Radiation & Health Risks
Neal M. Boucher, CNMT, CSI(ML) Radiation Safety Officer Dartmouth Hitchcock Medical Center
History of Exposure
Pioneer Radiologists Atomic Bomb Survivors Radium Dial Painters Uranium Miners Medical Irradiation Animal Studies Criticality Accidents Chernobyl
We know more about Radiation & its effects than any other agent
Research tool Medicine Dx & Rx Military weapons Industry precision gauges Irradiator sterilizer Accidents The accumulated knowledge is immense
Uncertainties
Natural Background Other carcinogens, mutagens Genetic predisposition Thresholds Precise dosimetry Clean data Adequate follow up Long time lines Other health issues
The Numbers Game
How much is dangerous? Deterministic/somatic effects Stochastic effects
Radiation Types & Origin
X-rays from atom outer shells
e- transitions
Gamma rays from nuclear decay
Higher E photons
Beta particles wide E range
e- and e+ ejections from nucleus
Alpha particles stripped He+2
Very Energetic MeV short range
Quality Factors
Damage Coefficient Relative Biological Effectiveness Ave weighting factors Rad X QF = Rem Gamma & X rays X 1 Beta X1 Alpha X 20 Neutrons X 20
Radiation Biology
Interaction with matter/tissue Ionization path LET > free radicals Absorption tolerance / Tissue sensitivity Cell damage
No effect Repairable damage, free radicals Dysfunctional proteins, enzymes, hormones Cell death by DNA or cellular function
Radiation Biology
Genetic Effects
Somatic cells precancerous Congenital defects during organogenesis Stem cell disruption
Germ Cells
Cell Death early in Meiosis Genetic defect passed on Expression early, late, next generation Dominant /recessive
Deterministic Effects
LD50/30 (Lethal Dose 50%/30 days) RAD/REM definition WB systemic vs local irradiation Acute vs chronic exposures Minimum detectable response GSD Genetically Significant Dose
Symptoms of acute exposure
Onset within minutes to hours Psychological effect Blood Counts, lymph platelets Gastro-Intestinal Synfdrome 300-500 Rad Neuro-Vascular Syndrome >1000 Rad Central Nervous Sys. shutdown 10,000 Rad Untreated, aplastic anemia, infection 30 days 500 Rad LD 50/30 Dermal effects if localized
Low Level Cancer Induction
Where’s the data? How does it translate to occupational exposures? What are the odds compared to natural background radiation? What impact does Medical exposure have? What about longevity?
Dose Effect Models
The Odds
1 mRem of exposure ^ risk by 1 in 106 Natural Background (NH) 350 mRem 1 Chest film PA & Lat 25 mRem 1 CT Scan 3000 mRem 1 Mammogram 10 mRem Trans-Atlantic flight 35K ft 1 mRem/hr Normal fatal CA incidence 1 in 7
2007 Estimated US Cancer Deaths*
Lung & bronchus Prostate Colon & rectum Pancreas Leukemia Liver & intrahepatic bile duct Esophagus Urinary bladder Non-Hodgkin lymphoma Kidney All other sites
31% 9% 9% 6% 4% 4%
4% 3% 3%
Men 289,550
Women 270,100
3% 24%
Lung & bronchus 15% Breast 10% Colon & rectum 6% Pancreas 6% Ovary 4% Leukemia 3% Non-Hodgkin lymphoma 3% Uterine corpus 2% Brain/ONS 2% Liver & intrahepatic bile duct 23% All other sites
26%
ONS=Other nervous system. Source: American Cancer Society, 2007.
Bone Cancer
Radium Dial Painters c 1920-50 First epidemiological study linking radioactive material to cancer Discovered by high incidence of anemia and bone cancers of the jaw
Leukemia
Most sensitive indicator Only shows up statistically after large doses Other Causes
Benzene, formaldehye Chemo Rx alkylating agents Downs Syn & other genetic disease Human T-cell Virus & Myelodysplastic Dis.
The Case of I-131 Therapy
First radionuclide widely used Long history circa 1940 Activity 30-200 mCi WB dose 15 Rem Thyroid dose 30-40,000 Rads No increase in head & neck Ca’s subsequent to treatments Why?
I-131 fallout
Principal Fission fragment Easily ingested and inhaled Long half life @ 8.02 days Food chain contaminant Children and pregnant women vulnerable to thyroid uptake Stable Iodine can block uptake
Widely debated public health issue
Radiation Hormesis
European spas and natural springs
Uranium, Thorium, Radium, Radon Gas Patent medicines prior to 1920
Immune system stimulation @ 5 Rem
Diagnostic studies
Long Term studies of Survivors
Cancer statistics are less than expected
Fetal Effects of Radiation
Embryonic death Teratogen Mutagen Carcinogen
Fetal Rat Study
400 Rad during gestation LD 50/30
Growth Stunting
150 Rad @ 13 days gestation