A new dose–volume-based Plan Quality Index for IMRT plan comparison

Background and purposesTo develop a dose–volume-based Plan Quality Index for IMRT plans.Materials and methodsThis 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.ResultsThe plan quality discerning power of PQI, COIN and CN was 20.6%, 8.2% and 5.5%, respectively, in prostate plans.ConclusionPQI improved the plan quality discerning power and was capable of discerning qualified and unqualified treatment plans.