This Australian study is the largest published experience of the use of Ga68 PSMA PET/CT imaging in the context of previous primary radiotherapy for prostate cancer. 

This study evaluated 276 men who had undergone a Ga68 PSMA PET/CT for which the majority had PSA biochemical failure (mean PSA 3.60 ng/mL, range 0.01–83 ng/mL). Overall, 86% (239/276) men had positive scans with morethan half having evidence of local disease recurrence. Clearly, there are some limitations given that in the relatively small number of 33 men who underwent a prostate biopsy, only 28 men (85%) were confirmed to histological recurrence. Lymph node metastases were identified in 122 men (44%) of which 49 men had positive lymph nodes that were located outside the template for an extended pelvic lymph node dissection. Bone metastases were documented in 50 men.

A PSA of ≥2 was used as a surrogate for biochemical failure due to the influence of neoadjuvant androgen deprivation therapy (ADT) on PSA levels, particular in those who had received external beam radiotherapy. Not all men who underwent imaging had PSA biochemical failure. As many 26% of the scans (73 men) had PSA levels that were below 2ng/mL and of these, 75% were positive for either locally recurrent or metastatic prostate cancer. Given that the Phoenix definition for PSA biochemical failure as remained essentially unchanged since defined in 2006, higher-resolution imaging questions its current validity.

A key take-home message from this study is that recurrent disease is highly probable with biochemical failure following radiotherapy and for the majority, it will be beyond eligibility for potential salvage curative treatment. Additionally, this data supports a review of the current definition for biochemical failure following radiotherapy.

Written by: Henry Woo, MBBS, FRACS, Professor of Surgery, The University of Sydney, Surgery, Sydney Adventist Hospital Clinical School, Director of Uro-Oncology, Professor of Robotic Cancer Surgery, Chris O’Brien LifeHouse, Sydney, Australia

Read the Full-Text Article: The Use of 68Ga-PET/CT PSMA to Determine Patterns of Disease for Biochemically Recurrent Prostate Cancer Following Primary Radiotherapy