A new dose-volume-based plan quality index for IMRT plan comparison

Background and purposes: To develop a dose-volume-based Plan Quality Index for IMRT plans. Materials and methods: This study used a H(ealthy) Tissue Conformity Index to describe the overall plan conformity, a M(erit) function to describe the target coverage and a P(enalty) function to evaluate doses to critical organs. The Euclidean distance (PQI) between (H, M, P) and (1, 1, 1) represented the quality of a treatment plan. By checking the polarity of each term in M and P, one might conclude if the plan was satisfied with the given treatment protocol. Ten prostate plans (3-DCRT and IMRT) and 20 NPC IMRT plans were used to test PQI, Conformation Number (CN), Conformal INdex (COIN). EUD was used as a vehicle to explain the results. This study defined the power of a quality index as the ratio of the absolute difference to the mean of the same index of two plans, to compare the discerning power of PQI, CN and COIN. Results: The plan quality discerning power of PQI, COIN and CN was 20.6%, 8.2% and 5.5%, respectively, in prostate plans. Conclusion: PQI improved the plan quality discerning power and was capable of discerning qualified and unqualified treatment plans. (c) 2007 Elsevier Ireland Ltd. All rights reserved.