A purpose-built iodine-125 irradiation plaque for low dose rate low energyirradiation of cell lines in vitro

The phenomenon of hyper-radiosensitivity (HRS) to very low acute single dos es of radiation has been demonstrated in several cell lines in vitro and in vivo, and has been studied in theory and in practice. The theory suggests a similar hypersensitivity when cells are continuously exposed to radiation at very low dose rates. These low dose rates are used when radioactive see d (iodine-125 or palladium-103) implants of the prostate are used as an alt ernative to surgery or external beam radiotherapy. To investigate the radio biology of hypersensitivity of this type on various cell lines in vitro, an iodine-125 seed irradiator has been designed and built for safe use in the Gray Laboratory. In practice, the calculated dose rate has been used for c onsistency. Discrepancies between calculated and measured dose rates are di scussed.