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Optically stimulated luminescence (OSL) of carbon‐doped aluminum oxide ( Al 2 O 3 : C ) for film dosimetry in radiotherapy
Author(s) -
Schembri V.,
Heijmen B. J. M.
Publication year - 2007
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 - 10.1118/1.2737160
Subject(s) - optically stimulated luminescence , dosimetry , materials science , dosimeter , irradiation , optics , ionization chamber , photon , dose profile , imaging phantom , luminescence , nuclear medicine , ionization , optoelectronics , chemistry , physics , medicine , ion , organic chemistry , nuclear physics
and Purpose: Conventional x‐ray films and radiochromic films have inherent challenges for high precision radiotherapy dosimetry. Here we have investigated basic characteristics of optically stimulated luminescence (OSL) of irradiated films containing carbon‐doped aluminum oxide ( Al 2 O 3 : C ) for dosimetry in therapeutic photon and electron beams. Materials and Methods: The OSL films consist of a polystyrene sheet, with a top layer of a mixture of single crystals ofAl 2 O 3 : C , ground into a powder, and a polyester base. The total thickness of the films is 0.3 mm . Measurements have been performed in a water equivalent phantom, using 4, 6, 10, and 18 MV photon beams, and 6 – 22 MeV electron beams. The studies include assessment of the film response (acquired OSL signal/delivered dose) on delivered dose (linearity), dose rate ( 1 – 6 Gy ∕ min ) , beam quality, field size and depth ( 6 MV , ranges 4 × 4 – 30 × 30cm 2 ,d max − 35 cm ). Doses have been derived from ionization chamber measurements. OSL films have also been compared with conventional x‐ray and GafChromic films for dosimetry outside the high dose area, with a high proportion of low dose scattered photons. In total, 787 OSL films have been irradiated. Results: Overall, the OSL response for electron beams was 3.6% lower than for photon beams. Differences between the various electron beam energies were not significant. The 6 and 18 MV photon beams differed in response by 4%. No response dependencies on dose rate were observed. For the 6 MV beam, the field size and depth dependencies of the OSL response were within ± 2.5 % . The observed inter‐film response variation for films irradiated with the same dose varied from 1% to 3.2% ( 1 SD ) , depending on the measurement day. At a depth of 20 cm , 5 cm outside the 20 × 20cm 26 and 18 MV beams, an over response of 17% was observed. In contrast to GafChromic and conventional x‐ray films, the response of theAl 2 O 3 : C films is linear in the clinically relevant dose range 0 – 200 cGy . Conclusions: Measurement of the OSL signal of irradiated films containingAl 2 O 3 : C is a promising technique for film dosimetry in radiotherapy with no or small response variations with dose rate, beam quality, field size and depth, and a linear response from 0 to 200 cGy .