Session Item

To assess the interfraction dose and volume variations of the organs at risk (OARs) in high dose rate (HDR) Computed Tomography (CT) guided intra cavitary brachytherapy (ICBT) in patients with carcinoma cervix.

This study included retrospective analysis of 40 women with carcinoma cervix FIGO stage IB2- IVA treated with concurrent chemo radiotherapy followed by ICBT. After an external beam radiotherapy (EBRT) dose of 46-50Gy, patients underwent three fractions of ICBT 7days apart. The target was to complete the whole treatment within 56days. Dose to Point A and the maximum doses to 2, 1, and 0.1cc volumes of bladder, rectum and sigmoid colon (OARs) along with their variation in volumes were recorded. Revised plans in 20 out of 40 patients for the second and third fraction(fr) were generated and superimposed on the treated plans. Paired t test was used to compare the difference in the mean values.

A total of 120 CT scans were considered for evaluation. The mean of the max dose to 2cc, 1cc and 0.1cc of bladder(bl) in the 1^st, 2^nd and 3^rd frs was 5.5+/-1.2Gy, 6.1+/-1.3Gy, 7.6+/-1.7Gy; 5.6+/-1.1Gy, 6.2+/-1.3Gy, 7.7+/-1.5Gy; and 5.3+/-1.3Gy, 5.8+/-1.4, 7.2+/-1.8 Gy respectively. Bl volume in the three frs was 65cc, 67.8cc, and 67.3cc. Doses were higher in the 2nd fr though not significant. Dose to 0.1cc was found to be significantly lower in the 3rd fr than 2nd fr (p=0.05). For the rectum(re); the corresponding mean values were 4.9+/-1.4Gy, 5.5+/-1.5Gy, 6.7+/-1.2Gy; 4.7+/-1.3Gy, 5.4+/-1.7Gy, 6.6+/-1.1Gy and 4.9+/-1.3Gy, 5.5+/-1.2Gy, 6.6+/-1.3Gy respectively for the three frs. Volume in the successive three frs was 37.6cc, 39.3cc and 38.2cc. Significant difference was found in doses to 1cc(p=0.05) and 0.1cc(p=0.001) between 1st and 2nd fr and for 0.1cc (p=0.003) between 2^nd and 3rd frs. The documented values of doses for sigmoid colon(sc) for three successive frs were 4.7+/-1.3Gy, 5.0+/-1.4Gy, 6.4Gy+/-1.4; 4.9+/-1.8Gy, 5.4+/-1.4Gy, 6.8Gy+/-1.2 and 5.3+/-1.7Gy, 6.0+/-1.5Gy, 6.6Gy+/-1.8 for 2, 1 and 0.1 cc respectively. 21.9cc, 23.6cc and 24.2cc was the mean value of volumes of sc in the three frs. There was noticeable difference in 0.1 cc doses between the 1st and 2nd fr(p=.0003) and between 1st and 3rd fr (p=<0.0001).. For the superimposed plans, the values of the mean of the maximum doses to 2cc, 1cc and 0.1 cc of bl were statistically significant for both the 2nd and the 3rd treated and revised plans. For re and sc statistical difference in means was found in doses to 0.1 cc in both treated and revised plans and to 1cc re between the delivered 2^nd and its revised plan(p=0.04) 

We found that though there was no significant inter fraction variation in the maximum doses to 2cc received by the OARs but significant difference was noted in the lower dose range (0.1cc) of re and sc. Also, in 60% of our patients tolerance was exceeded with treatment by the same plan. Thus, CT guided brachytherapy must be implemented for every fr treatment in carcinoma cervix.