Recent evidence suggests that both standard-time and delayed-time \[⁶⁸Ga\]Ga-PSMA PET acquisitions can reveal clinically relevant findings, and neither phase should be excluded a priori in routine practice. This study evaluates a streamlined dual-phase protocol consisting of:
* A standard whole-body PET/CT acquisition performed 60 minutes after radiotracer administration. * A delayed pelvic PET-only acquisition performed 90 minutes post-injection, reconstructed using the attenuation-correction CT (CT/AC) obtained from the initial whole-body scan.
Because the prostate gland and pelvic lymph nodes exhibit minimal physiological mobility, accurate PET-CT anatomical correspondence can be maintained through careful patient repositioning, without repeating the CT scan.
The main advantage of this protocol is a reduction in patient radiation exposure, as the delayed phase does not require a second CT scan. It also reduces in-department time and maintains diagnostic quality of PET interpretation, provided that the PET-CT alignment remains acceptable.
This method may additionally enhance workflow efficiency in the Nuclear Medicine Unit by allowing early identification-based on predefined clinical parameters-of patients most likely to benefit from delayed pelvic imaging.
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.
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).
Parallel
Intervention Group
Diagnostic testMatching of delayed PET images with the standard CT scan
Matching Quality of Delayed PET with Standard CT
Evaluation of the actual matching accuracy between delayed PET images-reconstructed and attenuation-corrected using the dedicated CT/AC dataset-and the standard CT scan within the new procedural approach to \[68\]Ga-PSMA PET/CT. Three Technologist of Medical Imaging (TSRM1, TSRM2, TSRM3) will evaluate the images independently, in a blinded manner, at three separate time points (t1, t2, t3). The registration accuracy between delayed PET images and the standard CT scan will be evaluated using a qualitative questionnaire based on the evaluators' professional experience (minimum of five years in Nuclear Medicine). Image registration will be scored on a 5-point ordinal scale, ranging from 1 (complete mismatch) to 5 (perfect registration). Unit of Measure: 5-point ordinal scale (1-5)
Radiation Dose Optimization
Change in CTDIvol (Computed Tomography Dose Index volume) in the experimental arm. CTDIvol (mGy) will be used to assess changes in radiation dose related to the experimental protocol. Unit of Measure: Milligray (mGy)
Patient Throughput and Experience
Comparison of patient experience in the Nuclear Medicine Unit between the two study groups. Patient experience will be evaluated using a structured, patient-reported questionnaire at the end of the \[68\]Ga-PSMA PET/CT examination, based on the perceived quality of staff information regarding waiting times. Unit of Measure: \- Patient experience: 5-level ordinal scale (Very poor → Excellent)
Radiation Dose Optimization
Change in Dose Length Product (DLP) in the experimental arm. DLP (mGy \* cm) will be used to assess changes in cumulative radiation dose along the scan length associated with the experimental protocol. Unit of Measure: Milligray·centimeter (mGy·cm) Notes: This measure is part of Secondary Outcome 2: Radiation Dose Optimization
Radiation Dose Optimization
Change in Effective Dose in the experimental arm. Effective dose (mSv) will be estimated to evaluate overall patient radiation exposure associated with the experimental protocol. Unit of Measure: Millisievert (mSv) Notes: This measure is part of Secondary Outcome 2: Radiation Dose Optimization
Patient Throughput and Experience
Comparison of perceived waiting time in the Nuclear Medicine Unit between the two study groups. Perceived waiting time will be reported by patients for each questionnaire item in minutes (m). Minutes (categorical ranges per questionnaire item, e.g., \<5, 5-10, 10-15, \>15) Notes: This parameter is part of the single secondary outcome 3: 3. Patient Throughput and Experience
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