Background: High-energy linear accelerator (linac) is a valuable tool and the most commonly device for external beam radiation treatments in cancer patients. In the linac head, high-energy photons with energies above the threshold of (γ,n) interaction produce photoneutrons. These photoneutrons deliver the extra dose to the patients in the planning treatment and increase the risk of secondary cancer. Objective: In this study, a simplified model of the linac head was simulated and photoneutron dose equivalent was calculated in the isocenter and maze for the sphere detector. In addition, the absorbed and equivalent dose of photoneutron were estimated in the some organs of the phantom. Methods: The simulations were made using the Monte Carlo code. The ICRP adult reference male voxel phantom was used as the human body model for Dosimetry calculations. Results: The results of dose calculations in the isocenter and maze showed that photoneutron dose decreases as the function of distance from the isocenter and increases with increasing the distance from the entrance maze. Conclusion: It is concluded that the simplified model of linac head is a useful and reliable method in dosimetry calculations. Calculations illustrated that the photoneutron dose is not negligible and duo to its harmful biological effects on body, it should be considered in the treatment plans.

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