Purpose of the study: Recent studies have shown that the incidence of certain cancers would be due to ionising radiation received during diagnostic radiological explorations. It is thus important to optimise dosimetry. In this context, slot scanners have demonstrated potential for generating images with a quality comparable with conventional systems but with a considerable reduction in dose. We wanted to verify this proposition.

Material and method: Radiographs were obtained in 50 scoliosis patients (posteroanterior and lateral incidences) using the slot scanner (EOS, Biospace) and with a conventional machine (FCR-7501S, Fuji). A dosimeter was placed on the patient after each exam. Phantoms were used to adjust radiographic parameters for each system in order to obtain comparable quality images. Patient images were then acquired ad the dose calculated at several entry points. These measures were used to compare skin radiation and to initialise a Monte-Carlo simulation calculating the effective dose. Two orthopaedic surgeons and two radiologists then evaluated the visibility of the structures of interest using a standard check list. They read the images in random order and were blinded to all information concerning the patient and the system used to acquire the images. Visibility was noted on a non-parametric scale with 4 levels. Wilcoxon’s test was used to compare the visibility scores.

Results: Mean radiation of the skin in the thoracoab-dominal region varied from 0.11 to 0.30 mGy (effective dose 0.057 mSv) for the EOS and 0.73 to 2.47 mGy (effective dose 0.460 mSv) for the FCR-7501S. EOS provided significantly superior visibility for all structures (frontal view, p< 0.006), lateral view p< 0.04) except for the posterior arch of the lumbar vertebrae in the lateral view for which visibility was superior for FCR-7501S (p< 0.003).

Discussion: Using the slot scanner, the patients received 6 to 9 times less radiation to the skin for the thoracoab-dominal region and an 8-fold reduction in effective dose than with the conventional system. In addition, the doses presented in the literature for the same exam are much higher than reported for EOS.

Conclusion: The EOS slot scanner offers image quality which is globally superior to conventional systems while considerably reducing radiation dose.