A Novel Medical Conformity Index (MCI) Integrating Spatial Distance and Target Volume Weighting for Enhanced Radiotherapy Plan Evaluation
Hye Jeong Yang, Chankyu Kim, Jason W. Sohn, Dae Yong Kim, Sung Ho Moon, Dongho Shin, Young Kyoung Lim, Jong Hwi Jeong, Se Byeong Lee, Haksoo KimIntroduction
Conventional conformity indices primarily quantify the geometric relationship between the target volume and the prescription isodose volume, which may not fully reflect clinically relevant dose deviations. This study aimed to develop a medical conformity index (MCI) that integrates geometric conformity with clinical considerations and to evaluate its performance in assessing radiotherapy plan quality.
Methods
The proposed MCI quantifies conformity by incorporating bidirectional local distance between the target volume (TV) and Prescription Isodose Volume (PIV) using an asymmetric Gaussian distance penalty function. Distinct penalty levels are assigned to under- and over-covered regions to reflect the clinical priority of target coverage and organ at risk (OAR) sparing. Additionally, a Target Volume Weight Function (TVWF) is integrated to ensure consistency across different target sizes, and OAR-specific constraints are introduced. The performance of the MCI was evaluated using synthetic 2D plans and clinical treatment plans, compared against conventional indices such as RTOG, SALT-Lomax, and CN.
Results
The proposed MCI provided more consistent and clinically relevant scoring compared to conventional indices, particularly in cases with complex geometric discrepancies. Unlike existing metrics, the MCI demonstrated superior sensitivity to spatial differences and allowed flexible evaluation through user-defined penalty levels. Furthermore, the index enabled a robust assessment of plan quality by reflecting the clinical impact of dose distribution variations.
Conclusions
The proposed MCI provides a quantitative conformity measure that integrates bidirectional spatial distance, asymmetric penalties, and target volume weighting. The results demonstrated that MCI can differentiate spatial conformity differences that may not be fully reflected by conventional conformity indices. Further clinical validation is required to determine clinically meaningful penalty levels and acceptance criteria.