Radiation in Radiology Department & The Truth

Though X-rays were discovered in 1895, it was not until 1928 when the first international commission on radiation protection was formed , that adverse effects of Radiation were widely appreciated or discussed.  Here we are presenting commentary on effects of radiation by Dr MGK Murthy, Dr Sumer Sethi

-----------------------

The exact    relationship between radiation induced cancer and diagnostic radiation is not understood even today.

The subject of exact  doses/ relationship with cancer if any is highly complex and not understood and these serve only as guidelines .

Every adult, if survives long enough, is at high risk for cancer (40% of population is at risk of getting cancer at any point in life) (Males>Females) (1in 2 males Vs 1 in 3 females) 

However the present scientific data can be  divided as follows

(A) Data that is Fearful/ Apprehensive/ of concern

1. WHO classifies Ionizing Radiation as Weakly carcinogenic.

2. USA had  performed appx 3 ,000,000 CT examinations in 1980 Vs 60,000,000 in 2005

and Nuclear medicine scans 7,000,000 in 1980 Vs 20,000,000 examinations in 2005

3.Current Total Annual radiation dose from estimated Medical exposure in USA, is roughly equal to Total worldwide collective dose  generated by chernobyl disaster

4. A survey  report released in 2004, indicated appx  1% of cancers in  USA could be  on account of  medical exposure 

(B) Data that is not so fearful/ reassuring/ confidence giver

1.Radiation induced cancers typically occur 1or 2 decades  or longer after  medical exposure 

2.Radiation is  a weak carcinogen and hence difficult to isolate radiation induced cancers from the combined carcinogens effects,, however some estimate, it may be 1 per1000 medical exposures , if exposure is  of >10mSV effective dose 

3. Most studies  Reiterate "BENEFITS OUTWEIGH RISKS"  in Medical exposures

4.Since a prospective study is not feasible for obvious reasons, the studies usually extrapolate  data from  Nuclear disasters of the world , which are not  similar .

5. The largest study pertains to Atomic bomb survivors of Japan, which concluded  that doses in excess of 50mSV , do produce significantly increased  cancers. They are not  sure , if  doses below this , do produce cancer .  Diagnostic radiation in most studies including CTs /Nuclear Medicine  give exposures in the range of 10-25mSV 

6. Determining the "DOSE" received in a study itself is highly complex and variable  as it depends on various factors 

Ideal dose == X-rays exposure  Vs Absorption by each organ . 

Various terminologies used are 

Radiation quantity                          Unit                          Determining  measurement 

Exposure                                        Roentgen                               Measurement 

Dose                                                    Gy                                Multiply exposure by  f- factor 

Equivalent dose                                   Sv                                    -do-                   by quality factor 

Effective dose                                      Sv                                    -do-      by Tisue weight age factor 

Sensitive patients are children/ Pregnant women

Sensitive  regions  are Fetus/ Thyroid/ Breast/ Gonads/ Bone Marrow/ GI Tract/ Eye 

7. Exact mechanism that produces radiation damage is not understood , and may related to DNA breakage, chromosomal aberrations/ gene mutations  etc

In  diagnostic radiation exposure, DNA repairs itself between the exposure, if sufficient time elapses (Origin of  Cumulative dose more important) 

8.We receive   Natural background  radiation in every day life and it comes from Home (Radon 2 mSV every year in US ), Natural cosmic radiation (in US considered as average 3 mSV per year) and a  round flight from coast-coast in USA gives additional cosmic radiation of 0.03 mSV 

9.  The subject of exact  doses/ relationship with cancer if any is highly complex and not understood and these serve only as guidelines . Every adult, if survives long enough, is at high risk for cancer (40% of population is at risk of getting cancer at any point in life) (Males>Females) (1in 2 males Vs 1 in 3 females) 

Test                              Adult appx dose  (mSV)                          comparable background duration

X-rays

Xray Chest                            0.1                                                          10 days 

Xray extremity                      0.001                                                        3 hours 

Intra oral film                          0.005                                                       1 day    

Xray Spine                             1.5                                                            6 months 

BMD (DEXA)                          0.001                                                        3 hours 

Mammography                        0.4                                                            7 weeks 

IVU                                          3.0                                                             1 year 

CT 

CT head                                    2.0                                                             8 months 

CT Chest                                   7.0                                                              2 years 

CT Abdomen and pelvis             10.0                                                            3 years

Cardiac CT calcium scoring         3.0                                                             1 year

Cardiac CT coronary angio          12                                                              4 years 

CT PET                                       25                                                                 8 years 

Conclusion based on  the available present data , seems to suggest : 

Diagnostic radiation need not be feared  , if an  indication exists . Screening studies if  spaced adequately  are extremely beneficial , as they play major role in reducing morbidity/ mortality from the  suspecting disease.  Appropriateness criterion   for each test , as developed by ACR, is less useful in third world countries like India ,   in view of the cost considerations and major health expenditure coming from out of pocket resources