A new plan quality index for nasopharyngeal cancer SIB IMRT

A new plan quality index integrating dosimetric and radiobiological indices was proposed to facilitate the evaluation and comparison of simultaneous integrated boost (SIB) intensity modulated radiotherapy (IMRT) plans for nasopharyngeal cancer (NPC) patients. Ten NPC patients treated by SIB-IMRT were enrolled in the study. Custom software was developed to read dose-volume histogram (DVH) curves from the treatment planning system (TPS). A plan filtering matrix was introduced to filter plans that fail to satisfy treatment protocol. Target plan quality indices and organ at risk (OAR) plan quality indices were calculated for qualified plans. A unique composite plan quality index (CPQI) was proposed based on the relative weight of these indices to evaluate and compare competing plans. Plan ranking results were compared with detailed statistical analysis, radiation oncology quality system (ROQS) scoring results and physician's evaluation results to verify the accuracy of this new plan quality index. The average CPQI values for plans with OAR priority of low, normal, high, and PTV only were 0.22 ± 0.08, 0.49 ± 0.077, 0.71 ± 0.062, and -0.21 ± 0.16, respectively. There were significant differences among these plan quality indices (One-way ANOVA test, p < 0.01). This was consistent with statistical analysis, ROQS results and physician's ranking results in which 90% OAR high plans were selected. Plan filtering matrix was able to speed up the plan evaluation process. The new matrix plan quality index CPQI showed good consistence with physician ranking results. It is a promising index for NPC SIB-IMRT plan evaluation.