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On Achievable Dose-Rates in a Small Animal Radiation Research Platform (SARRP) and Energy Dependency of EBT3, EBT-XD, and HD-V2 Radiochromic Films

D Mulrow1*, Y Hao2, W Lo2, T Mazur2, L Sobotka1, A Darafsheh2, (1) Department of Chemistry, Washington University in St. Louis, Saint Louis, MO, (2) Department of Radiation Oncology, Washington University School of Medicine in St. Louis, St. Louis, MO

Presentations

TU-D930-IePD-F3-2 (Tuesday, 7/12/2022) 9:30 AM - 10:00 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 3

Purpose: To investigate achievable dose rates in the Xstrahl SARRP and energy dependency of EBT3, EBTXD, and HD-V2 radiochrmic films when exposed to kilovoltage and megavoltage x-ray beams.

Methods: EBT-3, EBT-XD, and HD-V2 GafChromic film samples were irradiated at various doses using a SARRP (220 kV) and a linac (6 MV). For the SARRP irradiations, the Cu filter was removed, and film samples were placed on the surface of a solidwater phantom and irradiated at the isocenter of the system at source-to-surface distance (SSD) of 35 cm. For comparison, the same film models were irradiated at the same dose levels using a TrueBeam linac. The dose range delivered to the films varied depending on the film model: 0.25-10 Gy for EBT-3, 5-50 Gy for EBT-XD, and 10-250 Gy for HD-V2. To study achievable dose rates in the SARRP, the SSD was sequentially reduced to ~2 cm using a platform with adjustable height and different HD-V2 samples were irradiated. The net optical density (OD) was measured using a flatbed scanner 72 hours post-irradiation. The dose to each film sample was measured using a calibration curve, and dose rate was calculated by knowing the exposure time.

Results: The films irradiated with the SARRP showed an underresponse (8% for EBT3, 9% for EBT-XD, and 15% for HD-V2) in the net OD when compared to their counterparts irradiated with the megavoltage photons. We found that at 2.5 cm SSD the SARRP dose rate reaches ~120 Gy/s, and so the SARRP can be used for in vitro FLASH studies. The dose rate was shown to have an inverse square relationship with the distance from the source.

Conclusion: Radiochromic films shows an under-response in kV beams compared to MV beams. The SARRP can achieve ultra-high dose rates at SSD < 5 cm.

Keywords

Film, Dosimetry, X Rays

Taxonomy

TH- Small Animal RT: Experimental Dosimetry

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