Abstract

Intensity Modulated Radiation Therapy (IMRT) is a treatment alternative for cancer treatment. The primary objective of IMRT is to eradicate cancer cells from the tumour site while minimising harm to the surrounding Organs at Risk (OAR). The first step toward achieving this goal is determining the optimal beam angle configuration (BAC) for the treatment plan. In this paper, we propose studying the Basic Sequential Variable Neighbourhood Descent (BVND) algorithm that explores the search space using two types of movements. The first movement (N1) replaces a beam angle in the BAC by a ±5° beam angle, while the second movement (N2) replaces a beam angle in the BAC by a randomly chosen beam angle. Unlike traditional VNS algorithms, the BVND algorithm obtains a final solution that is locally optimal for the neighbourhood N1 and approximately locally optimal for neighbourhood N2. This BVND algorithm ensures that the final solution is locally optimal for neighbourhood N1 and approximately locally optimal for neighbourhood N2. Results show that N2 movement is more commonly used in early iterations, often giving better improvements, while N1 movement is more commonly used in later iterations, maintaining a stable improvement across iterations. We try our approach on a set of clinical prostate cases from a hospital in Chile. The BVND is a robust algorithm that can obtain high-quality treatment plans at the cost of more computational time compared to other VNS-based algorithms, although it is shown to perform quite well, too, under a limited number of function evaluations. The BVND proved to be a robust algorithm that can obtain high-quality treatment plans at the cost of more computational time than other VNS-based algorithms. Furthermore, it has also been shown to perform quite well under a limited number of function evaluations. © 2025