Radiation dose-response of human tumors

The dose of radiation that locally controls human tumors treated electively or for gross disease is rarely well defined. These doses can be useful in understanding the dose requirements of novel therapies featuring inhomogeneous dosimetry and in an adjuvant setting. The goal of this study was to compute the dose of radiation that locally controls 50% (TCD50) of tumors in human subjects.

Logit regression was used with data collected from single institutions or from combinations of local control data accumulated from several institutions treating the same disease.

90 dose response curves were calculated; 62 of macroscopic tumor therapy, 28 of elective therapy with surgery for primary control. The mean and median TCD50 for gross disease were 50.0 and 51.9 Gy, respectively. The mean and median TCD50 for microscopic disease control were 39.3 and 37.9 Gy, respectively. At the TCD50, an additional dose of 1 Gy controlled an additional 2.5% (median) additional patients with macroscopic disease and 4.2% (median) additional patients with microscopic disease. For both macro- and microscopic disease, an increase of 1% of dose at the TCD50 increased control rates approximately 1% (median) or 2-3% (mean). A predominance of dose response curves had shallow slopes accounting for the discrepancy between mean and median values.

Doses to control microscopic disease are approximately 12 Gy less than that required to control macroscopic disease, and are about 79% of the dose required to control macroscopic disease. The percentage increase in cures expected for a 1% increase in dose is similar for macroscopic microscopic disease, with a median value of approximately 1%/% and a mean of approximately 2.7%/%.