<prompt> Which of the following is used for permanent interstitial implant brachytherapy?BoronCesium 133PhosphorusIridium  <response>: Ans. b Cesium 133. Ref Introduction to Radiotherapy by Rafla, 7Following are the methods of treating with radiotherapy: External radiations is teletherapy Brachytherapy Systemic radiotherapyBRACHYTHERAPY internal radiation therapyshort distance therapy Definition : source of emission is within the bodytumor It is sealed Platinum coated sources placed within or near to the tumor for therapy. It includes:- Interstitial- Intracavitary- Mould therapy Interstitial radiations- Removabletemporary sources or implants Iridium-192 HDR Cesium 137 Cs - LDR Cobalt 60Co Californium Radium Tantalum- Permanent sources or implants 131Cs Yttrium Gold 1125 Radon Palladium--Mnemonic: CY GRIP- Intracavitary radiations- Removable: Radium Cesium 137 Cobalt - 60- Permanent: Colloidal radioactive gold Yttrium Radioactive iodine 131 IAgents used in Systemic radiation therapy: Iodine I31 I, Phosphorous 32p, Yttrium, Strontium, Samarium, Rhenium. 