In Medical physics ; h5-index 59.0
BACKGROUND : Patient-specific quality assurance (PSQA) is an indispensable and essential procedure in radiotherapy workflow, and several studies have been done to develop prediction models based on the conventional C-arm linac of single-layer multileaf collimator (MLC) with machine learning and deep learning techniques to predict PSQA results and improve efficiency. Recently, a newly designed O-ring gantry linac 'Halcyon' equipped with unique jawless stacked-and-staggered dual-layer MLC was released. However, few studies have focused on developing PSQA prediction models for this novel dual-layer MLC system.
PURPOSE : To evaluate the performance of machine learning to predict PSQA results of fixed field intensity-modulated radiation therapy (FF-IMRT) plans for linac equipped with dual-layer MLC.
METHODS AND MATERIALS : 213 FF-IMRT treatment plans, including 1383 beams from various treatment sites, were selected and delivered with portal dosimetry verification on Halcyon linac. Gamma analysis was performed using 1%/1mm, 2%/2mm, and 3%/2mm criteria with a 10% threshold. The training set (TS) of machine learning models consisted of 1106 beams, and an independent evaluation set (ES) consisted of 277 beams. For each beam, 33 complexity metrics were extracted as input data for training models. Three machine learning algorithms (Gradient Boosting Decision Tree/GBDT, Random Forest/RF, and Poisson Lasso/PL) were utilized to build the models and predict gamma passing rates (GPRs). To improve the prediction accuracy in the rare region, a method of reweighting for TS has been performed and compared to the unweighted results. The importance of complexity metrics was studied by permuted interesting features.
RESULTS : The GBDT model had the best performance in this study. In ES, the minimal mean prediction error for unweighted results was 1.93%, 1.16%, 0.78% under 1%/1mm, 2%/2mm, and 3%/2mm criteria respectively from GBDT model. Comparing to the unweighted results, the models after reweighting gained up to 30% improvement in the rare region, while the overall prediction error was slightly worse depending on the kind of models. For feature importance, two tree-based models (GBDT and RF) had in common the top 10 most important metrics as well as the same metric with the largest impact.
CONCLUSION : For linac equipped with novel dual-layer MLC, the machine learning model based on GBDT algorithm shows a certain degree of accuracy for GPRs prediction. The specific machine learning model for dual-layer MLC configuration could be a useful tool for physicists detecting PSQA measurement failures. This article is protected by copyright. All rights reserved.
Zhu Heling, Zhu Qizhen, Wang Zhiqun, Yang Bo, Zhang Wenjun, Qiu Jie
2022-Nov-07
dual-layer MLC, machine learning, portal dosimetry, quality assurance
