The goal of radiotherapy is to cure cancer tumors through ionizing radiation while saving the surrounding healthy tissues.These treatments require an accurate determina-tion of all those dosimetric parameters,which are required for treatment planning system(TPS).Many TPS in clinical use perform dose calculation by analytical method which is not accurate in inhomogeneous medium.Alternatively,the Monte Carlo(MC)parti-cle transport codes have been recognized as the most accurate method for radiotherapy treatment planning and dose calculation.Before calculating the dosimetric parameters through MC methods,it is important to test MC transport code for radiotherapy.Testing must be done with benchmark cases from IAEA(International Atomic Energy Agency),AAPM(American Association of Physicists in Medicine),experimental measurements and/or other validated Monte Carlo codes.In this work,SuperMC(Super Monte Carlo Program for Nuclear and Radiation Simulation)has been tested and validated for medical physics applications such as brachytherapy and boron neutron capture therapy(BNCT).Brachytherapy is a form of radiotherapy in which a sealed radiation source is placed inside or next to the area re-quiring treatment while BNCT is a noninvasive therapeutic modality for treating locally invasive malignant tumors such as primary brain tumors and recurrent head and neck cancer.Investigations for coupled modeling and simulation of brachytherapy source with water phantom and BNCT treatment head with computational human phantom have been carried out.The main and innovative research contents of this dissertation are briefly described below:(1)In this study.SuperMC has been tested and verified for high dose rate(HDR)brachythrapy source.Cylindrical geometry based brachytherapy source was modeled with SuperMC and dose calculations were carried out with the source placed at the center of spherical water phantom.The verification has been done by calculating the dosimetric parameters as recommended by AAPM in task group report 43 and 43U1(TG-43,TG-43U1)and by comparing these parameters with studies from other Monte Carlo codes such as EGSnrc,PENELOPE,MCTP,MCNP and published experimental data.It has been found that calculated parameters are in good agreement with published Monte Carlo studies and experimental data.The results show that SuperMC can be used for accurate and fast simulation and dosimetric calculation of HDR brachytherapy sources.(2)In this study,SuperMC has been applied to boron neutron capture therapy.For this purpose,a beam shaping assembly(BSA)has been designed to moderate mono en-ergetic high energy(14.1 MeV)neutron beam to epithermal energy range for the treat-ment of deep seated head and neck tumors.The BSA consists of moderator,reflector,filter,gamma shield and collimator.CT images of the patient’ s head were convert-ed to geometry model of SuperMC.The verification of the beam quality was done by comparing the dosimetric parameters as recommended by IAEA-TECDOC1223 and computational head phantom results were compared previous studies.In air and in phantom results are in good agreement with IAEA and previous studies.Dose analysis shows that the designed BSA is accurate,efficient and suitable for BNCT applications and SuperMC can be used for simulating BSA and dose calculations for BNCT.Testing and verifications has been done with benchmark cases from IAEA and AAPM to verify and validate the performance of SuperMC for radiotherapy and its ap-plications.SuperMC has also been applied for treatment planning of clinical cases.The obtained results with SuperMC are in very good agreement with results of benchmark cases.SuperMC was found to be accurate,efficient and capable for dose calculation and treatment planning.It is concluded that SuperMC can be used for the accurate mod-eling and simulation of dosimetric parameters in water and in heterogeneous phantoms and Monte Carlo based treatment planning system.