Dosimetric evaluation of sigmoidal and bowel doses in the treatment of carcinoma of cervix using CT based volumetric imaging technique

Abstract

Purpose: Radiation therapy is the main stray for the treatment of the cervical cancer. Normal organs such as bladder, rectum, sigmoid colon and bowel loops also get significant dose during treatment of carcinoma of cervix which often results late toxicity. The purpose of this study is evaluate CT image based volumetric doses of organ at risk and correlate the doses with the toxicity profile observed in cancer patients. Materials and Methods: Sixty high dose rate intracavitary brachytherapy applications were performed in thirty patients of carcinoma of cervix. External beam therapy was planned for 46 Gy in 23 fractions followed by two brachytherapy sessions of 9 Gy/session. External beam radiotherapy was given by four field box technique to each patient. CT based treatment planning was done for each intracavitary brachytherapy application. Dose volume histogram was used for analysis of volumetric dose parameters and correlated with the RTOG defined normal organ toxicity profile of the patients. Results: In the follow up of two years 2 (6.66%) patient had died, 12 (40%) patients had reported no significant problem, 3 (10%) patient got bladder toxicity of grade 2, 10 (33.33%) patients had reported small intestine toxicity of grade 1 and grade 2 while no information could be available for 3 (10%) patients. The average volume of rectum, sigmoid colon and bowel loops were 60.34 cc, 22.19 cc and 270.82 cc. The average, median and 2 cc volume doses for rectum 289 ± 121 cGy, 263 ± 113 cGy and 884 ± 444 cGy for sigmoid colon 409 ± 211 cGy, 366 ± 185 cGy and 693 ± 371 cGy resp. and for bowel loops 240 ± 169 cGy, 153 ± 59 cGy and 870 ± 222 cGy. The average and median sigmoid colon point doses were higher than rectum average (p= 0.000) and median doses (p =0.001) but 2cc volumetric doses of sigmoid colon are less than rectum 2cc volumetric doses (p = 0.013). For bowel loops the 2cc volumetric doses were much higher than average doses (p = 0.000) due to its large volume. The recto-sigmoidal toxicity profile were evaluated for sigmoidal max doses and rectum 2 cc volumetric dose profile. There was a poor correlation between rectum 2 cc volumetric dose and sigmoid 2 cc volumetric doses. Conclusion: According to dose toxicity profile, sigmoidal doses represent an important role for dose constrains but till now no protocol has been formed for reporting the sigmoidal doses. This study attracts the attention for reporting the sigmoidal and bowl loop doses. This study demonstrates the possibility and role of volumetric imaging and dosimetry for improvement in dose constraints.