3235 - Multivariate Survival Analysis Comparing Proton Therapy and IMRT for Localized Prostate Cancer: A Retrospective Observational Study

Purpose/Objective(s): This study retrospectively compares the clinical outcomes of proton therapy (PT) and intensity-modulated radiation therapy (IMRT) for localized prostate cancer while controlling for relevant covariates, with the objective of informing treatment decisions.

Materials/Methods: We analyzed data from the electronic medical record system of a single institution, from the period of January 1, 2010, to December 15, 2023. Inclusion criteria comprised all men diagnosed with localized prostate cancer who underwent PT or IMRT with curative intent. The primary outcomes evaluated were overall survival (OS), metastasis-free survival (MFS), and biochemical failure-free survival (BFFS). Adjusted survival analysis was performed using a multivariate Cox proportional hazards model and Kaplan-Meier plots. Covariates included patient age and race, initial androgen-deprivation therapy (ADT), and NCCN risk stratification.

Results: Summary statistics are shown in table 1. The cohorts had similar mean age and follow up time, but had statistically significant differences in patient race, risk scores, and use of ADT. Compared to the IMRT group, the proton therapy group had lower proportions of Black patients, high and very high-risk patients, and patients receiving ADT in combination with RT. Survival analysis using a multivariate Cox proportional hazards model showed no significant differences between the Proton and IMRT cohorts. Patients receiving PT had similar rates of BFFS (Hazard ratio (HR) = 0.97, p=0.83), MFS (HR=0.81, p=0.27), and OS (HR=0.82, p=0.44). The PT and IMRT cohorts had similar results when compared across risk groups, patient race, and use of ADT. Consistent with prior studies regarding the use of hormonal therapies combined with RT, patients receiving ADT had significantly higher BFFS and MFS compared to RT alone, regardless of radiation modality (BFFS: HR=0.25, p<0.001), MFS: HR=0.11, p<0.001).

Conclusion: In this retrospective analysis, we compared the efficacy of PT and IMRT for initial treatment in patients with localized prostate cancer, controlling for patient age, race, risk stratification, and the use of ADT in combination with RT. We find no evidence of any differences in rates of biochemical failure, metastasis, or overall survival between the PT and IMRT cohorts. For both radiation modalities, the use of ADT in addition to RT for initial treatment was associated with lower rates of BCR and metastasis.

Abstract 3235 - Table 1: Summary statistics