Conformity and Homogeneity Indexes for Cancer of the Pelvic Region Treated with Three-Dimensional Conformal Radiation Therapy at the National Hospital, Abuja, Nigeria

Anorectal, bladder, cervix and prostate cancers form 32.98% of cancer cases treated with threedimensional conformal radiation therapy (3DCRT) at the National Hospital Abuja. Conformity Index (CI) and Homogeneity Index (HI) have been identified as efficient tools for performing independent evaluation of radiotherapy treatment plans. This study aims to verify the influence of location of Tumour site, Total volume of the Planned Target Volume (PTV) and Energy of photon beam on Conformity and Homogeneity Indexes. It also aims to establish CI and HI as veritable tools for plan evaluation in the Centre. Forty (40) patients managed with radiation therapy between May and December 2018, were selected for this study. The PTV was delineated based on the recommendations of ICRU 50 and 62. The HI was evaluated according to ICRU 83and CI was evaluated according to the recommendations of ICRU 62. All cases were radical cases and treated with four beams at different direction (box technique). All plans were performed, reviewed and approved on Monaco 5.11 treatment planning system. In all, the percentages of anorectal, bladder, cervix and prostate cases selected were 17.50%, 15.00%, 42.50% and 25.00% respectively. A retrospective analysis of the CI and HI was done using Microsoft Excel 2013.The ideal value of Homogeneity Index (HI) is 0 (zero) while that of Conformal Index (CI) is 1 (unity). The cases were grouped into 2, 4 and 4 for volume of PTV, Tumour site location and energy respectively. The mean CI is 0.95 ± 0.05 while the mean HI is 0.168 ± 0.164 for the total number of cases. Uterocervix has the best CI and HI of 0.9708 ± 0.0244. The difference between the CI and HI of PTV below 1000 cm3 and above 1000cm3 is 0.0125 and 0.0016 respectively. The combination of 6MV and 10MV for AP/PA and lateral fields shows the best CI and HI of 0.971 and 0.1046 respectively. However, when tested statistically using paired t-test and ANOVA, these means were found not to be statistically different (p > 0.05).The result from this study suggests that HI and CI are not influenced by the size of the PTV, Tumour site location or energy. Conformity and Homogeneity indexes were further confirmed to remain effective tools in the analysis of treatment plans.