Dosimetric Optimization Of Postoperative Radiotherapy Of Uterine Cervical Carcinoma

Carcinoma of the uterine cervix is the second most common malignant neoplasm in women, after carcinoma of the breast in the world. Radiotherapy plays a very important role in the multidisciplinary treatment of uterine cervical carcinoma. The indication broadly involves from the definitive radiotherapy of early stage gynecological malignancy tumor to the palliative radiotherapy of the advanced gynecological malignancy disease.The pelvic external radiation modality is changed from AP/PA field to 3D-CRT/IMRT along with the development of the radiation therapy techn- ology. Much more protection of normal tissue and fatality to the tumor is needed badly in the clinical work. So even in the IMRT, the irradiation dosage of the small bowel, bladder and rectum is concerned by the radiologist. But there is no standard program of the evaluation of small bowel for its un- fixation.To the hysterectomy patient, the absence of uterine makes much more space for the small bowel's descent, so the traditional AP/PA pelvic irradiation surely increases the dosage of small bowel. Can we reduce the irradiation of small bowel by change the positioning, bladder filing status and radiation modality? In this study, we try to get a primal result of the idea.The goals of this study were to evaluate the effect of body position, bladder filling status and radiation modality on the postoperative radiation of uterine cervical cancer and to compare the dose–volume histograms (DVHs) and determine the potential impact on acute and long-term toxicity based on the dose to target and non-target tissues for each planning technique. Five patients referred for postoperative radiotherapy at the Cancer Center of China-Japan Union Hospital were selected. The TNM stage wasⅡA orⅡB according to the FIGO staging system. Each patient got the CT scan on different position and bladder filling status. Normal tissues and critical structures were contoured on axial CT slices. These regions included obturator, internal, external, common iliac and presacral nodal groups, rectum, bladder, and small bowel. Treatment planning included 3D four-field box using 10-MV photons designed to treat a volume from the superior border to the bottom of the PTV on the AP/PA field and shaped blocks on the lateral fields to minimize the dose to the rectum and small bowel. A seven-field technique using 6-MV photons was used for IMRT. The dose–volume histograms where then compared for both treatment delivery systems.The conformal index (CI) has tiny difference between supine and prone positioning, (0.506±0.004) vs. (3±0.004) respectively, P=0.032; and it similar no matter the bladder is empty or full, but it apparently different when the radiation modality shift, CIIMRT>CI3D-CRT>CI2F, P<0.001. The irradiated volu- me of each organ of interest, such as small bowel, bladder and rectum, decrease as the radiation fields increase, VIMRT