Implications of the density of clonogenic infestation in radiotherapy

Treatment schemes must be evaluated in a clinical context. It was observed by Coutard in the 1920s that exophytic tumors disappear by the third to fourth week of treatment and are more often controlled, stage for stage, than ulcerative and/or infiltrative tumors. It has also been demonstrated that the control rate is higher in patients whose tumor has clinically disappeared at the end of treatment than in those with clinically residual tumor. A possible explanation is that, after the clinical disappearance tumor cells that remain are euoxic during the latter part of treatment. Since some parameters, such as reoxygenation and proliferation, may work in opposite directions, a balance has to be found for each tumor mass. Furthermore, there are clinical facts that, although without explanation, must be considered.