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SU‐GG‐T‐354: Development and Evaluation of a Low Cost, EBT2 Film‐Based Real‐Time Dosimeter
Author(s) -
Du H,
Li S,
Zhou S,
Deng H,
Zhang M,
Chen S,
Schubert L
Publication year - 2010
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3468751
Subject(s) - dosimeter , photodiode , dosimetry , optics , linear particle accelerator , materials science , ionization chamber , signal (programming language) , radiosurgery , physics , diode , optoelectronics , nuclear medicine , radiation , beam (structure) , radiation therapy , medicine , ion , programming language , quantum mechanics , computer science , ionization
Purpose : To develop and evaluate a low‐cost GafChromic film‐based real‐time dosimeter for practical radiation dosimetry. Method : The dosimeter employs EBT2 film chips, LEDs at 680 nm and 618 nm, a photodiode, and plastic optical fibers. Red light from the LED, modulated by sinusoidal signal, is guided with a φ=1 mm fiber toward a film chip as small as 2×2 mm 2 . Transmitted light is carried by another φ=0.5 or 1 mm fiber toward the photodiode. A Java program generates the sinusoidal signal, samples the photodiode signal and computes its amplitude in real time via FFT. Dose response to 6MV photon beams was characterized with a Siemens Primus linac and a Varian Novalis radiosurgery linac. S cp of the Novalis linac was measured down to 0.6×0.6 cm 2 using multiple film chips. Results : The dosimeter has 16‐bit resolution with a SNR of ∼80 dB. At 680 nm, optical density responded to dose linearly at ∼10 −4 /cGy up to 75 Gy. At 618 nm, response was approximately 30 times greater. Response was non‐linear but easily approximated with a cubic polynomial. The accuracy of the dosimeter was estimated to be better than 2% if the film is allowed to settle for one day. The accuracy of the real‐time dosimetry is affected by the settling time the optical density takes to reach asymptotic value. The S cp , measured by the dosimeter was comparable to ion chamber and diode detectors down to sizes of 4.2×4.2 cm 2 , but was reduced as field size decreased, e.g. by ∼4% at 1.2×1.2 cm 2 . Conclusions : A real‐time, low‐cost dosimeter was developed based on radiochromic‐film at 618 nm. It can be easily implemented and conveniently used for in‐vivo dosimetry given its demonstrated accuracy. Research is supported by Department of Radiation Oncology, University of Nebraska Medical Center. GafChromic film is provided by the International Specialty Products.