Can the current radiation dose, in chest tomosynthesis, be reduced with retained image quality? A study in the context of lung cancer screening programs.

objectiveDigital chest tomosynthesis (DTS) is a low-cost and low- dose imaging technique that has not yet reached general use. It might, however, be well suited to lung cancer screening programs. In lung cancer screening, it is essential to keep radiation dose low, as a large number of healthy individuals have to be examined to detect one case of lung cancer. Lung cancer screening has been proven to lower deaths in lung cancer by approximately 20%, but this limited success comes at high cost. We believe that adding interval examination with DTS to lung cancer screening programs could increase survival and reduce cost, without significantly increasing the radiation dose to the individual. We therefore conducted this study to investigate if the current radiation dose, in chest tomosynthesis, could be reduced with retained image quality.

methods50 patients with known or suspected lung malignancy were imaged with chest X-ray equipment using the tomosynthesis option. Three DTS examination protocols were applied for each patient. One DTS examination was performed with the dose level as in the vendor-recommended protocol, and two other examinations were performed with low-dose protocols, reducing the exposure dose by 30% and 50%, respectively. Images from all three protocols were processed using the vendor-recommended post-processing settings, including a filtered back projection algorithm. The images generated by the DTS protocols were evaluated by four observers anonymously and in random order. The observers rated the quality of the reconstructed section images according to predefined quality criteria for different thoracic regions. Visual grading characteristics (VGC) were used to analyze the data, and the area under the VGC curve (AUCVGC) was used as a figure-of-merit.

resultsThe result of VGC analysis showed no reduction in imaging quality for the protocol with a 30% dose reduction compared with the vendor-recommended protocol for any of the classes of criteria, namely demarcation (AUCVGC = 0.51, p = 0.57), disturbance (AUCVGC = 0.51, p = 0.59) bone structure (AUCVGC = 0.50, p = 0.88), and tumor homogeneity (AUCVGC = 0.47, p = 0.09). For the protocol with a 50% dose reduction, image quality was reduced for the classes of criteria demarcation (AUCVGC = 0.47, p = 0.03) and disturbance (AUCVGC = 0.47, p = 0.02) compared with the vendor-recommended protocol, while no quality reduction was found for the classes of bone structure (AUCVGC = 0.50, p = 0.79) and tumor homogeneity (AUCVGC = 0.46, p = 0.10).

conclusionsThis study has not shown any reduction in image quality from reducing the radiation dose by 30%, compared with the vendor-recommended protocol, which might indicate that such a reduction could be used in clinical practice.