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ENTRANCE SKIN DOSE & PERCENTAGE DEPTH DOSE

Physics

ENTRANCE SKIN DOSE & PERCENTAGE DEPTH DOSE

1. HVL of human tissue is 3cm.

2. At 6cm, the radiation would have reduced to 25% of skin dose (2 HVLs).

3. Hence, assume PDD of 25% (2 HVL = 25%).

4. There will be a Back Scatter Fraction (BSF) of 30% Hence absorbed dose (at 6cm of human tissue) = 0.25 * ESD.

5. The Back Scatter Factor/Fraction is the factor by which dose is increased by radiation scattered back from the body.

6. ESD can be calculated from Dose Area Product (DAP) or measured directly using TLD or gafchromic film.


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REFERENCES

1. Bushberg, J. T. (2012). The essential physics of medical imaging. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins. Find it at Amazon
2. Heggie, J. C., Liddell, N. A., & Maher, K. P. (1997). Applied imaging technology. Melbourne: St. Vincents Hospital.

Ⓒ A. Manickam 2018

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