Plan Quality Index - An Integrated Dosimetric Approach for Plan Evaluation with Consideration of Quality of Dose Coverage to Tumors and Quality of Organs' Sparing.

PURPOSE: To find an integrated solution for plan evaluation with multiple dosimetric parameters in order to ensure quality of target dose coverage and sparing of organs collectively. MATERIALS AND METHODS: A mathematical logical expression called Plan Quality Index (PQI) was formulated. It includes two integrated indices 1.Integrated Dosimetric Index for tumor (IDITumor) dose coverage and 2.Integrated Dosimetic Index (IDIorgans) for Organs At Risk (OARs). PQI was used to select better dosimetric plan form multiple VMAT plans of a Nasopharynx case. In addition, the PQI was used for comparison of VMAT and IMRT plans of 64 patients with Head and Neck cancer. The plan with lesser PQI was considered as a better dosimetric plan. For statistical comparison between two techniques, paired't' and Wilcoxon signed rank test were used with consideration p< 0.05 as a statistically significant. RESULTS: The unambiguous evaluation results with PQI showed that VMAT plan was achieved the entire given dose constraints significantly better than IMRT plan in all the patients (p<0.001). CONCLUSION: Plan evaluation with PQI can be an unambiguous method. It evaluates the quality of tumor dose coverage (IDITumor) and sparing of OARs (IDIorgans) collectively. It enables to change the priority of evaluation criteria of a specified structure based on the clinical requirements. It does not require any specialized program. It can be calculated using ordinary excel program. Using the single value as PQI, the effective determination of a quality plan among many plans can be possible and it can be used for comparison of different techniques.

Evaluation of Healthy Tissue Dose at Different Regions between Volumetric-Modulated Arc Therapy and Intensity-Modulated Radiation Therapy Plans in the Treatment of Various Cancers.

BACKGROUND: Radiotherapy plays an important role in the management of cancer. Although the improved technologies increase therapeutic index, different delivery techniques deliver different dose pattern to the healthy tissue within and outside treatment volume. OBJECTIVE: The objective of this study was to evaluate the low, intermediate, and high dose to healthy tissue within and outside the treatment volume and to find the relation between tumor volume and various doses received healthy tissue volume. MATERIALS AND METHODS: A total of 150 patients were included. For all patients, planning computed tomography images were acquired. Tumors, critical structures, and healthy tissue volumes at different regions were delineated. Two sets of plans, one with volumetric-modulated arc therapy and another with intensity-modulated radiation therapy (IMRT) were created, optimized for 6 MV photons and dose was calculated. Dosimetry results for tumor, organs at risks (OARs), and healthy tissue from both the techniques were evaluated and compared. RESULTS: Tumor coverage and dose to OARs was significantly better with volumetric-modulated arc therapy (VMAT). Volume of healthy tissue received high-dose within the treatment volume as well as volume of healthy tissue received low and intermediate-dose out of treatment volume were significantly (P < 0.002) lesser with VMAT. Besides, the results showed that as the tumor volume increased, the various dose received healthy tissue volume also increased. CONCLUSIONS: VMAT plan can reduce the risk of secondary malignancy while treating different sites of cancer. VMAT is the most appropriate technique than IMRT, especially in the treatment of large tumor volume. Special attention has to be given, especially while treating women and children.

Comparison of Rapid Arc and Intensity-modulated Radiotherapy Plans Using Unified Dosimetry Index and the Impact of Conformity Index on Unified Dosimetry Index Evaluation.

The aim of this study was to evaluate the impact of conformity index in the unified dosimetry index (UDI) score for two different planning techniques namely intensity-modulated radiotherapy (IMRT) and Rapid Arc. Rapid Arc and IMRT plans of 57 patients were evaluated and compared using UDI score which incorporates four indices. To determine the impact of conformity index on the IMRT and Rapid Arc plans, UDI at conformity index one of all plan (UDIunit_CI) score was calculated by assuming conformity index is equal to one. Mean and standard deviations of all indices were calculated. Rapid Arc technique plans of different treatment sites of all patients scored lesser UDI than IMRT plans, and the conformity index of Rapid Arc plan was significantly better than IMRT plan. The average dose gradient, homogeneity, coverage, and conformity index of all sites with Rapid Arc plans were 0.212 ± 0.05, 1.123 ± 0.03, 0.959 ± 0.03, and 1.056 ± 0.09; with IMRT plans were 0.190 ± 0.05, 1.113 ± 0.04, 0.950 ± 0.04, and 1.172 ± 0.16, respectively. UDI score value with actual conformity index of Rapid Arc and IMRT plans differed significantly (P < 0.001). However, UDIunit_CI score values with assumed conformity index equal to one did not differ significantly (P = 0.528). In the comparison of IMRT and Rapid Arc plans using the UDI score, the impact of conformity index was significant.