Organ dose and effective dose in Full spine Eaxamniations by EOS® Stereo-radiography with micro-dose settings. A study on anthropomorphic phantoms describing patient radiation exposure in full spine examinations Peter Heide Pedersen1, Søren Peter Eiskjær1, Asger Greval Petersen2 1Orthopedic Department, University Hospital of Aalborg, Orthopedic department, 2Regional North Jutland, Røntgenfysik, Region North Jutland

Summary: For full spine examinations, the effective radiation dose with the EOS® micro-dose settings was reduced more than 90% compared to reported doses for conventional digital radiology(CR)(5,8,11) The Study was carried out on anthropomorphic phantoms. Aim of the study: To make first time organ dose measurements and evaluations in EOS® micro-dose settings To compare these findings to previously reported findings in standard settings (5,11) To reduce radiation dose given to our patients

Hypothesis: Estimated organ dose and effective dose in full spine examinations with EOS® micro-dose settings, measured in anthropomorphic phantoms, is at least 90% less than reported effective dose by CR. Design: Descriptive study Anthropomorphic phantoms were exposed to EOS scanner standard low dose and micro-dose settings. Dose measurements were compared to reported radiation doses by CR (5, 8, 11)

Introduction Large cohort studies show that continiuos radiographic imaging during childhood for spinal deformities eg. scoliosis, increases the lifetime risk of breast cancer.The EOS biplane x-ray imaging system (EOS® Imaging S.A, Paris France) has been developed to produce high quality images while at the same time reducing radiation dose (4-7,10) The goal of this study is to make first time organ dose and effective dose evaluations in micro-dose settings in full spine examinations, and compare these findings to previously reported EOS findings and CR. Organ dose delivered by the EOS standard-dose settings has previously been evaluated by Damet et al 2014(5). Organ dose was measured in anthropomorphic phantoms and showed a 35% effective dose reduction compared to CR

Why investigate a low dose scanner? Radiographic examinations are the most significant causes of ionizing radiation. Ionizing radiation potentially leads to tissue damage. It has been documented in large cohort studies that radiographic imaging during childhood for spinal deformities eg. scoliosis, increases the lifetime risk of breast cancer (1,2,3)

What are the theoretic risks of being exposed to ionizing radiation What are the theoretic risks of being exposed to ionizing radiation? Effective dose provides an approximate indicator of potential detriment from ionizing radiation A population of 1 million people receiving 1 mili-sievert (mSv) of absorbed radiation dose, theoretically results in 50 deaths over a lifetime(8) A CT scan of 10mSv thus theoretically results in 1 death in 2000 scans. An EOS scan of 0.290mSv = 1 death in 69000! = Low risk But, our patients have numerous radiographs and scans before and after surgery and the risk for adverse health effects from cancer is proportionel to the amount of radiation dose absorbed!

METHODS First time measurement with micro-dose settings in full spine examination were performed. Effective dose was estimated using mean organ doses and tissue weighting factors. Exposure from micro-dose settings were compared to standard low-dose settings from both our own measurements and previously reported results. Patient dosimetry was made in clinically validated anthropomorphic child phantoms, representing a 15- year-old and a 5-year-old(ATOM® Dosimetry Phantoms-CIRS)(9) Thermoluminiscent detectors TLD (MCN-P from TLD Poland, Krakow, Poland) were placed in pre-set locations within the phantoms (9) 298 TLD-Meassuring points in female 15-year-old 188 TLD-Measurring points in female 5-year-old Each phantom was scanned 20 times consecutively in order to accumulate sufficient dose and to minimize the uncertainties on measurements, a method previously used by Damet et al 2014) (5) Anterior-Posterior-Left-lateral position(APLL) were used.

