Program Information
Evaluating the Influence of the Treatment Couch in VMAT by CERR
R Zhang1,2 , W Bai2*, Y Feng1 , (1) Department of Biomedical Engineering, The College of Precision Instrument & Opto-electronics Engineering of Tianjin University, Tianjin,China (2) Department of Radiation Therapy, The Fourth Hospital of Hebei Medical University, Shijiazhuang, Hebei,China
Presentations
PO-BPC-Exhibit Hall-25 (Saturday, March 18, 2017) Room: Exhibit Hall
Purpose: Evaluation the impact of the iBEAM evo carbon fiber Couchtop EP on VMAT delivering accuracy were performed with CERR (a Matlab based graphical user interface for radiotherapy applications)in terms of dose volume histograms,depth dose curves and 3D-γtests with and without couch model included is presented to improved delivery accuracy for radiation therapy.
Methods: A patient with spinal cord compression syndromes was optimized in the Monaco TPS with three partial arcs Arc1 (180° to 220°), Arc2 (320° to 40°) and Arc3 (140° to 180° ) with an increment of 20 to study the impact of the couch on a clinical dose distribution. For the planning target volume (PTV) the prescription dose is 30Gy in 10 fractions. Cord, heart and lung were defined as organs at risk (OARs).Plan was optimized using the couch model while final dose calculation was performed with two different conditions (with and without couch model ). Two sets of plans data were imported and evaluated by CERR.
Results: Due to the couch absorption the surface dose increased increases from 0 Gy( without couch ) to 27.5 ~ 29.0 Gy(with couch inserted) almost the same as the prescription dose of PTV. the PTV of without and with couch model included changed from 30.4 Gy to 29.3 Gy decreased 2.3%. And with the couch insert the gamma pass rate of the sub-field decreased dramatically form 99.0% ( Arc2 without couch ) to 80.8% (Arc1 and Arc3, with couch inserted).
Conclusion: These results demonstrate that the presence of the iBEAM evo carbon fiber couch increases the surface dose and decreases the target dose and the gamma pass rate. For the VMAT plan when the beam intersects the treatment couch the increased beam attenuation and skin doses should be taking more notice.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the Introduction of Overseas Students of Hebei Province [C2015005006] and the Medical Science Foundation of the health department of Hebei Province [No. 20130253].
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