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Session: Therapy General ePoster Viewing [Return to Session]

Development of Supplemental Pre-Treatment Daily Quality Assurance On the Radixact Real-Time Tumor Tracking System

R Teboh Forbang*, B Lewis, A Ndlovu, Hackensack University Medical Center, Hackensack, NJ


PO-GePV-T-339 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: The ability to track a moving target in real time during radiotherapy remains challenging as a motion management strategy. Quality Assurance (QA) procedures supplemental to those developed for conventional systems must be in place to assure safe delivery. One such modality is the Accuray Radixact Synchrony system. We present a systematic pre-treatment QA approach on this system.

Methods: Setup the Tomo phantom with ion chamber (IC) at z=-0.5cm and 4 fiducial inserts, around the chamber. Scan and develop a treatment plan with fiducial tracking and a target drawn enclosing the IC. Setup the phantom via room lasers to the planning isocenter. By acquiring an MVCT and using image registration, the observed shifts correspond to the laser versus MVCT isocenter coincidence. Apply the shifts and proceed to treatment where the first step is kV imaging of fiducials. The observed offsets correspond to the kV versus MVCT isocenter coincidence. Complete the treatment delivery and note the IC reading (IC-0). In the treatment room, apply known shifts of 15mm(S/I) and 15mm(A/P) to displace phantom from its MVCT isocenter setup. Repeat treatment now without applying setup corrections after MVCT and noting the deduced setup misalignment using kV imaging. At the end of the 2nd treatment, the IC reading (IC-delta) is noted. For ideal tracking system, IC-0 equals IC-delta.

Results: Sample
results: (a) Laser versus MVCT isocenter coincidence (1mm, 0.5mm, 0.4mm) in the (lateral, longitudinal, vertical) respectively. (b) kV versus MVCT isocenter coincidence (0.2mm, 0mm, 0.4mm) (c) MVCT/kV imaging measured known shifts (0mm, 15mm, 15.5mm) / (0mm, 16mm, 15.5mm) respectively. (d) IC measured charge of 1.8nC (IC-0) and 1.75nC (IC-delta) thus giving a tracking delivery discrepancy of -2.78%.

Conclusion: A simple and systematic QA method has been presented which can be done in addition to the routine daily QA on the Radixact tracking system.


Tomotherapy, Quality Assurance, Radiation Therapy


TH- External Beam- Photons: Quality Assurance - Linear accelerator

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