Author: Sang Hyun Cho, Amrit Kaphle, Sunil Krishnan, Neerajan Nepal 👨🔬
Affiliation: The University of Texas MD Anderson Cancer Center, The University of Texas Health Science Center 🌍
Purpose: To determine the basic dosimetry parameters and characteristics of a commercial cabinet x-ray unit for small animal irradiation as well as the specific dosimetry parameters for concurrent irradiation of multiple mice using the partial body irradiation shields.
Methods: The x-ray irradiator consists mainly of a shielded cabinet of size 120 × 130 × 211 cm3 (irradiation chamber dimensions of 61 × 62 × 107 cm3) and an industrial x-ray source. For small animal irradiation, the x-ray source can produce up to a 225 kVp x-ray beam at 13.2 mA, filtered through 0.5 mm Al and 0.2 mm Cu. A Farmer-type ion chamber was placed at 2 cm depth within a solid water phantom to measure the in-phantom/water dose rate at a 74.6 cm source-to-detector distance (SDD) or 72.6 cm source-to-surface distance (SSD) using the TG61 protocol. At the same SDD or SSD, EBT3 radiochromic films were sandwiched between solid water slabs and irradiated up to 10 Gy dose to determine the film calibration curve. In-air x-ray beam profiles were also examined by film measurements. Additional radiochromic film measurements were performed at 60.3 cm SDD with four partial body irradiation shields arranged in the cross-shape for simultaneous irradiation of four mice. Based on the film results, the dose rate within the unshielded area was determined while ensuring the dose uniformity there.
Results: The ion chamber-measured in-phantom/water dose rate (at 2 cm depth, 72.6 cm SSD) was 0.6298 Gy/min. For simultaneous irradiation of four mice at 60.3 cm SDD using the partial body shields, the film-measured dose rates at four unshielded areas were found within 3% of an average dose rate of 0.8275 Gy/min.
Conclusion: The current results confirm that the irradiator produces the dose rate and the beam profile suitable for small animal irradiation in a reproducible manner.