Comparison of CTV-PTV setup margins during IMRT for cervical cancer patients with different body mass index by bladder volume measurement device-assisted CBCT

Objective: To investigate the clinical target volume (CTV)-planned target volume (PTV) setup margins during intensity-modulated radiotherapy (IMRT) for cervical cancer patients with different body mass index (BMI), aiming to provide reference for precise individual therapy. Methods: Forty patients diagnosed with cervical cancer undergoing IMRT in Cancer Hospital of Fudan University between March and September 2017 were recruited and assigned into the BMI ≤ 18.4, 18.5-23.9, 24.0-27.9 and ≥ 28 kg/m² groups according to the BMI classification criteria proposed by National Health and Family Planning Commission (NHFPC) of the People's Republic of China. Assisted with the bladder volume measurement device, 9 cycles of kilo-voltage cone beam computed tomography (CBCT) images were subject to online registration and imaging analysis. CTV-PTV setup margins were calculated based on the formula of M_PTV = 2.5Σ + 0.7σ among four groups. Single factor variance analysis was performed. LSD test was utilized for two-group comparison. Results: Among four groups, the CTV-PTV setup margins in the x, y and z directions were (6.87 mm, 6.06 mm, 8.49 mm), (3.13 mm, 3.02 mm, 3.14 mm), (4.70 mm, 4.86 mm, 5.31 mm) and (7.63 mm, 8.28 mm, 8.54 mm), respectively (P = 0.038, 0.048 and 0.004). Conclusions: The setup errors in the BMI ≤ 18.4 and ≥ 28 kg/m² groups are significantly larger compared with those in the remaining groups Consequently, CTV-PTV setup margins should be enlarged to certain extent for patients with BMI ≤ 18.4 and ≥ 28 kg/m². (authors)