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  4. Statistical Analysis of Commissioning Beam Data Using Stealth Reference Chamber: A Validation Study in Wedge Field

Statistical Analysis of Commissioning Beam Data Using Stealth Reference Chamber: A Validation Study in Wedge Field

S Kang1*, J Chung1 , J Kim2 , J Park2 , S Kim3 , H An2 , T Suh4 , J Kim1 , (1) Seoul National University Bundang Hospital, Seongnam-si, Gyeonggi-do, (2) Seoul National University Hospital, Seoul, SEOUL, (3) Virginia Commonwealth University, Richmond, VA, (4) Catholic university Medical College, Seoul, Seoul,

Presentations

(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: To quantitatively evaluate a commissioning beam data measured with novel reference chamber “stealth chamber� in wedge field.

Methods: The stealth chamber is a transmission ionization chamber which is intended to be used as reference signal chamber made for relative dosimetry. It has a total attenuation equivalent of less than 0.5 mm Al. A comprehensive set of data on all wedge fields for 6, 8, and 10 MV photon beam was measured with/without stealth chamber using a CC13 chamber as field chamber. When the stealth chamber is not used, the same CC13 chamber was used as the reference chamber. Percentage depth doses (PDDs) and dose profiles for field size given by 4ⅹ4 cm² to 20ⅹ20 cm² were obtained. PDD at 10 cm depth (D100), 5 cm depth (D50), and depth of maximum dose (dmax) were evaluated for the PDDs, root mean square error (RMSE) at dmax and depth at 10 cm (d10) were evaluated for profiles.

Results: A larger dosimetric difference was observed in build-up regions than beyond dmax for all energy. The difference of D100 and D50 in the dosimetric parameters of the PDD is less than 1% for all field sizes of all wedge angles. In multi regression analysis, the field size was significantly associated with a difference between with and without stealth chamber except for RMSE at dmax, whereas no significant association was confirmed for beam energy. Interestingly, wedge angle was significantly associated with a difference for both RMSE at dmax and d10 whereas no significant association was observed for dosimetric parameter of PDDs.

Conclusion: This study demonstrated that stealth chamber could be used in wedge field for commissioning beam data measurement. However, it is recommended to perform a control measurement to check large field size and large wedge angle to use commissioning beam data.

Funding Support, Disclosures, and Conflict of Interest: Current work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT)(No. 2017M2A2A7A02020643).

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