ABSTRACT
PURPOSE: Regional nodal irradiation improves disease-free and distant disease-free survival in patients with high-risk breast cancer (BC). Trials demonstrating this used 2- or 3-dimensional conformal radiation therapy (2-dimensional or 3-dimensional [3D] conformal radiotherapy [CRT]) fields based on bony anatomy. Modern volumetric-modulated arc therapy (VMAT) and pencil beam scanning proton therapy (PBSPT) may underdose regional nodes (RNs) not contoured but covered by 3D CRT. Multiple atlases guide modern treatment planning. This study addresses the risk of underdosing when relying on published atlases and treating with 3D CRT, VMAT, and PBSPT. METHODS AND MATERIALS: Targets per the Radiation Therapy Oncology Group (RTOG), European Society for Radiotherapy and Oncology (ESTRO), and Radiotherapy Comparative Effectiveness Consortium (RADCOMP) atlases were contoured on a representative patient CT scan. 3D CRT plans based on anatomic borders and VMAT and PBSPT plans for each set of target volumes were generated. Positron emission tomography/computed tomography (PET/CT) scans were reviewed. CT-positive and 18F-fluorodeoxyglucose (18F-FDG)-avid RNs (n = 389) were mapped from 102 patients with locally advanced (n = 51; median 2; range, 1-8 nodes) and metastatic (n = 51; median 4; range, 1-19 nodes) BC: axillary (AX; n = 284), supraclavicular (SCV; n = 60), and internal mammary nodal (IMN; n = 45). 18F-FDG-avid RNs falling within the 95% isodose line were considered adequately covered. RESULTS: 3D CRT plans provided excellent RN coverage. Low AX nodes were covered (≥99%) in all plans. Underdosing of 18F-FDG-avid RNs falling in the high AX (78%-92%), SCV (52%-75%), and IMN (84%-89%) volumes was observed following the RTOG and ESTRO atlases for VMAT and PBSPT plans. Use of the RADCOMP atlas provided coverage of these areas (89%-100%) with slightly increased heart and lung doses. Atlas guided VMAT/PBSPT plans provided cumulative nodal coverage as follows: ESTRO (89%/88%), RTOG (93%/91%), and RADCOMP (98%/96%). CONCLUSIONS: VMAT and PBSPT for regional nodal irradiation in patients with high-risk BC risks underdosage in the high AX, SCV, and IMN nodal regions unless comprehensive target delineation is performed.
Subject(s)
Breast Neoplasms/radiotherapy , Lymph Nodes/radiation effects , Proton Therapy/methods , Radiometry/methods , Radiotherapy, Conformal/methods , Female , Humans , Middle Aged , PhotonsABSTRACT
Accelerated partial breast irradiation has caused higher than expected rates of poor cosmesis. At our institution, a novel breast stereotactic radiotherapy device has demonstrated dosimetric distributions similar to those in brachytherapy. This study analyzed comparative dose distributions achieved with the device and intensity-modulated radiation therapy accelerated partial breast irradiation. Nine patients underwent computed tomography simulation in the prone position using device-specific immobilization on an institutional review board-approved protocol. Accelerated partial breast irradiation target volumes (planning target volume_10mm) were created per the National Surgical Adjuvant Breast and Bowel Project B-39 protocol. Additional breast stereotactic radiotherapy volumes using smaller margins (planning target volume_3mm) were created based on improved immobilization. Intensity-modulated radiation therapy and breast stereotactic radiotherapy accelerated partial breast irradiation plans were separately generated for appropriate volumes. Plans were evaluated based on established dosimetric surrogates of poor cosmetic outcomes. Wilcoxon rank sum tests were utilized to contrast volumes of critical structures receiving a percentage of total dose (Vx). The breast stereotactic radiotherapy device consistently reduced dose to all normal structures with equivalent target coverage. The ipsilateral breast V20-100 was significantly reduced (P < .05) using planning target volume_10mm, with substantial further reductions when targeting planning target volume_3mm. Doses to the chest wall, ipsilateral lung, and breast skin were also significantly lessened. The breast stereotactic radiotherapy device's uniform dosimetric improvements over intensity-modulated accelerated partial breast irradiation in this series indicate a potential to improve outcomes. Clinical trials investigating this benefit have begun accrual.
ABSTRACT
OBJECTIVE: Partial-breast irradiation (PBI) with external-beam radiotherapy has produced higher than expected rates of fair-to-poor cosmesis. Worsened outcomes have been correlated with larger volumes of breast tissue exposed to radiation. A novel breast-specific stereotactic radiotherapy (BSRT) device (BSRTD) has been developed at our institution and has shown promise in delivering highly conformal dose distributions. We compared normal tissue sparing with this device with that achieved with intensity-modulated radiation therapy (IMRT)-PBI. METHODS: Fifteen women previously treated with breast conservation therapy were enrolled on an institutional review board-approved protocol. Each of them underwent CT simulation in the prone position using the BSRTD-specific immobilization system. Simulated postoperative and preoperative treatment volumes were generated based on surgical bed/clip position. Blinded planners generated IMRT-PBI plans and BSRT plans for each set of volumes. These plans were compared based on clinically validated markers for cosmetic outcome and toxicity using a Wilcoxon rank-sum test. RESULTS: The BSRT plans consistently reduced the volumes receiving each of several dose levels (Vx) to breast tissue, the chest wall, the lung, the heart, and the skin in both preoperative and postoperative settings (p < 0.05). Preoperative BSRT yielded particularly dramatic improvements. CONCLUSION: The novel BSRTD has demonstrated significant dosimetric benefits over IMRT-PBI. Further investigation is currently proceeding through initial clinical trials.
