Program Information
Novel 3D Printed Water Phantom for Patient Specific Film QA of Single Isocenter Multitarget VMAT SRS Plans
J Mikell*, J Kamp , M Pillainayagam , K Lam , University of Michigan, Ann Arbor, MI
Presentations
SU-E-108-6 (Sunday, July 30, 2017) 1:00 PM - 1:55 PM Room: 108
Purpose: To design and construct a phantom for patient specific QA of single isocenter multitarget VMAT SRS plans.
Methods: A commercial resin printer (Form 2, FormLabs Inc., Somerville, MA) was used to print a phantom that holds water and allows insertion of an axial film every 2 mm. To show feasibility of performing QA with this phantom we performed patient specific QA using a previously treated 6 target VMAT SRS plan from our institution. Irradiations of film in the 3D printed phantom filled with water were compared with results obtained from films irradiated in the Sun Nuclear ArcCheck Multiplug, which is a solid phantom with a single machined film holder. EBT-XD Gafchromic film was used for each target. Film analysis was performed in Film QA Pro using triple-channel dosimetry and the one-scan protocol. The six axial planes nearest to the centroid of each PTV were selected to be slotted with film.
Results: For the water phantom with multiple films, the percentage of pixels passing 4%/1mm gamma was within 1.6% of the passing percentage for the corresponding film in solid phantom. Axial films allowed sampling within 0.5 mm of the PTV centroid on average with a maximum difference of 0.9 mm. All films were irradiated in a single plan delivery which took 13 minutes, whereas single film in a solid phantom required plan delivery for each film for a total of 78 minutes.
Conclusion: Film results in the water phantom were comparable to film results in solid phantom. The fine spacing of film slots makes it easy to select a film plane near the PTV centroid or critical structures. The 3D printed phantom enables film dosimetry of multiple targets in a single plan delivery which leads to significant savings in machine time.
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