Evaluation of air photoactivation at linear accelerators for radiotherapy

Abstract

High-energy x-rays produced by radiotherapy accelerators operating at potentials above 10 MV may activate the air via (γ, n) reactions with both oxygen and nitrogen. While the activation products are relatively short-lived, personnel entering the accelerator room may inhale some radioactive air, which warrants internal dosimetry assessments. This work illustrates a method based on the use of ammonium nitrate solutions for the evaluation of photon-induced air activation and for the estimate of internal doses to radiotherapy personnel. Air activation and internal dosimetry assessments based on our method are presented for some widespread radiotherapy linear accelerator models. Our results indicate that the equivalent dose to the lungs of radiotherapy personnel is negligible for beam energies below 18 MeV.

Evaluating inorganic compounds as air substitute materials in photon irradiation

“…Therefore, radiometric measurements of nitric acid samples irradiated in the high-energy photon field can substitute direct radiometric measurements of air photoactivation. Experimental and calculation procedures for monitoring the photonuclear reaction yields from nitrogen and oxygen in air by using different materials have been described in details in works [15][16][17][18] in order to evaluate the radiological hazard to personnel by operation of high-energy medical accelerators.…”

“…Figures 1, 2, 3 contain the calculated dependencies of the solid NH 4 NO 3 . The aqueous solutions of NH 4 NO 3 were used in works [15,17]. However, as shown in figure 4, none of the concentrations of NH 4 NO 3 in aqueous solution can achieve a similar result as for solution HNO 3 81 wt%.…”