients (21.3%) complained of transient chest wall/rib pain at any point in follow-up. Analysis showed a direct correlation between total dose received and volume of rib irradiated with the probability of developing rib/chest wall pain at any point after follow-up. The median maximum dose at volumes {>=}0.008 cc of rib in patients who experienced chest wall pain was 132% of the prescribed dose versus 95% of the prescribed dose in those patients who did not experience pain (p = 0.0035). Conclusions: Although the incidence of chest wall/rib pain is quite low with APBI brachytherapy, attempts should be made to keep the volume of rib irradiated at a minimum and the maximum dose received by the chest wall as low as reasonably achievable.« less