An on-line replanning scheme for interfractional variationsa)

Abstract

Ability of online adaptive replanning is desirable to correct for interfraction anatomic changes. A full-scope replanning/reoptimization with the current planning techniques takes too long to be practical. A novel online replanning strategy to correct for interfraction anatomic changes in real time is presented. The scheme consists of three steps: (1) rapidly delineating targets and organs at risk on the computed tomography of the day by modifying original planning contours using robust tools in a semiautomatic manner, (2) online segment aperture morphing (SAM) (adjusting beam/ segment apertures) by applying the spatial relationship between the planning target contour and the apertures to the new target contour, and (3) performing segment weight optimization (SWO) for the new apertures if necessary. The entire scheme was tested for direct-aperture-based IMRT on representative prostate and abdomen cases. Dose volume histograms obtained with the online scheme are practically equivalent to those obtained with full-scope reoptimization. For the days of small to moderate organ deformations, only the SAM is necessary, while for the large deformation days, both SAM and SWO are required to adequately account for the deformation. Both the SAM and SWO programs can be completed within 1 min, and the overall process can be completed within 10 min. The proposed SAM-SWO scheme is practically comparable to full-scope reoptimization, but is fast enough to be implemented for on-line adaptive replanning, enabling dose-guided RT.

Four‐dimensional intensity‐modulated radiation therapy planning for dynamic tracking using a direct aperture deformation (DAD) method

“…32 However, this scheme ignores the significant complexities [23][24][25] of respiratory-induced target movement and may lead to suboptimal plan quality. In this study, we adopted a DAD method 21,26 that directly modifies the aperture positions and shapes according to the geometric variation in the target. This method considers both the translation and the deformation of the target while avoiding a lengthy optimization process.…”

“…In this study, we develop a 4D IMRT planning technique using a direct aperture deformation ͑DAD͒ method 21 that morphs the aperture shape and position from a reference phase to the other phases. This method is simple and feasible for current clinical setup and considers both the rigid and nonrigid organ motions; meanwhile MLC connectivity between adjacent phases is also ensured.…”

Four‐dimensional dose distributions of step‐and‐shoot IMRT delivered with real‐time tumor tracking for patients with irregular breathing: Constant dose rate vs dose rate regulation

“…If the extension is purely based on the 3D trajectory of tumor centroid but tumor deformation during patient breathing is ignored, the approach results in a "SHIFT" 4D plan, as proposed by Suh et al 8 On the other hand, based on the planning 4D-CT, tumor deformation between breathing phases can be accounted for using approaches such as segment aperture morphing (SAM) algorithm. 13 Work has been reported demonstrating that a SAM scheme taking into account the phase-to-phase tumor deformation resulted in 4D-IMRT plans that have plan quality [in measures such as V 95% , conformity index, and dose volume histograms (DVHs)] comparable to IPO plans, and better than plans resulted from "SHIFT" scheme. 14 The interplay between the movement of MLC apertures and that of the patient anatomy during irradiation has been shown to potentially create large discrepancy between planned and delivered target dose, but has not been well integrated in 4D-IMRT treatment planning or delivery.…”

Adaptive radiotherapy strategies for pelvic tumors – a systematic review of clinical implementations

“…Deformable image registration was more frequently applied in the in silico studies, mostly for online re-planning/re-optimization [59,61,67,71,86,87,94] and offline re-planning/re-optimization strategies [60,63,66,69,75,107] but also applied for online MLC/field adjustments [77,89]. To facilitate adaptations, especially for online execution, modifications of the planning system or automatic activation/selection of plans was applied in 50% of the in silico studies [58][59][60][61][67][68][69]71,72,[74][75][76][77][78][79][80][82][83][84][85][86][87][88][92][93][94]. In view of the increasing speed of optimization algorithms, limited in-room imaging quality together with manual (re-)contouring remains the biggest bottlenecks for clinical implementation of many of the ART strategies and certainly limiting online applications.…”

“…In addition to one in silico implementation of online compensation [58], these were the only studies where feedback from delivered dose triggered adaptations. Contributing to differences in applied strategies and workflows could be the additional manual contouring, which was a pre-requisite in over 70% of the simulated ART workflows [22,59,60,[62][63][64][65][66][68][69][70]72,74,78,79,[81][82][83]85,86,88,89,91,93,[95][96][97][98][100][101][102][103][104][105][106][107]. To reduce the need of manual contours, the segmentation could be propagated using deformable image registration.…”