Radiation Dose Concerns

By Dr Sumer Sethi, MD, Dr MGK Murthy
Teleradiology Providers
www.teleradproviders.com

Radiation  Dose  Concern

Can we know how much radiation is falling on patient?
…… YES…. No definite readable meter on the machine

We can estimate…..

• mGy=0.239 by (Kvp)2 by mAs /(TSD)2by P by T

• TSD=target to skin dist, P=1 for 3 phase X ray
T= total filtration in mm of Al

•   At 72 Kvp and 10 mAs it amounts to =0.1235 mGy


Very difficult  to decipher this

Internatinal Council of Radiation Protection(ICRP) recommends
Effective dose i.e.. Weighed sum of organ dose multiplied by weighing factor for that organ
eg: if gonads receive 10 mrem and their weighing factor is 0.2  effective dose would be 2.


A very practical way used presently is talk about the whole diagnostic  radiation in terms of Chest Xrays

Why?
Probably because  it is least exposure  and most used


Av CXR=foot=ankle=head=arm=ankle=0.05 msv

American Scenario
The chest Xray involved in the routine protocol gives radiation dose same as 23 days of environmental background radiation received in village charlottesville(0.02mSV)(Rare Earth screens)  In India 0.05 mSV(Ca Tungstate  screens)

The precise risk from this not known but is thought to be small.


CTChest
Radiation dose is equal to 1000 days of environmental background radiation in the same place in USA.(8 mSV)

Special situations


• Chest CT in female= 10 to 15 ( 2 view)mammography
• Chest CT=400 Chest Xrays
• HRCT Chest==600 Chest X Rays
• CT virtual Bronchoscopy==3 to 5 times CT Chest
• CT angiography/FNAC=   DO


IRONY
• We have reduced the absolute dose from all examinations due to improved technology and protective measures

• However due to relative ease of performing and, speed and accuracy  and with modern helical CT scanners temptation to obtain head to pelvic or even head to toe examinations is  leading to increased community radiation dose.

• Av radiation to Radiologist in India is 1 mSV/year
• A single CT procedure gives patient dose equivalent  to 5-25 years of  work in radiology department
UK
• Nation wide study by NRPB , wall and hart etl found 30% reduction in patient dose for common rad  procedures compared to 10 years ago ,but 35% increase in abdominal and pelvic CT examinations!!!!!

Reason
• Volume scanning,thin slices,overlap sections,liberal inclusion of wider regions of body,demand for short scan time,demand for high resolution,better quality with high exp factors,frequent repeat studies
• Superficial organs such as breast,eyes, thyroid and testes get higher dose even though they are not the aim of investigation in majority situations
• Delivery of 10 mGy of radiation to a womans breast before 35 years increases  the risk of breast cancer by 13.6% over gen population
• Hoffman found 1036 cases of  on 26 yrs follow up  whole spine radiography in adolescent group(dose) 130 mGy  led to  11 cancers breast   VS   general  population should have been 6

What to Do?
Radiologist
• All techniques for low dose,protection for unexposed parts

Physician
• Clinical justification for a study