Evaluation of dose conformity and coverage of target volume for intensity-modulated radiotherapy of pelvic cancer treatment.

BACKGROUND: Better conformity may help in delivering minimum dose to organs at risk (OARs) and maximum dose to planning target volume (PTV). As per the requirements of modern radiotherapy, 95% isodose should cover the PTV, so conformity indices (CIs) are used for evaluating quality of conformation of treatment plans.

AIM: This study aimed to investigate degree of conformity for pelvic patients using intensity-modulated radiotherapy (IMRT) technique. Three formulas of CIs described in literature were analyzed in this study.

SETTINGS AND DESIGN: This study was performed to evaluate degree of conformity of 18 patients treated with radiotherapy treatment plan using cumulative dose volume histogram. Effectiveness of different CIs was explored for IMRT plans using 15 MV photon beam. Doses delivered to OAR were also studied.

STATISTICAL ANALYSIS USED: CI suggested by the International Commission on Radiation Units and Measurements, radiation CI and CI prescription isodose to target volume (PITV) had mean ± standard deviation values of 1.02 ± 0.018, 0.98 ± 0.017, and 1.63 ± 0.333, respectively.

RESULTS AND CONCLUSION: Dose distribution for all patients was highly conformal and clinically acceptable. Values of CI PITV exceeded acceptable value for 27% patients with minor deviation. No statistically significant differences were observed for three CIs reported. Target volume lies between 95% and 107% of prescribed dose which shows ideal target coverage. This simple parameter is advantageous since it is easy to interpret and helped determine quality of treatment plan. This study clearly demonstrated that favorable dose distribution in PTV and OARs is achieved using IMRT technique, and hence, the risk of damage to normal tissues is reduced.