Radiotherapy is one of the most important treatment methods of cancer, which is the worldwide disease nowadays. It is essential to protect the critical organs and healthy tissue inside the radiated area during the radiotherapy. For this reason, Cerrobend block (lipowitz alloy), which is made specifically for each patient, are commonly used in the hospitals. In the clinical application, the acceptable level of the gamma-ray transmission for Cerrobend blocks must be less than 5%. In this research, GEANT4 based GATE simulation program modelled to compare between gamma-ray transmissions of the standard Cerrobend block and newly designed Cerrobend blocks formed by adding the various number of the pure lead marbles. Experimental measurements were carried out with Alcyon II model Co-60 teletherapy machine for various field sizes by using Farmer type 0,6 cc ion chamber, PTW Unidos Dosimeter and solid phantom in Dr. Abdurrahman Yurtaslan Ankara Oncology Training and Research Hospital in 2010. The gamma-ray transmission of the newly designed Cerrobend block was found less than the standard block, therefore the protection of the critical organs for the patient could be better. The dose acquired by GEANT4 based GATE simulation program is consistent in experimentally measured radiation dose. Furthermore, the values of the linear attenuation coefficient theoretically obtained from XCOM software agree with the values acquired by experiment and simulation.

No commercially available detector system can measure alpha, beta and gamma-rays at the same time and separately with good efficiency, while being cost-effective, portable and offering real-time monitoring. The main purpose of an alpha-beta-gamma detector would be for safety management and nuclear decommissioning in the nuclear industry. This idea for a detector system became more valuable, after Fukushima in Japan, because nuclear waste can contain fission products and transactinide materials which not only emit gamma-rays but also emit alpha and beta particles and in some cases, neutrons. In this research, we investigated the best available alpha-beta-gamma radiation detector materials and their optimum thickness by using Geant4 based GATE simulation. The work revealed a better efficiency result for each radiation type than in previous work. In the simulation, 0.05 mm ZnS(Ag), 3.2 mm plastic scintillator and 1.75 mm BGO were found to be best for the detection and identification of alpha, beta and gamma-rays respectively. In nuclear medicine, this type of detector system could also modify to become a miniaturized radio-guided surgery beta-gamma probe beside of the modification into the robotic surgery. This research result will influence three different areas in imaging technology, homeland security and nuclear industry.