ESTRO 2024 - Abstract Book

S3718

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

ESTRO 2024

Figure 1 shows sinograms and LOT histograms typical of plans performed with RayStation and VOLO. These two images correspond to plans performed on the same patient. The image reveals a significant difference in the shape of the LOT histograms, in line with the similarity in mean open times (-2%±10% difference between RayStation and VOLO) and the substantial differences in the percentages of leaves with maximum open times (+90%±8% for RayStation compared to VOLO) and the percentages of leaves with times below 100ms (+29%±15% for RayStation compared to VOLO). This suggests that while RayStation aims to deliver treatments with long open time "sticks" and small modulation times to protect the organs at risk (OAR), VOLO's philosophy is to achieve a bell-shaped profile of leaf open times, with very frequent mean open times. Furthermore, differences in jaw size and percentages of leaves without maximum open times resulted in an increase in treatment time for dosimetry performed with VOLO (+65%±50%) compared to RayStation.

All of this leads to RayStation plans having lower modulation factors (2.2±0.2) compared to VOLO plans (2.7±0.2), resulting in less modulated plans.

Conclusion:

It has been observed that both a lower modulation factor (MF), shorter treatment times, and a higher percentage of leaves with maximum open times cause RayStation to optimize less modulated treatments than VOLO, leading to more optimal treatments for head and neck cancer patients.

Keywords: Tomotherapy, Raystation, Head and Neck