Clinical factors and dosimetry associated with the development of prostate brachytherapy-related urethral strictures: A matched case-control study.

PURPOSE: Urethral strictures are a rare complication of prostate brachytherapy (BXT), with prior studies showing radiation dose to the bulbomembranous urethra as being associated with stricture formation. This retrospective case-control study explored clinical and dosimetric parameters associated with the development of BXT-related urethral strictures. METHODS AND MATERIALS: A cohort of 34 patients developed urethral strictures after BXT at our institution for the period of 2008-2014. Each case was matched with two controls (68 controls) that had not developed a urethral stricture according to similar baseline clinical and dosimetric parameters. Stricture development was compared with clinical (i.e., age, smoking status, diabetes, hypertension, vascular disease, International Prostate Symptom Score, hormones) and dosimetric (i.e., prostate, urethra, urethral segments [base, midgland, apex, extraprostatic, and 5 mm margin]) variables. Statistical modeling approaches such as univariate, multivariate, and subset selection methods for risk prediction were applied to identify parameter(s) with best predictive ability of toxicity. The performances of models were ranked according to Akaike information criterion score. RESULTS: The results show that the R2 statistic increases from 6%, when only one parameter is included in the model, to almost 33%, when all the parameters are included. The best-fit subset of parameters included pretreatment International Prostate Symptom Score sum, urethra D30 Gy, urethra D5 Gy, and intraprostatic urethra with 5-mm margin V200 at the apex having the highest ability to predict the development of urinary strictures. CONCLUSIONS: This study used statistical modeling, a novel approach in prostate BXT dosimetric studies, to identify a subset of parameters with predictive ability in identifying patients who develop urethral strictures.

Quantifying 125I placement accuracy in prostate brachytherapy using postimplant transrectal ultrasound images.

PURPOSE: The quality of a prostate brachytherapy implant depends on the accurate placement of sources. This study quantifies the misplacement of 125I sources from the intended location using intraoperative ultrasound images. METHODS AND MATERIALS: 125I sources were manually identified in the postimplant ultrasound images and compared to the preoperative plan. Due to the subjective nature of the identifying sources, only sources identified with high confidence were included in the analysis. Misplacements from the original intended coordinate were measured along the X, Y, and Z axes and were stratified between overall misplacements and regions of the prostate gland. RESULTS: A total of 1619 125I sources using 357 strands were implanted in 15 patients' prostate glands, with 1197 (74%) confidently identified for misplacement analysis. The overall mean displacement was 0.49 cm and in the X, Y, and Z direction was 0.13, 0.15, and 0.38 cm, respectively. Greater source misplacement occurred in the anterior part of the prostate gland than the posterior part of the prostate gland by a factor 1.33 (p < 0.0001). Comparing sources in the lateral vs. medial regions of the prostate, no statistically significant differences on source misplacement were observed. Comparing misplacement in the base vs. midgland vs. apex identified the greatest difference between the base and midgland by a factor of 1.29 (p < 0.0001). CONCLUSIONS: This study has identified significant misplacement of 125I sources from their intended locations with the greatest error misplacement occurring in the Z direction. Source misplacement tends to occur more commonly in the anterior gland and in the base of the prostate.

Dosimetric prerequisites for routine clinical use of photon emitting brachytherapy sources with average energy higher than 50 kev.

This paper presents the recommendations of the American Association of Physicists in Medicine (AAPM) and the European Society for Therapeutic Radiology and Oncology (ESTRO) on the dosimetric parameters to be characterized, and dosimetric studies to be performed to obtain them, for brachytherapy sources with average energy higher than 50 keV that are intended for routine clinical use. In addition, this document makes recommendations on procedures to be used to maintain vendor source strength calibration accuracy. These recommendations reflect the guidance of the AAPM and the ESTRO for its members, and may also be used as guidance to vendors and regulatory agencies in developing good manufacturing practices for sources used in routine clinical treatments.