Abstract：To measure small field output factor, the tissue-phantom ratio (TPR20,10(10)) of the Elekta Synergy linear accelerator nominal radiation energy of 6MV and 10MV were measured using TRS-483 report method published by IAEA, which were 0.683 and 0.735.By calculating the minimum FWHM applicable to the ionization chamber, various measurable radiation field ranges of the ionization chamber were verified. The FWHM of the selected ionization chambers are between 3～4cm.By comparing the sensitive volume, linearity of measured dose and dose rate, leakage current, repeatability and stability, a total of 21 detectors from 18 different models were selected.Under the condition of TPR20,10(10)=0.683, 0.735, source skin distance (SSD) of 90cm and 100cm, 1cm×1cm,2cm×2cm, 3cm×3cm, 4cm×4cm, 5cm×5cm and 8cm×8cm square field to 10cm×10cm square field output factors were measured and multiplied by the correction factor reported by TRS-483.The maximum difference between the corrected radiation field output factor and the mean value is less than 0.025.The results show that using the correction factor reported by TRS-483 can improve the consistency of measurement of small field dose by different detectors.
Das I, Francescon P, Moran J, et al.Report of AAPM Task Group 155: Megavoltage photon beam dosimetry in small fields and non-equilibriumconditions.［J］. Medical physics, 2021,48(10):e866-e921.
Gao X, Yu Y J, Shi LW. Comparative Analysis of Film Dosimeter and Diode Detector in Small Field Dosimetry ［J］. Acta Metrologica Sinica, 2020, 41(7): 873-878.
Yin Z, Hugtenburg R P, Beddoe A H. Response corrections for solid-state detectors in megavoltage photon dosimetry. ［J］. Physics in medicine and biology, 2004, 49(16): 3691-702.
Luo S M, He Z J, Yuan J L, et al. Measurement of small field output factor of multi-blade collimator by micro-ionization chamber ［J］. Chinese medical equipment, 2020, 17(8): 46-51.
Li M H, Ma P, Tian Y, et al. Measurement and correction method of small field output factor based on IAEA 483 report ［J］. Chinese Journal of Radiation Oncology, 2019,28(6): 452-456.
［10］
Roy M, Carlan L, Delaunay F, et al. Assessment of small volume ionization chambers as reference dosimeters in high-energy photon beams ［J］. Physics in Medicine and Biology, 2011, 56 (17):5637-5650.
［14］
Buchegger N, Grogan G, Hug B,et al. CyberKnife reference dosimetry: An assessment of the impact of evolving recommendations on correction factors and measured dose ［J］. Medical Physics, 2020, 47 (8): 3573-3585.
Li G J, Li Q, Han J, et al. Study on the dosimetric characteristics of small segment dimensions in intensity modulated radiation therapy［J］.
［5］
Sargison G, Liu P, Weston S, et al. Small field dosimetric characterization of a new 160-leaf MLC ［J］. Physics in Medicine and Biology, 2013, 58(20):7343-7354.
Andreo P, Burns D T, Hohlfeld K, et al. Absorbed dose determination in external beam radiotherapy:IAEA Technical Report Series No. 398［R］.
［12］
Almond P R, Biggs P J, Coursey B M, et al.AAPM’s TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams［J］.Medical Physics,1999,26(9):1847-1870.
［16］
Smith C L, Montesari A, Oliver C P, et al.Evaluation of the IAEA-TRS 483 protocol for the dosimetry of small fields (square and stereotactic cones) using multiple detectors［J］. Journal of applied clinical medical physics, 2020, 21 (2): 98-110.
［17］
Huq M S, Hwang M S, Teo T P, et al. A dosimetric evaluation of the IAEA-AAPM TRS 483 code of practice for dosimetry of small static fields used in conventional linac beams and comparison with IAEA TRS-98, AAPM TG 51, and TG 51 Addendum protocols ［J］. Medical Physics, 2018, doi: 10.1002/mp.13092.
Luo C, Fan Y D, Wang K, et al. Comparation on the Absorbed Dose to Water in 398/277 Report for Linacs High Energy Photon Beams in Beijing District［J］. Acta Metrologica Sinica, 2021, 42 (1): 100-104.
［1］
IAEA. Dosimetry of Small Static Fields Used in External BeamRadiotherapy: An International Code of Practice for Reference and Relative Dose Determination.［DB/OL］［2018-03-25］. https: //www. pub. iaea. org/MTCD/Publications/PDF/D483_web. pdf
Alfonso R, Andreo P, Capote R, et al.A new formalism for reference dosimetry of small and nonstandard fields［J］.Medical Physics,2008,35(11):5179-5186.
［6］
Cranmer-Sargison G, Weston S, Sidhu N P, et al. Experimental small field 6MV output ratio analysis for various diode detector and accelerator combinations. ［J］. Radiotherapy and Oncology, 2011, 100(3): 429-435.
［13］
Sauer O A. Determination of the quality index (Q) for photon beams at arbitrary field sizes［J］.Medical Physics, 2009,36(9): 4168-4172.
2023, Vol. 44 
