Intra-prostatic Fiducial Markers and Concurrent Androgen Deprivation

Abstract

To document the case of a man with adenocarcinoma of the prostate treated with external beam radiotherapy and concurrent androgen deprivation. The man, who received 79.8 Gy in 42 fractions of radiotherapy over 8.5 weeks using three intra-prostatic gold fiducial markers for on-line set-up correction, started an anti-androgen 2.5 weeks before radiotherapy, on the day of his planning computed tomography, and a gonadotropin-releasing hormone agonist on his first day of radiotherapy. In the sixth week of radiotherapy, the distance between the fiducial markers had diminished: superior to posterior-mid (from 19 to 11 mm), posterior-mid to inferior (from 19 to 15 mm), and superior to inferior (from 31 to 22 mm), so the patient was rescanned. Between the two planning computed tomographies, the prostate volume had decreased from 44.3 to 28.3 cm3 (-36%). Had the planned radiotherapy been delivered to the anatomy of the rescan, the dose to the rectal wall would have exceeded the planned dose-volume histogram constraints. However, with the patient set up to the fiducial markers, the dose-volume histogram constraints for the rectal wall and bladder wall were met throughout the course of radiotherapy. Involution of the prostate owing to concurrent androgen deprivation may cause in-migration of implanted fiducial markers and excessive dose to the rectal wall. With concurrent androgen deprivation, daily on-line set-up correction to fiducial markers can aid in safe dose escalation.