ESTRO 2024 - Abstract Book

S3638

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

ESTRO 2024

FFF energy were used. The target volume position was verified with cone beam CT before each fraction. Exhalation phase CT scans were used for treatment planning for CK. GTV was delineated using CT/MR imaging with contrast agent. CTV was created using 2-5 mm margins. An additional 3 mm isotropic extension was used to define the PTV. Treatment plans were created using step-and-shoot IMRT and 6MV FFF energy. Two weeks before the planning CT gold markers were implanted close to the tumour bed for Synchrony fiducial respiratory motion tracking treatments. The PTV coverage was evaluated using V95% and V100% parameters. According to the SBRT clinical protocol of our institution - based on the RTOG0438 recommendation - DVH parameters of organs at risk (OARs) such as aorta, chest wall, esophagus, heart, liver, spinal canal and stomach have been analysed.

Results:

The biological effective doses (BED) were between 85.5-151.2 Gy for LINAC and 112.5-180 Gy for CK. The PTV V95% and V100% values were 99.46% and 94.95% for LINAC, and 99.35% and 96.68% for CK. The average of GTVs treated with LINAC was smaller than with CK. As a consequence of the chosen motion control approach the average of PTVs was smaller with CK (Table 1.).

Table 1.: GTV, CTV, PTV values for LINAC and CK.

There were clinically relevant differences in the D30cm3 parameter of chest wall, but the values of D1cm3 were similar. D0.1cm3 of the aorta, esophagus and the heart were lower in CK. Parameters for spinal canal and stomach were similar for the two techniques. Relative DVH parameters for the aorta, chest wall, esophagus, heart, spinal canal and stomach are shown in Figure 1.

Figure 1. Relative DVH values of OARs on LINAC and on CK.

The average volume of the liver for LINAC and for CK was 1433cm3 and 1756cm3, respectively. V19.2Gy parameter for the spared liver was required to be under 700cm3. This constrain was met with both techniques. The irradiated volumes with 19.2Gy of liver were 206cm3 and 123cm3 on average with LINAC and with CK, respectively.

Conclusion: