Purpose: In recent years, volumetric arc therapy combined with 4DCT for moving target, became more popular. It can be either performed by gating or tracking the tumour. The purpose of this dosimetric study to validate the rapid arc gating technique for lung and liver stereotactic body radiation therapy (SBRT) with an in-house made 4D wax phantom.
Methods: 4DCT scan of the phantom with CC13 ion chamber inserted into the groove given, acquired using real-time position management system (RPM) (Varian Medical System, Palo Alto, CA) for respiratory motion monitoring. Appropriate phases were selected for delineation purpose, and the plan created in eclipse V13.5. The respiratory pattern of phantom recorded at the time of the 4DCT scan serves as a reference pattern during dose delivery. We took a gated cone-beam computed tomography (CBCT) scan for the setup verification before dose delivery. Quality assurance performed on in-house made 4D wax phantom having CC13 ion chamber inserted. Dosimetric validation of rapid arc gating technique has been performed for gated rapid arc plans created with 6MV, 6MV-FFF, 10MV, 10MV-FFF energies.
Results: Dosimetric evaluation for gated rapid arc plans created with 6MV, 6MV-FFF, 10MV, 10MV-FFF energies showed ≤3% variation for all the cases. Plans created for 6MV showed 0.50% and 1.00% variation, plans created for 6MV-FFF, 10MV, 10MV-FFF energies respectively showed the variation of 1.59%, 2.60%, 3.00%, additionally we have created conformal arc plan which showed variation within tolerance limit between the treatment planning system (TPS) dose and measured dose with ion chamber.
Conclusion: This dosimetric study showed that the Point dose validation of a rapid arc gating technique carried out successfully using indigenous 4D wax phantom is well within tolerance limits compared to TPS calculated dose. So, Gated RapidArc can clinically be used to treat SBRT lung and liver.
Gating, Ionization Chamber, Phantoms
TH- Radiation Dose Measurement Devices: ion chamber: air cavity