ESTRO 2024 - Abstract Book

S3717

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

ESTRO 2024

Factors such as field size, pitch, modulation factor, and treatment times affect the quality of the treatment plan and, consequently, the proper treatment of the patient. The quality of treatments performed with both TPS has been compared for head and neck (H&N) cancer patients.

Material/Methods:

Treatment plans were performed on 10 H&N patients simulation CT images using RayStation (Raysearch Laboratories) and Precision with VOLO (Accuray) for a Radixact linear accelerator (Accuray) with a dose rate of 1000cGy/min at the depth of the maximum dose. The prescription used is shown in Table 1. It is a 33 fractions treatment for irradiating the tumor and positive nodes to 69.96Gy, while the remaining lymph node chains receive 54Gy. Efforts were made to achieve the same dose limits in both planners, resulting in the mean coverages and organs at risk doses (with standard deviations (k=1)) as seen in Table 1.

All treatments were planned with a pitch of 0.43 and jaw apertures of 5.04cm and 2.51cm as needed to achieve prescription.

Differences in the resulting treatment times were evaluated, as well as the modulation factor (MF), the average leaf open time (LOT), and the percentages of leaves with maximum open times and with times below 100ms.

Results:

Given that dosimetry performed with RayStation was used as a reference, jaw sizes in Precision plans were adjusted to achieve the same prescription goals previously obtained. Treatments were obtained with both jaw sizes in RayStation (7 treatments with 5.04cm and 3 with 2.51cm), but only with the 2.51cm jaw in Precision.