Commissioning and Acceptance Testing of the existing linear accelerator upgraded to volumetric modulated arc therapy

Aim

The RapidArc commissioning and Acceptance Testing program will test and ensure accuracy in DMLC position, precise dose-rate control during gantry rotation and accurate control of gantry speed.

Background

Recently, we have upgraded our linear accelerator capable of performing IMRT which was functional from 2007 with image guided RapidArc facility. The installation of VMAT in the existing linear accelerator is a tedious process which requires many quality assurance procedures before the proper commissioning of the facility and these procedures are discussed in this study.

Materials and methods

Output of the machine at different dose rates was measured to verify its consistency at different dose rates. Monitor and chamber linearity at different dose rates were checked. DMLC QA comprising of MLC transmission factor measurement and dosimetric leaf gap measurements were performed using 0.13 cm³ and 0.65 cm³ Farmer type ionization chamber, dose 1 dosimeter, and IAEA 30 cm × 30 cm × 30 cm water phantom. Picket fence test, garden fence test, tests to check leaf positioning accuracy due to carriage movement, calibration of the leaves, leaf speed stability effects due to the acceleration and deceleration of leaves, accuracy and calibration of leaves in producing complex fields, effects of interleaf friction, etc. were verified using EDR2 therapy films, Vidar scanner, Omnipro accept software, amorphous silicon based electronic portal imaging device and EPIQA software.^1–8

Results

All the DMLC related quality assurance tests were performed and evaluated by film dosimetry, portal dosimetry and EPIQA.⁷

Conclusion

Results confirmed that the linear accelerator is capable of performing accurate VMAT.