Responses of an experimental solid tumour to irradiation: A comparison of modes of fractionation.

Several radiotherapeutic schedules compatible with continued structural-functional integrity of the gastrointestinal (GI) mucosa were compared utilizing the P815X2 murine mastocytoma grown as a solid subcutaneous tumour. Both the tumour and underlying normal tissues were irradiated during the treatments. The tumour exhibited a Do that increased from 210 rad to 397 rad as the tumour aged and in all instances demonstrated minimal shoulders in survival curves. In spite of a relative radioresistance of cells within the solid tumour, quite effective control of localized disease could be accomplished with radiotherapy schemes compatible with GI tolerance limits. Schedules evaluated utilizing this model included acute exposures to 1122 rad, daily exposure to 187 rad, 5 days/week exposures to 281 rad, twice weekly exposures (561 rad on Mondays and 374 rad on Thursdays) and a high dose, two fractions per day, schedule. Tumours were followed for changes in growth patterns during these schedules. Efficacy of tumour control was determined and schedules were compared on this basis. Aggressive radiotherapy approaching the tolerance limits of any of the fractionation schemes proved most effective

Cell kinetics in vivo and in vitro for c3h/he spontaneous mammary tumors.

Cell kinetics in spontaneous C3H/HeJ mammary tumors of retired-breeder mice was studied by in vivo and in vitro techniques. The [3H]TdR labeling index (LI), the DNA synthesis time (TS), and the primer-dependent DNA polymerase assay LI [an in vitro estimate of tumor growth fraction (GF)] were compared to similar measurements made in vivo. These measurements as well as the calculated cell kinetic parameters derived from these data were not different in in vivo and in vitro studies. Furthermore, the cell kinetic parameters in tumors classified histologically as type A or type B mammary tumors were also similar. Although considerable variation in volume doubling times (Td's), [3H]TdR LI's, potential doubling times, cell cycle times (Tc's), and cell loss was found, Ts's were similar in all mammary tumors. No correlation between tumor volume or tumor weight and cell kinetic parameters was seen. However, the most slowly growing tumors (i.e., tumors with the longest Td's) tended to have the lowest [3H]TdR LI's, the longest Tc's, and the highest cell loss factors. No correlation was found between the GF and Td. However, tumors with the most rapidly proliferating cell populations tended to have the highest GF's