Olowookere, C.J. Dept of Physics Ajayi Crowther University, Oyo

Olowookere, C.J. Dept of Physics Ajayi Crowther University, Oyo

RADIATION AND DIAGNOSTIC IMAGING

APPLICATIONS diagnosis (clinical) treatment industrial use preservation of food & crops generation of energy etc. RADIATION EFFECTS lesions Instant death (lethal dose) promotes cancer severe skin injury mutation of genes Leukemia ageing process eye cataract

Particle Radiation E- M Radiation Alpha Particle: Beta particle highly massive, has intense ionization Short range in air deadly if ingested Radiowaves Infra red NON- IONIZING Visible spectrum Ultraviolet X-rays Gamma rays IONIZING Cosmic rays

NATURAL SOURCES SOIL---U-238, Th-232, K-40, Rn-222 ROCKS WATER SPACE MAN-MADE SOURCES X-ray Tubes Accelerators Nuclear Reactors Weapon Testing (Cs) Cathode Ray Tubes

Involves the use of X-rays to examine the structural abnormalities in the body. It has greatly assisted in easy detection and treatment of some diseases and abnormalities It is used in chest imaging, Barium Enema, Barium meal, Barium swallow, HSG, CT (Sinuses) However, diagnostic imaging is the greatest contributor to the man-made ionizing radiation to which the public is exposed (Sonawane, 2009)

In relation to the healthcare from worldwide average, about 80% of the dose to the population is caused by medical diagnostic examinations (Bennet, 1991). ICRP recommended that all medical exposures should be subjected to the radiation safety principles of justification, optimization & dose constraint (ICRP, 1990). Principle of justification benefits > risks Principle of optimization- dose administered should be as low as reasonably achievable (ALARA Principle).

ICRP also requires that radiation dose be measured in every hospital to ascertain the level of exposure especially in pediatric patients. Measurement of children dose is important because of the radiosensitive nature of children. risk of detrimental radiation effects are higher for pediatric than for adult (NRPB, 1993)

it helps to optimize dose to children (Montgomery, 2000). In Nigeria several thousands of children diagnostic imaging are carried out annually with little or no dose records. Objectives of the Study to determine organ dose received by children during routine diagnostic imaging, and to estimate the number of cancer incidence and mortality arising from chest diagnostic imaging in Nigeria.

Twelve purposely selected radiodiagnostic centers consisting of 15 units in five states(lagos, Ogun, Oyo, Osun & Ekiti) of SW are included in the study. A total of 689 consented patients were examined during the study for different projections chest PA, abdomen AP, skull AP etc.

Entrance Surface Dose ESD Organ Dose (OD) Organ Dose Calibrated Thermoluminescent Dosimeter Chips(LiF Crystal DoseCal Software (Kyriou et al. 1996) Lifetime attributable Risk (LAR) -- eqns (1) Attributable Risk Fractioneqn (2)

,,.,,,,,,, (1) =dose dose rate effectiveness factor =2,,, = healthy survivor function for solid cancer,,,, =Excess Absolute Risk,,,,,,,,,,,,, 100% (2),,, =Lifetime background risk (ICRP, 2007a)

Mean dose of male and female patients with mean age of 7 yrs and 5 yrs respectively, were used for the computation of LAR and ARF (incidence and mortality). For chest PA examination, organs of interest are: Lung, Liver, Esophagus, Breast and Stomach The calculated LAR (inc & mort) were extrapolated to the population of children in SW and Nigeria based on the report CIA world factbook (2013) :

According to the report 43.8 % of Nigeria population are children Total Population Population of SW=32.4 million. Population of Nigeria 174.5 million Children Population Population of children between (0-14) in SW is 14.19 million. Population of children between (0-14) in Nigeria is 76.4 million

Table 1: Organ dose and equivalent LAR for SW and Nigeria (5 yr-male) Organ Organ dose (mgy) LARin/ LARin 10 4 SW LARin NIG LARmor/ LARmort 10 4 SW LARmort NIG Percentage of mortality (%) Lung 0.87 0.00697 97.5 532.70 0.0658 92.02 502.90 94.4 Breast 0.21 - - - - - - - Esophagus 0.32 0.00790 11.05 60.38 0.00585 8.18 44.72 74.0 Stomach 0.17 0.0238 33.28 181.91 0.0123 17.20 94.04 51.70 Liver 0.34 0.0296 41.39 226.24 0.0259 36.22 197.96 87.5 All Solid 0.91 2.096 2931.25 16020.50 1.109 1550.9 8476.5 52.9

