ESTRO 2023 - Abstract Book

S1525

Digital Posters

ESTRO 2023

Numerous studies have aimed to develop dosimetric indexes that allow to accurately represent the homogeneity of the treatment plan while minimizing time-consuming DVH-based analysis. The recently developed mean absolute dose deviation (MADD) index (Vinh-Hung et al, 2020) has been successfully applied in several breast studies. The present study aims to re-evaluate eighty prostate treatment plans using a penalty score that weights the mean absolute dose deviations (MADD) for the different structures. Materials and Methods Eighty prostate cases were retrospectively identified for this study: 22 with 6FFF Volumetric Modulated Arc Therapy (VMAT) plans for a Varian TrueBeam STx, 24 Fixed-Field Intensity-modulated radiation therapy (FF-IMRT) plans and 34 plans with Helical TomoTherapy (HT). Radiation doses to rectum, bladder, femoral heads, sigmoid and planned target volume (PTV) were evaluated using the mean absolute dose deviation (MADD). This metric measures how widely the dose delivered to a structure i deviates from a reference dose. That reference dose represents the prescription dose in the case of the target volume and zero for the organs at risk (OAR). The total penalty score sums all the MADD values weighted by a relative factor of w(i). Calculations were performed with an in-house Matlab R2016 code by importing the treatment planning system (TPS) DVH data. Results Figures 1 and 2 summarize the corresponding MADDs for the target and organs at risk. MADD valures are expressed as a percentage of the prescribed dose to make the MADD from the OARs dose-independent since different total dose prescriptions were used.

Figure 1

Figure 2 The average MADD value is higher for the FF-IMRT technique (0,96±0,33%) and VMAT and HT techniques achieve the same homogeneity in the target: 0,74±0,29% and 0,75±0,21%, respectively. By calculating the penalty score with the same relative weight assigned to all structures, HT achieved the lowest index value (26.4±6,1%), indicating that HT showed better OARs sparing.