Studies in dose-time-volume relationships in bladder and tongue radium implants

The clinical results of 26 tongue and 31 bladder radium implants were analysed in terms of proposed dose specification parameters that describe the dose-time-volume relationships of the implant. Tongue cases that recurred within two years were mostly those with a relatively short treatment time and in which a relatively large dose reduction factor had to be applied. The dose-time factor did not differ significantly in the groups of bladder implants having different clinical results. A higher incidence of necrosis was noted in bladder cases. This was associated with a significantly higher mean dose and a somewhat greater degree of dose inhomogeneity. Recurrences were generally linked with greater mean dose, target volume and dose inhomogeneity. These unfavourable dose-volume relationships were frequently associated with poor distribution of needles. The reported experimental and clinical findings pertinent to the differential sparing of normal tissues associated with protraction of continuous irradiation are outlined. In the light of these, it is felt that the results of tongue implants could have been improved by omission of the dose-time adjustment factor for treatment time of 3-10 days without undue risk of necrosis. However, bladder results could have been improved by attainment of a better implantation technique while keeping the treatment time within 6-8 days in view of the lower tolerance.