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An End-To-End VMAT QA Procedure Using a Customized Anthropomorphic Phantom Head

P Iwai

P Iwai*, S Hara , Ghelfond Diagnostics, Sao Paulo, Sao Paulo


SU-I-GPD-T-390 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Volumetric modulated arc therapy can deliver complex dose distributions used in radiation therapy treatments. Due to it's complexity, a quality assurance program is needed. A method to test the overall treatment delivery precision consists in performing a so-called "end-to-end test", which can make use of an anthropomorphic phantom.

Methods: An anthropomorphic phantom head was made using a hollow plastic dummy head filled with paraffin. A central axial hole was drilled from the top of the head as an insert for a CC01 type ionization chamber to be placed. A VMAT plan was planned in Elekta's Monaco treatment planning system and dose distribution was calculated by a Monte Carlo algorithm (XVMC)considering heterogeneity corrections. Measured mean dose was used as reference to assess the percentage deviation from treatment planning system calculated dose.

Results: The construction method applied in the phantom head produced a consistent external anatomy shape. The heterogeneities found in final product actually helped exploring the treatment planning system dose calculation capabilities while also not compromising dosimetric accuracy due to lack of ion chamber electronic equilibrium. The percentage dose deviation obtained was 2,47%.

Conclusion: The ICRU Report 44 recommends a maximum percentage dose deviation of 3%. Since our measurements showed a percentage dose deviation bellow this recommended threshold, we could assume our institution overall treatment delivery precision to be in accordance to the highest international protocols.

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