Andrej Bece
St George Hospital
Radiation Oncology Fellow

Komiti Enari
Medical Physicist
St George Hospital

Andrew Howie
Medical Physicist
St George Hospital

Yaw Chin
Radiation Oncologist
St George Hospital

Joseph Bucci
Radiation Oncologist
St George Hospital

Background:

Dose parameters on post-implant dosimetry (PID), particularly prostate D90, have been correlated with biochemical disease outcome following permanent prostate brachytherapy (PPB)1. As such, routine PID is recommended by international consensus guidelines2. In cases of suboptimal dosimetry both supplemental external beam radiation (EBRT) and permanent seed re-implantation (RI) have been utilised. To date there are only limited case series describing RI for suboptimal PID. We aim to report our technical and clinical experience with RI in this subset of patients.

Methods:

1,116 patients underwent PPB using Iodine-125 seeds between February 2002 and November 2016. Post-implant dosimetry with US-CT fusion was performed at day 30. All patients were followed up at 4-12 month intervals for biochemical or clinical recurrence. Toxicity and quality of life (QOL) was assessed prospectively using validated tools (IPSS, IIEF, QLQ C30, EPIC Bowel). Patients were offered RI where PID was poor (D90 < 119 Gy or V100 < 75%) or suboptimal (D90 < 130 Gy or V100 < 85%) and where dose deficiency correlated with known disease on biopsy. An analysis of all patients undergoing RI was undertaken, reviewing dosimetric, biochemical, clinical and toxicity outcomes.

Results:

8 patients were identified who underwent RI since March 2011. 543 patients over this same period had a single PPB implant. Day 30 post-implant median D90 and V100 were 126 Gy (82.5-135.0 Gy) and 78.0% (47.5-84.74%), respectively. 7-24 (mean 13) additional seeds were re-implanted at a median 63 days (42-252 days) after initial implant. Biopsy-proven disease was present at the site of under-dosing in all patients. Re-implantation dosimetry was excellent in all patients with median cumulative D90 and V100 of 157 Gy (140-175 Gy) and 93.9% (86.2-98.0%), respectively. Median follow up for patients treated prior to 2016 (n=5) was 22 months. There were no biochemical or clinical recurrences and toxicity and QOL outcomes were comparable to contemporaneous patients undergoing a single implant. No grade 3 adverse events occurred in these patients. One patient developed a benign PSA bounce.

Conclusions:

We present the largest series of PPB re-implantation for patients with initially suboptimal dosimetry. RI improves subsequent PID while avoiding the need for supplemental EBRT. There were no biochemical or clinical failures in these patients and no increase in toxicity over that expected from primary PPB. Judicious use of RI should be considered a standard approach in experienced centres where PID is inadequate.


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