Determination of dosimetric parameters for shielded ¹⁵³Gd source in prostate cancer brachytherapy

Abstract

BackgroundInterstitial rotating shield brachytherapy (I-RSBT) is a recently developed method for treatment of prostate cancer. In the present study TG-43 dosimetric parameters of a 153Gd source were obtained for use in I-RSBT.Materials and methodsA 153Gd source located inside a needle including a Pt shield and an aluminum window was simulated using MCNPX Monte Carlo code. Dosimetric parameters of this source model, including air kerma strength, dose rate constant, radial dose function and 2D anisotropy function, with and without the shields were calculated according to the TG-43 report.ResultsThe air kerma strength was found to be 6.71 U for the non-shielded source with 1 GBq activity. This value was found to be 0.04 U and 6.19 U for the Pt shield and Al window cases, respectively. Dose rate constant for the non-shielded source was found to be 1.20 cGy/(hU). However, for a shielded source with Pt and aluminum window, dose rate constants were found to be 0.07 cGy/(hU) and 0.96 cGy/(hU), on the shielded and window sides, respectively. The values of radial dose function and anisotropy function were tabulated for these sources. Additionally, isodose curves were drawn for sources with and without shield, in order to evaluate the effect of shield on dose distribution.ConclusionsExistence of the Pt shield may greatly reduce the dose to organs at risk and normal tissues which are located toward the shielded side. The calculated air kerma strength, dose rate constant, radial dose function and 2D anisotropy function data for the 153Gd source for the non-shielded and the shielded sources can be used in the treatment planning system (TPS).

Systematic Review of Intensity-Modulated Brachytherapy (IMBT): Static and Dynamic Techniques

“…In prostate cancer IMBT, mostly dynamicshielded techniques have been studied. 65,66,68,70,71 They have been able to improve OAR sparing known to be associated with lower rates of toxicitydespecially in relation to the urethra. 65,66,68 In breast cancer, IMBT techniques could possibly expand the number of patients who would be eligible for APBI by decreasing the number of patients whose anatomy would otherwise preclude them from that treatment option, although IMBT may not be able to offer sufficient advantages over SAVI to make its pursuit worthwhile in this context.…”

“…23,25,26,107 Regarding technique, dynamic shielded-applicator RSBT (Fig. 1 Q-T) [65][66][67][68][69][70][71][74][75][76][77][78][79][80]136 and static shieldedapplicator DirMBT approaches have been widely investigated ( Fig. 1 K-M).…”

“…Techniques were considered "dynamic" if the shield was translated or rotated during treatment relative to the source or regions of interest as part of the treatment plan. The subcategories of dynamic IMBT were "dynamic-shielded applicator" 24,25,67,69,[74][75][76][77][78][79][80] or "dynamic-shielded source," 65,66,68,[70][71][72][73] again based on whether the shield was associated with the applicator or the source. It is helpful to refer to Figure 1 throughout the following descriptions to visualize unfamiliar applicators and techniques.…”

“…1O) rotates within a nitinol needle (1.6 mm). 66 The dosimetric parameters of this applicator were studied for a 153 Gd source 71 and extensively with a multisource (up to 20) angular drive mechanisms and remote afterloader for practical implementation (with loss of inner nitinol catheter and alterations of various dimensions), 68 and the follow-up study used more patient-simulated plans and focused on urethral sparing and dose escalation. 65 Delivery time increases of 1283%-1440% (154 vs 12 minutes and 216 vs 15 minutes, respectively) were observed with dynamic shields associated directly with the source for use in interstitial prostate IMBT using 153 Gd when compared with conventional HDR-BT using 192 Ir.…”

“…"Dynamic" IMBT encompasses techniques in which the shield changes orientation relative to the source or tissue during treatment. Such approaches include rotating-shield brachytherapy (RSBT) [65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80] and dynamic modulated brachytherapy (DMBT). 24,25 In this study, we conduct a systematic review of the IMBT literature and then analyze the investigations by disease site, technique, planning algorithm, and study type.…”