This study demonstrated that thyroid gland is affected by radiotherapy significantly and the TSH increased after radiotherapy. Protecting thyroid gland during radiation and follow-up of patients with breast cancer RT are suggested for the assessment of thyroid gland dysfunction.

Background: Considering that some vital organs exist in the head and neck region, the treatment of tumors in this area is a crucial task. The existence of air cavities, namely sinuses, disrupt the radiotherapy dose distribution. The study aims to analyze the effect of maxillary, frontal, ethmoid and sphenoid sinuses on radiotherapy dose distribution by Monte Carlo method.Materials and Methods: In order to analyze the effect of the cavities on dose distribution, the maxillary, frontal, ethmoid and sphenoid sinus cavities were simulated with (3×3.2×2) cm3, (2×2×3.2) cm3, (1×1×1.2) cm3 and(1×1×2) cm3 dimensions.Results: In the analysis of the dose distribution caused by cavities, some parameters were observed, including: inhomogeneity of dose distribution in the cavities, inhomogeneity of dose on the edges of the air cavities and dispersion of the radiations after the air cavity. The amount of the dose in various situations showed differences: before the cavity a 0.64% and a 2.76% decrease, a 12.06% and a 17.17% decrease in the air zone, and a 2.25% and a 5.9% increase after the cavity.Conclusion: The results indicate that a drop in dose before the air cavities and in the air zone occurs due to the lack of scattered radiation. Furthermore, the rise in dose was due to the passage of more radiation from the air cavity and dose deposition after the air cavity. The changes in dose distribution are dependent on the cavity size and depth. As a result, this has to be noted in the treatment planning and MU calculations of the patient.

Background: Considering that some vital organs exist in the head and neck region, the treatment of tumors in this area is a crucial task. The existence of air cavities, namely sinuses, disrupt the radiotherapy dose distribution. The study aims to analyze the effect of maxillary, frontal, ethmoid and sphenoid sinuses on radiotherapy dose distribution by Monte Carlo method.Materials and Methods: In order to analyze the effect of the cavities on dose distribution, the maxillary, frontal, ethmoid and sphenoid sinus cavities were simulated with (3×3.2×2) cm3, (2×2×3.2) cm3, (1×1×1.2) cm3 and(1×1×2) cm3 dimensions.Results: In the analysis of the dose distribution caused by cavities, some parameters were observed, including: inhomogeneity of dose distribution in the cavities, inhomogeneity of dose on the edges of the air cavities and dispersion of the radiations after the air cavity. The amount of the dose in various situations showed differences: before the cavity a 0.64% and a 2.76% decrease, a 12.06% and a 17.17% decrease in the air zone, and a 2.25% and a 5.9% increase after the cavity.Conclusion: The results indicate that a drop in dose before the air cavities and in the air zone occurs due to the lack of scattered radiation. Furthermore, the rise in dose was due to the passage of more radiation from the air cavity and dose deposition after the air cavity. The changes in dose distribution are dependent on the cavity size and depth. As a result, this has to be noted in the treatment planning and MU calculations of the patient.

Introduction: Metal prostheses in patients affect the radiotherapy dose distribution. Metal prostheses with high density and atomic number cause major changes in scattering and attenuation of radiation. The present study aims to assess the impact of metal knee prosthesis with various dimensions and materials on radiotherapy dose distribution. Material and Methods: In this research, the Varian Linac and water phantom were simulated using the MCNPX code. Dose distribution of photon beam in a water phantom, with and without the presence of knee prostheses made of cobalt-chromium-molybdenum alloy, steel, titanium, and titanium alloy used in men and women was investigated using the Monte Carlo simulation.Results: The prosthesis led to an increase in dose in comparison with cases that there was used no prosthesis. According to values of the depth dose percentage, the maximum dose increase was found to be 6.8%, 6.1%, 4%, and 4.29%, and dose reduction 41.18%, 40.66%, 37.76%, and 37.51% for prosthetics with men’s knee dimensions made of cobalt-chromium-molybdenum alloy, steel, titanium alloy, and titanium, respectively. Above all, does increasing to 6.4%, 5.9%, 3.8%, and 3.94% and doses reducing to 40.87%, 40.36%, 36.94%, and 36.69 were observed in prosthetics for women. The highest amount of dose reduction for men’s prostheses made of mentioned materials was found to be 48.75%, 47.7%, 45%, and 45.8%, respectively. In addition, it was 46.36%, 45.8%, 43.8%, and 43.95% for women’s prostheses, respectively.Conclusion: Material will have a significant impact if a part of the knee bone places behind the prosthesis. According to the obtained values, it is recommended to utilize prostheses made of titanium and titanium alloys for knee arthroplasty. The prosthesis can either increase or decrease dose in tumor or lead to increase dose at organs at risk.

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