|Abstract / Summary|
Radiographic imaging is the second most significant cause of ionizing radiation. The use of medically induced ionizing radiation, especially Computed Tomography (CT) has been on the rise for the past many decades. The Atom bomb survivor studies have shown that the risk of adverse health effects such as radiation induced cancer is proportional to the amount of radiation dose absorbed to the human body. Studies from historic cohorts of scoliosis patients undergoing repeat x-ray imaging show an increased risk of cancer compared to the background population. Especially breast cancer has been of concern. Children and young adults are believed to be more sensitive to the adverse effects of ionizing radiation.
When first diagnosed with scoliosis, patients are primarily children or young adults. Primary assessments of scoliosis, followed by monitoring of curve progression as well as intraoperative imaging result in repeated radiographic imaging. The consequence is potential high levels of cumulative dose absorption, and subsequent potential risk of increased adverse effects from ionizing radiation. To this day, there is no known lower dose limit to which amount of radiation that could potentially be harmful and lead to detrimental changes within the body and development of malignant disease. Thus, keeping radiation exposure to our patients as low as possible while still providing adequate imaging is of great importance.
Dose optimization is an issue of great concern and much effort has gone into revising dose-protocols, optimizing/modernizing x-ray equipment as well as developing new techniques. To address the issue of dose optimization, the low-dose EOS scanner was taken into use at our institution in the fall of 2014. This particular scanner has been shown to markedly reduce radiation dose compared with standard x-ray modalities, while at the same time providing images of high quality.
The aims of the studies in this PhD thesis was to investigate this new EOS scanner both with regard to radiation dose exposure and to investigate ways of optimizing low-dose protocols even further. Another aim was making an overall view of total dose accumulation in patients treated for idiopathic scoliosis at our institution including conventional x-rays, EOS scans, intraoperative imaging and ancillary CT scans and compare these findings with literature. Finally, to investigate and develop a method to reduce time spent on precise organ dosimetry with thermoluminescent dosimeters (TLDs).
Five studies were conducted, three of these published in international peer reviewed journals. Study I was the first study to report and publish results on organ doses and effective dose for the new EOS micro-dose protocol. Claims by manufacturer of level of dose exposure was confirmed. Findings on regular standard-dose were comparable to previous reports.
Studies II and III investigated, and found a way of establishing new reduced dose full-spine protocols. This was achieved by semi-quantitative phantom image analysis, resulting in two clinically validated reduced dose protocols; in study II a protocol for 3D reconstruction of the spine, and in study III a protocol allowing repeatable 2D Cobb angle measurements.
In study IV a first report was made on total radiation dose from CR, EOS, O-arm and ancillary CT during the course of current scoliosis treatment at our institution. A survey forwarded to nine international spine centers asking for information on current routines regarding scoliosis treatment and radiographic follow-up was used for comparison with own institution. The survey showed varying degrees of inter center agreement and no strict adherence to current consensus guidelines.
Study V investigated a way of possibly determining a reduced number of dosimeters to be used for organ dosimetry without compromising validity of results. The study was based on phantom liver organ dosimetry after exposure in the EOS. By statistical and practical analysis, it was found that reliable mean organ dose measurements could be performed using less than 25% of available dosimeter allocations.
The aims of the studies were met. Reliability of measurements were confirmed within studies and when compared with literature. Two new dose-optimized reduced-dose protocols are ready for clinical application. By evaluating the total amount of accumulated radiation dose during treatment of scoliosis a measure to evaluate potential risk of radiation induced cancer is at hand. A tool was presented proposing a way of reducing time spent on organ dosimetry without compromising certainty of dose measurements. Currently a strategy of how to implement one or both reduced-dose protocols is being worked out at our institution. The tools and methods presented in the thesis and those published in international journals are at hand for other institutions and for future research.