2005 - Clinical Toxicity Profiles of Neoadjuvant Volumetric Modulated Arc Radiotherapy and Proton Beam Radiotherapy for Soft Tissue Sarcoma: A Single-Institution Retrospective Analysis

02:30pm - 04:00pm PT

Hall F

Screen: 31

POSTER

Presenter(s)

Alexander Allen, MD - University of Maryland Medical Center, Baltimore, MD

A. J. Allen¹, K. Sun¹, A. A. Olabumuyi¹, Z. Keepers¹, S. S. Valluri², H. Ryan III³, H. R. R. Cherng⁴, S. M. Bentzen⁵, M. Kim⁶, D. Kunaprayoon¹, and W. F. Regine Jr¹; ¹Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, ²University of Maryland School of Medicine, Baltimore, MD, ³Department of Radiation Oncology, Baltimore, MD, ⁴Department of Radiation Oncology, University of Maryland Medical Center, Baltimore, MD, ⁵Department of Epidemiology and Public Health, Biostatistics and Bioinformatics Division, University of Maryland School of Medicine, Baltimore, MD, ⁶Radiation Oncology Dept, University of Maryland, Baltimore, MD

Purpose/Objective(s): Since the advent of limb-sparing surgery for soft tissue sarcoma (STS), treatment goals for this malignancy have focused on reducing toxicities that impair patient quality of life while maintaining a high rate of local control. In the treatment of STS, proton beam radiotherapy (PBT) can better spare adjacent soft tissue and bone due to superior dose-fall off compared to photon-based modalities such as volumetric modulated arc therapy (VMAT). While there is evidence documenting the dosimetric advantages of PBT, there is sparse literature assessing whether these advantages translate into clinical benefits. We hypothesized that, for patients with STS receiving neoadjuvant radiotherapy (RT) followed by resection, the use of PBT would be associated with a lower rate of physician-reported fibrosis, edema, and joint stiffness of the treated extremity compared to VMAT.

Materials/Methods: We performed a retrospective review of patients with STS who received neoadjuvant VMAT or PBT between 1/1/2012 and 6/1/2024 within a single health system prior to surgical resection. Patients undergoing re-irradiation, patients who received 3DCRT or electron neoadjuvant RT, and patients who did not undergo resection after RT, were excluded. A Fine-Gray model was used was used to compare the cumulative incidences of physician-reported toxicities between treatment groups (with adjustment for death as a competing risk factor) by generating a subdistribution hazard ratio (SHR).

Results: The analysis included 80 patients, of whom 47.5% (38/80) received VMAT and 52.5% (42/80) received PBT. Median age was 60 years [48.8 – 69.8] and median follow-up time was 29 months [16.5–52.8]. There were no statistically significant inter-group differences for the following variables: ECOG status, initial tumor size (median 10.1 cm [6.9-13.2]), distance from tumor to nearest joint (median 5 cm [2.2–11.2]), upper or lower extremity location of tumor, radiation dose (median 50.4 Gy [50-50.4]), days spent in hospital for tumor resection, or need for flap or reconstruction. There was no difference in acute post-operative wound complications between the two modalities (p=0.446). Compared to VMAT, PBT was associated with a decreased cumulative incidence of joint stiffness (SHR 0.611 [CI 0.452 – 0.852] p=0.001) and joint fibrosis (SHR 0.584 [CI 0.434–0.786] p=0.0001). PBT was associated with a decreased cumulative incidence of extremity edema, however, this was not statistically significant (SHR 0.849 [CI 0.693 – 1.04] p=0.112). Overall local control was 88.8% and there was no difference in local failure between the two modalities (p=0.141)

Conclusion: This retrospective data shows that, in the treatment of STS with neoadjuvant RT, PBT is associated with decreased physician-reported rates of joint fibrosis and stiffness of the treated extremity when compared to VMAT. These findings suggest that a prospective clinical trial is warranted to definitively compare the toxicity profiles of these two radiation modalities.