An Inverse Dose Optimization Algorithm for Three-Dimensional Brachytherapy.

Xianliang Wang,Jie Li,Shengwei Kang,Bin Tang,Pei Wang,Lintao Li,Qing Hou,Lucia Orlandini,Chengjun Gou,Zhangwen Wu,Jinyi Lang

doi:10.3389/fonc.2020.564580

Abstract

PurposeTo investigate an implementation method and the results of an inverse dose optimization algorithm, Gradient Based Planning Optimization (GBPO), for three-dimensional brachytherapy.MethodsThe GBPO used a quadratic objective function, and a dwell time modulation item was added to the objective function to restrict the dwell time variance. We retrospectively studied 4 cervical cancer patients using different applicators and 15 cervical cancer patients using the Fletcher applicator. We assessed the plan quality of GBPO by isodose lines for the patients using different applicators. For the 15 patients using the Fletcher applicator, we utilized dose-volume histogram (DVH) parameters of HR-CTV (D100%, V150%) and organs at risk (OARs) (D0.1cc, D1cc, D2cc) to evaluate the difference between the GBPO plans and the IPSA (Inverse Planning Simulated Annealing) plans, as well as the GBPO plans and the Graphic plans.ResultsFor the 4 patients using different applicators, the dose distributions are conformable. For the 15 patients using the Fletcher applicator, when the dwell time modulation factor (DTMF) is less than 20, the dwell time deviation reduces quickly; however, after the DTMF increased to 100, the dwell time deviation has no remarkable change. The difference in dosimetric parameters between the GBPO plans and the IPSA plans is not statistically significant (P>0.05). The GBPO plans have a higher D100% (3.57 ± 0.36, 3.38 ± 0.34; P<0.01) and a lower V150% (55.73 ± 4.06, 57.75 ± 3.79; P<0.01) than those of the Graphic plans. The differences in other DVH parameters are negligible between the GBPO plans and the Graphic plans.ConclusionsThe GBPO plans have a comparable quality as the IPSA plans and the Graphic plans for the studied cervical cancer cases. The GBPO algorithm could be integrated into a three-dimensional brachytherapy treatment planning system after studying more sites.

Highlights

Compared with external beam radiation therapy, brachytherapy has the characteristics of high dose near the source and rapid dose drop-off away from the source
Dose optimization methods of 3D brachytherapy can be divided into forward optimization and inverse optimization
The differences in other dose volume histogram (DVH) parameters are negligible between the GBPO plans and the Graphic plans

Summary

Introduction

Compared with external beam radiation therapy, brachytherapy has the characteristics of high dose near the source and rapid dose drop-off away from the source. Because the applicator is implanted in the tumor region, brachytherapy reduces the dosimetric uncertainties caused by anatomical change and setup error. These advantages ensure the irreplaceable role of brachytherapy in radiotherapy [1]. Dose optimization methods of 3D brachytherapy can be divided into forward optimization and inverse optimization. In a forward optimization process, a planner manually enters the dwelling weight/time or drags isodose lines based on the planner’s clinical experience to achieve a desirable dose distribution. In an inverse optimization process, a planner inputs the objectives and penalty weights of targets and organs at risk (OARs) based on the prescription dose and patient’s anatomy. Inverse optimization algorithms of brachytherapy, such as IPSA (Inverse Planning Simulated Annealing) and HIPO (Hybrid Inverse Planning Optimization), have been reported in literatures and implemented in 3D TPSs [2,3,4,5]

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