Assessment of I-125 seed implant accuracy when using the live-planning technique for low dose rate prostate brachytherapy

Abstract

BackgroundLow risk prostate cancers are commonly treated with low dose rate (LDR) brachytherapy involving I-125 seeds. The implementation of a ‘live-planning’ technique at the Royal Adelaide Hospital (RAH) in 2007 enabled the completion of the whole procedure (i.e. scanning, planning and implant) in one sitting. ‘Live-planning’ has the advantage of a more reliable delivery of the planned treatment compared to the ‘traditional pre-plan’ technique (where patient is scanned and planned in the weeks prior to implant). During live planning, the actual implanted needle positions are updated real-time on the treatment planning system and the dosimetry is automatically recalculated. The aim of this investigation was to assess the differences and clinical relevance between the planned dosimetry and the updated real-time implant dosimetry.MethodsA number of 162 patients were included in this dosimetric study. A paired t-test was performed on the D90, V100, V150 and V200 target parameters and the differences between the planned and implanted dose distributions were analysed. Similarly, dosimetric differences for the organs at risk (OAR) were also evaluated.ResultsSmall differences between the primary dosimetric parameters for the target were found. Still, the incidence of hotspots was increased with approximately 20% for V200. Statistically significant increases were observed in the doses delivered to the OAR between the planned and implanted data; however, these increases were consistently below 3% thus probably without clinical consequences.ConclusionsThe current study assessed the accuracy of prostate implants with I-125 seeds when compared to initial plans. The results confirmed the precision of the implant technique which RAH has in place. Nevertheless, geographical misses, anatomical restrictions and needle displacements during implant can have repercussions for centres without live-planning option if dosimetric changes are not taken into consideration.

A comparison of treatment planning techniques for low-dose-rate (LDR) prostate brachytherapy

“…Intraoperative plans produced significantly higher urethra D 10 (%), urethra D 30 (%), rectum D 2cc (Gy), and rectum D 0.1cc (Gy) values than preplans. Urethra and rectum doses were both approximately 3% higher in intraoperative plans than preplans, but these differences were not considered clinically significant (21). In this study, all three retrospectively applied techniques produced plans with significantly lower rectum D 0.1cc (Gy) values than delivered USLS plans.…”

“…Postimplant dosimetry of delivered plans can vary from theoretical preplanned dosimetry because of operatorrelated, patient-related, and prostate-related factors (21). This study compared idealized dosimetry of retrospective plans to the postimplant dosimetry of delivered plans.…”