Case-Matched Outcomes of Proton Beam and Intensity-Modulated Radiation Therapy for Localized Prostate Cancer

Alicia Bao; Andrew R Barsky; Stefan Both; John P Christodouleas; Curtiland Deville Jr; Zelig A Tochner; Neha Vapiwala; Russell Maxwell

doi:10.14338/IJPT-23-00002.1

Case-Matched Outcomes of Proton Beam and Intensity-Modulated Radiation Therapy for Localized Prostate Cancer

Int J Part Ther. 2023 May 18;10(1):1-12. doi: 10.14338/IJPT-23-00002.1. eCollection 2023 Summer.

Authors

Alicia Bao¹, Andrew R Barsky², Stefan Both³, John P Christodouleas⁴, Curtiland Deville Jr⁵, Zelig A Tochner⁴, Neha Vapiwala⁴, Russell Maxwell⁴

Affiliations

¹ Ohio State College of Medicine, The Ohio State University, Columbus, OH, USA.
² Department of Radiation Oncology, Lynn Cancer Institute, Baptist Health South Florida, Boca Raton, FL, USA.
³ Department of Radiation Oncology, University Medical Center Groningen, Groningen, the Netherlands.
⁴ Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, USA.
⁵ Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University, Baltimore, MD, USA.

Abstract

Purpose: Although both intensity-modulated radiation therapy (IMRT) and proton beam therapy (PBT) offer effective long-term disease control for localized prostate cancer (PCa), there are limited data directly comparing the 2 modalities.

Methods: The data from 334 patients treated with conventionally fractionated (79.2 GyRBE in 44 fractions) PBT or IMRT were retrospectively analyzed. Propensity score matching was used to balance factors associated with biochemical failure-free survival (BFFS). Age, race, and comorbidities (not BFFS associates) remained imbalanced after matching. Univariable and covariate-adjusted multivariable (MVA) Cox regression models were used to determine if modality affected BFFS.

Results: Of 334 patients, 176 (52.7%) were included in the matched cohort with exact matching to National Comprehensive Cancer Network (NCCN) risk group. With a median follow-up time of 9.0 years (interquartile range [IQR]: 7.8-10.2 years), long-term BFFS was similar between the IMRT and PBT matched arms with 8-year estimates of 85% (95% CI: 76%-91%) and 91% (95% CI: 82%-96%, P = .39), respectively. On MVA, modality was not significantly associated with BFFS in both the unmatched (hazard ratio [HR] = 0.75, 95% CI: 0.35-1.63, P = .47) and matched (HR = 0.87, 95% CI: 0.33-2.33, P = .78) cohorts. Prostate cancer-specific survival (PCSS) and overall survival (OS) were also similar (P > .05). However, in an unmatched analysis, the PBT arm had significantly fewer incidences of secondary cancers within the irradiated field (0.6%, 95% CI: 0.0%-3.1% versus 4.5%, 95% CI: 1.8%-9.0%, P = .028).

Conclusions: Both PBT and IMRT offer excellent long-term disease control for PCa, with no significant differences between the 2 modalities in BFFS, PCSS, and OS in matched patients. In the unmatched cohort, fewer incidences of secondary malignancy were noted in the PBT group; however, owing to overall low incidence of secondary cancer and imbalanced patient characteristics between the 2 groups, these data are strictly hypothesis generating and require further investigation.

Keywords: intensity-modulated radiation therapy; prostate cancer; proton therapy; radiation therapy; secondary malignancy.