Similar-Case-Based Optimization of Beam Arrangements in Stereotactic Body Radiotherapy for Assisting Treatment Planners

Abstract

Objective. To develop a similar-case-based optimization method for beam arrangements in lung stereotactic body radiotherapy (SBRT) to assist treatment planners. Methods. First, cases that are similar to an objective case were automatically selected based on geometrical features related to a planning target volume (PTV) location, PTV shape, lung size, and spinal cord position. Second, initial beam arrangements were determined by registration of similar cases with the objective case using a linear registration technique. Finally, beam directions of the objective case were locally optimized based on the cost function, which takes into account the radiation absorption in normal tissues and organs at risk. The proposed method was evaluated with 10 test cases and a treatment planning database including 81 cases, by using 11 planning evaluation indices such as tumor control probability and normal tissue complication probability (NTCP). Results. The procedure for the local optimization of beam arrangements improved the quality of treatment plans with significant differences (P < 0.05) in the homogeneity index and conformity index for the PTV, V10, V20, mean dose, and NTCP for the lung. Conclusion. The proposed method could be usable as a computer-aided treatment planning tool for the determination of beam arrangements in SBRT.

Similar-cases-based planning approaches with beam angle optimizations using water equivalent path length for lung stereotactic body radiation therapy

“…According to a previous study [11], there were no significant differences in V5, V10, V20, and mean dose for the lung between the original plans and OSC plans ( P > 0.05 ). On the contrary, OSC plans with WEPL in this study significantly decreased using the same evaluation indices as the previous study.…”

“…Since WEPL is the radiological path length based on material electron density, the proposed approach could search for shorter WEPLs from optimum beam angles to avoid lower and higher density materials such as lungs and ribs. The difference between this study and the previous study of Magome et al [11] was that the ribs were added as OAR in the cost function and beam paths were corrected by WEPL.…”

“…The beam angle configurations in the ISC plans for the test cases were determined using a 3D affine linear registration technique with respect to the lung region between each similar case and the test case [10,11]. Each beam direction vector in the original beam angle configuration of the similar case was calculated from the gantry angle and couch angles.…”

“…To overcome the issues, beam angle selection [8] and beam angle optimization [9] approaches have been investigated to reduce the intra-and inter-planner variations in SBRT planning. Magome et al developed a computerassisted approach to automatically determine beam angle configurations for an undersigned lung cancer case, based on similar cases selected in terms of the planning target volume (PTV), lung, and spinal cord [10,11]. Moore et al developed an automatic treatment planning interface to produce a number of SBRT pancreas treatment plans within short time frames using a database of prior treated patients, which were assumed to be similar cases [12].…”