ESTRO 2024 - Abstract Book

S4618

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTR0 2024

Treatment plans of three patients with soft-tissue tumors of the lower extremities were created on DECT scans with a prescribed dose to the clinical target volume (CTV) of 50 Gy(RBE) delivered in 25 fractions. A single lateral beam from 90° with a range shifter of 6.5 cm was applied using a horizontal pencil beam scanning beamline. The dose distributions were robustly optimized with 3%/3mm for the CTV. The dose distributions were recomputed on the same DECT with BDO of the bone (tibia and fibula of 1.85 g/cm3), bone marrow (0.90 g/cm3), and water (1.00 g/cm3) for the remaining body. Dose distributions (Figure 1) were compared based on a gamma analysis (2%/2mm and 3%/3mm with a dose threshold of 10%). The difference between the dose distributions was determined in terms of D2%, D98%, D50% for the CTV, tibia and fibula. The homogeneity index (HI) of the CTV was defined as (D2%-D98%)/D50%. The dose difference for all voxels was determined as a measure for the dose calculation accuracy, excluding doses lower than 1 Gy.

Figure 1 Dose distributions (upper part), dose difference (lower left) and gamma index (lower right) of patient #1 comparing DECT without and with BDO for bone, bone marrow and remaining tissues.

Results: