Ionizing Radiation in Medical Imaging and Efforts in Dose Optimization

Medical-related radiation is the largest source of controllable radiation exposure to humans and it accounts for more than 95% of radiation exposure from man-made sources. Its direct benefits in modern day medical practices are beyond doubt but risks-benefits ratios need to be constantly monitored as the use of ionizing radiation is increasing rapidly. From 1980 to 2006, the per-capita effective dose from diagnostic and interventional medical procedures in the United States increased almost six fold, from 0.5 to 3.0mSv, while contributions from other sources remained static (NCRP report no 160, 2009). This chapter will review radiation exposure from medical imaging initially starting from a historical viewpoint as well as discussing innovative technologies on the horizon. The challenges for the medical community in addressing the increasing trend of radiation usage will be discussed as well as the latest research in dose justification and optimization.link_to_OA_fulltex

Cone Beam Computed Tomography and Impacted Maxillary Canines : Dose, Optimisation, and Justification

Retinerte hjørnetenner i overkjeven som er sperret av andre tenner for å vokse ut, er den vanligste grunnen til bruk av Cone Beam Computed Tomography (CBCT) hos barn og unge. Hvis diagnostisering av de retinerte hjørnetenner mangler eller kommer sent, kan rotresorpsjon forekomme på de permanente nabo tennene. Resorpsjonene kan senere føre til behov for kjeveortopedisk behandling, kirurgiske ekstraksjoner og i noen tilfeller implantat eller andre proteseløsninger. Retinerte hjørnetenner oppdages vanligvis hos barn ved klinisk undersøkelse i kombinasjon med intraorale og panorama røntgenbilder. Når mer informasjon er nødvendig for diagnostikk og planlegging, er CBCT-undersøkelse berettiget. På grunn av råd om strålevern er det enighet om at CBCT ikke bør brukes ved førstehånds undersøkelse, men det er fortsatt ingen konsensus om hvorvidt CBCT påvirker terapiplanlegging blant klinikere. Den ideelle radiografiske modaliteten og eksponering varierer, avhengig av den klinisk situasjonen. Når ioniserende stråling benyttes for å undersøke pasienter, må man være oppmerksom på balansen mellom fordelene for pasienten og klinikeren og risikoen ved stråling. Denne doktorgradsavhandlingen hadde som mål å vurdere belastningen ved strålingsdose for barn der retinerte hjørnetenner ble undersøkt. Avhandlingen ser også på metoder for å begrense doseeksponering ved å bruke protokoller for å optimaliserte en lav dose og begrense CBCT-undersøkelsene. Første artikkel i avhandlingen hadde som mål å se effektiv dose ved å sammenligne todimensjonale (2D) undersøkelser (panorama og periapikale røntgenbilder) og tredimensjonale (3D) CBCT. Dosen fra 2D-undersøkelse og CBC fra to enheter (Promax3D og NewTom 5G) ble sammenlignet etter måling av doser på et antropomorft barnefantom. Dosen fra CBCT-undersøkelsen var fra 15 til 140 ganger høyere enn for de konvensjonelle 2D-undersøkelsene, avhengig av CBCT-enhet og type 2D-undersøkelse. Andre artikkel evaluerte bildekvalitet og synlighet av anatomiske strukturer på lavdose CBCT-skanning og effekten av et støyreduksjonsfilter for vurdering av overkjevens front. Flere CBCT-protokoller (Promax3D), blant annet fire lavdoseprotokoller, ble testet på skallefantomer for å sammenligne bildekvalitet og synlighet av anatomiske strukturer som er relevante for vurdering av retinerte hjørnetenner. Tre av lavdoseprotokollene gav akseptabel diagnostisk bildekvalitet, selv om dosen ble redusert med 61 % – 77 %. I tredje artikkel ble det undersøkt hvordan CBCT påvirker behandlingsplanen til pasienter med retinerte hjørnetenner, samt mulige kliniske og 2D-bilde markører for planlagt CBCT-bruk. For å avgjøre om CBCT var berettiget for planlegging av behandling, evaluerte og planlagt en tverrfaglig gruppe 89 kasus med retinerte hjørnetenner. Mer enn halvparten av CBCT-undersøkelsene ble vurdert som uberettiget. Planlagt behandling ble endret i 9,8 % av tilfellene. Variable målt før CBCT som predikerte behovet for ytterligere CBCT, var horisontalt plasserte hjørnetenner, strategi for ekstraksjon på permanente tenner, og bukkalt posisjonerte hjørnetenner. Denne avhandlingen