The term "altered factionation" is relative to the conventonal fractionation, which is defined as follows: for curative treatment of most cancers, 180 to 200 cGy per fraction is given once a day, 5 times per week, to a total dose determined by the tumor being treated and the tolerance of critical normal tissues within the target volume, usually 60 to 70 Gy within 6 ~ 7 weeks. The basic rationales for altered fractionation can be summaried by (1) The late - responding tissues are much more sensitive to fraction size than the early - responding tissues, with multiple smaller fractions. The late responding tissues can tolerate an increased total dose and the effects on the tumor therefore may be increased by the higher total radiation dose with improved tumor control; (2) Reduction in overall treatment time decreases the opportunity of accelerated regeneration of tumor cells during treatment and therefore inceases the probability of tumor control for a given total dose. In general, altered fractionation schemes can be categorically divided in to the following:
(1) Hypofraction
(2) Split - course radiation therapy
(3) Hyperfractionation
(4) Accelerated fractionation
(5) Accelerated hyperfractionation
In recently years, we have tested various altered fractionation schedules for the treatment of nasopharyngeal, esophageal and lung cancer. For the nasopharyngeal caricnoma, hyperfractionation was used firstly by 1.1 Gy/F, 2F/day with an interval of > 6hrs, followed by concomitant boost to a total dose of 74 Gy within 6 weeks. In lung cancer, the program was 1.15 ~ 1.25 Gy per fraction, two fractions per day for a total dose of 70 Gy with overall treatment time about 6 to 7 weeks. Esophageal cancer, conventional fractionation was given to total dose about 41 Gy followed by a boost for an additional 28 Gy by 1.5 Gy per fraction twice daily with overall treatment time about 6.3 weeks.
Our preliminary treatment data showed that the local tumor control rates were higher in these study groups than the conventional groups and the acute reactions were increased as expected but tolerable. The main points of altered fractionation radiation schedules are also discussed.
