ESTRO 2024 - Abstract Book

S3293

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

[2] Galve, P., Catana, C., Herraiz, J. L., & Udía, J. M. (2020). GPU based fast and flexible iterative reconstructions of arbitrary and complex PET scanners: application to next generation dedicated brain scanners. In 2020 IEEE Nuclear Science Symp. and Medical Imaging Conf. Proc. (NSS/MIC).

[3] Onecha, V. V., Galve P., et al, (2022). Dictionary-based software for proton dose reconstruction and submilimetric range verification. Physics in Medicine & Biology, 67(4), 045002.

1894

Digital Poster

Beam control system with pulse forming network sync for safe and precise delivery of FLASH-RT

Elise Konradsson 1 , Pontus Wahlqvist 2 , Andreas Thoft 2 , Börje Blad 1,2 , Crister Ceberg 1 , Kristoffer Petersson 2,3

1 Lund University, Medical Radiation Physics, Lund, Sweden. 2 Skåne University Hospital, Department of Hematology, Oncology and Radiation Physics, Lund, Sweden. 3 University of Oxford, Oxford Institute for Radiation Oncology, Department of Oncology, Oxford, United Kingdom

Purpose/Objective:

We have previously described the process of adapting a clinical linear accelerator (Elekta Precise, Elekta AB) to enable an ultra-high dose rate (UHDR) electron beam (1). As a step towards clinical implementation, we have upgraded the beam control system to enhance the safety and precision of the UHDR delivery. This report presents the upgrades and assesses the associated improvements.

Material/Methods:

The upgraded beam control system comprises of three modules: a monitor unit (MU) module, a pulse-counter module, and a pulse forming network (PFN) synchronization module. The system is designed to interrupt the beam based on one of the following criteria: 1) a preset number of monitor units (MU) measured by a monitor detector, 2) a preset number of pulses measured by a pulse-counting diode, or 3) a preset delivery time. For UHDR delivery, an optocoupler is used to enable external control of the accelerator’s thyratron trigger pulses. Given that most real-time detectors exhibit recombination effects at UHDR, the detector in the current setup was a reconfigured transmission ionization chamber (Elekta AB) situated in the upper part of a 10x10 cm 2 electron applicator and corrected for recombination effects using a logistic model (2,3). The corrected chamber signal was calibrated such that 100 MU corresponds to 1 Gy in the reference geometry (i.e., 2.2 cm depth at a source-to-surface distance (SSD) of 100 cm of a 10 MeV electron beam). The measurement setup consisted of a 10 cm solid water phantom at SSD=100 cm, with EBT3 film placed at the reference depth and a Farmer-type ionization chamber positioned at 9 cm depth in the bremsstrahlung tail of the electron beam. To maximize the output of the electron beam, a beam tuning process was performed based on Farmer-type chamber measurements. The short- and long-term repeatability of the beam delivery was assessed. To evaluate the accuracy of the transmission chamber in determining the delivered number of MUs under UHDR conditions, we investigated the linearity between the calculated MUs and the dose measured with film for various preset numbers of pulses. The PFN synchronization module was constructed to monitor the