title: Assessment and evaluation of MV image guidance system performance in radiotherapy.
abstract: OBJECTIVE
  The clinical use of imaging system in image guided radiotherapy (IGRT) necessitates performing periodic quality assurance of the system to be confident in applying corrections for patient set-up errors. We aim to develop and implement a quality assurance (QA) programme for megavoltage (MV) based image guidance system and assess its long term performance for a period of 3 years.
  
  
  METHODS
  Periodic QA tests were performed for the MV planar and cone beam computed tomography (CBCT) imaging system to assess the system safety, mechanical and geometrical accuracy, image quality and dose. The tests were performed using the equipment supplied by the manufacturer along with the image guidance system and using simple methods developed in-house. The test results were compared with expected or baseline values established during commissioning.
  
  
  RESULTS
  The safety system was found to be functional. The results of mechanical and geometrical tests were in good agreement with the expected results. The system mechanical positioning was stable and reproducible within ±2 mm accuracy. The image quality and the imaging dose of the planar and CBCT imaging were found to agree with the baseline values and the manufacturer specifications.
  
  
  CONCLUSIONS
  Throughout the three-year period, all the QA tests were within the specification. The mechanical and geometrical tests are most crucial as they directly affect the patient positioning accuracy.
  
  
  CONCLUSIONS
  We conclude that the MV image guidance system is efficient to perform IGRT and insist to perform periodic QA tests and calibration for the system.
authors.affiliation: Department of Radiation Oncology, Medwin Cancer Center, Hyderabad, India ; Photonics, Nuclear and Medical Physics Division, VIT University, Vellore, India.
authors.forename: Nithya
authors.initials: N
authors.lastname: Kanakavelu
authors.affiliation: Photonics, Nuclear and Medical Physics Division, VIT University, Vellore, India.
authors.forename: E James Jebaseelan
authors.initials: EJ
authors.lastname: Samuel
keywords: Image guidance system; Megavoltage imaging; Quality assurance