A Novel Patient Quality Assurance System for Both Outer and Inner Dose Verification in Volumetric Modulated Arc Therapy
J Peng1*, W Hu1, (1) Fudan University Shanghai Cancer Center, Shanghai,SU-E-T-156 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: The general commercial patient specific QA systems for volumetric modulated arc therapy (VMAT) provide either O (Arccheck) or X (Delta4) shape plane measurements. The purpose of this study is to develop a cylindrical phantom with radiochromic film to concurrently verify the dose planes in outer (O shape plane) and inner (X shape plane) geometric for the VMAT treatment.
Methods:A novel patient specific phantom consists of polyethylene and radiochromic film was designed. Films can be wrapped and shaped and inserted in the phantom for simultaneous measurement of the O and X dose planes. One rolled-up and two specifically cut EBT3 films were used for the O and X dose planes measurements, respectively. A clinically approved head-and-neck RapidArc plan was hybrid to the phantom for patient specific QA. The calculated dose planes were extracted from treatment planning system with homemade Matlab software and compared to the measurements. The O plane was rolled out into a rectangle plane and the X geometric plane was departed into two rectangle planes for final analysis in the Film QA software. The gamma analysis with criteria [3mm, 3%] and dose profile comparison were performed.
Results:A novel phantom with both O and X dose planes measurements was created. Worked with the gafchromic film, the phantom can be used for patient specific QA. For the test case, the gamma passing rates for O and two X planes were 95.5%, 98.6% and 96.0%, respectively. The dose profile analysis also showed good consistency between calculated and measurement dose planes.
Conclusion:The developed phantom system provides a practical and reliable QA method for VMAT technique. It can be employed as an alternative tool for patient specific QA besides the commercial ones.
Funding Support, Disclosures, and Conflict of Interest: This study was sponsored by grant KY0413 from Ministry of Public Health, PRC.