Abstract
The prediction of an additional space for the dose sparing of organs at risk (OAR) in radiotherapy is still difficult. In this pursuit, the present study was envisaged to find out the factors affecting the bladder and rectum dosimetry of cervical cancer. Additionally, the relationship between the dose-volume histogram (DVH) parameters and the geometry and plan dose-volume optimization parameters of the bladder/rectum was established to develop the dose prediction models and guide the planning design for lower OARs dose coverage directly. Thirty volume modulated radiation therapy (VMAT) plans from cervical cancer patients were randomly chosen to build the dose prediction models. The target dose coverage was evaluated. Dose prediction models were established by univariate and multiple linear regression among the dosimetric parameters of the bladder/rectum, the geometry parameters (planning target volume (PTV), volume of bladder/rectum, overlap volume of bladder/rectum (OV), and overlapped volume as a percentage of bladder/rectum volume (OP)), and corresponding plan dose-volume optimization parameters of the nonoverlapping structures (the structure of bladder/rectum outside the PTV (NOS)). Finally, the accuracy of the prediction models was evaluated by tracking d = (predicted dose-actual dose)/actual in additional ten VMAT plans. V30, V35, and V40 of the bladder and rectum were found to be multiple linearly correlated with the relevant OP and corresponding dose-volume optimization parameters of NOS (regression R2 > 0.99, P < 0.001). The variations of these models were less than 0.5% for bladder and rectum. Percentage of bladder and rectum within the PTV and the dose-volume optimization parameters of NOS could be used to predict the dose quantitatively. The parameters of NOS as a limited condition could be used in the plan optimization instead of limiting the dose and volume of the entire OAR traditionally, which made the plan optimization more unified and convenient and strengthened the plan quality and consistency.
Highlights
Cervical cancer (CC) is one of the most common malignant carcinomas among women worldwide and remains the fourth most common cancer worldwide
Radiation therapy has traditionally been combined with consecutive external beam radiotherapy (EBRT) and intracavitary brachytherapy (ICBT) in the treatment of cervical cancer
ICBT is usually started after EBRT since the organs at risk (OAR) near the target is not completely free from the dose during treatment planning [28]
Summary
Cervical cancer (CC) is one of the most common malignant carcinomas among women worldwide and remains the fourth most common cancer worldwide. In order to find out the influencing factors of OAR dose for meeting the target dose while maximizing the protection of the OAR and make planning optimization more flexible and convenient for improving plan design efficiency and plan quality and homogeneity, the present study employed the bladder/rectum region of the nonoverlapping target area as a structure and the dose limit of this structure was applied in the optimization of the plan instead of traditional plan optimization parameters of entire OARs. e dose-volume parameters of nonoverlapping structure in the study can be as plan optimization parameters. E aim of this study was to develop a model-based method for prediction of the bladder and rectum dose based on the geometric and radiotherapy planning parameters in cervical cancer radiotherapy. Because each patient’s overlapping volume is fixed, the impact of dose distribution of nonoverlapping structure on the dose of entire OAR cannot be ignored, and the dose distribution in this region can be adjusted, which makes planning optimization more convenient and flexible and its clinical practicability and operability stronger. e aim of this study was to develop a model-based method for prediction of the bladder and rectum dose based on the geometric and radiotherapy planning parameters in cervical cancer radiotherapy. e study was structured in two parts: the first part focused on determining the factors affecting the bladder/ rectum dose to develop the models, by retrospectively studying the volumetric-modulated arc therapy (VMAT) plans of 30 patients. e second part verified the feasibility and accuracy of the forecasting models in 10 patients
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