background: during radiotherapy treatment, critical organs are shielded using lead and cerrobend blocks. the objective of this study is to compare the effects of lead and cerrobend shielding blocks on incident photon beam. methods: collimator scatter factors were measured for open square fields (3 x 3 cm to 40 x 40 cm) defined by collimator jaws and for fields blocked down to smaller asymmetric...

Introduction: During intensity modulated radiation therapy (IMRT) technique, theoretically, presence of flattening filter (FF) across the beamline of clinical linear accelerator (linac) is not essential to obtain uniform lateral profiles due to intensity modulation of photon beams by multileaf collimators (MLCs). The aim of this study was to investigate the dosimetrical propert...

objective: using megavoltage photons generated by medical linear accelerator is a common modality for the treatment of malignant. the crucial problem for using photon beams >8mv is the photoneutron yields that increase the risk of secondary cancer that treated with high-energy photon beams. the contaminated neutrons produced in different components of the accelerator head and rely on many param...

Background: During intensity modulated radiation therapy (IMRT) technique, theoretically, presence of flattening filter (FF) across the beamline of clinical linear accelerator (linac) is not essential to obtain uniform lateral profiles due to intensity modulation of photon beams by multileaf collimators (MLCs). The aim of this study was to investigate the dosimetrical properties of 18 MV photon...

Objective: Using Megavoltage photons generated by medical linear accelerator is a common modality for the treatment of malignant. The crucial problem for using photon beams >8MV is the photoneutron yields that increase the risk of secondary cancer that treated with high-energy photon beams. The contaminated neutrons produced in different components of the accelerator head and rely on many param...

Objective: Using Megavoltage photons generated by medical linear accelerator is a common modality for the treatment of malignant. The crucial problem for using photon beams >8MV is the photoneutron yields that increase the risk of secondary cancer that treated with high-energy photon beams. The contaminated neutrons produced in different components of the accelerator head and rely on many param...

Purpose: To investigate the energy dependence/spectral sensitivity of silicon diodes designed for small-field dosimetry and obtain response factors (RFs) for arbitrary photon spectra using Monte Carlo (MC) simulations.   Methods: The EGSnrc user-code DOSRZnrc was used to calculate the dose deposition in water and in the active volume of a stereotactic diode f...

introduction: nowadays,  considerable developments  in  the field  of  radiotherapy have  been  achieved.  they  include  the  advances  made  in  the  equipments  and  treatment  planning  techniques  which  require  highly complex calculations. such achievements have made it possible to treat cancer patients not only  with  higher  radiation  dose  but  also  with  higher  precision  and  con...

background: monte carlo method (mc) has played an important role in design and optimization of medical linacs head and beam modeling. the purpose of this study was to compare photon beam features of two commercial linacs, varian 21ex and elekta sl-25 using mcnp4c mc code. materials and methods: the 6mv photon beams of varian 21ex and elekta sl-25 linacs were simulated based on manufacturers pro...