Abstract
We have formulated a unified dosimetry index (UDI) that computes, for any given treatment plan, its deviations in terms of dose coverage, conformity, homogeneity, and dose gradient vis‐à‐vis an ideal plan (which we define as a dosimetry plan of perfect dose coverage, conformity, homogeneity, and step‐wise fall‐off to zero dose outside the planning target volume). In order to validate the UDI scoring system, 21 stereotactic cranial radiosurgery cases were evaluated retrospectively. The cases were planned on the BrainSCAN treatment planning system (BrainLAB, Feldkirchen, Germany) using 6 to 8 non‐coplanar static beams collimated with the micro multi‐leaf collimator (mMLC). We suggest a technique for creating a ranking system that can be utilized for plan evaluation and comparison between multiple plans. Under this system treatment plans are classified as “excellent”, “good”, “average”, or “poor”. The proposed ranking system can be utilized as a general guide for generating an optimal dosimetry plan for external beam radiation therapy.
Highlights
Treatment plan evaluation tools are necessary for judging how well dosimetry plans meet the preset planning objectives
The unified dosimetry index (UDI) score of a dosimetry plan is a single number that gives its overall evaluation in terms of dose coverage, dose conformity, dose homogeneity, as well as dose gradient
Evaluation of the dose volume histogram (DVH) plots of the planning target volume (PTV) for cases 9 and 11 show that in both cases the PTV receives excellent dose coverage
Summary
Treatment plan evaluation tools are necessary for judging how well dosimetry plans meet the preset planning objectives. Traditional methods such as three dimensional dose distributions, and dose volume histogram (DVH), are adequate for qualitative evaluations, but not well suited for efficient comparison of multiple plans. Dosimetry planning objectives typically consist of (a) achieving full uniform dose coverage to the target (i.e., covering close to 100% of the target with the prescribed dose), (b) attaining high target dose conformity, (c) minimizing the volume of normal tissue receiving very high dose, and (d) limiting the dose to critical structures below their tolerance. Quantifying the dose gradient is an indirect way of scoring the fourth objective mentioned above
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