PO60

Abstract

Purpose Isolated intraprostatic recurrence of prostate adenocarcinoma post radiotherapy presents a clinically challenging situation as surgical salvage options are associated with high morbidity. Brachytherapy can be used in these cases but supportive data are limited. The present study aims to present the acute toxicity results from patients who received salvage high-dose-rate prostate brachytherapy (sHDR-BT) for intraprostatic recurrence of prostate adenocarcinoma. Materials and Methods Fourteen consecutive patients treated with sHDR-BT between 2019 and 2022 were prospectively evaluated. To be considered for sHDR-BT, patients were required to have had received curative intent prostate radiotherapy previously and have biochemical failure. Patients were evaluated with bone scan and CT imaging of the chest abdomen and pelvis or PSMA-PET imaging. All patients had MRI of the prostate and trans-rectal ultrasound (US) guided biopsy proven confirmation of intraprostatic recurrence of disease. For patients who received prior BT, sHDR-BT was standardized with prescribed dose of 27Gy in 2 fractions to prostatic regions with confirmed disease on MR or biopsy. For patients had no history of prior BT, sHDR-BT was standardized with a prescribed dose of 21Gy in 2 fractions to the entire prostate with integrated boost irradiation of 27Gy in 2 fractions to the prostatic zones with confirmed disease on MR or biopsy. All plans were designed using trans-rectally acquired US image sets in Oncentra Prostate®. Post-treatment monitoring consisted of either in person or telephone (due to COVID-19) evaluation with AUA and CTCAE symptom assessments at 1, 3 and 12 months post treatment and yearly thereafter. Descriptive statistics were used to describe outcomes and the Mann-Whitney-Wilcoxon or Fisher-Freeman-Halton test used for comparisons. Results Median (inter-quartile-range) age prior to salvage treatment was 72 (67-76) years for the cohort. Seven (50%) patients had received external beam radiotherapy (EBRT) monotherapy (74-78Gy) as initial treatment for prostate cancer. One (7%) received EBRT (46Gy) + low-dose-rate BT (LDR-BT) (110Gy) and six (43%) received LDR-BT (144Gy) monotherapy as initial treatment. Four (29%) had received elective nodal irradiation (46Gy) with EBRT. Median time from initial radiotherapy to biopsy confirmation of recurrent disease was 77 (54-111) months. At baseline prior to sHDR-BT, 7 (50%) patient had significant lower urinary tract symptoms. Median AUA score was 8 (3-20) prior to sHDR-BT [Table 1]. 3 (21%) patients reported irregular bowel function and 2 (14%) reported hematochezia prior to sHDR-BT. At first fraction of sHDR-BT rectal D100cc was 8 (6-9)Gy, urethra D10% was 12 (11-15)Gy, urethra Dmax was 15 (13-16)Gy. At second fraction of sHDR-BT rectal D100cc was 8 (7-9)Gy, urethra D10% was 12 (12-14)Gy and urethra Dmax was 13 (12-16)Gy. At 1-month post treatment, median AUA score was 13 (18-21; p=0.48). On review of CTCAE scoring, at 1-month, there were no cases of grade 2+ bowel or rectal toxicity and no cases of grade 3+ urinary toxicity. Reported grade 2 urinary toxicities included 8 (57%) cases of bladder spasms, 2 (14%) cases of incontinence, 1 (7%) urinary obstruction and 2 (14%) reports of urinary urgency. Conclusions This study adds to the existing literature in confirming the acute toxicity profile of sHDR-BT is acceptable even without intraoperative MR guidance or software based MR-US image registration. Further study is ongoing to determine long-term efficacy and toxicity of treatment. Isolated intraprostatic recurrence of prostate adenocarcinoma post radiotherapy presents a clinically challenging situation as surgical salvage options are associated with high morbidity. Brachytherapy can be used in these cases but supportive data are limited. The present study aims to present the acute toxicity results from patients who received salvage high-dose-rate prostate brachytherapy (sHDR-BT) for intraprostatic recurrence of prostate adenocarcinoma. Fourteen consecutive patients treated with sHDR-BT between 2019 and 2022 were prospectively evaluated. To be considered for sHDR-BT, patients were required to have had received curative intent prostate radiotherapy previously and have biochemical failure. Patients were evaluated with bone scan and CT imaging of the chest abdomen and pelvis or PSMA-PET imaging. All patients had MRI of the prostate and trans-rectal ultrasound (US) guided biopsy proven confirmation of intraprostatic recurrence of disease. For patients who received prior BT, sHDR-BT was standardized with prescribed dose of 27Gy in 2 fractions to prostatic regions with confirmed disease on MR or biopsy. For patients had no history of prior BT, sHDR-BT was standardized with a prescribed dose of 21Gy in 2 fractions to the entire prostate with integrated boost irradiation of 27Gy in 2 fractions to the prostatic zones with confirmed disease on MR or biopsy. All plans were designed using trans-rectally acquired US image sets in Oncentra Prostate®. Post-treatment monitoring consisted of either in person or telephone (due to COVID-19) evaluation with AUA and CTCAE symptom assessments at 1, 3 and 12 months post treatment and yearly thereafter. Descriptive statistics were used to describe outcomes and the Mann-Whitney-Wilcoxon or Fisher-Freeman-Halton test used for comparisons. Median (inter-quartile-range) age prior to salvage treatment was 72 (67-76) years for the cohort. Seven (50%) patients had received external beam radiotherapy (EBRT) monotherapy (74-78Gy) as initial treatment for prostate cancer. One (7%) received EBRT (46Gy) + low-dose-rate BT (LDR-BT) (110Gy) and six (43%) received LDR-BT (144Gy) monotherapy as initial treatment. Four (29%) had received elective nodal irradiation (46Gy) with EBRT. Median time from initial radiotherapy to biopsy confirmation of recurrent disease was 77 (54-111) months. At baseline prior to sHDR-BT, 7 (50%) patient had significant lower urinary tract symptoms. Median AUA score was 8 (3-20) prior to sHDR-BT [Table 1]. 3 (21%) patients reported irregular bowel function and 2 (14%) reported hematochezia prior to sHDR-BT. At first fraction of sHDR-BT rectal D100cc was 8 (6-9)Gy, urethra D10% was 12 (11-15)Gy, urethra Dmax was 15 (13-16)Gy. At second fraction of sHDR-BT rectal D100cc was 8 (7-9)Gy, urethra D10% was 12 (12-14)Gy and urethra Dmax was 13 (12-16)Gy. At 1-month post treatment, median AUA score was 13 (18-21; p=0.48). On review of CTCAE scoring, at 1-month, there were no cases of grade 2+ bowel or rectal toxicity and no cases of grade 3+ urinary toxicity. Reported grade 2 urinary toxicities included 8 (57%) cases of bladder spasms, 2 (14%) cases of incontinence, 1 (7%) urinary obstruction and 2 (14%) reports of urinary urgency. This study adds to the existing literature in confirming the acute toxicity profile of sHDR-BT is acceptable even without intraoperative MR guidance or software based MR-US image registration. Further study is ongoing to determine long-term efficacy and toxicity of treatment.