viser at, CBCT medfør høyere effektiv dose for pasienter sammenlignet med konvensjonell 2D røntgenbilder. Dosene pasienter får ved undersøkelse av retinerte hjørnetenner kan minimeres ved å 1) optimalisere protokoller for lavdose CBCT og 2) begrense bruk av CBCT til tilfeller der ytterligere 3D-informasjon er viktig for videre terapeutisk behandling.Impacted maxillary canines are the most common reason for Cone Beam Computed Tomography (CBCT) examinations of the anterior maxilla in children and adolescents today. If impacted canines are missed or diagnosed late, root resorptions may occur on permanent adjacent incisors. In turn, these resorptions may lead to the need for further orthodontic treatment, surgical extractions, and even implants or other prosthetic solutions. Impacted canines are usually discovered in children via clinical examinations in combination with intraoral periapical radiographs and panoramic images. When more diagnostic information is needed, the next step is a CBCT examination. While regulating authorities in radiation protection agree that CBCT should not be used first-hand, there is still no consensus over whether CBCT alters therapy planning amongst clinicians. The ideal radiographic modality and exposure parameters vary, depending on each individual clinical task. When using ionizing radiation to examine patients, attention must be paid to the balance between the benefit to the patient and clinician contra the radiation risk. This thesis aimed to assess the radiation dose burden to children examined for impacted canines and explore methods of limiting dose exposure by applying optimised low-dose protocols and by limiting CBCT examinations through a justification process performed at the therapeutic thinking level. The first paper aimed to measure the effective dose using two-dimensional (2D) examinations (panoramic and periapical radiographs) and three-dimensional (3D) CBCT devices. 2D examination doses and CBCT doses from two devices (Promax3D and NewTom 5G) were compared after measuring organ doses on an anthropomorphic child phantom. The dose from CBCT examinations ranged from 15 to 140 times higher than conventional 2D examinations, depending on the CBCT unit and the type of 2D examination. The second paper evaluated overall image quality and visibility of anatomic structures on low-dose CBCT scans and the effect of a noise reduction filter for assessment of the anterior maxilla. Multiple CBCT protocols (Promax3D), including four low-dose protocols, were tested on dry skull phantoms to compare overall image quality and visibility of anatomic structures pertinent to impacted canine assessment. Of the low-dose protocols, three provided acceptable diagnostic image quality while reducing the dose by 61% – 77%. The third paper investigated how CBCT affects the treatment plan of patients with impacted canines, as well as identified possible clinical and 2D imaging markers for the justified CBCT examination at the therapeutic thinking level. To decide whether CBCT was justified for therapy planning, an interdisciplinary therapy-planning group evaluated impacted canine cases and decided treatment alternatives, first without and later in addition to diagnostic information from CBCT examinations. More than half of the CBCT examinations were considered unjustified, and the therapy plan changed in 9.8% of the cases. Variables measured prior to CBCT that predict the need for further CBCT examinations were horizontally positioned canines (OR= 10.9, p = 0.013 when compared to vertically positioned canines), when extraction strategy was involved (OR = 6.7, p = 0.006), and buccally positioned canines when compared to palatal (OR = 5.3, p = 0.047), central (OR = 25.0, p = 0.001), and distal or uncertain positions (OR =7.7, p = 0.005). Even when optimised, CBCT examinations come at the cost of a higher radiation dose than conventional 2D images. Based on the papers comprising this thesis, patient dose burdens can be minimized when assessing impacted maxillary canines in radiosensitive paediatric patient populations by 1) optimising low-dose CBCT protocols and 2) limiting CBCT exposures to cases where additional 3D information is important for therapeutic thinking and planning.Doktorgradsavhandlin

