A novel ¹⁶⁹Yb‐based dynamic‐shield intensity modulated brachytherapy delivery system for prostate cancer

Abstract

Purpose Intensity modulated brachytherapy (IMBT) is a novel high dose rate brachytherapy (HDR BT) technique which incorporates static or dynamic shielding to increase tumor coverage and/or spare healthy tissues. The purpose of this study is to present a novel delivery system (AIM‐Brachy) design that can enable dynamic‐shield IMBT for prostate cancer. Methods The AIM‐Brachy system dynamically controls the rotation of platinum shields, placed within interstitial catheters, which partially collimate the radiation emitted from an 169Yb source. Conventional HDR BT (10 Ci 192Ir) and IMBT (18 Ci 169Yb) plans were generated for 12 patients using an in‐house column generation‐based optimizer, coupled to a Geant4‐based dose calculation engine, RapidBrachyMC. Treatment plans were normalized to match the same PTV D90 coverage as the clinical plan. Intershield attenuation effects were taken into account. A sensitivity analysis was performed to evaluate the dosimetric impact of systematic longitudinal source positioning errors (±1 mm, ±2 mm, and ±3 mm) and rotational errors (±5∘, ±10∘, and ±15∘) on clinically relevant parameters (PTV D90 and urethra D10). Results The platinum shield reduced the dose rate on the shielded side at 1 cm to 18.1% of the dose rate on the unshielded side. For equal PTV D90 coverage, the urethral D10 was reduced by 13.3% ± 4.7%, without change to other plan quality indices (PTV V100, V150, V200, bladder V75, rectum V75, HI, COIN). Delivery times for HDR BT and IMBT were 9.2 ± 1.6 min and 18.6 ± 4.0 min, respectively. In general, the PTV D90 was more sensitive to source positioning errors than rotational errors, while the urethral D10 was more sensitive to rotational errors than source positioning errors. For a typical range of positioning errors (±1 mm, ±5∘), the overall tolerance was <2%. Conclusions The AIM‐Brachy system was proposed to deliver dynamic‐shield IMBT for prostate cancer with the potential to create a low dose tunnel within the urethra. The urethra‐sparing properties are desirable to minimize the occurrence and severity of urethral strictures or, alternatively, to provide a method for dose escalation.

A novel minimally invasive dynamic‐shield, intensity‐modulated brachytherapy system for the treatment of cervical cancer

“…9,18 Famulari et al recently reported on a miniature 18 Ci 169 Yb-based IMBT delivery system for interstitial prostate BT capable of delivering a 15 Gy prostate treatment in 20 min with a single source and achieving urethral D 10 (dose to medium in medium, D m,m ) sparing of 13.3% without affecting target coverage. 9 The purpose of this study was to evaluate plan quality improvements using needle-free 192 Ir-, 75 Se-, and 169 Yb-based IMBT compared to conventional 192 Ir IC-BT and IC/ IS-BT for cervical cancer. The MRI-compatible IMBT delivery prototype system for treatment of cervical cancer used in this study builds on our prior work.…”

169Yb‐based rotating shield brachytherapy for prostate cancer

“…Specifically, as long as positional error is kept below 1 mm and the angular orientation error is kept below 7° then the PTV D90% uncertainty is expected to be below 1.5% and urethra D10% uncertainty is expected to be below 3% 35 . Given the degree to which the measured average source positional error of 0.18 ± 0.12 mm and angular positioning error of 0.07° ± 0.78° of the prototype system exceeded that of previously validated thresholds, an extensive sensitivity analysis of source positioning was not performed in the current work 36 . Although mechanical accuracy requirements were met by the constructed prototype system, other factors affecting plan quality for a high‐dose‐gradient plan were not evaluated, such as catheter reconstruction accuracy, needle movement after insertion, and organ motion relative to needles.…”

Monte Carlo dosimetric characterization of a new high dose rate Yb brachytherapy source and independent verification using a multipoint plastic scintillator detector

“…A dwell time of 1 min was programmed for each of the four positions. The dose rates measured by the mPSD were compared to MC‐calculated data generated in a previous study 7 for this combined source and shield model. The dose distribution is centered along the catheter’s longitudinal axis and considers a source offset of 0.4 mm.…”

“…Recently, an 169 Yb source was proposed to deliver dynamicshield intensity modulated brachytherapy. 7 The source can be combined with a rotating platinum shield inside of an interstitial catheter to produce a highly anisotropic dose distribution. Platinum was selected as the shielding material due to its high density, high atomic number, machinability, and ferromagnetic properties.…”

“…Static and dynamic IMBT approaches can be used to modulate the dose distribution to the shape of the tumor, reduce the dose to organs at risk, provide a method for dose escalation, or allow for fewer catheters to be implanted. Recently, an Yb source was proposed to deliver dynamic‐shield intensity modulated brachytherapy 7 . The source can be combined with a rotating platinum shield inside of an interstitial catheter to produce a highly anisotropic dose distribution.…”