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Development of Simplified Measurement Technique for Small Field Output Factor

M Kim1,2*, S Park3 , S Ahn1 , J Kim1 , K Park1 , H Lee1 , (1) Yonsei Cancer Center, Yonsei University College of Medicine, Yonsei University Health System, Seoul, Korea, (2) Department of Biomedical Engineering, Research Institute of Biomedical Engineering, The Catholic University of Korea, (3) Department of Radiation Oncology, Jeju University College of Medicine, Jeju National University Hospital, Jeju, Korea


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

Room: Exhibit Hall

Purpose: The current study presents the simplified measurement method for output factor of small field by utilizing commercialized solid water phantom and various ionization chamber. The measurement result was quantified and the feasibility of the simplified measurement method has been discussed.

Methods: The output factor (OF) is defined as DFS/D10×10, the ratio of dose at given field size (DFS) to the dose at 10×10 cm². Measurement was performed on available photon beam energies used (6 and 10 MV). Applied small field size was 1×1 to 5×5 cm²and 8×8 cm² as a regular field size and 10×10 cm² for reference field size with 90 cm SSD. The OFs for small field were measured by MicroDiamond 60019 (MD), Pinpoint3D 31016 (PP3D), Extradin A16 (A16) The simplified measurement method utilized the Blue Water phantom (BW in the following). The BW is solid water phantom and offers the customized chamber holder, which could be located at the center of the phantom, perfectly. The density of the BW was slightly different from water and the effective depth for measurement of output factor was considered and was calculated as 9.2 cm from the guidance of TRS-398.

Results: Output factor for small field using PP3D in solid water phantom could be possible approach because of the lowest percentage differences ranged from 0.00-1.66%. Differences from reference data was varied according to photon beam energy and the measured data for 1 x 1 cm²required to be eliminated in our comparison because of unreliable data which has known to be caused by volume averaging effect in very small field.

Conclusion: The result demonstrated here are intended to offer efficiency for measurement of output factor for small field in case of emergency or to serve as a guide to help potentially identify gross error in measurement using solid water phantom.


Not Applicable / None Entered.


TH- External beam- photons: Development (new technology and techniques)

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