Delayed Pelvic Imaging With [68]Ga-PSMA PET/CT in a Patient With High-risk Prostate Cancer.

This study evaluates a modified dual-phase [⁶⁸Ga]Ga-PSMA PET/CT protocol designed to reduce radiation exposure and streamline workflow while maintaining diagnostic quality in the assessment of prostate cancer. Conventional imaging often includes a standard whole-body PET/CT acquisition at approximately 60 minutes post-injection followed by a delayed pelvic PET/CT, which can provide additional lesion detectability but requires a second CT scan. The additional CT increases both radiation dose and examination duration.

The proposed protocol replaces the delayed CT with a PET-only pelvic acquisition performed 90 minutes post-injection. Delayed PET images are reconstructed and attenuation-corrected using the CT dataset obtained during the initial whole-body acquisition. This approach is feasible because pelvic structures relevant to prostate cancer-such as the prostate gland and pelvic lymph nodes-exhibit limited physiological motion compared with intraperitoneal organs, allowing reliable PET-CT anatomical correspondence through optimized patient repositioning.

The study adopts a randomized, two-arm design including patients undergoing staging for newly diagnosed prostate cancer or evaluation of biochemical recurrence. Randomization is stratified by prior radical prostatectomy to account for potential anatomical variability. The control arm follows the standard clinical workflow with both standard and delayed PET/CT acquisitions. The intervention arm undergoes standard whole-body PET/CT at 60 minutes and delayed PET-only imaging at 90 minutes.

Anatomical matching between delayed PET images and the CT dataset will be independently evaluated by three Medical Imaging Technologists (TSRM1, TSRM2, TSRM3) across three blinded reading sessions. Each rater will score image alignment using a standardized 1-5 Likert scale. The primary endpoint is the quality of PET-CT matching, assessed through Fleiss' kappa statistics to quantify interrater agreement and compare matching performance between the two imaging workflows.

Secondary objectives examine the potential reduction in radiation exposure, measured through CTDIvol and DLP values obtained from the CT Dose Report, and the impact on patient experience and departmental efficiency. Patient-perceived waiting time and comfort will be assessed through a short questionnaire administered after the examination, while objective in-department duration will be extracted from institutional scheduling records.

If effective, the streamlined protocol may support broader adoption of CT-free delayed pelvic imaging by demonstrating that optimized technologist-led positioning can maintain diagnostic interpretability while improving patient-centered outcomes and reducing overall radiation burden.

Inclusion criteria

• Newly diagnosed prostate cancer undergoing staging, or
• Biochemical recurrence following prior radical-intent therapy (surgery and/or radiotherapy), or
• High-risk prostate cancer, defined as Gleason Score ≥ 8 or PSA ≥ 20 ng/mL.
• Written informed consent and authorization for personal data processing.

Exclusion criteria

• Genitourinary comorbidities that could interfere with imaging or interpretation.
• Intermediate- or low-risk prostate cancer.
• Delayed acquisition performed on a PET/CT scanner different from the standard acquisition.
• Additional PET/CT required due to artifacts compromising diagnostic quality (e.g., urinary retention, excessive motion).
• Patients previously enrolled who require repeat PET/CT as a new visit.
• Inability to provide informed consent or impaired decision-making capacity.
• Known hypersensitivity to the radiopharmaceutical or its components.
• Contraindications to PET/CT (e.g., severe claustrophobia, morbid obesity, inability to cooperate).