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

Overview

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.

Detailed description

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.

Interventions

• Diagnostic test Intervention Group
  Matching of delayed PET images with the standard CT scan

Primary outcome measures

• Matching Quality of Delayed PET with Standard CT [Time frame: Up to completion of the study, on average 1 year.]

Secondary outcome measures (2)

• Radiation Dose Optimization [Time frame: Up to completion of study, on average 1 year.]
• Patient Throughput and Experience [Time frame: Up to completion of study, on average 1 year.]

Eligibility criteria

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).

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: No

Study design

Allocation

Randomized

Model

Parallel assignment

Masking

Single blind

Primary purpose

Diagnostic

Study locations

Italy · 1 center

• IRCCS - Policlinico Universitario di Sant'Orsola — Bologna

Publications

• Hoffmann MA, Buchholz HG, Wieler HJ, Rosar F, Miederer M, Fischer N, Schreckenberger M. Dual-Time Point [68Ga]Ga-PSMA-11 PET/CT Hybrid Imaging for Staging and Restaging of Prostate Cancer. Cancers (Basel). 2020 Sep 28;12(10):2788. doi: 10.3390/cancers12102788. PMID 32998432
• Rahbar K, Afshar-Oromieh A, Bogemann M, Wagner S, Schafers M, Stegger L, Weckesser M. 18F-PSMA-1007 PET/CT at 60 and 120 minutes in patients with prostate cancer: biodistribution, tumour detection and activity kinetics. Eur J Nucl Med Mol Imaging. 2018 Jul;45(8):1329-1334. doi: 10.1007/s00259-018-3989-0. Epub 2018 Mar 14. PMID 29541812
• Haupt F, Dijkstra L, Alberts I, Sachpekidis C, Fech V, Boxler S, Gross T, Holland-Letz T, Zacho HD, Haberkorn U, Rahbar K, Rominger A, Afshar-Oromieh A. 68Ga-PSMA-11 PET/CT in patients with recurrent prostate cancer-a modified protocol compared with the common protocol. Eur J Nucl Med Mol Imaging. 2020 Mar;47(3):624-631. doi: 10.1007/s00259-019-04548-5. Epub 2019 Nov 1. PMID 31673789
• Derlin T, Weiberg D, von Klot C, Wester HJ, Henkenberens C, Ross TL, Christiansen H, Merseburger AS, Bengel FM. 68Ga-PSMA I&T PET/CT for assessment of prostate cancer: evaluation of image quality after forced diuresis and delayed imaging. Eur Radiol. 2016 Dec;26(12):4345-4353. doi: 10.1007/s00330-016-4308-4. Epub 2016 Mar 24. PMID 27011373
• Beheshti M, Manafi-Farid R, Geinitz H, Vali R, Loidl W, Mottaghy FM, Langsteger W. Multiphasic 68Ga-PSMA PET/CT in the Detection of Early Recurrence in Prostate Cancer Patients with a PSA Level of Less Than 1 ng/mL: A Prospective Study of 135 Patients. J Nucl Med. 2020 Oct;61(10):1484-1490. doi: 10.2967/jnumed.119.238071. Epub 2020 Feb 14. PMID 32060214
• Fonti R, Conson M, Del Vecchio S. PET/CT in radiation oncology. Semin Oncol. 2019 Jun;46(3):202-209. doi: 10.1053/j.seminoncol.2019.07.001. Epub 2019 Jul 26. PMID 31378377
• Fanti S, Minozzi S, Antoch G, Banks I, Briganti A, Carrio I, Chiti A, Clarke N, Eiber M, De Bono J, Fizazi K, Gillessen S, Gledhill S, Haberkorn U, Herrmann K, Hicks RJ, Lecouvet F, Montironi R, Ost P, O'Sullivan JM, Padhani AR, Schalken JA, Scher HI, Tombal B, van Moorselaar RJA, Van Poppel H, Vargas HA, Walz J, Weber WA, Wester HJ, Oyen WJG. Consensus on molecular imaging and theranostics in pro PMID 30507436
• Purohit RS, Shinohara K, Meng MV, Carroll PR. Imaging clinically localized prostate cancer. Urol Clin North Am. 2003 May;30(2):279-93. doi: 10.1016/s0094-0143(02)00184-2. PMID 12735504

Identifiers

NCT: NCT07357259 · SPIR202302

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