ABSTRACT
Intensity modulated radiation therapy [IMRT] is one of the cancer treatment methods. It is important to selectively aim at the target in this way, which can be performed using a multileaf collimator [MLC]. In order to specifically irradiate the target volume in radiotherapy to reduce the patient absorbed dose, the use of multileaf collimator has been investigated in this work. Design and simulation of an MLC was performed by a Monte Carlo method and the optimum material for manufacturing the leaves was determined using MCNP4C. After image processing [CT or MRI] in this system, the tumor configuration is determined. Then the linear accelerator is switched on and the beam irradiates the cancerous cells. When the MLC leaves receive a command from the mircrocontroller, they start to move and absorb the radiation and modulate its intensity. Consequently, the tumor receives maximum intensity of radiation but minimum intensity is delivered to healthy tissues. According to the simulations and calculations, the best material to manufacture the leaves from is tungsten alloy containing copper and nickel which absorbs a large amount of the radiation; by using a 8.65 cm thickness of alloy, 10.55% of radiation will transmit through the leaves. Lead blocks are conventionally used in radiotherapy. However, they have some problems like cost, storage and manufacture for every patient. Certainly, the MLC is the most efficient device to specifically irradiate the tumor in IMRT. Furthermore, it facilitates treating the target in different views by rotation around the patient. Thus the patient's absorbed dose will decrease and the tumor will receive maximum dose