ASTRO 2021: Detection Failure Patterns Using Advanced Imaging in Patients with Biochemical Recurrence Following Low Dose Rate Brachytherapy for Prostate Cancer

(UroToday.com) The 2021 American Society for Radiation Oncology (ASTRO) Hybrid Annual Meeting included a presentation by Dr. Kilian Salerno discussing detection failure patterns using advanced imaging in patients with biochemical recurrence following low dose rate brachytherapy for prostate cancer.

 Dr. Salerno emphasized that using prostate mpMRI, PSMA-based PET/CT, and confirmatory pathology, the objective of this study was to identify patterns of failure among patients with biochemical recurrence after definitive radiotherapy, including LDR brachytherapy. Patients were included in this study if they had clinical progression or biochemical recurrence after LDR brachytherapy +/- external beam radiotherapy +/- ADT and were enrolled on one of three prospective IRB approved protocols of advanced imaging. All patients underwent a 3T mpMRI, a subset underwent PSMA-based PET/CT, and pathologic confirmation was obtained unless contraindicated. The location of the recurrence within the prostate, seminal vesicles, pelvic lymph nodes, or distant metastases was scored.

There were 58 patients evaluated with mpMRI (January 2011-April 2011) of which seven were censored. The patient characteristics stratified by brachytherapy versus brachytherapy + external beam radiotherapy are as follows:

 

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The median external beam radiotherapy dose was 45 Gy (41.1-52.5), 2/36 patients undergoing brachytherapy had ADT, and 10/15 patients undergoing brachytherapy + external beam radiotherapy had ADT. For patients undergoing mpMRI, prostate/seminal vesicle lesions were detected in 43 of 51 patients. For patients undergoing PSMA-based imaging (n=32), the site of detection was the prostate (n=17) and seminal vesicles (n=11), pelvic lymph nodes (n=16), distant metastasis (n=6), and penile bulb (n=1). The site of recurrence was confirmed with a biopsy in 34 of 36 patients, including the prostate/seminal vesicles (n=34), lymph node (n=1), and lung (n=1). Specific to the prostate/seminal vesicle biopsies, recurrence was confirmed in 32 of 34 patients, including the prostate (n=27) and seminal vesicles (n=14). With regards to pattern of recurrence, these are summarized in the following table:

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For patients with prostate only recurrence, this occurred more commonly in brachytherapy (36.1%) than brachytherapy + external beam radiotherapy (13.3%) patients, whereas patients undergoing brachytherapy alone and no distant only sites of metastasis compared to 6.7% for brachytherapy + external beam radiotherapy. As follows are representative images of mpMRI and DCFPyL imaging showing isolated recurrence in the right seminal vesicle:

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Within the prostate, recurrences were most common in the mid gland (69.7%) followed by base (60.6%), and apex (48.5%):

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Dr. Salerno concluded her presentation with the following take-home messages:

  • In this cohort of patients with recurrence of prostate cancer following LDR brachytherapy +/- external beam radiotherapy, the predominant pattern of recurrence was local and involving the prostate and seminal vesicles (67% and 39%), the anterior prostate and transition zone recurrences were overrepresented relative to typical distributions at diagnosis, and isolated distant failure was rare
  • mpMRI and PSMA-based imaging provided complementary information to localize sites of recurrence
  • PSMA corroborated the majority of mpMRI findings and often demonstrated occult lymph node involvement or distant metastasis
  • These results should be confirmed in larger subsets with available post-implant dosimetry
  • If confirmed, these findings could support the use of pretreatment mpMRI to guide patient selection and inform LDR implant technique

 

Presented By: Kilian Salerno, MD, National Cancer Institute, Bethesda, MD

Written By: Zachary Klaassen, MD, MSc – Urologic Oncologist, Assistant Professor of Urology, Georgia Cancer Center, Augusta University/Medical College of Georgia, @zklaassen_md on Twitter during the 2021 American Society for Radiation Oncology (ASTRO) Hybrid Annual Meeting, Sat, Oct 23 – Wed, Oct 27, 2021.

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