Dosimetric and preparation procedures for irradiating biological models with pulsed electron beam at ultra-high dose-rate

• Published in: Radiotherapy and oncology 2019-10, Vol.139, p.34-39
• Main Authors: Jorge, Patrik Gonçalves, Jaccard, Maud, Petersson, Kristoffer, Gondré, Maude, Durán, Maria Teresa, Desorgher, Laurent, Germond, Jean-François, Liger, Philippe, Vozenin, Marie-Catherine, Bourhis, Jean, Bochud, François, Moeckli, Raphaël, Bailat, Claude
• Format: Article
• Language: English
• Subjects: Dosimetry; Electrons - therapeutic use; FLASH; Humans; Models, Biological; Particle Accelerators; Passive dosimetry; Radiotherapy; Radiotherapy Dosage; Ultra-high dose-rate
• ISSN: 0167-8140; 1879-0887
• DOI: 10.1016/j.radonc.2019.05.004

•At conventional dose-rates (few Gy/min), the alanine, the Gafchromic films, the TLD and the ionization chamber agree within 2%.•For dose-rates up to 1050 Gy/s, the alanine, the Gafchromic films and the TLD agree within 3%, showing no dose-rate dependency.•Thanks to the dosimetric procedure, the uncertainty in the delivered dose for the biological experiments is estimated to be about 3%.•Without this dosimetric procedure, deviations between the delivered dose and the prescription dose can reach 15%. Preclinical studies using a new treatment modality called FLASH Radiotherapy (FLASH-RT) need a two-phase procedure to ensure minimal uncertainties in the delivered dose. The first phase requires a new investigation of the reference dosimetry lying outside the conventional metrology framework from national metrology institutes but necessary to obtain traceability, repeatability, and stability of irradiations. The second consists of performing special quality assurance procedure prior to irradiation. The Oriatron eRT6 (PMB-Alcen, France) is an experimental high dose-per-pulse linear accelerator, delivering a 6 MeV pulsed electron beam with mean dose-rates, ranging from a few Gy/min up to thousands of Gy/s. Absolute dosimetry is investigated with alanine, thermo-luminescent dosimeters (TLD) and radiochromic films as well as an ionization chamber for relative stability. The beam characteristic and dosimetry are prepared for three different setups. A cross-check between alanine, films and TLD revealed a dose agreement within 3% for dose-rates between 0.078 Gy/s and 1050 Gy/s, showing that these dosimeters are suitable for absolute dosimetry for FLASH-RT. In absence of appropriate setup dependent corrections, active dosimetry can reveal dose deviations up to 15% of the prescribed dose. These differences reduce to less than 3% when our dosimetric procedure is applied. We developed procedures to accurately irradiate biological models. Our method is based on validated absolute dosimeters and extends their use to routine FLASH irradiations. We reached an agreement of 3% between the delivered and prescribed dose and developed the requirements needed for workflows of preclinical and clinical studies.