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SRS Cone Output Factors: TRS-483 Correction Factors Vs. Daisy Chain Method

V Gutti*, V Gutti , S Oddiraju , R McDermott , Baylor Scott & White Health, Temple, TX


(Sunday, 7/14/2019) 2:00 PM - 3:00 PM

Room: 302

Purpose: The SRS cone output factors are very sensitive to the measurement technique and the detector used. Variety of small field detectors yield varying results for output factors. Correction factors for various small field detectors are published recently as a function of field size as beam quality varies with field size. In this study, we present the clinical significance and impact on patient treatment dose by comparing the output factors from Radiochromic film, and two stereotactic diodes with use of the published small field correction factors and the daisy chain technique.

Methods: SRS output factors are measured for Varian ICVI SRS cones using IBA dosimetry SFD diode, Sun Nuclear Edge diode, and Gafchromic EBT-XD film. Output factors were measured at 1.5 cm depth to use in Brainlab iPlan Cone Planning and at 5 cm depth to use in Varian Eclipse Cone Planning system with SAD setup. Water tank setup was used for diodes and solid water for gafchromic film. Daisy chain technique was employed for with an intermediate field size of 3 cm and using a CC13 intermediate volume ion chamber. An ADCL calibrated farmer ion chamber (0.6cc) was used to determine the dose at calibration conditions.

Results: Calibration curves were established for the Gafchromic film EBT-XD based dose measurements. The film analysis was all done in Film QA pro software. The results from the daisy chain technique and the using the correction factors from IAEA TRS-483 are presented in tabular format.

Conclusion: The IAEA-TRS 483 based corrected output factors appear to be matching better between multiple dose measurement devices and techniques. Correction factors were not available for Edge diode detector for small field sizes corresponding to 7.5, 5.0 and 4.0 mm conical collimators.


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