Clinical application of Catalyst system in cervical cancer radiotherapy

Objective: To evaluate the clinical application of Catalyst system in positioning patients during cervical cancer radiotherapy, and to analyze its correlation with the bladder volume and body mass index (BMI) of patients. Methods: A total of 33 patients diagnosed with cervical cancer from July to December 2017 in our hospital were included in the study. All patients were auxiliary positioned by an optical surface imaging system (C-Pad Catalyst) before each treatment. The CBCT imaging was executed twice a week. The setup errors from Catalyst and CBCT in the anterior-posterior (AP), superior-inferior (SI) and leg-fight (LR) directions were recorded. Each patient's bladder volume and BMI were also recorded. Results: The setup errors between Catalyst with masks and CBCT had the significant difference in SI (P < 0.05) and LR (P < 0.05). For Catalyst without masks, the setup errors with the bladder volume of 200-300 ml had the significant association in SI (R = -0.316, P < 0.05). For the bladder volume of > 300 ml, the setup errors for Catalyst with masks had the significant association in AP (R = -0.493, P < 0.05), and that without masks had the significant association in SI and LR (R = 0.335, P < 0.05, R = -0.348, P < 0.05). For patients of < 25 kg/m², setup errors for Catalyst with masks had the significant association with the BMI in LR (R = 0.197, P < 0.05); for ≥ 25 kg/m², that with masks had the significant association in AP and SI (R = 0.818, P < 0.05; R = -0.498, P < 0.05), that without masks had the significant association in AP and LR (R = 0.652, P < 0.05; R = -0.558, P < 0.05). Conclusion: Unlike CBCT system, the patient positioning by Catalyst system was easily affected by the bladder volume and BMI of patients. (authors)