3209 - Oncologic Outcomes of Upfront Radiation Therapy vs. Surgery, while Accounting for Intraprostatic Tumor Volume

M. T. King¹, M. Rowan², G. Pratt², J. Parisi³, C. Belant³, K. N. Lee⁴, L. K. Lee⁵, D. D. Yang⁴, N. E. Martin¹, P. L. Nguyen¹, A. V. DAmico², and P. F. Orio III⁶; ¹Department of Radiation Oncology, Brigham and Women’s Hospital/Dana-Farber Cancer Institute, Boston, MA, ²Brigham and Womens Hospital/Dana-Farber Cancer Institute, Boston, MA, ³Dana-Farber Cancer Institute/Brigham and Womens Hospital, Boston, MA, ⁴Harvard Radiation Oncology Program, Boston, MA, ⁵Department of Radiology, Brigham and Womens Hospital, Boston, MA, ⁶Department of Radiation Oncology, Dana-Farber Cancer Institute, Boston, MA

Purpose/Objective(s): Previously, we have shown that intraprostatic tumor volume from magnetic resonance images (MRI), was independently prognostic for metastasis for patients treated with radiation therapy (RT) and radical prostatectomy (RP). Herein, we compare oncologic outcomes by treatment type, while adjusting for tumor volume. Materials/

Methods: We conducted a single-institutional retrospective study of patients who had a pre-treatment MRI prior to RT or RP between 2010-2017. We trained nnUNet to provide tumor segmentations on 288 patients treated with RT utilizing 5-fold cross-validation, and applied the model to all remaining patients. Tumor volume (V_AI) was the volume of the segmentation result. First, we utilizing a multivariable linear regression model to evaluate the impact of NCCN risk, treatment type (RP vs RT), and their interaction on V_AI. Second, we utilized multivariable cox regression models to evaluate associations of treatment type with biochemical failure and metastasis, while adjusting for age, V_AI, and risk category. Finally, for the subset of patients who experienced a biochemical recurrence (BCR: PSA >= 0.1 ng/mL for RP; nadir + 2 for RT), we evaluated how upfront treatment was associated with time to metastasis, while adjusting for age at BCR, interval to BCR, initial NCCN risk category, and initial V_AI.
Results: We identified 1095 patients. 438 patients underwent RT +/- ADT at a median age of 68. Median ADT durations were 6 and 18 months for UIR and high risk, respectively. Over a median follow-up of 7.9 years, the numbers of patients who experienced BCR and metastasis, were 61 and 28. 657 patients underwent RP +/- neoadjuvant ADT (50) at a median age of 60. Over a median follow-up of 5.9 years [5.7, 6.1], the numbers of patients who experienced BCR and metastasis were 189 and 55. Although there were no significant differences in V_AI by treatment type for low/FIR or UIR, RT had larger V_AI for high-risk disease by 1.44 mL (0.44, 2.44, p=0.005). Compared with RP, RT was associated with a lower risk of BCR (adjusted hazard ratio (AHR): 0.31 (0.22, 0.43, p<0.001)) and metastasis (AHR: 0.50 (0.29, 0.84, p=0.009). On subgroup analyses, a significant difference was noted only for high-risk (AHR: 0.44 [0.23-0.86]; p = 0.016) disease. The 6-year cumulative incidence of metastasis for high-risk disease was 17.9% for RP [4.1, 8.7] versus 9.2% for RT [1.9, 5.7]. Among subset of 250 patients with BCR (189 RP at median 1.1 years versus 61 RT at median 4.9 years), RT was associated with greater risk of metastasis (AHR: 4.62 (2.42-8.85, p<0.001). The 3-year cumulative incidence of metastasis was 9.8% [5.4, 14.2] for RP compared with 45.9 [31.1, 60.7] for RT. Of note, AHRs for V_AI were significant in all models.
Conclusion: Compared with RP, RT was associated with greater tumor volume for high risk disease. RT was associated with lower rates of metastasis after upfront treatment, but greater risk of metastasis for the subset of patients who experienced biochemical recurrence.