Table 1: Organ dose and equivalent LAR for SW and Nigeria (7 yr-female female) Organ Organ dose (mgy) LARin/ LARin 10 4 SW LARin NIG LARmor/ LARmort 10 4 SW LARmort NIG Percentage of mortality (%) Lung 0.47 0.0725 101.39 554.15 0.0712 99.57 541.21 97.66 Breast 0.12 0.0638 89.22 487.65 0.0289 40.42 220.89 45.30 Esophagus 0.16 0.00232 3.25 17.73 0.00230 3.22 17.58 99.15 Stomach 0.017 0.0148 20.69 113.12 0.0102 14.27 77.96 68.92 Liver 0.15 0.00600 8.31 45.86 0.00550 7.69 42.04 91.67 All Solid 0.92 1.559 2180.26 11916.04 0.7042 984.82 5382.47 45.17

Tables 1 and 2 show that the estimated risk of lung cancer is higher in female than male even at a relatively lower dose by a factor of 1.08. Table 2 indicates that chest diagnostic imaging such as this might lead to about 488 breast cancer cases in Nigeria. During chest imaging, male pediatric patients are more prone to lung, stomach and liver cancers. Female pediatric patients are more susceptible to lung, breast and stomach cancer. Percentage of mortality were recorded in lung cancer, esophagus and liver cancer in male. In female patient, higher percentage of mortality were obtained in lung cancer (97.7%), esophagus cancer (99.15) and liver cancer (91.7). This is in agreement with the work of Habron et al. 2016.

Higher mortality rate in female could be attributed to the physiological constitution of females. This trend calls for proper collimation, shielding of organ of little interest during diagnostic examinations. Dose optimization should be adopted in Nigeria. Presently, the preoccupation of Radiographers, Radiologist and physician is image quality at the expense of patient dose.

Lung shuttering could be used to reduce lung dose (Habron et al., 2016). Adequate filtration (min of 2.5mmm Al) should be used to prevent undesirable dose to patient. Female patient breast should be tilted during examination to avoid x-ray primary beam. Alternative diagnostic imaging procedures using non-ionizing radiation could be used instead of ionizing radiation. Retraining of Imaging Scientist could be carried out to ensure better performance.

ARF (%) per year 0.012 0.01 0.008 0.006 0.004 0.002 0 0 20 40 60 80 Attained age Attributable Risk Fraction of Lung Cancer incidence following a single exposure of 7 year old male with a mean organ dose of 0.87 mgy ARF(% ) p e r y e a r 0.025 0.020 0.015 0.010 0.005 0.000 0 20 40 60 80 Attained age Figure : Attributable risk fraction for incidence of lung cancer following a single exposure of a 5-year old girl with a dose of 0.47 mgy from a conventional chest radiography Figure 1a: ARF vs Attained age for 7 yr-old male (Lung) Figure 1b:ARF vs Attained age for 5yr-old female (Lung)

0.008 ARF (%) per year 0.007 0.006 0.005 0.004 0.003 0.002 0.001 0 0 20 40 60 80 Attained age Attributable Risk Fraction of Easophagus cancer incidence following an exposure of 7-year old male with organ dose of 0.32 mgy from a conventional Chest X-rays A R F (% ) p e r y e a r 0.0025 0.0020 0.0015 0.0010 0 20 40 60 80 Attained age Figure : Attributable risk fraction for incidence of Easophagus cancer following a single exposure of a 5-year old girl with a dose of 0.16 mgy from a conventional chest radiography. Figure 2a:ARF vs Attained age for 7 yr-old male (Esoph.) Figure 2b: ARF vs Attained age for 5yr-old female (Esoph.)

Figures 1a & b show that the graph of ARF vs Attained age for lung cancer in both male and female have the same pattern. The ARFs in each case, increases gradually from exposed ages(7yrs and 5 yrs respectively) until it peaked at attained age of 40 yrs before it falls gradually.

In Figures 2a the value of ARF Vs Attained age for male decreases gradually until the age of 75. Meanwhile, the values ARF Vs Attained age for female increases rapidly between the age range of 20-60 yrs (peaked at 60 yrs) before it finally falls. Between the age of 20 and 60 yrs, the lifetime attributable risk fraction of esophagus is higher in female than male

The incidence and mortality of lung cancer arising from radiation exposure is higher in female than in male in spite of female lower organ dose. Male ped patients are likely to have more incidence of Lung, liver and stomach cancers. Female ped. patients are more susceptible to lung, breast and stomach cancers, and higher mortality rate were found in lung, esophagus and liver cancer.

This trend calls for dose optimization in Nigeria. Regular training of imaging personnel on the modern way of reducing patient dose is essential, and factors that lead to higher doses. This study provides information on the incidence of cancer and mortality resulting from diagnostic imaging. This study will help Physicians, Radiologist and Radiographers in decision making before carrying out diagnostic examinations. It will also assist them in communicating risk to the patients and their family members.

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