3274 - Prostate Salvage Brachytherapy Utilization and Efficacy over Two Decades at a Single Institution

D. B. Rosen¹, M. Rowan², G. Pratt², B. A. Mahal³, G. Alban⁴, D. D. Yang¹, T. C. Harris⁵, C. V. Guthier⁶, D. Brivio⁷, I. Buzurovic⁸, P. F. Orio III⁹, P. L. Nguyen¹⁰, A. V. DAmico², and M. T. King¹⁰; ¹Harvard Radiation Oncology Program, Boston, MA, ²Brigham and Womens Hospital/Dana-Farber Cancer Institute, Boston, MA, ³Department of Radiation Oncology, University of Miami/Sylvester Comprehensive Cancer Center, Miami, FL, ⁴Oncoclinicas do Brasil, Salvador, Bahia, Brazil, ⁵Department of Physics, University of Heidelberg, Heidelberg, Germany, ⁶Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, ⁷Brigham & Womens Hospital, Dana Farber Cancer Institute and Harvard Medical School, Boston, MA, ⁸Brigham and Women’s Hospital and Dana-Farber Cancer Institute, Boston, MA, ⁹Department of Radiation Oncology, Dana-Farber Cancer Institute, Boston, MA, ¹⁰Department of Radiation Oncology, Brigham and Women’s Hospital/Dana-Farber Cancer Institute, Boston, MA

Purpose/Objective(s): Locally, radiorecurrent prostate cancer (RRPCa) can be treated with salvage brachytherapy. The introduction of prostate-specific PET imaging to detect RRPCa and the establishment of HDR brachytherapy salvage at our institution have led to increased brachytherapy salvage utilization. We investigated the patient make-up and outcomes of this new cohort in comparison to the last two decades of MRI and TRUS guided LDR salvage. Materials/

Methods: A retrospective review of 101 RRPCa patients with whole-gland brachytherapy (2000-2021) with at least 3 years of follow-up was performed. All were biopsy-proven, locally-recurrent, with no evidence of metastatic progression and received pre-salvage MRI. 30 patients received MRI-guided LDR (Cohort 1: 2000-10), 39 with trans-rectal ultrasound (TRUS)-guided LDR (Cohort 2: 2011-20), and 32 patients with (TRUS guided: 22, CT planned: 10) HDR (Cohort 3: 2017-2021). Percentages are actuarial and calculated using cumulative incidence. Survival analysis was conducted first via Log-Rank test, and Cox proportional hazards for univariate and multivariate analyses.

Results: At median follow-ups of 20.5, 6.9, and 3.4 years, 3y freedom from BCR were (cohort 1- 79.3%, cohort 2- 78.6%, cohort 3- 75.1%). There was no statistical difference for time to BCR (p = 0.4). As the MRI patients (cohort 1) have been previously reported [Nguyen PL, Cancer 2007] and TRUS LDR is often utilized as an HDR alternative, we further analyzed TRUS and HDR patients. OS, DMFS, Local (Intraprostatic or SV) recurrence, or LRR were not statistically different (p >= 0.05). Long-term GU grade 3 toxicity (90d to 3 y) was not statistically different (Cohort 2: 4/39 (10%), Cohort 3: 4/32 (13%)). There was similarly no difference for long-term GI grade 3 toxicity (Cohort 2: 1/39 (2.6%), Cohort 3: 1/32 (3.1%)). PSA DT < 12 mo trended towards an association with BCR (p = 0.12) and LRR (p = 0.088) on UVA (Table). SVI on pre-salvage MRI was negatively prognostic, UVA (p = 0.045 and p = 0.027) and MVA of cohort and PSA DT (p= 0.038 and p = 0.022) for BCR and LRR, respectively. HDR recurrences were: 1 LR only, 2 regional recurrence only, 3 LRR.

Conclusion: In this single-institution retrospective comparison study, modern, salvage HDR brachytherapy for RRPCa (BCR, LRR, OS) appears similar to historical methods (MRI guided LDR) and contemporary alternatives (TRUS LDR). Additionally, long-term GU and GI toxicities are rare for both HDR and TRUS LDR. As the majority of LRR failures included intraprostatic or SV failure (4/6) for HDR therapy, prospective studies involving further dose-escalation to PSMA-avid lesions may be warranted.

Abstract 3274 – Table 1: Factors associated with BCR (UVA)

Covariate			HR	95% CI		p-value
Salvage	HDR	TRUS-LDR	0.97	0.40	2.36	0.95
Imaging	None
		NM Bone Scan	0.93	0.30	2.85	0.90
		Axumin	1.38	0.53	3.61	0.51
ADT at salvage	None	Present	1.79	0.66	4.84	0.25
ADT time	mo		1.01	0.98	1.04	0.59
PSA DT	< 12 mo	>= 12 mo	0.44	0.16	1.23	0.12
Extraprostatic extension	None
		Only extracapsular	0.65	0.09	4.85	0.67
		Any SVI	3.05	1.02	9.07	0.045