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T he International Commission on Radiation Units and Measurements (ICRU) has provided recommendations that the radiation dose must be delivered within ±5% of prescribed dose. When commissioning treatment planning dose calculation algorithms for radiotherapy, often, the aim is to achieve good agreement between the calculated dose (D C ) and measured dose (D m ), within 1%-2%, for open and wedge (block or compensators) fields in water. [1][2][3][4][5][6][7][8] This is possible using measurement and model-based algorithms in water phantoms; however, such an agreement is usually not possible for measurement-based algorithms in phantoms with heterogeneities. This can be explained based on Objectives: The treatment outcome in patients can be improved with a fast and accurate treatment planning system (TPS) algorithm. The aim of this study was to design a novel head and neck phantom and to use it to test whether the accuracy of the irregular field algorithm of the Precise Plan 2.16 (Elekta Instrument AB, Stockholm, Sweden) TPS was within ±5% of the International Commission on Radiation Units and Measurements (ICRU) limit for homogenous and inhomogeneous media by rotating the Elekta Precise linear accelerator gantry angle using 2 fields. Methods: A locally designed acrylic phantom was constructed in the shape of a block with 5 inserts. Acquisition of images was performed using a HiSpeed NX/i computed tomography scanner (GE Healthcare, Inc. Chicago, IL, USA); the Precise Plan 2.16 TPS was used to determine the beam application setup parameters and an Elekta Precise linear accelerator was used for radiation dose delivery. A pre-calibrated NE 2570/1 Farmer-type ion chamber with an electrometer was used to measure the dose. The mimicked organs were the brain, temporal bone, trachea, and skull. Results: The maximum percentage deviation for 10×10 cm and 5×5 cm inhomogeneous inserts was 1.62 and 4.6, respectively, at a gantry angle of 180°, and that of the 10×10 cm homogeneous insert was 3.41 at a gantry angle of 270°. The percentage deviation for only the bone insert (homogeneous) and for all inserts (inhomogeneous) using parallel opposed beams was 2.89 and 2.07, respectively. Also, the percentage deviation between the locally designed head and neck phantom and the solid water phantom of the linear accelerator was 0.3%. Conclusion:The validation result of our novel phantom in comparison with the solid water phantom was good. The maximum percentage deviations were below the ICRU limit of ±5%, irrespective of gantry angles and field sizes.

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Purpose: This study aimed to evaluate the shielding integrity of a typical radiotherapy facility using the Monte Carlo (MC) method. Materials and Methods: EGSnrc MC code was used to design a radiotherapy bunker with appropriate materials and thicknesses. A concrete density of 2.36 g/cm3 was used as a shielding material for primary and secondary barriers. The lead slab was used in the entrance door. The complex geometries of the bunker were modeled by using the egs++ application code embedded in the software. Phase-space generated from a linac machine built with BEAMnrc codes was used as a source of 18 MV X-ray beam set at 100 cm source–surface distance with a field size of 40 cm × 40 cm. Energy deposited in each geometrical region was evaluated and analyzed. Results: Energy deposited at the entrance door, supervised and controlled areas were found to be approximately 0%. No significant difference in the energy deposition on the geometries was observed when the gantry angles were set at either 90° or 270° (P = 1). Conclusion: The findings in this study revealed that the EGSnrc MC code can be used as a veritable tool in the design and evaluation of structural shielding efficiency in a radiotherapy facility.