Evaluation of Time-Dose Factors in Glottic Tumors

Experience has shown excellent tumor control and functional results following radiation therapy for limited squamous carcinoma of the vocal cords (BUSCHKE & VAETH 1963, FLETCHER & KLEIN 1964, GOFFINET et coll.1973).Most treatment schemes have been based on five or six fractions per week with a range of 6 000 to 7 000 rad (super-voltage) given over a period of five to seven weeks.ARISTIZABAL & CALDWELL (1972) in reviewing a number of reports have recommended a tumor dose biologically equivalent to 1960 ret, utilizing the nominal standard dose formula of ELLIS (1968).The basic dose recommended for 6oCo therapy by FLETCHER & KLEIN (1964) is 6000 rad in five-and-one-half weeks (27 fractions) for minimal disease, plus an additional boost of 500 to 1000 rad in 2 to 5 fractions for bulky disease.Control rates for T1 and T2 tumors approximate 80 to 90 per cent with a very low rate of severe edema or cartilage necrosis unless a dose biologically equivalent to 2000 ret is exceeded.Because of a sigmoid curve relationship of tumor control to dose, a control rate of 90 per cent is probably as high as can be obtained in vocal cord carcinoma without an unacceptably high level of necroses.Despite the very abrupt changes in tumor control rates and necrosis rates with different fractionation schemes in other tumor sites, changes in fractionation from 5 days per week to 3 or 4 days per week do not appear to show similar effects in This research