Treatment planning of microbrachytherapy with 3D NSGA-II
An innovative form of radiotherapy, microbrachytherapy, is under development for solid, inoperable, radioresistant tumors. A method of treatment planning is proposed using a multi-objective algorithm, NSGA-II.
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Abstract— An innovative form of radiotherapy, microbrachytherapy, is under development for solid, inoperable, radioresistant tumors. A method of treatment planning is proposed using a multi-objective algorithm, NSGA-II. A suitable treatment plan was found that treated the tumor (a sphere of 10 mm radius) with 6 injections. Each injection had a volume of 5 µL, containing 90Y microspheres with an initial activity of 50 MBq. The treatment plan respected both the constraint on the tumor (95% of the tumor to receive at least 95% of the target dose, 100 Gy) and the constraint on a nearby organ at risk (no more than 10% of the organ to receive over 10 Gy). Optimization time was less than 7 minutes for a population of 800 treatment plans over 100 generations with a 2.5 GHz quad-core MacBook Pro. Keywords— Radiotherapy, microbrachytherapy, treatment planning, multi-objective, NSGA-II
I. INTRODUCTION
The goal of radiotherapy is to maximize the irradiation of the tumor whilst minimizing the irradiation of surrounding healthy tissue. Brachytherapy is being used increasingly for tumors, such as prostate cancers, where a high absorbed dose deposition is required but where the tumor is close to radiosensitive organs at risk (OARs), such as the rectum and bladder. An extension of brachytherapy, microbrachytherapy, has been developed. Microbrachytherapy differs from standard brachytherapy in that, instead of inserting radioactive metallic grains directly into the planning target volume (PTV), a liquid containing radioactive microspheres is used instead. Such microspheres are already used in selective internal radiation therapy (SIRT), where they are injected into arteries that lead to the tumor [1]. By changing from injecting metallic grains in brachytherapy to injecting liquid in microbrachytherapy, the volume of each injection is significantly decreased, meaning that the absorbed dose profiles of the resulting treatments can be further concentrated on the tumor. Nowadays, treatment planning is necessary for all forms of radiotherapy. Hence, for a new form of radiotherapy, a new, tailored method of producing treatment planning is required. © Springer Nature Singapore Pte Ltd. 2018 H. Eskola et al. (eds.), EMBEC & NBC 2017, IFMBE Proceedings 65, DOI: 10.1007/978-981-10-5122-7_113
This article therefore discusses an algorithm and a set of cost functions that are capable of producing satisfactory treatment plans for microbrachytherapy. II. MATERIALS AND METHODS
A. Treatment setup A spherical PTV of radius 10 mm has been chosen as a test case. An identical OAR is placed such that the surfaces of the PTV and OAR touch (their centers are separated by 20 mm). # The target absorbed dose to the PTV (!"#$ ) is 100 Gy. Treatment plans are considered acceptable, however, when at # . least 95% of the PTV receives at least 95% of !"#$ The OAR is considered as a parallel organ. Parallel organs can continue functioning provided not too much of the organ is over-irradiated. It was decided that the OAR would continue functioning as long as les
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