Technical note: Characterization and practical applications of a novel plastic scintillator for online dosimetry for an ultrahigh dose rate (FLASH)
Yannick Poirier and Junliang Xu have contributed equally to the manuscript and should be considered co-first authors.
Although flash radiation therapy (FLASH-RT) is a promising novel technique that has the potential to achieve a better therapeutic ratio between tumor control and normal tissue complications, the ultrahigh pulsed dose rates (UHPDR) mean that experimental dosimetry is very challenging. There is a need for real-time dosimeters in the development and implementation of FLASH-RT. In this work, we characterize a novel plastic scintillator capable of temporal resolution short enough (2.5 ms) to resolve individual pulses.
We characterized a novel plastic dosimeter for use in a linac converter to deliver 16-MeV electrons at 100-Gy/s UHPDR average dose rates. The linearity and reproducibility were established by comparing relative measurements with a pinpoint ionization chamber placed at 10-cm water-equivalent depth where the electrometer is not saturated by the high dose per pulse. The accuracy was established by comparing the plastic scintillator dose measurements with EBT-XD Gafchromic radiochromic films, the current reference dosimeter for UHPDR. Finally, the plastic scintillator was compared against EBT-XD films for online dosimetry of two in vitro experiments performed at UHPDR.
Relative ion chamber measurements were linear with plastic scintillator response within ≤1% over 4–20 Gy and pulse frequencies (18–180 Hz). When characterized under reference conditions with NIST-traceability, the plastic scintillator maintained its dose response under UHPDR conditions and agreed with EBT-XD film dose measurements within 4% under reference conditions and 6% for experimental online dosimetry.
The plastic scintillator shows a linear and reproducible response and is able to accurately measure the radiation absorbed dose delivered by 16-MeV electrons at UHPDR. The dose is measured accurately in real time with a greater level of precision than that achieved with a radiochromic film.
CONFLICT OF INTEREST
François Therriault-Proulx is Co-founder and CEO at MedScint Inc., a company developing scintillation dosimetry systems. This work was not financially supported by MedScint.
DATA AVAILABILITY STATEMENT
The research data for this study are available from the authors upon request.
- 1, , . Physics and biology of ultrahigh dose-rate (FLASH) radiotherapy: a topical review. Phys Med Biol. 2020; 65(23):23TR03.
- 2, , , et al. Irradiation in a flash: unique sparing of memory in mice after whole brain irradiation with dose rates above 100 Gy/s. Radiother Oncol. 2017; 124(3): 365–369.
- 3, , , et al. Clinical translation of FLASH radiotherapy: why and how?. Radiother Oncol. 2019; 139: 11–17.
- 4, , , et al. Ultrahigh dose-rate FLASH irradiation increases the differential response between normal and tumor tissue in mice. Sci Transl Med. 2014; 6(245):245ra93.
- 5, , , et al. The advantage of FLASH radiotherapy confirmed in mini-pig and cat-cancer patients. Clin Cancer Res. 2019; 25(1): 35–42.
- 6, , . Biological benefits of ultra-high dose rate FLASH radiotherapy: sleeping beauty awoken. Clin Oncol. 2019; 31(7): 407–415.
- 7, . On the capabilities of conventional x-ray tubes to deliver ultra-high (FLASH) dose rates. Med Phys. 2019; 46(12): 5690–5695.
- 8 IntraOp Medical Corporation. IntraOp and OSU Announce Collaboration in FLASH; n.d.
- 9, , , et al. High dose-per-pulse electron beam dosimetry: commissioning of the Oriatron eRT6 prototype linear accelerator for preclinical use: commissioning. Med Phys. 2018; 45(2): 863–874.
- 10, , , et al. X-rays can trigger the FLASH effect: ultra-high dose-rate synchrotron light source prevents normal brain injury after whole brain irradiation in mice. Radiother Oncol. 2018; 129(3): 582–588.
- 11, , , et al. Design, implementation, and in vivo validation of a novel proton FLASH radiation therapy system. Int J Radiat Oncol Biol Phys. 2020; 106(2): 440–448.
- 12, , , et al. Experimental platform for ultra-high dose rate FLASH irradiation of small animals using a clinical linear accelerator. Int J Radiat Oncol Biol Phys. 2017; 97(1): 195–203.
- 13, , . PHASER: a platform for clinical translation of FLASH cancer radiotherapy. Radiother Oncol. 2019; 139: 28–33.
- 14, , , et al. Commissioning of an ultra-high dose rate pulsed electron beam medical LINAC for FLASH RT preclinical animal experiments and future clinical human protocols. Med Phys. 2021; 48: 3134–3142.
- 15, , , et al. AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams. Med Phys. 1999; 26(9): 1847–1870.
- 16, , , et al. Radiation shielding and safety implications following linac conversion to an electron FLASH-RT unit. Med Phys. 2021; 48: 5396–5405.
- 17, , , , . Charge collection efficiency in ionization chambers exposed to electron beams with high dose per pulse. Phys Med Biol. 2006; 51(24): 6419–6436.
