Photon and photon-neutron experimental dosimetry in Grid therapy with 18 MV photon beams

Propose: Spatially fractionated Grid radiation therapy (SFGRT) in an effective technique for bulky and radio-sensitive tumours. SFGRT using a constructed block has been used to evaluate the photon and photo-neutron (PN) dose measurement in 18-MV photon beam energy. Methods and materials: A mounted Grid block on to a Varian Clinac 2100c linear accelerator was used to perform photon dosimetry. The percentage depth dose, in-plane and cross-plane beam profile and output factor was measured by ionization chamber in water. The PN contamination was measured after photon dosimetry using the combination of thermoluminescence dosimetry types 600 and 700, and Polycarbonate Film dosimeters on the surface and in the maximum depth dose (dmax) of solid water™ slabs. Results: The valley-to-peak ration for 6 and 18 MV photon beams obtained from the beam profiles was ~35 and 72%, respectively. Fast and thermal PN equivalent dose decreased in the Grid field compared to an open field (without Grid). Conclusion: The Grid therapy dosimetry compared to the conventional radiotherapy (without the grid) the production of fast and thermal neutrons were reduced. Using of a Grid block in high-energy photon beams for a long period of the treatment continuously might be a new source of contamination due to the interaction of photon beam resulting the activation of the Grid block.