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Unanticipated late effects in neutron and heavy ion therapy, not attributable to overdose, imply a qualitative difference between low and high LET therapy. We identify that difference as 'ion kill', associated with the spectrum of z/beta in the radiation field, whose measurement we label 'ion-kill dosimetry'.
Radiation therapy confers enormous benefits that must be balanced against the possibilities for harm including late toxicity in normal tissues and radiation-induced second malignancies. A small percentage of patients experience severe late complications. The question is, do these late sequelae occur randomly, or are they confined to individuals who are genetically predisposed to radiosensitivity. Experiments with knockout mice and with patients demonstrate that individuals heterozygous for a number of genes appear to be radiosensitive. If radiosensitive patients were identified prospectively by genetic analysis, they could be spared the trauma of late sequelae. Several large studies have shown a statistically significant excess of radiation-induced malignancies in radiotherapy patients. Most second cancers are carcinomas, developing in the lining cells of the body often remote from the treatment site. Radiation-induced sarcomas appear only in the heavily irradiated areas. These are small in number but appear with a very high relative risk.