Scanning the Phantom APLL position Phantom representing a 15-year-old Phantom-imaging with the EOS® scanner

Results: Mean Organ Doses Organs: EOS standard dose,Damet et al 2014. 15-year-old APLL mSv: EOS Micro dose Current study, 5-year-old Tissue weighting factors: Red bone Colon Lungs Stomach Gonads Breasts Bladder Liver Thyroid Skin Others 0.20 0.28 0.27 0.42 0.12 0.34 0.24 0.45 0.38 1.11 Effective dose 0.290mSv 0.032 0.027 0.038 0.060 0.014 0.053 0.020 0.036 0.067 0.021 0.058 Effective dose 0.038mSv 0.023 0.025 0.016 0.035 0.017 0.033 Effective dose 0.027mSv 0.08 0.04 0.01 0.02-0.12 Results:

Comparing Effective doses 15-year-old: CR full spine examination APLL 0.450mSv (100%) (Damet2014) EOS Standard dose APLL 0.290mSv (64%) (Damet2014) EOS Standard dose APLL 0.227mSv (50%) Current study EOS Micro-dose APLL 0.038mSv (8.4%) 5-year-old: EOS Standard dose APLL 0.200mSv (Damet 2014) EOS Micro-dose APLL 0.027mSv Micro-dose full spine examination. An 11 fold reduction compared to CR, and a 6 fold reduction compared to standard dose.

Conclusion Our study has documented a substantial reduction in absorbed organ dose and effective dose in micro-dose settings, compared to standard dose settings and conventional radiology(CR) For the first time anthropomorphic phantoms have been used to evaluate the effective dose, in EOS micro-dose settings. The effective dose was reduced by more than 90% compared to conventional radiology. Previous studies have indicated that image quality in standard dose and micro-dose setting, is comparable to CR (5, 6,10). The study has been in accordance with the pediatric radiation safety principles of ALARA, to keep diagnostic radiation dose as low as possible. Theoretically, reducing potential risk of radiation induced cancer.

References 1. Ronckers, C. M. et al. Cancer mortality among women frequently exposed to radiographic examinations for spinal disorders. Radiat. Res. 174, 83–90 (2010). 2. Doody, M. M. et al. Breast cancer mortality after diagnostic radiography: findings from the U.S. Scoliosis Cohort Study. Spine (Phila. Pa. 1976). 25, 2052–2063 (2000). 3. Inskip, P. D. et al. Radiation dose and breast cancer risk in the childhood cancer survivor study. J. Clin. Oncol. 27, 3901–3907 (2009). 4. Kalifa, G. et al. Evaluation of a new low-dose digital X-ray device: First dosimetric and clinical results in children. Pediatr. Radiol. 28, 557–561 (1998). 5. Damet, J. et al. Occupational and patient exposure as well as image quality for full spine examinations with the EOS imaging system Occupational and patient exposure as well as image quality for full spine examinations with the EOS imaging system. 063901, (2014). 6. Yvert, M. et al. Radiography of scoliosis: Comparative dose levels and image quality between a dynamic flat-panel detector and a slot- scanning device (EOS system). Diagn. Interv. Imaging (2015). doi:10.1016/j.diii.2015.06.018 7. Deschênes, S. et al. Diagnostic imaging of spinal deformities: reducing patients radiation dose with a new slot-scanning X-ray imager. Spine (Phila. Pa. 1976). 35, 989–994 (2010) 8 Strålebeskyttelse-Sundhedsstyrrelsen < https://sundhedsstyrelsen.dk/da/straalebeskyttelse , Danish National Board of health, radiation protection services. 9. Dose, W. B., Dose, O. & Radiation, T. ATOM Dosimetry Phantoms. at <http://www.cirsinc.com> 10. Ilharreborde, B., Ferrero, E., Alison, M., & Mazda, K. (2016). EOS microdose protocol for the radiological follow-up of adolescent idiopathic scoliosis. European Spine Journal, 25(2), 526–531. 11. Luo, T. D., Stans, A. A., Schueler, B. A., & Larson, A. N. (2015). Cumulative radiation exposure with EOS imaging compared with standard spine radiographs. Spine Deformity, 3(2), 144–150. http://doi.org/10.1016/j.jspd.2014.09.049