Measurement uncertainty analysis of low-dose-rate prostate seed brachytherapy: post-implant dosimetry

Abstract

The minimal dose covering 90 % of the prostate volume--D 90--is arguably the most important dosimetric parameter in low-dose-rate prostate seed brachytherapy. In this study an analysis of the measurement uncertainties in D 90 from low-dose-rate prostate seed brachytherapy was conducted for two common treatment procedures with two different post-implant dosimetry methods. The analysis was undertaken in order to determine the magnitude of D 90 uncertainty, how the magnitude of the uncertainty varied when D 90 was calculated using different dosimetry methods, and which factors were the major contributors to the uncertainty. The analysis considered the prostate as being homogeneous and tissue equivalent and made use of published data, as well as original data collected specifically for this analysis, and was performed according to the Guide to the expression of uncertainty in measurement (GUM). It was found that when prostate imaging and seed implantation were conducted in two separate sessions using only CT images for post-implant analysis, the expanded uncertainty in D 90 values were about 25 % at the 95 % confidence interval. When prostate imaging and seed implantation were conducted during a single session using CT and ultrasound images for post-implant analysis, the expanded uncertainty in D 90 values were about 33 %. Methods for reducing these uncertainty levels are discussed. It was found that variations in contouring the target tissue made the largest contribution to D 90 uncertainty, while the uncertainty in seed source strength made only a small contribution. It is important that clinicians appreciate the overall magnitude of D 90 uncertainty and understand the factors that affect it so that clinical decisions are soundly based, and resources are appropriately allocated.

Feasibility and Clinical Value of CT-Guided 125I Brachytherapy for Pain Palliation in Patients With Breast Cancer and Bone Metastases After External Beam Radiotherapy Failure

“…125 I brachytherapy was a feasible treatment modality for bone metastases in this study, with a success rate of up to 97.6%. According to disease progression, we could implant the 125 I seeds to the same or other lesions after the first treatment cycle without increasing the risk of complications (21). In this study, TPS was used to plan 125 I seed implantation in accordance with the American Brachytherapy Society guidelines (more than 95% of the tumor receives 100% of the prescribed dose) (12).…”

Development of an MRI-Based Workflow for Post-implant Dosimetry of Prostate Low-Dose-Rate (Ldr) Brachytherapy

“…values (Gregory, Pattison, & Bibbo, 2015) and V100 (volume that is receiving 100% of the prescribed dose) has been reported to be extremely sensitive to prostate contouring errors and uncertainties (Mashouf et al, 2016). Recently magnetic resonance imaging (MRI) has been introduced to the LDR post-implant dosimetry workflow to benefit from its superior soft-tissue contrast (Ash et al, 2000;Davis et al, 2012;Segedin & Petric, 2016).…”

The impact of body mass index on dosimetric quality in low-dose-rate prostate brachytherapy

“…Although a D 90 > 130 Gy is considered adequate by the American Brachytherapy Society [8], various studies have shown that a D 90 ≥ 140 Gy is associated with improved biochemical control [9, 10]. Previous studies have found that specific factors such as prostate volume, post-implant prostatic edema, and the number of seeds implanted can influence D 90 [11, 12, 13]. …”