To assess the safety of using combined Ga68-PSMA-PET/CT and multiparametric mpMRI for planning dominant intra-prostatic lesion (DIL) boost in prostate stereotactic radiotherapy (SBRT).
Patients with intermediate- or high-risk prostate adenocarcinoma with DIL identified on mpMRI and Ga68-PSMA-PET/CT and suitable for SBRT were enrolled in this phase II trial. Ga68-PSMA-PET/CT was fused with mpMRI for gross tumor volume (GTV) delineation. Semi-automatic contouring of DIL was performed using 20%-90% of SUVmax (DILx%). Concordance metrics were used to select DILx% matching closest to GTVMRI (GTVPET). Prostate (36.25Gy), pelvic nodes (25Gy), GTVunion: GTVPET ∪ GTVMRI (40Gy) and GTVoverlap: GTVPET ∩ GTVMRI (42.5Gy) were planned for 5 fraction SBRT. All patients received ADT for 6 months. The primary endpoint for the present analysis was concordance (volumetric and spatial) between GTVMRI and GTVPET. Secondary endpoints included the percentage SUVmax threshold for GTVPET contouring (%SUVGTV-PET) and cumulative acute (≤ 90 days) urinary and gastrointestinal (GI) toxicity using CTCAE v5.0.
Thirty patients (54% intermediate-risk, 46% high-risk) were enrolled. GTVMRI and GTVPET showed strong volumetric correlation (Spearman's correlation coefficient rho=0.817, 95% CI 0.64-0.91; p<0.001). Median dice similarity coefficient (DSC), jaccard index (JI), and mean Hausdorff distance (HDmean) for PET and MRI boost volumes were 0.56, 0.37, and 2.2, respectively. The median %SUVGTV-PET was 48% (IQR, 40%-58%). There was an inverse correlation between DIL SUVmax and %SUVGTV-PET (Spearman's correlation coefficient rho = -0.598, 95% CI lower -0.79, upper -0.29; p<0.001). Cumulative grade 2 acute urinary and GI toxicity were 13.3% and 6.6%, respectively, with no grade ≥3 toxicities.
Boost volumes on Ga68-PSMA-PET/CT and mpMRI were volumetrically similar, however, with poor spatial concordance. The %SUVmax threshold for GTVPET contouring correlated inversely with DIL SUVmax and was a median of 48%. Based on the favorable acute toxicity profile, PSMA-PET guided intra-prostatic boost is likely to be safe for dose escalation in prostate SBRT.
International journal of radiation oncology, biology, physics. 2025 Mar 28 [Epub ahead of print]
Maneesh Singh, Aparna Katdare, Suchismita Ghosh, Sayak Choudhury, Reena Phurailatpam, Divya Patil, Mahima Tiwari, Muhammed Anaz, Nazneen Husain Chougle, Nilesh Sable, Archi Agrawal, Akash Pawar, Venkatesh Rangarajan, Priyamvada Maitre, Vedang Murthy
Department of Radiation Oncology, Tata Memorial Centre, Homi Bhabha National Institute, Mumbai, India. Electronic address: ., Department of Radiodiagnosis, Tata Memorial Centre, Homi Bhabha National Institute, Mumbai, India., Department of Nuclear Medicine, Tata Memorial Centre, Homi Bhabha National Institute, Mumbai, India., Department of Medical Physics, Tata Memorial Centre, Homi Bhabha National Institute, Mumbai, India., Clinical Research Secretariat, Tata Memorial Centre, Homi Bhabha National Institute, Mumbai, India., Department of Radiation Oncology, Tata Memorial Centre, Homi Bhabha National Institute, Mumbai, India., Department of Radiation Oncology, Tata Memorial Centre, Homi Bhabha National Institute, Mumbai, India. Electronic address: .