ESTRO 2024 - Abstract Book

S3439

Physics - Dose calculation algorithms

ESTRO 2024

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2121

Digital Poster

Should we switch to convolution algorithm when treating AVMs embolized with Onyx?

Hui-Chuan Wang 1 , Bin S Teh 1 , Ramiro Pino 1 , Edward B Butler 1 , Dershan Luo 2

1 Houston Methodist Hospital, Radiation Oncology Department, Houston, USA. 2 UT M D Anderson Cancer Center, Radiation Physics, Houston, USA

Purpose/Objective:

Sometimes the first line of management for arteriovenous malformations (AVMs) is embolization with Onyx, which has a high atomic number. GammaPlan has traditionally performed calculations using TMR10 algorithm, which assumes uniform water density inside the skull. With a high-density material inside the skull, a Gamma Knife (GK) planner may want to know how much the difference is if convolution algorithm is used. Several studies 1-3 have compared the dosimetric differences between TMR10 and convolution under the same prescription (Rx) and concluded no significant dose differences but with an increase in mean beam-on-time (BOT) of 7.4% 1 – 8.4% 2 under normal circumstances. It is generally believed that convolution has better dose accuracy 4 . Small differences between using Onyx’s physical constants and replacing it with water under Monte Carlo calculations 5 , and negligible effect for MV beams for Onyx material < 8mm 6 motivated us to investigate convolution algorithm’s clinical application on AVMs embolized with Onyx.

Material/Methods:

Since Icon’s installation, we have treated 32 AVM patients, of which 8 patients had been embolized with Onyx at the time of GK treatment. We imported these 8 patients’ diagnostic CTs into GammaPlan to define electron density for convolution. Four patients have both pre-Onyx and post-Onyx CTs, 3 have only post-Onyx CT, and 1 has only pre Onyx CT (his only post-Onyx CTs are the GK planning and treatment CBCTs, whose suitability for dose calculation is still being investigated 7,8 ). These diagnostic CTs have been acquired with the same CT protocols as simulation CTs for