The photon interactions with the soft tissue have been discussed mainly in terms of mass attenuation coefficient, mass energy absorption coefficient, kerma relative to air, effective atomic number and energy absorption buildup factor in the energy range 0.01e10 MeV and penetration depth up to 40 mfp (by using GP fitting method). Over past 2 decades, interest has been growing for theoretical and computational works on photon buildup factor in soft tissue. Actually, besides dosimetry, in radiation therapy and imaging the buildup of X-and gamma photons introduces remarkable error.

Abstract:Bremsstrahlung photon beams produced by medical linear accelerators are currently the most commonly used method of radiation therapy for cancerous tumors. Photons with energies greater than 8-10 MeV potentially generate neutrons through photonuclear interactions in the accelerator's treatment head, patient's body, and treatment room ambient. Electrons impinging on a heavy target generate a cascade shower of bremsstrahlung photons which energy spectrum shows an end point equal to the electron beam energy. By varying the target thickness, an optimum thickness exists for which, at the given electron energy, maximum photon flux is achievable. If a source of high-energy photons i.e. bremsstrahlung, is conveniently directed to a suitable D2O target, a novel approach for production of an acceptable flux of filterable photoneturons for boron neutron capture therapy (BNCT) application is possible. This study consists of two parts: 1. Comparison and assessment of deuterium photonuclear cross section data. 2. Evaluation of heavy water photonuclear source.

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