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Generalization of the homogeneity index for multi-target radiotherapy plans

evidence-based-medicine
oncology
radiology-and-medical-imaging
surgery-and-surgical-specialties
healthcare-services

Abstract

Background and Purpose: Considering the inaccuracies of current homogeneity index (HI) formulas in multi-target plans, we have redefined the V PTV in the formula for calculating the HI value of target volumes in multi-target plans, providing a reference for clinical applications.

Methods and Materials: Given the inaccuracies of the three widely used HI formulas in evaluating multi-target treatment plans, we have redefined the V PTV calculation formula to ensure that the computed HI values more accurately reflect the dose homogeneity within the target volumes. Fifteen clinically treated breast cancer (BC) patients with conserving surgery patients and fifteen nasopharyngeal carcinoma (NPC) patients were chosen. Using our proposed formula, we calculated the VPTV with the name of VPTVpro and the HIpro1 , HIpro2 , and HIpro3 . A paired, two-tailed non-parametric Wilcoxon signed-rank test was utilized to compare VPTV ori and VPTVpro , HIori1 and HIpro1 , HIori2 and HIpro2 , HIori3 and HIpro3 . The correlations between HI ori1 and HIpro1, HIori2 and HIpro2, and HIori3 and HIpro3 were also analyzed, and Pearson’s correlation coefficients were calculated.

Results: For PTV of BC and PTV1 of NPC, the VPTVpro values calculated using our proposed method were significantly smaller than the original VPTVori values. The HI values calculated from the three formulas, as well as the HIori and HIpro values, showed statistically significant differences, with HIpro being significantly lower than HIori. For PTV of BC and PTV1 of NPC, the correlation coefficient values between HIori1 -HIpro1, HIori2 -HIpro2, and HIori3 -HIpro3 showed variations, though all demonstrated positive correlations with statistically significant p-values <0.01. The computational results for these two target volumes revealed a consistent pattern: the HIori1-HIpro1 pair exhibited the highest correlation coefficient values, while HIori2-HIpro2 consistently showed the lowest values among the three method comparisons.

Conclusions: The new VPTV subtracts the high-dose target volume within the low-dose target volume, making it more reasonable and accurate than previous formulas in reflecting the HI value of the analyzed low-dose target volume. Additionally, the new VPTV proposed in this paper is also applicable for HI calculation in a single-target volume. We suggest using the new VPTV proposed in this study to calculate the HI value of the target area for multi-target plans, such as BC with conserving surgery and NPC. Meanwhile, we recommend employing Formula 1 for the calculation of the target HI among the three formulas.

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