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Comparative Analysis of 68Ga-Prostate-Specific Membrane Antigen Positron Emission Tomography/Computed Tomography and Multiparametric Magnetic Resonance Imaging for Gross Tumor Volume Delineation in Radiation Therapy Planning of Prostate Cancer

Year: 2025

Type: article

Abstract: Objective Magnetic resonance imaging (MRI) with multiparametric assessment is a cornerstone in radiation therapy planning for primary prostate cancer (PCa), offering potential for focal dose escalation to dominant intraprostatic lesions to enhance PCa management. The prostate-specific membrane antigen (PSMA), frequently overexpressed in PCa, has led to the development of 68 Ga-labelled PSMA inhibitors for positron emission tomography/computed tomography (PET/CT), showing promising results in PCa detection. This study aimed to conduct a comparative analysis of 68 Ga-PSMA PET/CT and mpMRI in delineating the gross tumor volume (GTV) in PCa. Materials and Methods A retrospective analysis was performed on 25 PCa patients who underwent 68 Ga-PSMA PET/CT and mpMRI at two distinct centers. The GTVs were delineated on MRI (GTV-MRI) by two nuclear medicine physicians and one radiation oncologist independently, while GTVs based on PET/CT were outlined by two nuclear medicine physicians (GTV-PET). The laterality (left, right, and bilateral prostate lobes) on mpMRI and PET/CT was assessed. To account for registration uncertainties, both GTV-PET and GTV-MRI were expanded isotropically by 5mm to form the planning target volume (PTV), and the overlap between specific PTVs and their corresponding GTVs was quantified. Results The average GTV-MRI and GTV-PET were 5.468±11.6 cm³ and 11.136±14.3 cm³, respectively, with GTV-PET significantly larger than GTV-MRI (p=0.003). GTV-MRI exhibited an intersection with GTV-PET of 3.5 ± 6.0 cm³. The PTV derived from PSMA PET/CT encompassed 62 ± 27% of GTV-MRI, with 44.4% of patients having the PTV covering 100% of GTV-MRI. Conversely, the PTV based on GTV-MRI covered 50 ± 31% of GTV-PET. Conclusion 68 Ga-PSMA PET/CT and mpMRI demonstrated consistent outcomes in 47% of patients (40% - 54% of lesions). Notably, GTV-PET was larger than GTV-MRI, indicating a potential role for 68 Ga-PSMA PET/CT in radiation therapy planning for targeted radiation delivery to prostate cancer.

Source: Advances in Radiation Oncology

DOI: 10.1016/j.adro.2025.101821