Abstract
Dose painting radiotherapy is considered a promising radiotherapy technology that enables more targeted dose delivery to tumor rich regions while saving critical normal tissues. Obviously, dose painting planning would be more complicated and hard to be evaluated with current plan quality index systems that were developed under the paradigm of uniform dose prescription. In this study, we introduce a new plan quality index, named “index of achievement (IOA)” that assesses how close the planned dose distribution is to the prescribed one in a dose painting radiotherapy plan. By using voxel‐based comparison between planned and prescribed dose distributions in its formulation, the index allows for a single‐value evaluation regardless of the number of prescribed dose levels, which cannot be achieved with the conventional indices such as conventional homogeneity index. Benchmark calculations using patient data demonstrated feasibility of the index not only for contour‐based dose painting plans, but also for dose painting by numbers plans. Also, it was shown that there is strong correlation between the new index and conventional indices, which indicates a potential of the new index as an alternative to conventional ones in general radiotherapy plan evaluation.PACS number: 87.55.D‐
Highlights
Since its introduction in 2000, dose painting (DP) in radiotherapy has been accepted as a promising technique for the treatment of cancers where high-risk tumor subvolumes are associated within.[1]
Contourbased DP, obviously simpler to be implemented than voxel-based DP, was already found to be effective in several clinical studies.[1,4,5] On the other hand, DPBN has been an active subject of research in recent years, and its potential benefits have currently been reported by researchers.[6,7] Even though the importance of DP is increasingly recognized in radiation therapy, little attention has been paid, so far, in the aspect of plan evaluation.[8]. For example, single-valued indices, such as the conformity index (CI) and the homogeneity index (HI), that are commonly used in routine clinical practice for plan evaluation need to be modified for DP planning, since such indices are formulated based on the paradigm of uniform dose prescription
The calculated value of the conventional index is a mean value for all three PTVs in each plan, which can be applied to only contour-based DP cases, not DPBN cases
Summary
Since its introduction in 2000, dose painting (DP) in radiotherapy has been accepted as a promising technique for the treatment of cancers where high-risk tumor subvolumes are associated within.[1]. Homogeneity index (HI) (or uniformity index) is a tool to assess the planned dose distribution in a target volume. Several indexing formulas have been introduced in literatures.[9,10,11] The basic concept of these methods is to calculate the ratio of the dose value of high-dose region to the reference dose value (such as prescription dose or dose value of normal-dose region) within a target. Since DP is basically pursuing “nonuniform” dose distribution in a target volume, assessing dose homogeneity itself may be no longer meaningful. Dose standard deviation (STD) in a target volume, which is an alternative to HI,(12) is inappropriate for the use in the evaluation of DP treatment plans
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