Effect of split dose TBI on hematopoietic stem-cell survival in combined radiation-drug exposures

The effect of sequence and time interval between cyclophosphamide and total body irradiation on lung and bone marrow damage following bone marrow transplantation in mice

The compromise between bone marrow killing effect and toxicity (mainly on the lungs) of the conditioning protocol used prior to bone marrow transplantation (BMT) determine to a great extent the final outcome. In search of an optimal balance between minimum lung damage and maximum bone marrow cell kill, we have tested the effect of varying the sequence and time interval between cyclophosphamide (CTX) and total body irradiation (TBI). CTX was administered almost concomitantly with TBI (i.e., 15 min before TBI) or 1-7 days before or after TBI. Lung damage was assessed by the lethality (LD) of the mice between day 28 and day 180 after treatment, bone marrow damage by the LD of the mice between day 7 and day 28 after treatment and by the spleen colony assay. Mice chosen for lung damage testing were rescued from death due to bone marrow ablation by transplantation with syngeneic marrow cells. CTX potentiated radiation damage in both bone marrow and lungs. The effect on the bone marrow was greater when CTX was given after TBI than when given before TBI and this effect was significantly more than additive when the interval between the two agents was 3 days. Lung toxicity, on the other hand, was greater when CTX was given before TBI than when given after TBI. A therapeutic gain factor (TGF) was estimated by dividing the dose enhancement ratio (DEF) of bone marrow damage over the DEF of lung damage at all the time intervals studied. The results were consistently higher when CTX was given after TBI than when given before.(ABSTRACT TRUNCATED AT 250 WORDS)

Advances in pediatric radiotherapy in the last ten years and future proposals

Advances made can be divided into five main categories. Firstly, the problem of geographic miss which has been reduced by delivering effective radiation doses with greater precision. This has been accomplished with more sophisticated diagnostic and therapeutic equipment, immobilization techniques and computerized treatment planning. Second is the recognition of the interplay of radiation and chemotherapy on normal tissue tolerance and local tumor control. This interaction has necessitated reduction in both dose and volume of irradiation. Third is the use of wide field irradiation as a systemic treatment. Fourthly, the utilization of cooperative group trials to define the role of irradiation. Finally, with the improvement in survival has come the recognition of late effects of irradiation in the growing child and the means of reducing such effects. The current role of radiation therapy in childhood malignancies is summarized, controversies are identified, and future prospects explored.