Photoneutron and capture gamma dose equivalent for different room and maze layouts in radiation therapy

Abstract

In this paper the effect of treatment room and maze layout on the photoneutron and capture gamma dose equivalent in the maze was studied. MCNPX Monte Carlo (MC) code was used to simulate the Varian 2100 C/D Clinac 18 MV and four different room layouts. Two analytical methods, Wu-McGinley and McGinley, were used for dose calculations. The analytical methods overestimated the photoneutron dose (13-43 %) and gamma capture dose (16-95 %) comparing with the MC method at the maze entrance door. The results of MC method revealed that additional bend can cause a great reduction in photoneutron (5000 times) and capture gamma dose (50 times) in the maze entrance door.

Does concrete composition affect photoneutron production inside radiation therapy bunkers?

“…2 and the MC method showed that our MC model overestimated the neutron fluence at a point of almost 17% in comparison to the analytic method. However, the observed discrepancy between the MC and analytical methods has been reported by other investigations [11,13,14].…”

“…2). The MC model had been validated and used in previous studies [10,11]. The water phantom with 40-cm length, 25-cm thickness and 30-cm width, resembling an average patient body on a table, was also simulated at a source-to-surface distance of 100 cm.…”

Conversion coefficients for determination of dispersed photon dose during radiotherapy: NRUrad input code for MCNP

“…On the other hand, some previous works focused on detailed simulation of the human phantom with the isocenter of a Linac, but over-simplified details in the treatment room such as the maze, primary and secondary shielding (e.g., refs. [20, 21]). Many of these results were also obtained for single or non-generic irradiation scenarios, e.g.…”

Gamma Radiation in the Vicinity of the Entrance to Linac Radiotherapy Room

“…Production of neutron secondary radiation during emission of high-energy photon therapeutic beams is generally known and widely studied issue [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]48]. Also, the phenomenon of high-energy X-rays and secondary neutron-induced radioactivity is well recognized [57].…”

“…Additional lamination of maze walls as well as using multibend geometries are the solutions advised for increasing the neutron absorption before reaching the entrance. These solutions help to slim down the room door or even built the door-less entrance, minimizing secondary radiation at the entrance [48]. Typical door construction contains the most inner layer of neutronabsorption material (polyethylene, paraffin, or borax), enclosed with heavy photon-absorption layer (lead, tungsten) coated with industrial material, typically of stainless steel or wood.…”