S. Ramadan1, D. A. Loblaw2, A. Dhar1, H. Fakir1, L. Mendez1, M. Wronski3, J. Conyngham4, Z. Kassam5, V. S. Tan1, P. Crivellaro5, A. Ward6, J. Thiessen6, T. Y. Lee6, D. Laidley7, and G. S. Bauman1; 1Department of Radiation Oncology, London Health Sciences Centre, London, ON, Canada, 2Department of Radiation Oncology, Odette Cancer Centre, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada, 3Department of Medical Physics, Odette Cancer Centre, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, 4Patient Partner, London, ON, Canada, 5St. Josephs Hospital, London, ON, Canada, 6Department of Medical Biophysics, Western University, London, ON, Canada, 7University of Western Ontario, London, ON, Canada
Purpose/Objective(s): Stereotactic body radiation therapy (SBRT) with boosting of dominant intraprostatic lesions (DILs) has been shown to be effective in managing unfavorable-intermediate and high-risk prostate cancer. The ARGOS-CLIMBER trial is a phase I/II study utilizing a combined PSMA PET/MRI approach to identify DILs and affected lymph nodes in this patient population. This interim analysis looked at the acute toxicity resulting from five fraction SBRT treatments with simultaneous boosting of focal disease. Materials/
Methods: Patients were included if they had unfavorable-intermediate or high-risk disease, were ECOG 0-1, age >18 with histologically confirmed carcinoma of the prostate. Patients with clinical T4, prior prostate treatment, or those who could not receive PET/MRI were excluded. SBRT treatments were planned to 35Gy/5 fractions to the prostate with a maximum boost up to 50Gy/5 fractions. Seminal vesicles (SV) and pelvic lymph nodes could receive 25Gy/5 with a maximum boost up to 35Gy/5 fractions for positive nodes (up to 50Gy/5 for involved SV). Toxicity was assessed according to CTCAE V5.0 during and at 6 weeks post-treatment. Results: In total 50 patients were treated. A minority were rural (9%) or low-income (11%) from a socioeconomic perspective. Patients were found to have the following T staging by MRI: T0 n=1 (2%), T1c n=8 (16%), T2a n=9 (18%), T2b n=4 (8%), T2c n=2 (4%), T3a n=18 (36%), T3b n=6 (12%), T4 n=2 (4%). Nodal staging by MRI found N0: n=45 (90%) and N1: n=5 (10%) whereas PET imaging identified N0: n=40 (80%) and N1: n=10 (20%). Overall, n=36 (72%) had lymph nodes electively covered to 25 Gy with a median D99 of 24.1 Gy (range: 23.79 – 25.3). A total of n=10 (20%) of patients had PET-identified lymph node disease boosted to 35Gy with a median D99 of 34.8 Gy (range: 33.97-35.7). The median D99% DIL coverage was 42.5 Gy (range 40.0 – 50.5). SBRT-related acute toxicity was collected. The highest acute GI toxicity per patient was no toxicity n=20 (40%), grade 1 n=20 (40%), grade 2 n=9 (18%), and grade 3 n=1 (2%). The highest acute GU toxicity per patient was no toxicity n=13 (26%), grade 1 n=21 (42%), grade 2 n=15 (30%), and grade 3 n=1(2%). The highest acute sexual toxicity per patient was no toxicity n=40 (80%), grade 1 n=4 (8%), grade 2 n=2 (4%), grade 3 n=4 (8%). The grade three toxicities were categorized as follows: GI - diarrhea n=1, GU - pain from fiducials and catheterization n=1, Sexual - Erectile dysfunction n=4. The highest other acute toxicities per patient were no toxicity n=35 (70%), Grade 1 n=14 (28%), and Grade 2 n=1 (2%). Other toxicities included pain, fatigue, insomnia, and anxiety. There were no acute grade 4 or 5 toxicities identified. Conclusion: PSMA PET and MRI-guided SBRT boosting of DILs was found to be both feasible and safe with a limited acute toxicity profile. Ongoing follow-up is underway to identify late toxicities, quality of life, and disease-free survival associated with focused SBRT treatments.
