The dose contribution due to photonuclear reactions during radiotherapy

Abstract

The dose equivalent due to photonuclear reactions within a patient irradiated with 24-MeV bremsstrahlung has been calculated to be about 1% of the photon dose. This is more than two times smaller than the previously accepted estimate.

Does concrete composition affect photoneutron production inside radiation therapy bunkers?

“…A recent review on photoneutron characteristics in radiation therapy has been published and is recommended for further detailed information [4]. Neutrons with higher radiobiological effectiveness or weighting factors up to 20 relative to photon beams increase unwanted whole-body radiation doses to the staff and patient, and consequently increase the probability of harmful effects such as cancers [5].…”

Charged photoparticle production in tissue during radiotherapy

“…6 The present calculation gives corresponding particle yield ratios of 1.00:1.76:0.23. The small difference in the proton ratio is due to improvements in the neutron calculation since 1982.…”

“…3 Cross sections for the (␥,xp) and (␥,x␣) reactions were also taken from the literature. 6 With the exception of hydrogen the contribution of the minor constituent isotopes of each element to the charged particle yields can be ignored because for these reactions the thresholds for the minor isotopes are comparable to or higher than those for the major isotopes ͑Table I͒. All significant reactions involving 2 H, 12 C, 14 N, and 16 O with thresholds below 20 MeV have been included in the calculation.…”

“…While many studies of the neutron component have been published, 1-4 much less information is available concerning the charged particle reactions. 5,6 Both of the latter papers deal with photonuclear reactions occurring within tissue equivalent material during irradiation with 24 MeV bremsstrahlung. The aim of the present work is to calculate charged photoparticle yields from tissue over the full range of bremsstrahlung energies from 3 to 28 MeV.…”

A review on photoneutrons characteristics in radiation therapy with high-energy photon beams

“…26 Flattening filters are often made of medium atomic number materials such as iron and copper which do not have considerable cross sections for photoneutron production. 34,35 Removal of flattening filters from linacs has been proposed and studied in several investigations as a way to increase the dose rate for radiosurgery and intensity-modulated radiation therapy (IMRT) treatments. 25,[36][37][38][39][40] It was shown that neutron fluence for a 18 MeV beam of Varian linac was about 69% lower for a flattening filter free beam measured by gold foil activation in neutron moderators.…”