Exhibit Hall | Forum 7
Purpose: Use of Varian TrueBeam Developer mode and Varian TrueBeam couch (6-DOF) to simulate various motion patterns and to counteract the phantom motion in real time by moving couch in the reverse direction.
Methods: Software was developed for either writing an XML code for user-defined sinusoidal couch motions with various amplitudes and periods or converting an existing respiratory trace to replicate equivalent TrueBeam couch motion. The motion of QUASAR™ Respiratory Motion Phantom with varying periods (3s, 4s, and 5s) and amplitudes was converted into XML code and then simulated by the TrueBeam couch. Ability and reliability of the couch motion was done by studying either the trajectory log or an in-house developed method. Dosimetrically, the gamma passing rate was studied using a Gafchromic film while the absorbed dose measurements were done using a 0.125 cc ion chamber to study that the couch counteract the three-dimensional motion of the QUASAR™ Phantom with motion range (3-4cm) and period (4-6s) in real time by comparing phantom and couch simulated motion in opposite direction. The results were compared with a case when both phantom and couch are stationary.
Results: The couch successfully simulated both user-defined sinusoidal patterns and motion phantoms with the correlation value greater than 0.98. The ion-chamber ratio ranged between 1.005 to 1.038 and gamma passing rate was between 86.8-95.3% for 3%/3 mm criteria when couch counteracted the 3D QUASAR™ Phantom motion by moving in opposite direction.
Conclusion: TrueBeam couch can effectively simulate user-defined sinusoidal patterns and mimic phantom motion by moving the couch in 6D allowing the possibility of converting a stationary phantom into equivalent motion phantom. It is also possible to make the couch move in reverse direction to counteract the motion of the phantom in real time which can help in reducing PTV margins and hence normal tissue irradiation.
Phantoms, Film, Linear Accelerator
TH- External Beam- Photons: Motion management - intrafraction