BackgroundDose rate variation is a critical factor affecting radionuclide therapy (RNT) efficacy. Relatively few studies to date have investigated the dose rate effect in RNT. Therefore, the aim of this study was to benchmark 90Y RNT (at different dose rates) against external beam radiotherapy (EBRT) in vitro and compare cell kill responses between the two irradiation processes.ResultsThree human colorectal carcinoma (CRC) cell lines (HT29, HCT116, SW48) were exposed to 90Y doses in the ranges 1–10.4 and 6.2–62.3 Gy with initial dose rates of 0.013–0.13 Gy/hr (low dose rate, LDR) and 0.077–0.77 Gy/hr (high dose rate, HDR), respectively. Results were compared to a 6-MV photon beam doses in the range from 1–9 Gy with constant dose rate of 277 Gy/hr. The cell survival parameters from the linear quadratic (LQ) model were determined. Additionally, Monte Carlo simulations were performed to calculate the average dose, dose rate and the number of hits in the cell nucleus.For the HT29 cell line, which was the most radioresistant, the α/β ratio was found to be ≈ 31 for HDR–90Y and ≈ 3.5 for EBRT. LDR–90Y resulting in insignificant cell death compared to HDR–90Y and EBRT. Simulation results also showed for LDR–90Y, for doses ≲ 3 Gy, the average number of hits per cell nucleus is ≲ 2 indicating insufficiently delivered lethal dose. For 90Y doses 3 Gy the number of hits per nucleus decreases rapidly and falls below ≈ 2 after ≈ 5 days of incubation time. Therefore, our results demonstrate that LDR–90Y is radiobiologically less effective than EBRT. However, HDR–90Y at ≈ 56 Gy was found to be radiobiologically as effective as acute ≈ 8 Gy EBRT.ConclusionThese results demonstrate that the efficacy of RNT is dependent on the initial dose rate at which radiation is delivered. Therefore, for a relatively long half-life radionuclide such as 90Y, a higher initial activity is required to achieve an outcome as effective as EBRT.
Although landfill gas emission can be greatly reduced by extraction and converting gas to energy, in practice not all gas can be collected and some leaks can still occur. Management of landfill gas can be improved if leaks can be detected and rectified effectively. This paper provides a brief review of methods available for detecting landfill leakage, with a focus on infrared thermography. It then describes a study which was conducted to test if an infrared camera can be used to detect gas leaks accurately by identifying them as anomalies. It examined the applicability and limitations of the technique by investigating fundamental factors such as weather conditions, ground conditions and distance of sensor from source. The paper also describes a test case conducted to reinforce the findings. It concluded that unless all the fundamental factors are clearly understood and addressed, the technique currently can only be used as a screening tool rather than as a precise tool to detect landfill gas leakages. For this reason, it would be difficult to use the technique as a basis for modelling gas emission from landfills.
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