The Deliverability of Dynamic Conformal Arc Therapy (DCAT) and Its Influence On Patient Dose
C Kim1*, H Kim2, D Jung2, D Kim1**, J Kim1, (1) Department of Radiation Oncology, Yonsei University College of Medicine, Seoul, KR, (2) Department of Radiation Oncology, Yonsei Cancer Center, Seoul, KR
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PO-GePV-T-202 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: The purpose of this study is to investigate the deliverability of DCAT according to the number of control points and to evaluate its impact on patient dose.
Methods: Elekta LINACs have intrinsic inter-segment break for every 1000 MU, and gantry wobble might be occurred at these break points. As the number of control points is highly correlated with gantry speed, it may directly affect to the deliverability of DCAT and therefore perturb patient dose differently than planned. In this work, the deliverability of DCAT according to the number of control points was evaluated by using ArcCHECK phantom, semi-3D cylindrical diode array, which is capable of measurement according to beam angle. Treatment machine log files were also analyzed to check delivery errors. The effect of detected delivery errors on patient dose was investigated through dose re-calculation with modified RT-Plan that changed MU weights according to delivery error. Moreover, actual dose measurements were performed by using Octavius 1000 SRS, 2D liquid-filled ionization chamber detector array.
Results: It was observed that, when the number of control points is small, the amount of gantry wobble increases and thus the frequency of occurrence of delivery errors at inter-segment breakpoints increased. The changes in delivered dose due to such errors demonstrated through re-calculation and actual measurement were less than 1%.
Conclusion: The number of control points affects the deliverability of DCAT, but perturb the patient dose by less than 1%. However, in the case of pre-treatment QA with equipment that measures dose according to beam angle, such as ArcCHECK, the delivery errors may have a significant impact on QA results, thus these characteristics should be considered at the treatment planning step.
Keywords
Quality Assurance, Linear Accelerator
Taxonomy
TH- External Beam- Photons: Quality Assurance - IMRT/VMAT
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