ESTRO 2024 - Abstract Book

S3546

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

treatment and a reference treatment plan (TP CT ) was optimised to deliver 50 Gy (10Gy x 5 fractions) at Unity MR Linac; criteria of at least 80% of the target volume covered by the prescription dose while complying with the OARs limits[4] were adopted. For each patient, contains all the information to use for the plan adaptation in the adapt to-shape workflow (ATS), particularly the contours including their average EDs and layering. To assess the accuracy of the dosimetry of the MRI-based sCT plans, each plan was recalculated on the ideal sCT (sCTref) obtained from the reference CT by forcing the drawn contours to the average EDs as defined on TP CT [5]. Targets and organs at risk (OARs) dose-volume histograms of the CT and sCTref plans were compared within each group. Statistical analysis of the data was performed by using SPSS software, used to test the consistency of the dosimetric results obtained within each group; paired t-test or Wilkinson signed-rank tests were used after the normality test; a value of p < 0.05 was considered statistically significant difference.

Figure 1: Visual illustration of the different tumour site locations: in the central, lateral, and middle part of the lung (C, L, M, respectively).

Results:

Each reference CT treatment plan complies with the clinical indication of target coverage and constraints of OARs. The electronic densities calculated by Monaco for each organ and used for the MRI-based sCT calculation are 0.85±0.07, 0.29±0.07, 1.08±0.03, 1.19 ±0.03 for the GTV, lungs, heart, and ribs, respectively and consistent with the values indicated in the Report ICRU 46. For patients with a tumor in the central area, the reference CT and corresponding sT plan calculations highlighted no statistical difference ( p > 0.05) in the dosimetry of the target or OARs; patients with tumor located in the medial or lateral area presented a significant difference ( p <0.05) in the target and lung dosimetry while the heart was not affected. The results obtained are detailed in Table 1.