3357 - Salvage Comprehensive Nodal VMAT with PSMA PET-Guided Boost plus ADT for Node-Only Relapse after Definitive Prostate IMRT

12:45pm - 02:00pm PT

Hall F

Screen: 26

POSTER

Presenter(s)

Haripriya Vettivelu, BMed - Mid North Coast Cancer Institute (MNCCI) Coffs Harbour, Coffs Harbour, NSW

H. K. Vettivelu¹, R. W. J. Lim², T. Salma³, and T. P. Shakespeare⁴; ¹Mid North Coast Cancer Institute, Coffs Harbour, Australia, ²South Western Sydney Local Health District, Sydney, Australia, ³Northern NSW Local Health District, Cudgen, Australia, ⁴Rural Clinical School, University of New South Wales, Coffs Harbour, Australia

Purpose/Objective(s): Several guidelines for lymph node (LN) failure after prior prostate-only radiation therapy (RT) recommend curative salvage RT treating the whole pelvis electively, with simultaneous integrated boost (SIB) to PSMA PET +ve LNs, and long term ADT. Few series evaluate outcomes of this comprehensive salvage nodal therapy (CSNT) approach, specifically in patients who received prior prostate RT without elective LN RT. Our primary endpoint was to evaluate progression-free survival (PFS) after CSNT, with secondary endpoints metastasis-free survival (MFS), prostate cancer-specific survival (PCaSS), overall survival (OS), and factors impacting PFS.

Materials/Methods: We retrospectively reviewed our EMR for men with PSMA PET +ve LN failure after prior prostate-only RT (without initial elective LN RT) and salvaged with CSNT between 2016-2023. PFS, MFS, PCaSS and OS were evaluated via the Kaplan Meier method, and univariate and multivariable (MVA) analyses conducted using cox regression. Variables included fractionation (conventional vs hypofractionation), number of LNs (1 vs 2 or more), common iliac (CI) or paraaortic (PA) LN involvement vs pelvic only, risk group at initial prostate RT (intermediate vs high), PSA level prior to CSNT (<2 vs 2 or more), and time between initial prostate RT and initiation of CSNT (4 years or less vs >4 years).

Results: A total of 41 patients were eligible, with a median follow up of 49 months (range 16-105 months). All patients had received prior dose-escalated prostate-only RT and ADT for intermediate risk 44% or high risk 56% localised disease. At LN failure, the median number of PET +ve LNs involved was 2 (range 1-16), and the median PSA prior to CSNT was 1.51 (range 0.7-9.9). CI or PA involvement occurred in 32%. All salvage RT was delivered via VMAT, and all men received neoadjuvant and adjuvant ADT. 63% patients were hypofractionated over 20Fx: the median SIB dose to PET positive LNs was 55Gy (range 55-60Gy) and elective LN median dose 45Gy (range 44-45Gy). The median SIB dose for conventional fractionation was 81Gy (range 73.8-81Gy) in 1.8-2.0Gy/Fx, and median elective LN dose was 60Gy (range 54-60Gy). Median duration of ADT with CSNT was 3 years (range 6 months-5 years). 5 year PFS, MFS, PCaSS and OS was 60%, 93%, 100% and 92% respectively. On MVA, patients with prior RT to high risk disease (p=0.03), higher PSA at relapse (p=0.049) and shorter time between prior RT and CSNT (p=0.01) had worse PFS.

Conclusion: Salvage comprehensive nodal VMAT with PSMA PET-guided boost and ADT for LN-only failure after definitive prostate RT results in high rates of cancer control and survival. The success of CSNT may partially mitigate any benefit from elective LN RT when treating localised prostate cancer. Future research should confirm efficacy and predictive factors, and whether CSNT offers an alternative to elective LN RT when first treating localised disease.