- 18, , , et al. High dose-per-pulse electron beam dosimetry – a model to correct for the ion recombination in the advanced Markus ionization chamber. Med Phys. 2017; 44(3): 1157–1167.
- 19, , , et al. Calorimeter for real-time dosimetry of pulsed ultra-high dose rate electron beams. Front Phys. 2020; 8:567340.
- 20, , , . Response characterization of EBT-XD radiochromic films in megavoltage photon and electron beams. Med Phys. 2019; 46(9): 4246–4256.
- 21, , , et al. Modifying a clinical linear accelerator for delivery of ultra-high dose rate irradiation. Radiother Oncol. 2019; 139: 40–45.
- 22, , , et al. Dosimetric and preparation procedures for irradiating biological models with pulsed electron beam at ultra-high dose-rate. Radiother Oncol. 2019; 139: 34–39.
- 23, , , et al. Electron FLASH delivery at treatment room isocenter for efficient reversible conversion of a clinical LINAC. Int J Radiat Oncol Biol Phys. 2021; 110(3): 872–882.
- 24, , , et al. High dose-per-pulse electron beam dosimetry: usability and dose-rate independence of EBT3 Gafchromic films: usability. Med Phys. 2017; 44(2): 725–735.
- 25, , , et al. Dose rate dependence for different dosimeters and detectors: TLD, OSL, EBT films, and diamond detectors. Med Phys. 2012; 39(5): 2447–2455.
- 26, , , et al. Dosimetry for FLASH radiotherapy: a review of tools and the role of radioluminescence and Cherenkov emission. Front Phys. 2020; 8: 26.
- 27, , , , . Evaluation of the uncertainty in an EBT3 film dosimetry system utilizing net optical density. J Appl Clin Med Phys. 2016; 17(5): 466–481.
- 28, , , et al. Optimization of alanine measurements for fast and accurate dosimetry in FLASH radiation therapy. Radiat Res. 2020; 194(6): 573–579.
- 29. Postirradiation effects in alanine dosimeter probes of two different suppliers. Phys Med Biol. 2008; 53(5): 1241–1258.
- 30, , , et al. Validating plastic scintillation detectors for photon dosimetry in the radiologic energy range. Med Phys. 2012; 39(9): 5308–5316.
- 31, , , , , . Plastic scintillation dosimetry: optimal selection of scintillating fibers and scintillators. Med Phys. 2005; 32(7): 2271–2278.
- 32, , , . Characterization of a plastic scintillating detector for the small animal radiation research platform (SARRP). Med Phys. 2019; 46(1): 394–404.
- 33, , , . Preclinical dose verification using a 3D printed mouse phantom for radiobiology experiments. Med Phys. 2019; 46(11): 5294–5303.
- 34, , , et al. The challenge of ionisation chamber dosimetry in ultra-short pulsed high dose-rate very high energy electron beams. Sci Rep. 2020; 10(1): 9089.
- 35, , . Comparative optic and dosimetric characterization of the HYPERSCINT scintillation dosimetry research platform for multipoint applications. Phys Med Biol. 2021; 66(8):085009.
- 36, , , . A mathematical formalism for hyperspectral, multipoint plastic scintillation detectors. Phys Med Biol. 2012; 57(21): 7133–7145.
- 37, , , , . Measurement accuracy and Cerenkov removal for high performance, high spatial resolution scintillation dosimetry. Med Phys. 2006; 33(1): 128–135.
- 38, , , . Development of a novel multi-point plastic scintillation detector with a single optical transmission line for radiation dose measurement. Phys Med Biol. 2012; 57(21): 7147–7159.
- 39, , , , . Impact of a 1.5 T magnetic field on DNA damage in MRI-guided HDR brachytherapy. Phys Medica. 2020; 76: 85–91.
- 40, , , . Assessing DNA damage of proton vs. photon beams using plasmid DNA. Med Phys. 2019; 46(6): E457.
- 41, , , . Quantifying the DNA-damaging effects of FLASH irradiation with plasmid DNA. Int J Radiat Oncol. 2022; S0360-3016(22): 00095-5.
- 42, , , et al. Dosimetry with a clinical linac adapted to FLASH electron beams. J Appl Clin Med Phys. 2021; 22(6): 50–59.
- 43, , , et al. Implementation and validation of a beam-current transformer on a medical pulsed electron beam LINAC for FLASH-RT beam monitoring. J Appl Clin Med Phys. 2021; 22(11): 165–171.
- 44, , . Feasibility of plastic scintillator dosimeters for FLASH therapy. Med Phys. 2020; 47(6):e783.
- 45, , , et al. Technical note: single-pulse beam characterization for FLASH-RT using optical imaging in a water tank. Med Phys. 2021; 48(5): 2673–2681.
- 46, , , et al. Spatial and temporal dosimetry of individual electron FLASH beam pulses using radioluminescence imaging. Phys Med Biol. 2021; 66(13):135009.