ESTRO 2024 - Abstract Book

S3483

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

ESTRO 2024

410

Digital Poster

Development of a shell fixing table for brain SRT in helical IMRT

Kazunori Miyaura 1 , Kouzou Murakami 2 , Tomoki Fujii 3 , Michio Ozaki 3 , Yoshinori Ito 2 , Yoshikazu Kagami 2

1 Showa university, Graduate School of Health Science, Tokyo, Japan. 2 Showa university, School of Medicine, Radiation oncology, Tokyo, Japan. 3 Showa university hospital, Deportment of Radiological technology, Tokyo, Japan

Purpose/Objective:

Since October 2019, Showa university hospital has introduced the helical IMRT device (Radixact TM ) and has been performing brain SRT. Concerns have arisen about the concentric distribution of dose when using helical arc irradiation. To reduce the radiation dose to normal tissues, it is necessary to use non-coplanar irradiation to disperse the low-dose regions and enhance the dose concentration to the target. Therefore, we developed a dedicated brain SRT shell fixation system for Radixact TM that allows setting of pitch and yaw angles. This enables virtual non-coplanar (VNCP) irradiation, and we report on its verification.

Material/Methods:

Using the dedicated shell fixation system developed in this study, pitch and yaw angles were set to 0/-5/5 degrees, and 30 Gy/3 fractions VNCP plans were created using treatment planning system with the head phantom. VNCP plans were created for each combination. PTV was set up in three sizes to simulate clinical practice(φ12, 15, 20 mm). DVH parameters of normal brain doses (V23.1, V19.6, V10, V5Gy) were compared between CP (clinical plans assuming no pitch and yaw angles) and VNCP to evaluate the results.

Results:

DVH parameters showed a reduction in normal brain doses with VNCP compared to CP. Specifically, for V23.1, V19.6, V10, and V5 Gy, the reductions were -0.2%, -0.7%, -5.0%, and -5.8%, respectively. For tumors ≤ 2 cm in size, it was possible to converge V23.1 Gy and V19.6 Gy to less than 5 cm 3 . Furthermore, specific combinations of pitch and yaw angles, such as pitch angle 15 degrees and yaw angles 0/-5/5 degrees, demonstrated a reduction in normal brain dose by approximately -5.0%. Additionally, pitch angle 5 degrees and yaw angles 0/-5/5 degrees showed a dose reduction of approximately -1.5%. No significant differences in DVH parameters were observed based on angle combinations in this verification.

Conclusion:

Using the dedicated shell fixation system developed in this study for VNCP planning, a reduction in normal brain radiation dose was achieved. This suggests the potential for reducing the incidence of adverse events in the normal brain following brain SRT.

Keywords: Brain SRT, non-coplanar irradiation, Helical IMRT