Design of an Implant for First Metatarsophalangeal Joint Hemiarthroplasty

Osteoarthritis (OA) is the most common form of arthritis and it affects 27 million US adults. OA disease involves all of the tissues of the diarthrodial joint and ultimately, may lead to softening, ulceration, loss of articular cartilage, sclerosis and polished appearance of the subchondral bone, osteophytes, and subchondral cysts. The first metatarsophalangeal joint (MTPJ1) is affected in up to 42 cases of OA. Besides osteoarthritis, other conditions such as rheumatoid arthritis and gout also affect the MTPJ1. Involvement of MTPJ1 with these conditions invariably leads to deformed toe such as hallux valgus and hallux rigidus. Over 150 surgical techniques exist for treatment of hallux deformity, which includes cheilectomy, arthrodesis, osteotomy, resection arthroplasty, and replacement of part or the entire articular surface with an implant. A hemi-implant, which partially replaces the 1st metatarsal head with minimal bone resection and without altering the sesamoid articulation has shown promising results and gives superior postoperative range of motion and pain reductions. But the geometry of such implants has not been explained in any literature and there are no details of the data used for designing such implants. An anatomically based approach to design the geometry of an MTPJ1 implant is needed in order to best fit the articulating surface of the adjacent phalanx. In the current study, a method was developed for designing a hemiarthroplasty implant for MTPJ1 based upon the morphology of metatarsal. Ninety-seven metatarsal osteological specimens were scanned using a laser scanner to obtain 3D surface data. After aligning the surface data, the articular surface of each metatarsal head (MTH1) superior to the inter-condylar ridge were characterized by a section of an ellipsoid using non-linear unconstrained optimization (NLUO) and the section of the ellipsoid forms the surface of the implant. The implants based upon osteological specimens had a very good fit to metatarsal articulating surface with root mean

Improving Dose-Response Correlations for Locally Advanced NSCLC Patients Treated with IMRT or PSPT

The standard of care for locally advanced non-small cell lung cancer (NSCLC) is concurrent chemo-radiotherapy. Despite recent advancements in radiation delivery methods, the median survival time of NSCLC patients remains below 28 months. Higher tumor dose has been found to increase survival but also a higher rate of radiation pneumonitis (RP) that affects breathing capability. In fear of such toxicity, less-aggressive treatment plans are often clinically preferred, leading to metastasis and recurrence. Therefore, accurate RP prediction is crucial to ensure tumor coverage to improve treatment outcome. Current models have associated RP with increased dose but with limited accuracy as they lack spatial correlation between accurate dose representation and quantitative RP representation. These models represent lung tissue damage with radiation dose distribution planned pre-treatment, which assumes a fixed patient geometry and inevitably renders imprecise dose delivery due to intra-fractional breathing motion and inter-fractional anatomy response. Additionally, current models employ whole-lung dose metrics as the contributing factor to RP as a qualitative, binary outcome but these global dose metrics discard microscopic, voxel-(3D pixel)-level information and prevent spatial correlations with quantitative RP representation. To tackle these limitations, we developed advanced deformable image registration (DIR) techniques that registered corresponding anatomical voxels between images for tracking and accumulating dose throughout treatment. DIR also enabled voxel-level dose-response correlation when CT image density change (IDC) was used to quantify RP. We hypothesized that more accurate estimates of biologically effective dose distributions actually delivered, achieved through (a) dose accumulation using deformable registration of weekly 4DCT images acquired over the course or radiotherapy and (b) the incorporation of variable relative biological effectiveness (RBE), would lead to statistically and clinically significant improvement in the correlation of RP with biologically effective dose distributions. Our work resulted in a robust intra-4DCT and inter-4DCT DIR workflow, with the accuracy meeting AAPM TG-132 recommendations for clinical implementation of DIR. The automated DIR workflow allowed us to develop a fully automated 4DCT-based dose accumulation pipeline in RayStation (RaySearch Laboratories, Stockholm, Sweden). With a sample of 67 IMRT patients, our results showed that the accumulated dose was statistically different than the planned dose across the entire cohort with an average MLD increase of ~1 Gy and clinically different for individual patients where 16% resulted in difference in the score of the normal tissue complication probability (NTCP) using an established, clinically used model, which could qualify the patients for treatment planning re-evaluation. Lastly, we associated dose difference with accuracy difference by establishing and comparing voxel-level dose-IDC correlations and concluded that the accumulated dose better described the localized damage, thereby a closer representation of the delivered dose. Using the same dose-response correlation strategy, we plotted the dose-IDC relationships for both photon patients (N = 51) and proton patients (N = 67), we measured the variable proton RBE values to be 3.07–1.27 from 9–52 Gy proton voxels. With the measured RBE values, we fitted an established variable proton RBE model with pseudo-R2 of 0.98. Therefore, our results led to statistically and clinically significant improvement in the correlation of RP with accumulated and biologically effective dose distributions and demonstrated the potential of incorporating the effect of anatomical change and biological damage in RP prediction models

