13.07.2015 Views

Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Atomic-bomb detonation exposures and falloutSurvivorsOffspring of survivors<strong>Medical</strong> exposuresTreatment of tinea capitisX-ray treatment of ankylosing spondylitisPrenatal diagnostic x-rayX-ray therapy <strong>for</strong> enlarged thymus glandsFluoroscopic guided pneumothorax <strong>for</strong> the treatment <strong>for</strong> tuberculosisThorotrast (radioactive contrast material used in angiography, 1925-1945)Treatment of neoplastic diseases (e.g., breast cancer, Wilms' tumor, cancer of the cervix andleukemia)Occupational exposuresRadium dial painters (1920s)Uranium miners and millersNuclear dockyard workersNuclear-materials enrichment and processing workersParticipants in nuclear weapons testsConstruction workersIndustrial photography workersRadioisotope production workersReactor personnelCivil aviation and astronautic personnelPhosphate fertilizer industry workersScientific researchersDiagnostic and therapeutic radiation medical personnelEpidemiologic comparisons of areas with high background radiationcontrol <strong>for</strong> exposure to other known carcinogens, an inadequate period of observationto allow <strong>for</strong> full expression of cancers with long latent periods, the use ofinappropriate control populations, and (in retrospective studies) incomplete orinaccurate health records or the use of questionnaires that relied on people's recollectionsto estimate dosage. Table 25-7 summarizes details of some of the principalepidemiologic investigations on which current dose-response estimates arebased.Risk Estimation ModelsDose-ResponseCurvesWithin the context of the limitations described, scientists have developed doseresponsemodels to predict the risk of cancer in human populations from exposureto low levels of ionizing radiation. <strong>The</strong>se models lead to dose-response curves whoseshape can be characterized as nonthreshold linear, linear-quadratic, and quadratic.Figure 25-15 shows two of these dose-response curves (linear and linear-quadratic).A nonthreshold linear curve is more likely to overestimate the incidence of cancerat lower doses from low-LET radiation and there<strong>for</strong>e is used in radiation protectionguidance <strong>for</strong> estimating the overall cancer risk from occupational and diagnosticexposures. <strong>The</strong> linear-quadratic dose-response model predicts a lower incidence ofcancer than the linear model at low doses and a higher incidence at intermediate

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!