Development of a Vaginal Immobilization Device: A Treatment-planning Study of Carbon-ion Radiotherapy and Intensity-modulated Radiation Therapy for Uterine Cervical Cancer

Aim: We developed a vaginal immobilization device for external radiotherapy in gynaecological malignancies and evaluated its bowel dose-reduction effect during carbon-ion radiotherapy (CIRT) and intensity-modulated radiation therapy (IMRT) in patients with cervical cancer. Patients and Methods: Computed tomographic images obtained with and without the device in seven patients with cervical cancer were assessed. Treatment plans for CIRT and IMRT were generated, and dose-volume parameters (V-20, V-25, V-35, and D-2cc) of the rectum, sigmoidal colon, and bladder were evaluated. Results: The mean +/- standard deviation of the rectal volume in CIRT for V35 with and without the device were 2.1 +/- 2.1 and 13.6 +/- 4.4 ml, respectively, and those in IMRT were 2.0 +/- 2.2 and 13.7 +/- 3.8 ml, respectively; these values were significantly lower in CIRT and IMRT using this device. Conclusion: Using our novel vaginal immobilization device, high rectal doses were largely reduced in CIRT and IMRT.