Design of an Implant for First Metatarsophalangeal Joint Hemiarthroplasty

Osteoarthritis (OA) is the most common form of arthritis and it affects 27 million US adults. OA disease involves all of the tissues of the diarthrodial joint and ultimately, may lead to softening, ulceration, loss of articular cartilage, sclerosis and polished appearance of the subchondral bone, osteophytes, and subchondral cysts. The first metatarsophalangeal joint (MTPJ1) is affected in up to 42 cases of OA. Besides osteoarthritis, other conditions such as rheumatoid arthritis and gout also affect the MTPJ1. Involvement of MTPJ1 with these conditions invariably leads to deformed toe such as hallux valgus and hallux rigidus. Over 150 surgical techniques exist for treatment of hallux deformity, which includes cheilectomy, arthrodesis, osteotomy, resection arthroplasty, and replacement of part or the entire articular surface with an implant. A hemi-implant, which partially replaces the 1st metatarsal head with minimal bone resection and without altering the sesamoid articulation has shown promising results and gives superior postoperative range of motion and pain reductions. But the geometry of such implants has not been explained in any literature and there are no details of the data used for designing such implants. An anatomically based approach to design the geometry of an MTPJ1 implant is needed in order to best fit the articulating surface of the adjacent phalanx. In the current study, a method was developed for designing a hemiarthroplasty implant for MTPJ1 based upon the morphology of metatarsal. Ninety-seven metatarsal osteological specimens were scanned using a laser scanner to obtain 3D surface data. After aligning the surface data, the articular surface of each metatarsal head (MTH1) superior to the inter-condylar ridge were characterized by a section of an ellipsoid using non-linear unconstrained optimization (NLUO) and the section of the ellipsoid forms the surface of the implant. The implants based upon osteological specimens had a very good fit to metatarsal articulating surface with root mean

CT Scanning

Since its introduction in 1972, X-ray computed tomography (CT) has evolved into an essential diagnostic imaging tool for a continually increasing variety of clinical applications. The goal of this book was not simply to summarize currently available CT imaging techniques but also to provide clinical perspectives, advances in hybrid technologies, new applications other than medicine and an outlook on future developments. Major experts in this growing field contributed to this book, which is geared to radiologists, orthopedic surgeons, engineers, and clinical and basic researchers. We believe that CT scanning is an effective and essential tools in treatment planning, basic understanding of physiology, and and tackling the ever-increasing challenge of diagnosis in our society

Artificial Intelligence in Oral Health

This Special Issue is intended to lay the foundation of AI applications focusing on oral health, including general dentistry, periodontology, implantology, oral surgery, oral radiology, orthodontics, and prosthodontics, among others