A Retrospective Comparison of Acute Toxicities in Patients Receiving Pelvic Radiation for Newly Diagnosed Gynecologic Primaries with Intensity Modulated Proton Therapy and Volume Modulated Arc Therapy

• Published in: International journal of radiation oncology, biology, physics Vol. 120; no. 2; pp. S189 - S190
• Main Authors: Brown, M.H., Pollock, A.E., Li, E., Sun, K., Risher, H., Rao, G., Roque, D., Bentzen, S.M., Mohindra, P., McAvoy, S.A., Nichols, E.M.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.10.2024
• ISSN: 0360-3016
• DOI: 10.1016/j.ijrobp.2024.07.2241

Multiple national randomized trials comparing proton and photon therapy are ongoing, including CNS, prostate, breast, and esophageal primaries. While gynecologic malignancies are common and have a high rate of radiation utilization, no such randomized trial exists comparing proton to photon therapy. Retrospective data on the use of proton therapy in gynecologic cancers is also limited. The objective of this analysis is to retrospectively compare acute toxicities in patients treated with intensity modulated proton therapy (IMPT) to those treated with photon therapy using volume modulated arc therapy (VMAT). We retrospectively analyzed all patients treated at our downtown facility and closest geographical community site since the installment of our proton center (2016-2023). Patients who received pelvic nodal irradiation, standard fractionation, as part of curative treatment for a cervical, endometrial or vaginal primary were included. Patients with any prior course of pelvic radiation or who did not complete treatment were excluded. Multivariate analysis (MVA) was performed using binary logistic regression comparing IMPT to VMAT with factors showing significant impact on acute toxicity. Factors tested included age, race, use of concurrent chemotherapy, ECOG status, stage, use of a boost beyond 45-50.4 Gy, recurrent disease, inclusion of para-aortic nodes, recent definitive surgery and primary site of disease. A descriptive analysis was performed to see which factors were associated with the use of IMPT. In total 155 patients with a median age of 61 (30-90) years (82 white, 64 black, 9 other) were eligible for analysis, with 49 IMPT and 106 VMAT cases. MVA showed rates of all non-hematologic acute grade 2 toxicities were improved with IMPT (26.53%, n=13) compared to VMAT (43.4%, n=46) [OR 0.34 (0.14-0.81) p=0.0153]. Use of IMPT improved acute grade 2 GI toxicity 10.2% (n=5) versus VMAT 24.53% (n=26), [OR 0.24 (0.07-0.79) p=0.019]. Toxicity related treatment breaks or prematurely discontinued treatment course were more frequent in the VMAT cohort, 13.21 % (n=14) versus 4.08% (n=2, p=0.083) in the IMPT cohort. Older age, cervical site, concurrent chemo, and boost volumes yielded worse overall non-hematologic acute grade 2 toxicity. Patients with endometrial primary (75.5% v 63.2%), recurrent disease (32.7% v 9.43%), para-aortic nodal treatment (34.7% v 18.9%) or receipt of a boost (53.1% v 33.0%) were statistically more likely to be selected for IMPT. This retrospective analysis shows significantly lower acute grade 2 GI toxicity with IMPT, as well as lower overall non-hematologic acute grade 2 toxicity. Patients receiving IMPT had fewer toxicity related treatment breaks or early treatment terminations albeit not significantly. Given the known detriment of prolonged or abbreviated treatments, particularly in definitive management of cervical cancer, these data warrant further exploration and consideration of a randomized study.