Different fractionation schemes tested by histological examination of autopsy specimens from lung cancer patients.

The biological effects of different fractionation schemes have been evaluated by the histological examination of bronchial carcinomas removed at operation or autopsy following radiotherapy. Radiation was given in daily, small fractions (200 cGy (rad)), large fractions (600 cGy (rad)) every fifth day, or a single high dose followed by daily low-dose treatment. The highest proportion of tumours free of viable cells was found in patients who had received small daily fractions in both operable and inoperable tumours. A hypothesis is put forward to explain this apparent change in radio-sensitivity with different fractionation schemes.