RESPONSES OF VARIOUS CLASSES OF HUMAN TUMOR-CELLS TO HIGH X-RAY DOSES - IMPLICATIONS FOR STEREOTAXIC EXTERNAL-BEAM IRRADIATION

We have tabulated the radiation survival characteristics of 152 exponentially growing lines of human tumor cells in vitro (sarcomas, lung cancers, breast cancers, colo-rectal cancers, melanoma, brain tumors, ovarian, and head and neck cancers) to x-irradiation. This information was used to extrapolate survival to a single high dose of 20 Gy for each tumor line. These values were then intercompared among tumor classes with the intent of relating the results to the use of radiosurgery for treatment of brain metastases or primary brain tumors. Extrapolated levels of survival after a single high dose of 20 Gy indicated that radiosensitivities could roughly be divided into two groups. The more radiosensitive group included: sarcoma, small-cell lung cancer, non-small cell lung cancer, colorectal cancer and melanoma, while the more radioresistant group included breast, primary brain tumors, ovarian tumors, and head and neck cancers. There was a difference in the degree of cell killing of a factor of 7,600 between the most radiosensitive tumors (sarcomas) to the most resistant (head and neck cancers). Using a paradigm of a typical 3 cm diameter brain lesion containing about 1.4 x 10(9) cells, the calculated effective single doses needed were: sarcoma and small cell lung cancers-21 Gy; non-small cell lung cancer-24 Gy; colorectal cancer-26 Gy; melanoma-27 Gy; breast, primary brain tumors, ovarian tumors, and head and neck cancers-34-37 Gy. We conclude that available information on human tumor cells indicate significant differences in intrinsic radiosensitivity relevant to the single high doses used in radioneurosurgery. Therefore both the size of the lesion as well as intrinsic radiosensitivity should be considered in determining the administered dose.