SU-F-BRA-11: Dynamic Modulated Brachytherapy (DMBT): Concept, Design, and Application

Abstract

Purpose: To build, from grounds up, a novel dynamic modulated brachytherapy (DMBT) system for treating intracavitary tumors, such as rectal, breast, and vaginal cancers. The key component of the innovation is in enabling “dynamic” modulation (i.e., Ir‐192 source is highly collimated and dynamically moved during delivery) to create an unparalleled dose conformality compared with the currently available commercial systems/applicators. We show that our proposed prototype system (both soft‐ and hard‐ware) is extremely efficient in maximizing target volume coverage while minimizing dose to healthy tissues. Methods: Our system uses a 1.9‐cm diameter tungsten‐shield, with density of 18.5g/cc, to create a highly collimated Ir‐192 source radiation profiles. Various window openings in the shield have been simulated with the MCNP code for planning. The code itself was validated against TG43 parameters. The shield is controlled by an in‐house built, computer‐controlled, robotic arm which allows for 360° rotations and 1‐D translational motions. An in‐house coded planning system with the simulated annealing algorithm was used to design optimal plans on ideal rectal anatomies and patient cases. The optimal DMBT plans were then compared with the state‐of‐the‐art commercial Intracavitary Mold Applicator (ICMA)‐based plans. Results: The various simulations encompassing target sizes up to 5‐cm longitudinal and radial directions, with circumferential volumes from 45‐degree to 360‐degree were simulated. Results consistently show that the DMBT system yields broader shoulder past prescription dose in target DVH initially and drops off quicker at higher doses, compared with ICMA, which reflects better dose conformality. More spectacularly, however, up to 50% decrease in normal tissue dose across all dose range were observed. This will translate into clinically observable reduction in acute/late toxicities. Conclusions: Our preliminary results show that DMBT offers exceptional degrees of dynamics for achieving unparalleled dose conformality in brachytherapy. Further research is needed to validate our work in various clinical sites.

Asymmetric dose–volume optimization with smoothness control for rotating‐shield brachytherapy

“…In S-RSBT, the source is assumed to be partially covered by a detachable and rotatable shield with a single emission window, thus the azimuthal emission angle is fixed during the delivery. 10,11,13,14,34,35 To get the full delivery efficiency curve of S-RSBT, the rapid emission angle selection algorithm is used to detect the most proper shield opening size for S-RSBT. 12 The current conceptual D-RSBT applicator design 22 features with two layers of partially opening shields, each of which covers 180 • azimuthal emission angle.…”

Paddle‐based rotating‐shield brachytherapy

“…Intensity-modulated brachytherapy techniques such as rotating-shield brachytherapy (RSBT) [11][12][13] and dynamic modulated brachytherapy (DMBT) [14][15][16] were introduced as a means of improving intracavitary brachytherapy dose distributions for rectal and cervical cancer. When used as proposed by the authors, RSBT works by using a shield that partially occludes an electronic brachytherapy (eBT) source (Xoft Axxent™, iCAD, Inc., Nashua, NH, USA), which rotates in a manner that directs radiation away from healthy sensitive tissues and into cancerous tissue.…”

Rotating-shield brachytherapy for cervical cancer

“…In this work, rotating shield brachytherapy (RSBT) is considered, which is an alternative technique to IS+ICBT for improving tumor coverage for bulky cervical cancer relative to ICBT without compromising OAR sparing. The concept of RSBT was first introduced by Ebert (2002), and studies of RSBT were performed with clinically realizable delivery systems for rectal (Webster et al 2011), breast (Lin et al 2008, Webster et al 2011, and vaginal (Webster et al 2011) cancer. No studies on RSBT for cervical cancer have been published.…”