Aim: To analyse and correct inter­fractional set up error in cervical carcinoma patients with intact cervix, treated with VMAT technique through daily online kilo voltage cone beam CT. 

Materials and Methods: The present study was conducted in for 2 years to assess interfractional setup error by online CBCT in VMAT technique in patients of intact carcinoma cervix. A total of 30 patients, as per inclusion and exclusion criteria who opted for VMAT are included in our study. They were planned as per guidelines. 

Results: 63.33% of patients included in our study were in the age group of 41­60 years of age. 43.33% of patients were Stage IIB was the most common stage of presentation in our study. Squamous cell carcinoma was the most common type of histopathology in our study. Systematic error in X­Axis was 0.19cm, in YAxis was 0.17cm, and in Z­Axis was 0.15cm and the average systematic error in all three directions was 0.17cm. Random error in X­Axis was 0.40cm, in YAxis was 0.44cm and in Z­Axis was 0.36cm and average random error in all three directions was 0.40cm. P value was >0.05 in X and Z directions, setup error wasnot significant in these directions. On YAxis, P value was <0.05 and setup error was significant in Y direction. In X­Axis (Medial­Lateral direction) CTV­PTV margin was 0.75cm, in Yaxis(Superior­Inferior direction) CTV­PTV margin was 0.73cm and in Z­Axis (Anterior­Posterior direction) CTV­PTV margin was 0.63cm. Bladder average D35 dose was 49.41Gy with standard deviation of 2.37; average D50 dose was 47.33Gy with standard deviation of 2.96. In VMAT due to minimum CTV­PTV margin, dose to Organ at Risk (OAR) was less. 

Conclusion: use of daily online cone beam CT in cervical carcinoma patients treated with VMAT, we can achieve a lesser CTV­PTV margin, which can thus minimise the dose to organs at risk.

Keywords: Cone Beam Computed Tomography, (CBCT); Volumetric Modulated ARC Therapy
(VMAT); Cervical Carcinoma.