Comparison of the energy-response factor of LiF and Al2O3 in radiotherapy beams

Abstract

A Monte Carlo study of the energy-response factor of aluminium oxide (Al2O3) and lithium fluoride (LiF) TLDs in kilovoltage and megavoltage photon beams relative to 60Co gamma rays has been performed using EGSnrc Monte Carlo simulations. The sensitive volume of the detector was simulated as a disc of diameter 2.85 mm and thickness 1 mm. The phantom material was water and the irradiation depth was 2.0 cm in kilovoltage photon beams and 5.0 cm for megavoltage photon beams. The results show that the energy-response of the Al2O3 and LiF-TLDs is constant within 3% for photon beam energies in the energy range of 60Co gamma rays to 25 MV X rays. However, both detectors show an enhanced response for kilovoltage photon beams, which in the case of 50 kV X rays is 3.2 times higher than that for 60Co gamma rays. The energy-response factor was 1.46 for LiF irradiated in 50 kV X rays. The Al2O3 detector has an energy-response that is 2.2 times higher than that of LiF in 50 kV X rays decreasing to 1.19 for 250 kV X rays. The results show that the addition of 0.1 or 1% of carbon by weight (as dopant) into the Al2O3 does not change the Monte Carlo determined energy-response factor by more than 1%.

AAPM TG 191: Clinical use of luminescent dosimeters: TLDs and OSLDs

“…For kV photons, TLDs over‐respond by a factor of up to 1.4 relative to 60 Co. Of note, this beam quality dependence can vary with different sizes and shapes of TLD. The magnitude of over‐response to low‐energy beams is much greater for OSLDs, which over‐respond by a factor of as much as 3 to 4 relative to 60 Co . If the calibration is done in a kV environment, the beam quality correction factor will be less.…”

Management of radiotherapy patients with implanted cardiac pacemakers and defibrillators: A Report of the AAPM TG‐203†

“…Thus, the traditional “dose” (as in dose‐to‐water) will be an underestimation of the dose to the device, particularly outside the treatment field where the spectrum is softer . Although not directly quantified, SiO 2 would be expected (based on similar know use of Al 2 O 3 ) to overrespond relative to tissue by ~20–30% outside of a 6‐MV treatment field, and potentially by more than a factor of 3 for kV energies . Ultimately, accurately calculated tissue dose serves as a good estimate of dose to the device inside the megavoltage treatment field, but is an increasingly poor estimate out of the beam or in kV environments.…”

Measurement of Dose outside a 6 MV Field Edge Using Optically Stimulated Luminescent Nano Dot Dosimeters

“…Energy response factor of Al2O3 in photon beams [7] . 그러나 모비트 등( Mobit et al)에 의한 광자 빔의 평균에너지는 조사야 10×10 ㎠에서 kV 광자 빔에 대하여 2 ㎝ 깊이에서, 그리고 MV 광자 빔에 대하여 5 ㎝ 깊이에서 산출하였다 [9] . 반응(over-response)을 나타낸다 [6] .…”

“…불균일한 에너지 반응을 나타낸다 [1]- [9] . (near) 방사선 치료에 사용되는 선형가속기의 조사야 내에서 선량계 교정 위치와 조사야 가장자리 바깥 위치에서 광자 스 펙트럼들은 차이가 있다 [6]- [9] .…”