2745 - Comparative Evaluation of 3D-CRT, VMAT, and PBS-PT for Bilateral Breast/Chest Wall and Regional Nodal Irradiation
Presenter(s)
G. J. Haber1, M. B. Bernstein1, A. Lozano2, I. Lin3, A. Shim3, A. Hanlon2, Q. LaPlant1, J. J. Cuaron1, D. A. Roth O’Brien4, B. McCormick1, S. N. Powell1, A. J. Khan1, L. Z. Braunstein1, and I. J. Choi1; 1Memorial Sloan Kettering Cancer Center, New York, NY, 2Center for Biostatistics and Health Data Science, Department of Statistics, Virginia Tech, Roanoke, VA, 3New York Proton Center, New York, NY, 4Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY
Purpose/Objective(s): Bilateral breast/chest wall and regional nodal irradiation (BL-RNI) involves treatment of extensive target volumes (TVs), creating challenges for achieving adequate coverage while limiting dose to organs-at-risk (OARs). In this study, we compare BL-RNI delivery with 3D conformal radiation therapy (3D-CRT), volumetric-modulated arc therapy (VMAT), and pencil beam scanning proton therapy (PBS-PT); we hypothesize that PBS-PT provides superior TV coverage with lower OAR dose.
Materials/Methods: Patients treated with BL-RNI between 2017–2025 were reviewed. Clinical, pathologic, and radiation (RT) details were recorded. TVs and OARs were modified as needed for consistency. Pulmonary toxicity was graded per CTCAE v5. Dose to 95% of the clinical target volume (CTV D95%) was used for PBS-PT evaluation and planning target volume (PTV) D95% for 3D-CRT and VMAT. Descriptive statistics were used to quantify endpoints of interest.
Results: The cohort consisted of 49 patients (3D-CRT=10; VMAT=27; PBS-PT=12). Median follow-up was 64, 29, and 27 months, respectively. Deep inspiratory breath hold was used in 3/10 (30%) 3D-CRT, 25/27 (93%) VMAT, and 2/12 (17%) PBS-PT. Rates of prior breast cancer RT were 0/10 (0%), 5/27 (19%), and 4/12 (33%); rates of pre-existing pulmonary conditions were 1/10 (10%), 4/27 (15%), and 3/12 (25%) for 3D-CRT, VMAT, and PBS-PT, respectively. DVH metrics are listed in Table 1. Overall, 9/49 (18%) developed grade =2 pneumonitis with a median onset of 3.2 months (IQR 2.6-12.1); 2/10 (20%) received 3D-CRT, 7/27 (26%) VMAT, and 0/12 (0%) PBS-PT. Of these patients, 7/9 (78%) had either a history of prior RT (4/9, 44%) or pre-existing pulmonary conditions (3/9, 33%). In the 3D-CRT group, 2/10 (20%) patients developed cardiac toxicity (left ventricular ejection fraction (LVEF) decline=1, atrial fibrillation=1), compared to 4/27 (15%) (LVEF decline=3, heart failure=1) and 0/12 (0%) in the VMAT and PBS-PT groups, respectively.
Conclusion: In the first study of BL-RNI comparing 3D-CRT, VMAT, and PBS-PT, 3D-CRT offers substantially inferior TV coverage compared to VMAT and PBS-PT. Both photon techniques delivered more cardiopulmonary RT dose and had higher rates of cardiac and pulmonary toxicity compared to PBS-PT, although interpretation is limited by small and heterogenous cohorts. When available, PBS-PT should be considered the RT technique of choice for BL-RNI. Longer follow-up and further study in larger cohorts will provide additional clarity on the clinical impact of RT modality.
| Table 1 | |||
| Metric (median [IQR]) | 3D-CRT | VMAT | PBS-PT |
| TV D95% | 44% [32–55] | 96% [95–100] | 97% [95–98] |
| IMN D95% (lower of left/right) | 57% [32–89] | 98% [97–102] | 97% [96–100] |
| Total Lung V20Gy | 32% [29–33] | 27% [23–29] | 18% [16–19] |
| Total Lung V5Gy | 64% [59–68] | 93% [87–97] | 44% [37–48] |
| Mean Heart Dose (Gy) | 4.9 [4.2–5.6] | 6.8 [6.0–7.0] | 0.9 [0.74–1.0] |