ESTRO 2024 - Abstract Book

S2533

Clinical - Urology

ESTRO 2024

Vedang Murthy 1 , Indranil Mallick 2 , Gargee Mulye 1 , Arunsingh Moses 2 , Priyamvada Maitre 1 , Luca Valle 3 , Michael Steinberg 3 , Thomas Kennedy 4 , Andrew Loblaw 4 , Amar Kishan 3 1 Tata Memorial Centre, Homi Bhabha National Institute, Radiation Oncology, Mumbai, India. 2 Tata Medical Centre, Radiation Oncology, Kolkata, India. 3 UCLA, Radiation Oncology, Los Angeles, USA. 4 Sunnybrook Hospital, Radiation Oncology, Toronto, Canada

Purpose/Objective:

The role of prophylactic nodal irradiation in high-risk prostate cancer is established. Ongoing randomised trials and prospective studies are evaluating its safety and efficacy with ultra-hypofractionation (SBRT). While 25Gy/5# is routinely used as the prophylactic pelvic dose, largely based on experience from rectal cancers, its adequacy for controlling prostate micro-metastasis is unknown. We aim to analyse the patterns of failures and outcomes, with particular emphasis on pelvic control, in patients receiving prophylactic pelvic radiotherapy for high risk prostate cancer using 25Gy in five fractions.

Material/Methods:

The SHARP consortium [1] comprises multi-institutional pooled prospective data of patients diagnosed with node negative, high-risk, non-metastatic prostate cancer treated with SBRT at participating centres in India, USA, and Canada. This database was queried for patients treated with SBRT to the prostate along with a prophylactic dose of 25Gy/5# to the pelvic regional lymph nodes. Biochemical failure post-radiotherapy was defined according to the Phoenix criteria. Recurrence was classified as local (intra-prostatic), regional (in pelvic nodes), or distant, or a combination of these. Clinical outcomes including biochemical failure-free survival (BFFS, biochemical failure or death), metastasis-free survival (MFS, distant metastases or death), and overall survival (OS, death due to any cause) were estimated using Kaplan-Meier method.

Results:

A total of 171 patients were eligible for analysis. Study cohort characteristics are described in Table 1. Two-thirds of the patients had Gleason grade group 4-5 cancer. About half of the cohort received 40 Gy in five fractions to the prostate, while the rest received 35-36.25Gy. After a median follow up of 51 months, biochemical failure was recorded in 19 (11.1%) patients. Of these, only three patients had a recurrence within the pelvic nodes, yielding a pelvic control of 98.2%. Only one patient had an isolated recurrence limited to the pelvic node. Majority (15/19) of the patients had a component of recurrence in distant sites, while 9/15 had isolated distant recurrence (Figure 1). Four-year BFFS was 86.1%, MFS was 91.3%, and OS was 94.6%.

Table 1. Cohort Characteristics

N=171 (100%)

Age (years)

Median, IQR

72 (68-78)

PSA at diagnosis (ng/mL)

Median, IQR

15.0 (8.5-25.0)