Oral & Poster Presentation – Clinical Abstracts Archive

UK & Ireland Prostate Brachytherapy Conference 2016

Abstract number 8

A single centre analysis of change in dosimetric outcomes through implementing a 1-Stage intraoperative implant technique 

Keating F*; Gandon L*; Medford B* 
*Kent Oncology Centre, Maidstone Hospital 

AIMS/INTRODUCTION: The technique at this Centre for I-125 seed implant changed in June 2015 from a pre-planned 2-stage implant technique to a 1-stage intraoperative method. A dosimetric analysis was carried out comparing the accuracy of the intraoperative dosimetry with post-implant dosimetry. This was also compared with previously obtained 2-stage results. 

MATERIALS/METHODS: All pre-planning, intraoperative, and post-implant dosimetry was carried out using the Varian Variseed 8.0 treatment planning system. All implants employed fully-stranded seeds. 2-stage insertions were planned on volume studies taken up to 4 weeks prior to implant, from which customised pre-loaded needle kits were ordered. The intraoperative technique involved ordering seeds based on nomograms, as per the ‘4D Brachytherapy’ technique provided through BXTAccelyon. Pre-Loaded strands were ordered for the periphery. Loose seeds were ordered for constructing customised central strands based on the dosimetry seen after the peripheral strands had been implanted. These strands were constructed on-site during the procedure using a Manual Isoloader device. 

RESULTS: Number of seeds predicted by the nomogram was on average within two seeds of the final plan. Nine patients received >10% more seeds than the nomogram suggested. The average 2-step pre-planned prostate V100 was 99%, with the corresponding post-implant dosimetry showing V100 of 93%. The intraoperative technique averaged 98% planned V100, resulting in 97% post-implant dosimetry. Pre-planned prostate D90 was 122% 2-step, with 106% post-implant. Intraoperative D90 was 119% with 116% post-implant. Four 2-step, and six intraoperative patients receive a rectum D2cc > 145Gy. The average planned D30 to the urethra in the 2-step technique was 198Gy, and 183Gy in the intraoperative technique. 

CONCLUSIONS: Intraoperative insertion enabled an increase to average prostate D90 and V100 achieved by this centre. Urethral doses appear to have been reduced using the intra-operative technique. This has not yet been confirmed with post-implant dosimetry. Rectal doses have increased.