Dosimetric comparison between the intensity modulated radiotherapy with fixed field and Rapid Arc of cervix cancer

Purpose. - Concurrent radio-chemotherapy is the standard treatment for locally advanced cervical cancer. This treatment is responsible for bowel and hematologic toxicities. The use of intensity-modulated radiotherapy (IMRT), in static beams, allows a decrease of this toxicity. The technique of RapidArcR IMRT could lower the dose delivered to the organs at risk and improve the homogeneity of the planning target volume coverage, while decreasing the processing time. Patients and materials. - For 20 patients, treatment plans performed with IMRT and RapidArcR were compared. The target volumes were: the clinical target volume (gross tumour volume, uterus, upper third of the vagina, the hypo-gastric, iliac and pre-sacral nodal regions), and the planning target volume (clinical target volume + 1 cm). The delineated organs at risk were: rectum, bladder, bowel and bone marrow. The dose was 45 Gy in 25 fractions. IMRT were delivered with five beams and RapidArcR with two arcs. The comparisons were made by the non-parametric test of Wilcoxon. Results. - Medium coverage of the planning target volume was better with RapidArcR (P = 0.01). It was also better regarding the sparing of bowel (P 0.01) and IMRT was better regarding the sparing of bladder (P = 0.01) and rectum (P = 0.05). The total volume receiving 20 Gy was less important with RapidArcR (P < 0.001). RapidArcR allowed to decrease the treatment time (3 versus 12 minutes with IMRT) and the number of monitor units (MU) (376.5 versus 962.2, on average, P = 0.0001). Conclusion. - The technique of RapidArcR seems to obtain better dosimetric results compared to RCMI, with fewer MU, and a significant decrease in treatment time. (authors)