Beam angle optimization in IMRT: are we really optimizing what matters?

Abstract

Intensity‐modulated radiation therapy (IMRT) is a modern radiotherapy modality that uses a multileaf collimator to enable the irradiation of the patient with nonuniform maps of radiation from a set of distinct beam irradiation directions. The aim of IMRT is to eradicate all cancerous cells by irradiating the tumor with a prescribed dose while simultaneously sparing, as much as possible, the neighboring tissues and organs. The optimal choice of beam irradiation directions—beam angle optimization (BAO)—can play an important role in IMRT treatment planning by improving organ sparing and tumor coverage, increasing the treatment plan quality. Typically, the BAO search is guided by the optimal value of the fluence map optimization (FMO)—the problem of obtaining the most appropriate radiation intensities for each beam direction. In this paper, a new score to guide the BAO search is introduced and embedded in a parallel multistart derivative‐free optimization framework that is detailed for the extremely challenging continuous BAO problem. For the set of 10 clinical nasopharyngeal tumor cases considered, treatment plans obtained for optimized beam directions clearly outperform the benchmark treatment plans obtained considering equidistant beam directions typically used in clinical practice. Furthermore, treatment plans obtained considering the proposed score clearly improve the quality of the plans resulting from the use of the optimal value of the FMO problem to guide the BAO search.

A fast deep learning approach for beam orientation optimization for prostate cancer treated with intensity‐modulated radiation therapy

“…CG has been shown to be effective for BOO in radiation therapy problems. 15,21,61 While CG does not guarantee an optimal solution, the CG algorithm has been shown to have superior performance when compared to clinical plans, 10,15,21,30,50,52,53,[62][63][64][65][66][67][68][69][70] and the algorithm is summarized in the sections that follow. A list of all indices, parameters, variables, and functions used in this paper and their definitions are provided in Table I.…”

“…The final objective function in these works is usually a function of the differences between the actual and prescribed dosage received by healthy tissues, organs at risk (OARs), and the PTV . But computing the dose influence matrices and the FMO are both very complex and time intensive operations, taking hours to compute dose influence matrices and minutes to solve the FMO, which ultimately hampers the implementation of BOO in clinical routines . Breedveld et al used a “wish list” to prioritize constraints and objective functions related to OARs and the tumor and to iteratively add new beam orientations to the set of currently selected beams.…”

“…[16][17][18][19][20][21][22][23][24][25][26][27][28] But computing the dose influence matrices and the FMO are both very complex and time intensive operations, 29 taking hours to compute dose influence matrices and minutes to solve the FMO, which ultimately hampers the implementation of BOO in clinical routines. 13,20,24,[30][31][32] Breedveld et al 13 used a "wish list" to prioritize constraints and objective functions related to OARs and the tumor and to iteratively add new beam orientations to the set of currently selected beams. Yarmand et al 31 scored beamlets of candidate beams based on their contributions to irradiating tumors and weighted the average of the total dose received by OARs.…”

An Optimization Approach for Noncoplanar Intensity-Modulated Arc Therapy Trajectories

“…An alternative formulation of the BAO problem has been considered in our works. All possible continuous beam angle directions around the tumor have been considered instead of a discretized set of beam directions, leading to a continuous global optimization problem [24,25,26,27,28]. The continuous formulation of the noncoplanar BAO problem is briefly described next.…”

Optimization of Highly Noncoplanar Arc Therapy Trajectories: A Dosimetric Approach

“…In this paper, we propose a two-step approach based on dosimetric criteria for the optimization of noncoplanar arc trajectories. In the first step, an initial set of anchor points (noncoplanar beam directions) is computed taking advantage of the work previously developed in BAO for step-and-shoot IMRT [7][8][9][10][11][12][13]. In the second step, anchored in the beam directions already calculated, the noncoplanar arc trajectory is defined by iteratively computing additional anchor points considering the same dosimetric criteria used for the noncoplanar BAO.…”