clinical reference dosimetry
Post on 24-May-2015
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- Vibha Chaswal (07-15-2008 – 09/11/2008)
The resident should gain an understanding of the accuracy and precision of each radiation measurement system, as well as its appropriate application.
Commissioning of Dose Measurement Systems Ion Chambers / Electrometers Film Metal Oxide Semiconductor Field Effect Transistor (MOSFET)
Commissioning of 3D Water Tank Ion chamber Dosimetry System Effects
Leakage Stem Effect Signal-to-noise for different chamber volumes Variation with bias level and polarity at different dose rates Variation with changes in water temperature
Perform dose profile measurements with each detector and compare results. Manual Film Densitometry
H&D curve creation (10x10 field size, 6VM x-rays) depths of 1.5 cm and 10 cm in solid water, EDR2 film and XV
Know dosimetric systems Have a feel for numbers you see in any
dosimetric calculations routinely in the clinic Learn to design experiments to understand
concepts Assign applications to dosimeters – which one
for which
Ion Chambers Electrometers MOSFET Diodes Films Water tank (?)
Linearity Stem effect Polarity effect Angular dependence Collection Efficiency Signal to Noise ratio b/w three ion chambers nC/cc/cGy of cylindrical ion chambers
SNR b/w three electrometers Leakage – cable current (from IC cable alone and from IC
cable and tri-axial cable together) with and without connecting assembly to ion
chambers
Linearity Sensitivity or nominal response Reproducibility SSD/Instantaneous dose rate/pulse rate
dependence Temperature dependence Field size dependence
Missed out on: Angular dependence
Linearity Sensitivity Fading effect Dose uncertainty Entrance and exit doses vs PPC measured dose Reproducibility
H and D curve for the XV film H and D curve of the EDR film Depth dependence of film SNR and variance or response along a film,
tested using XV film
Accuracy and precision of detector positioning Reproducibility
Energy dependence Dose rate dependence Comparison of profiles and PDD by each Photons vs Electrons EDR films and Water tank
0 1 2 3 4 5 6 7 8
Weekly interactions
RE* • CPE = concept permanently engraved
• Perfect CPE = inside the head dissipation of concept
• Imperfect CPE = over the head transmission of concept
CPE failure
Perfect CPE imperfect CPE
* No chargers produced initially, it is all a steady state bliss
Thank you very much!
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