[Assessments setup errors and target margin by 6D couch for primary cervical cancer].

OBJECTIVE: To explore the inter and intra-fractional setup variations of HexaPOD evo RT 6-degree-of-freedom treatment couch plus kilovoltage (KV) cone-beam computed tomography (CBCT) in patients with primary cervical cancer and calculate the proper margins of CTV for clinical use. METHODS: From May 2013 to April 2014, 16 consecutive patients with primary cervical cancer were enrolled. Elekta AXESSE™ image guided radiation therapy (IGRT) modalities and vacuum pad were employed. All patents were treated in a prone position after Lac light correction. Then daily CBCT scans prior to were performed treatment delivery, another CBCT scan after 6D couch online correction and a third one after each treatment. After automatic registration to planning CT, three translational X, Y, Z and three rotational Rx, Ry, Rz shifts were analyzed for intra and inter-fraction assessments and CTV margins. RESULTS: CBCT plus 6D couch could reduce the inter-fraction errors of X (t = 3.87, P = 0.000), Z (t = -7.92, P = 0.000), Rx (t = 3.05, P = 0.003), Ry (t = -6.87, P = 0.000) statistically and Ry was significantly different between pre and post-treatment (t = 3.242, P = 0.002). As to intra-fraction variations, the CTV margins were 2.74 mm, 3.9 mm and 2.87 mm on X, Y and Z directions respectively. CONCLUSION: Corrections with CBCT and HexaPOD evo RT 6D may considerably reduce the translational and rotational setup variations and gain lower PTV volume for intact cervical cancer. Thus it protects normal tissues better and improves the accuracy of high-precision treatments.