Presenter(s)
M. Mathai1, A. D. Thompson2, L. H. D. D. Escobal3, G. Singh4, D. Alicia5, S. Ruff4, S. Koduri6, M. Kidorf4, M. J. Ferris4, S. Cheston4, W. Citron7, A. N. Patel4, M. Rao4, S. A. McAvoy4, E. M. Nichols8, S. A. Dudley9, and M. A. L. Vyfhuis4; 1University of Maryland School of Medicine, Baltimore, MD, United States, 2Department of Radiation Oncology, University of Maryland Medical Center, Baltimore, MD, 3University of Maryland Radiation Oncology, Baltimore, MD, 4Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, 5Department of Radiation Oncology, Maryland Proton Treatment Center, Baltimore, MD, 6Department of Radiation Oncology, NYU Langone Health, New York City, NY, 7University of Maryland, School of Medicine, Baltimore, MD, 8University of Maryland School of Medicine, Baltimore, MD, 9Johns Hopkins Medicine, Department of Radiation Oncology, Baltimore, MD
Purpose/Objective(s): Radiation therapy (RT) for locally advanced breast cancer (LABC) patients can be associated with significant cardiopulmonary toxicities. Proton therapy can potentially reduce these toxicities, but the RADCOMP phase III trial results are years away. Therefore, we compared the incidence of post-RT cardiac and pulmonary toxicities in LABC patients undergoing comprehensive nodal irradiation (CNI) with proton or photon RT at our institution. Materials/Methods: A retrospective study of 943 LABC patients curatively treated with CNI from March 1, 2016 to December 31, 2023 was conducted at our institution. ?2 or Mann-Whitney-U-tests assessed differences in patient socioeconomic demographics, cancer characteristics, and treatments rendered between the RT modalities. Binary logistic regression with forward modeling selection was used to determine clinical predictors of cardiac or pulmonary toxicity. Results: With a median follow-up of 26 months, 59% of patients with LABC received photon RT (N=557) and 41% received intensely modulated proton therapy (IMPT) (N=386). Patients treated with IMPT were younger (median age: 52 vs. 57; p<0.001), self-identified as White (White: 56%; Black: 31%; p<0.001), less likely to have Medicare insurance (20% vs. 7%; p=0.053), and had better ECOG PS (p=0.033). Patients who received IMPT were more likely to have left-sided malignancies (69.4% vs. 44.5%; p<0.001), receive a higher total RT dose (median dose: 60 Gy vs. 58 Gy; p<0.001), and receive neoadjuvant (60% vs. 50%; p=0.003), concurrent (14.4% vs. 4%; p<0.001) and adjuvant chemotherapy (38.9% vs. 30.4%; p=0.008). There were no differences in baseline cardiac or pulmonary conditions between RT groups. However, patients who received photon RT had a higher rate of new pulmonary conditions (9.9% vs. 5.4%; p=0.014). There were no differences in new cardiac events between RT groups (photons: 10.5% vs. IMPT: 7.3%; p=0.106). In the MVA model, cardiac toxicity predictors after RT included a new diagnosis of hypertension (OR:3.41, 95% CI: 1.99 – 5.84; p<0.001) or hyperlipidemia (OR:2.03, 95% CI: 1.24 – 3.33; p=0.005). Pulmonary toxicity predictors included triple negative disease status (OR:2.79, 95% CI:1.66 – 4.70; p=0.014) and type of RT used, where photon RT increased the risk of pulmonary toxicity nearly two-fold (OR:1.97, 95% CI: 1.15 – 3.39; p=0.014). Conclusion: Patients with LABC treated with comprehensive IMPT are less likely to develop new pulmonary events after RT compared to those treated with photons, despite receiving higher total RT doses. Although no significant differences in cardiac toxicity were observed between the two RT groups, longer follow-up may be required to discern differences in cardiac events. As we await results from the phase III RADCOMP study, our future work will investigate dosimetric contributions to post-treatment cardiopulmonary events.
