By John T. Lett
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Radium and LDR dosage were initially determined by the amount of 226Ra (milligrams) left in the tumor or placed in an organ for periods of time (milligram-hours or mg-hr). Since excessive amounts or speed of dose could lead to undesirable side effects, this system of therapy led to the use of implanted, sealed sources over a period of hours or days. In radiotherapy, LDR radiation dose rates were examined in terms of thera peutic effects. 5-2 Gy/min and shorter treatment times (Henschke et al. 1966; Joslin, 1989) for pelvic cancers.
Using the mitotic index as a method to study cell renewal, Lang and Aponte (1965) studied the cervix mucosa after biopsy. They found no increase in mitotic activity in squamous or colum nar epithelium with healing and concluded that cells covered a uniform biopsy defect mainly by cell migration from the edges. Cell migration cov ered the gap and healed the wound. F. Cytological Methods to Assess Tumor Response Therapeutic radiation to the pelvic organs can lead to pelvic reactions and fibrosis.
These appeared to be prob ably well-oxygenated zones of the tumor. It appears that acute and chronic hypoxia are both important; however, the chronically hypoxic zones may be largely nonviable while the acutely hypoxic zones represent the regions of tumor that respond to radiation in a fractionated schedule by reoxygenation. Factors that contribute to tumor perfusion and tumor cell death probably contribute to tumor hypoxia. Cell death may well be closely associated with the stasis and occlusion of blood vessels.