A New Plan Quality Index for Dose-Painting Radiotherapy
Y Park1*, S Kim2, S Park3, J Park4, (1) Massachusetts General Hospital, Boston, MA, (2) Mayo Clinic, Jacksonville, FL, (3) Seoul National University, Seoul, Korea, (4) Seoul National University Hospital, Seoul, KoreaSU-E-T-686 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: In dose-painting by numbers, conventional plan quality indices such as homogeneity index (HI) and dose-standard-deviation (STD) have limitations in application. This study aims to introduce new indices for evaluating treatment plans of this radiotherapy technique.
Methods:Deviation-from-prescription-index (DFPI) was formulated as the volume-weighted average of the deviation between prescription dose and planned dose. Two sub-indices, index-of-hotness (IOH) and index-of-coldness (IOC) were also defined specifically for selected voxels of which planned dose was higher and lower than the prescribed dose, respectively. The new indices were first tested for 9 IMRT/VMAT plans having 3 different dose prescription levels. For comparison purpose, 4 conventional indices (three types of HI and STD) and difference between V98 and V110 [V110 + (100-V98)] were calculated in each prescription region, and then averaged. Using the Spearman rank correlation test, the relationship was investigated between the DFPI-based ranks and the composite ranks based on all of 5 conventional indices. The new indices were also evaluated in 9 theoretically-generated plans having a continuously varying function of dose prescription where the conventional indices are not applicable.
Results:The plan quality ranks according to DFPI were found to be highly correlated with that from the composite of conventional indices (correlation coefficient = 0.95, where 1 means perfect correlation). It was also demonstrated that the new indices are applicable to dose painted plans in a continuously varying dose prescription.
Conclusion:It was shown that the new plan quality indices formulated with voxel-based prescription dose can be appropriately used for dose-painting radiotherapy. The indices allow for a single-value evaluation regardless of the number of prescribed dose levels, which cannot be achieved using the conventional indices.