ABSTRACT
Grid radiation therapy, using the megavoltage X-ray beam, has been proven to be an effective method for management of large and bulky malignant tumors. This treatment modality is also known as Specially Fractionated Radiation Therapy [SFRT]. In this treatment technique a grid block converted the open radiation field into a series of pencil beams. Dosimetric characteristics of an external beam grid radiation field have been investigated using experimental and Monte Carlo simulation technique. Dose distributions [%DD as well as the beam profiles] of a grid radiation field have been determined using experimental and Monte Carlo simulation technique, for 6- and 18 MV X-ray beams from a Varian Clinics 2100C/D. The measurements were performed using LiF TLD and film in Solid Water phantom Material. Moreover, the MCNP Monte Carlo code was utilized to calculate the dose distribution in the grid radiation field in the same phantom material. The results of the experimental data were compared to the theoretical values, to validate this technique. Upon the agreement between the two techniques, dose distributions can be calculated for the grid field with different patterns and sizes of holes, in order to find an optimal design of the grid block. The results of dose profiles for 6 MV X-ray beams obtained with the Monte Carlo simulation technique was in good agreement with the measured data. In addition, the 3D dose distribution of the grid field generated by the Monte Carlo simulation gave more detailed information about the dose pattern of the grid. The grid block can be used as a boost for treatment of bulky tumors. The Monte Carlo simulation technique can be utilized to optimize the pattern, size and spacing between the holes, for optimal clinical results