Analysis of Different Evaluation Indexes for Postoperative Brain Cancer Radiation Therapy Plans: Conformity Index, Homogeneity Index, and Total Coverage Index

Abstract

Objective: This study analyzed different planning target dose–volume evaluation parameters, target mean dose, homogeneity index (HI), conformity index (CI), and Target Coverage Index (TCI) for different conformal techniques. The purpose of this article was to analyze these three parameters in the assessment of the treatment plans in ten patients undergoing postoperative conformal radiotherapy treatment. Materials and Methods: We retrospectively evaluated that the treatment plans of ten patients with a prescribed dose was 60 Gy delivered at 2.0 Gy per fraction using 6 MV photon energy. The dosimetric comparison was done by performing two plans for the same patient; prescription dose and normal tissue constraints were identical for both plans. A total of ten patients underwent computed tomography treatment planning in conjunction with magnetic resonance imaging fusion. Prescription dose and normal tissue constraints were identical for both conformal plans. The irradiated patients were retrieved and replanned with three-dimensional conformal radiation therapy (3DCRT) techniques, and a dosimetric comparison was done by performing two plans for the same patient. Results: The Student's t-test was used to perform statistical analysis to determine the differences between the dose–volume constraints used for planning. The cumulative dose–volume histogram of target volumes (TVs), target coverage, target homogeneity, target conformity, and normal tissue sparing with two different conformal planning was compared. The intensity-modulated radiation therapy (IMRT) plan yielded superior target coverage as compared with the 3D-CRT plan. Specifically, minimum and mean planning TV cone-down doses were 46.80 ± 4.16 Gy and 60.72 ± 1.00 Gy for IMRT and 49.06 ± 4.98 Gy and 61.04 ± 1.15 Gy for 3D-CRT P < 0.519, respectively. The CI was approximately equal in both the modalities with an average value of 0.962 ± 0.041 in IMRT compared to 0.969 ± 0.039 in 3DCRT (P < 0.481). The average HI in IMRT was 0.187 ± 0.176 and 0.099 ± 0.0500 in 3DCRT (P < 0.165). Therefore, IMRT achieved an improvement in HI. The target coverage index (TCI) in IMRT was 0.7213 ± 0.2050 and 0.5970 ± 0.194 in 3DCRT. Statistical analysis was performed to determine the differences. Conclusions: These indexes can all be objective tools for the evaluation of plan quality. The IMRT plan yielded superior target coverage and reduced radiation dose to the brain, brainstem, and optic chiasm. With the availability of new cancer imaging tools and more effective systemic agents, IMRT may be used to intensify tumor doses when minimizing toxicity, therefore potentially improving outcomes in patients.

Keywords

• conformity
• homogeneity
• intensity-modulated radiotherapy
• plan quality