SHOULD CARBOGEN AND NICOTINAMIDE BE GIVEN THROUGHOUT THE FULL COURSE OF FRACTIONATED RADIOTHERAPY REGIMENS

Purpose: Tumor radiosensitization with carbogen and nicotinamide (CON) was compared when both agents were given throughout fractionated radi otherapy with the sensitization observed when administered with only h alf of the fractions. The effect of overall treatment time on the loca l control of tumors irradiated in air or with CON was also investigate d. Methods and Materials: Local tumor control of a rodent adenocarcino ma, CaNT, was studied using eight different 20-fraction x-ray regimens . An overall time of either 10 or 20 days was used and CON was given w ith all, the first half or last half of the treatment. Results: Relati ve to air, all six sensitizer combinations gave a large and significan t increase in sensitization (p much less than 0.00001). Enhancement ra tios were 1.9 and 2.1 when CON was given with all 20 fractions in eith er 10 or 20 days, respectively. For both overall times, enhancement ra tios were reduced by 15-25% when CON was given with only half of the f ractions. In air, reducing the treatment time from 20 to 10 days gave a small but significant decrease in the isoeffective doses. When CON w as administered with either all or part of a schedule, varying the tre atment time had little or no effect on local tumor control. No toxic s ide-effects were encountered when the sensitizers were administered 10 or 20 times, either once or twice per day. Conclusion: CON is an effe ctive and non-toxic tumor radiosensitizer. In CaNT tumors, a significa ntly greater effect is seen when CON is given with every fraction of t he schedule. The sensitizers reduced or abolished the sparing effect o f overall time.