PSMA MRI Guided Prostate SABR ARGOS-CLIMBER Phase I/II Trial: A Primary Endpoint Analysis.

Objective: The XXXXX trial is a multi-institutional phase I/II study utilizing a combined PSMA PET/MRI approach to treat dominant intraprostatic lesions (DILs) and affected lymph nodes in unfavorable intermediate and high-risk prostate cancer using a five fraction SABR and simultaneous in-field boost (SIB) technique. Here we report on the primary endpoint of toxicity within 6 months of treatment.

Methods: SIB volumes were defined utilizing a PET/MRI acquired using 18F-PSMA 1007. Five fraction SABR was planned to deliver doses (maximum SIB) to prostate 35 Gy (50 Gy), SV 25 Gy (50 Gy) and lymph nodes 25 Gy (35 Gy) while respecting OAR's. Toxicity and QOL were assessed according to CTCAE 5.0 and EPIC-26 during radiation, at 6 weeks post-treatment and at 6 months post treatment.

Results: In total 50 patients were treated, 23 patients had unfavorable intermediate risk disease, 23 were high risk, and 4 were very high-risk prostate cancer. Median prostate SIB of 41.6 Gy (IQR: 39.3-44.8 Gy) was delivered to a median of 1 intra-prostatic lesion. Eighteen patients received nodal treatment. There was a single acute grade 3 GI toxicity of diarrhea and a single late grade 4 GI toxicity of bleeding. With a median follow-up of 12 months, the EPIC-26 scale showed an increase in urinary irritation (p < 0.001) and no differences for urinary incontinence (p=0.12) and GI QOL (p=0.65) and a decrease in hormonal/sexual QOL (p < 0.001 and p < 0.001). Mean ± SD PSA, maximum SUV on PET and maximum MRI PiRADS scores at baseline to 6 months were 15.4 ± 10.3 to 0.18 ± 0.40 ng/mL, 25.5 ± 19.5 to 4.5 ± 7.7, and 4.7 ± 0.6 to 2.9 ± 1.5 respectively.

Conclusions: XXXXX demonstrated acceptable toxicity using 5 fraction SABR with PET/MRI directed SIB to prostate and lymph nodes.