Abstract
SU-F-T-298: The Impact of Modeling the Treatment Couch On Patient Specific VMAT QA
Medical physics (Lancaster), Vol.43(6), pp.3531-3531
06/2016
DOI: 10.1118/1.4956483
Abstract
Purpose:
The aim of this work is to quantify the impact of modeling the treatment couch on the passing rate of ion chamber measurements during VMAT quality assurance.
Methods:
For the initial characterization, attenuation and surface dose measurements were performed following the guidelines of TG-176 for the Civco Universal couch top using an Elekta VersaHD accelerator at an energy of 6 MV. A simulation CT was performed to aid in the creation of contours for representing the shape and size of the couch top in the treatment planning system (TPS). A uniform value of density for the couch wall was determined by comparing the ratios of ion chamber measurements made in a 30×30×11 cm3 water phantom with the TPS dose values of a plan with the same geometry. At our institution, patient specific quality assurance is performed using a Sun Nuclear ArcCheck with a multi-plug for chamber measurements, a 0.125cc PTW TN31010 chamber, and a Sun Nuclear 1010 electrometer. Ten VMAT plans were transferred into the phantom geometry created in the TPS with two settings: with and without the couch. The chamber measurements were compared to both treatment plans.
Results:
A maximum attenuation of 3.6% was observed when the gantry angle was set to 120 and 240 degrees, passing obliquely through the couch. A uniform density of 0.6 g/cm3 for the couch wall was determined in the TPS by comparison with measured data. The VMAT ion chamber measurement/plan ratios systematically improved by 1.79% ±0.53% for all patients when the couch was included in the calculation.
Conclusion:
The attenuation and surface dose changes produced by the Civco couch can generate observable dose difference in VMAT plans. Including a couch model in the phantom plan used for patient specific VMAT QA can improve the ionization chamber agreement by up to ∼2%.
Details
- Title: Subtitle
- SU-F-T-298: The Impact of Modeling the Treatment Couch On Patient Specific VMAT QA
- Creators
- E Gelover - University of Iowa Hospitals & Clinics, Iowa City, IAA Dalhart - University of Iowa Hospitals & Clinics, Iowa City, IAD Hyer - University of Iowa Hospitals & Clinics, Iowa City, IA
- Resource Type
- Abstract
- Publication Details
- Medical physics (Lancaster), Vol.43(6), pp.3531-3531
- DOI
- 10.1118/1.4956483
- ISSN
- 0094-2405
- eISSN
- 2473-4209
- Number of pages
- 1
- Language
- English
- Date published
- 06/2016
- Academic Unit
- Roy J. Carver Department of Biomedical Engineering; Radiation Oncology
- Record Identifier
- 9984046827602771
Metrics
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