Purpose: The Precision X-Ray X-Rad 320 is a popular x-irradiator for radiobiology research, providing beam energies up to 320 kVp. An optional interface allows the user to select a dose for delivery based on a vendor-provided calibration, with no correction for phantom or collimator scatter. Many radiobiology labs do not have access to medical physicist support so will rely on this calibration. Here we perform absolute and relative dosimetry to commission delivery to a variety of experimental setups and evaluate the vendor calibration.
Methods: Absolute dosimetry of a 320 kVp beam hardened with a Thoraeus filter was performed with a Farmer chamber according to TG-61 to the extent practical and via EBT3 radiochromic film calibrated on a 6 MV therapy linac. Mouse and rat phantoms based on CT scans of animal carcasses were printed with inserts for EBT3 film and used to measure the dose in simulated experimental conditions. Film was also used across open fields to characterize cellular irradiation in 96-well plates. Measurements were performed in an open field and with vendor-supplied rectangular and conical collimators as appropriate for each experimental condition.
Results: The vendor calibration was found to deliver 7% to 30% more dose at body midline than was set for the various setups explored. The center of the usable flat dose distribution for an open field was found to be 4 cm to the left of the beam axis due to the hell effect.
Conclusion: Because dose errors of greater than 5% can cause unacceptable errors in many radiobiology experiments, medical physicists should commission each experimental setup to be used on this model of irradiator to adjust calibration and determine profiles as needed.
Radiobiology, Commissioning, Phantoms