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.

Figure 1

Overall scheme of our similar-case-based optimization method for beam arrangements in SBRT.

Figure 2

The determination of beam arrangements based on a linear registration technique. T is a transformation matrix.

Figure 3

The available beam direction space, which was used in past cases including the RTP database. The blue area represents the applicable combination of the gantry and couch angles.

Figure 4

The first to fifth most similar cases to the objective case obtained by the proposed method: (a) an objective case and ((b)–(f)) the first to fifth most similar cases.

Figure 5

Dose distributions determined by beam arrangements without and with the beam angle optimization step: (a) the similar-case-based beam arrangements based on the linear registration technique, and (b) the optimized similar-case-based beam arrangement determined by the local optimization of each beam direction.

Figure 6

(a) A plan obtained from the original beam arrangement, which was determined by an experienced radiation oncologist. (b) A plan obtained by the most usable beam arrangement based on the proposed method.

Figure 7

Dose-volume histograms obtained from the original beam arrangement in Figure 6(a) (solid lines) and optimized similar-case-based beam arrangement in Figure 6(b) (dotted lines). Planning target volume (red), lung (blue), and spinal cord (green).