Verification of prostate conformal radiotherapy planning protocol on an XiO treatment planning system
Steyn, Joseph Martinus
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The evaluation of a prostate three-dimensional conformal radiotherapy (3D-CRT) treatment plan is based on the aims of the specific treatment. An assessment of the plan is therefore performed to reach a certain class of plan-quality. Several parameters are, however, available for such assessment. Without a standardised protocol, the assessment of a plan for the same tumour volume may therefore differ between treatment planners and take a considerable length of time to complete. To minimise not only the variation in the assessment of prostate 3D-CRT treatment plans, but also to shorten the time needed to do so, a reduced list of prioritised parameters needs to be used for plan-evaluation. The aim of this study was to find the parameters with the highest covariance within a dataset of prostate 3D-CRT planning parameter-values obtained from several treatment plans. Thereafter the application of these parameters to improve prostate 3D-CRT treatment quality was verified. To obtain the parameter-data, nineteen different dosimetrists each created a prostate 3D-CRT treatment plan for the target volume and boost volume of the same patient on nineteen XiO treatment planning systems. The data of four physical and eight dosimetric parameters, which are frequently referred to in clinical trials for prostate cancer radiotherapy, were extracted from the plans created. The factor-loadings of each component of the covariance-matrix of the data were calculated using principal component analysis. Varimax-rotation was used to optimise each parameter’s loading. The high loadings (>0,75) not only provided the variables with the highest contribution to variance within the parameter-dataset, but also gave their ranking (prioritisation) in this regard. The highest contribution to covariance among the dosimetric parameters were shown by the minimum dose, heterogeneity-index, the mean dose and the V65 dose-volume constraint of the rectum. The number of beams, the number of opposing beams and the average field-size displayed the highest relation of variance among the physical parameters. These are the limited list of parameters to be used for plan-evaluation, prioritised in terms of their contribution to treatment plan quality. As a test for the application of these parameters, four treatment planners made use of these parameters to evaluate and improve twenty prostate 3D-CRT treatment plans which were randomly obtained from various planning sites. The twenty, altered treatment plans were evaluated using eleven dosimetric parameters frequently used in clinical trials. The use of this list of parameters as an evaluation-protocol for prostate 3D-CRT treatment planning was investigated and verified. The application of these parameters showed that the list can be used as a protocol to evaluate and effectively improve the quality of prostate 3D-CRT treatment plans.