Variation of organ position and dose for cervical cancer patients treated with helical tomotherapy

Objective: To observe the interfractional variation and actual dose for cervical cancer patients treated with tomotherapy. Methods: Five patients who received tomotherapy were chosen from Aug 2013 to Feb 2014. A megavohage computed tomography (MVCT) scan was performed before treatment and then registered with the planning CT images. Dose distributions were recalculated and targets were contoured on the MVCT images. The differences between the actual radiation and planning were analyzed. Results: In the patients received external radiotherapy, the decline in cervix volume and maximum diameter was 68.90% and 26.91%, respectively (t = 5.21, 8.39, P < 0.05). Cervix, uterus and CTV movement in left-right, anteroposterior, superoinferior were 1.43, -7.72, 0.02, -0.40, -1.24, -6.51, -0.43, -1.68 and -0.22 mm. The median CTV V_95% was 99.40% (95.96% - 100%), and missing volume was 6.94 cm³ (0-32.30 cm³). Conclusions: During radiotherapy for cervical cancer patients, the volume, position and doses are different between initial plan and actual radiation. Based on image guided radiation therapy (IGRT), missing targets are limited. (authors)