Dosimetric characterization of a graphite calorimeter and TLDs for FLASH radiotherapy

FLASH radiotherapy (FLASH-RT) is a novel technique that employs Ultra-High Dose Rate (UHDR) beams (> 40 Gy/s) and total irradiation times < 200 ms, significantly different from conventional radiotherapy (CONV-RT, ∼ Gy/min, ∼ minutes). Its main advantage is an enhanced sparing of normal tissues without compromising tumor control with respect to CONV-RT. However, FLASH-RT clinical translation remains limited by several challenges. In dosimetry, under UHDR conditions, ionization chambers-the gold standard in CONVRT-experience significant ion recombination, thus motivating the investigation of alternative dosimeters. Recently, a portable graphite calorimeter realized by the NPL (UK) and thermoluminescence dosimeters (LiF:Mg,Ti and CaF2 : Mn) were characterized by the INFN-CT and University of Catania research groups using UHDR electron beams at the Centro Pisano for FLASH Radiotherapy (CPFR, Pisa). Their response was compared with the one obtained with the reference FlashDiamond (PTW) detector. Both dosimeters showed dose rate independence up to ∼ 9 · 10^5 Gy/s, supporting their reliability for dose measurements under UHDR conditions.