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Analysis of Variation in Dmax Values in Small Fields with Eight Different Detectors

M Manavalan1*, D Manigandan2 , S Vikraman3 , G Krishnan4 , C Beltran5 , B Martinez6 , A Perez7 , (1)Apollo Speciality Hospitals(2) Medanta The Medicity, Gurgaon, HARYANA, (3) Omega Hospitals, Noida, ,(4) Apollo Speciality Hospital, Chennai, Tamil Nadu, (5) PTW Latin America, Rio De Janeiro, RJ, (6) PTW Latin America, Rio De Janeiro, RJ, (7) PTW Latin America, Rio De Janeiro, RJ


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

Room: Exhibit Hall

Purpose: The aim of this study is to analyze the variation in dmax values in small fields from measurements performed with eight different detectors.

Methods: The PDD measurements was performed in G4 Cyberknife Radiosurgery system with PTW Photon Diode, PTW Electron Diode, PTW SRS Diode, PTW Pin Point chamber, PTW microdiamond, SCanditronics PFD, Scanditronics EFD and Scanditronics SFD detectors in PTW water phantom. The PDD measurements were performed for all the twelve fixed collimators starting from 5mm till 60mm at 80 cm SSD.

Results: We noticed that with PTW photon diode the Dmax was lesser for the entire range of field size from 5 mm to 60 mm and the Dmax was maximum with PTW pin point chamber. The minimum Dmax value observed for 5mm collimator was with PTW photon diode which was 7.01 mm and maximum with PTW Pin Point chamber which was 12.01mm. The difference in Dmax values between smaller and larger field sizes(5mm and 60 mm collimator) was minimum with Scanditronics EFD with a difference of 5.54mm. Similarly the difference in Dmax values between smaller and larger field sizes was maximum with Scanditronics SFD having a difference value of 7.99 mm. We also noticed that the variation of Dmax was steep from field sizes ranging from 5 mm to 20 mm for almost with all the detectors. And from 20 mm till 60 mm the variation in Dmax with field size was minimal. We could see a maximum difference in Dmax value of 7.97 mm for a field size ranging from 5mm till 20 mm. However the maximum difference was only 2.99 mm for field size ranging from 20 mm till 60 mm.

Conclusion: In small field dosimetry one has understand the limitations and carefully select the detector as it has noticeable impact in the dosimetric values.


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Not Applicable / None Entered.

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