ESTRO 2024 - Abstract Book

S3644

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

ESTRO 2024

• Dose to organs at risk (Spinal Cord D0.05ccm, Lung V13Gy, Esophagus D0.05ccm, Heart D1ccm, Ribs D0.05ccm, Skin D1ccm, Thoracic wall (TW) D0.05ccm and D1ccm).

We also obtained target volumes for each plan and distance from GTV to TW. Total work time for each of the two plans was recorded for one patient for comparison.

Results:

Complete data was available for 39 patients. The median irradiated isodose volumes from 5 Gy to 60 Gy were all significantly reduced tested with the Wilcoxon Signed Rank test (p < 0.05), with the largest reductions in the low dose volumes, see Fig. 1.

The median of the irradiated volume of 66 Gy was 0.60 ccm higher when using the robust optimization strategy (p = 0.07).

The doses to the OAR’s were significantly reduced with the robust optimization strategy for all OAR volumes, but the reductions were small, with medians between 0.5 and 2.44 Gy.

Figure 2 shows data for GTV, PTV, distance to TW, TW dose and MU.

Three of the robust plans could only be made robust in 13 of the 14 scenarios, due to normal tissue constraints.

The time used to prepare the two treatment plans differed widely – 18 minutes was required to prepare the normal plan compared to 96 minutes for the robust plan, thus requiring a factor 5 of more time. We believe that the measured difference is representative of the time used for all the patient plans, as this particular patient was of medium complexity.