Experimental study on optimized fractionated radiation schedule for subclinical breast cancer / 中华放射肿瘤学杂志

ABSTRACT

Objective To determine the optimized fractionated radiation schedule by comparing the dose-response relationship between different fractionated radiation schedules with a total dose of 40 Gy or 60 Gy in subclinical breast tumor.Methods Balb/c nude mice bearing subclinical human breast cancer (injected subcutaneously into the hind legs with 1.5 × 105 or 3.1 × 105 exponentially growing MCF-7 cells) were assigned randomly to blank control group (without radiation),conventionally fractionated radiation group (200 cGy,once daily,10 times/week),hyperfractionated radiation group (160 cGy,twice daily with an interval of 6 h,5 times/week),first hypofractionated radiation group (300 cGy,once daily,5 times/ week),and second hypofractionated radiation group (400 cGy,once every other day,3 times/week) ;the total dose was 40 Gy or 60 Gy.The measurement indices were tumor formation rate,short-term tumor control rate,long-term tumor control rate,the time of tumor recurrence,and the maximum diameter of the bottom of tumor.The observation lasted 24 weeks.Data were compared between these groups by chi-square test.Results With a total dose of 40 Gy (the number of injected cells was 1.5 × 105,the tumor formation rate of the blank control group was 2/8),hyperfractionated radiation was the optimized schedule.With a total dose of 60 Gy (the number of injected cells was 3.1 × 105,the tumor formation rate of the blank control group was 11/11),the first hypofractionated radiation (300 cGy,once daily,5 times/week) was the optimized schedule (P =0.001);the short-term and long-term tumor control rates of the conventionally fractionated radiation group,hyperfractionated radiation group,second hypofractionated radiation group,and first hypofractionated radiation group were 0/0 (tumor formation rates8/8 and 8/8),50％/25％ (tumor formation rates4/8 and 6/8),25 ％/25 ％ (tumor formation rates6/8 and 6/8)),and 67 ％/67 ％ (tumor formation rates4/12 and 4/12),respectively.Conclusions The optimized fractionated radiation schedule for subclinical breast cancer and its total dose vary with the number of injected tumor cells.When the tumor formation rate is 100％,hypofractionated radiation (300 cGy,once daily,5 times/week) is the optimized schedule in terms of long-term tumor control.