I'm considering doing a study to measure thyroid dose during neurointerventional procedures, using a biplane unit with an undercouch x-ray tube. Would the measurements done with a dosimeter on the neck over the thyroid be accurate?
Not very accurate, it will just give you an idea of the order of magnitude. Normally you measure the X-Ray dose with TLDs placed on the surface of the skin, next to the organ of interest. But that is not the dose in the organ (in the thyroid, in your case), but the entry dose and, if you place also TLDs on the skin at the exit point, you can also measure the exit dose. Knowing these two quantities you can use a Monte Carlo method to calculate the actual organ dose.
I agree with Radu but you have seek a suitable conversion factor to convert the absorbed dose measured by TLD in Gy to effective dose in Sv..
There is a NaI-based scintillation dose rate meter (Model SCINTO Thyroid) available from SEA, Germany. The detector is of spherical shape, suitable for the neck region covering the thyroid area very well. The technical pamphlet of the manufacturer gives a table showing estimation of expected thyroid dose for various measured doses (uSv/hr) for adults and children. Reference is provided for dose calculation.
For theoretical estimation of thyroid dose, a text book on Nuclear Medicing may be consulted.
Is this helpful?
Be careful, the NaI based detector can be used for nuclear medicine techniques, not for RX immaging techniques. If your question was for the dose resulting from injecting a radionuclide (like radioiodine), then the detector described by Sankaran Anantharayanan is the answer. If you want the dose resulting from an X Ray exposure, than you have to use the TLDs and then the calculation.
I did some research on the Nal based detector and realised that fact. It definitely is not applicable to my study. Thank you very much for your contributions Radu.
I did send a second answer which has perhaps crossed Radu's comments this morning but my network failed. I am now re-sending the text which I carefully preserved:
The NaI detector-based dosimeter is more suitable for measurement of thyroid dose after a nuclear medicine procedure or for emergency monitoring after a nuclear accident. Since your requirement is a measurement of thyroid dose after an x-ray exposure, we can monitor the dose in mGy on the two lobes of the thyroid with tissue equivalent TLD chips calibrated for the particular effective energy of the beam and taking the average value.For quick measurement, one may also use a DIGITAL pocket dosimeter (with a small GM counter) with integration facility, calibrated in mGy in tissue for the x-ray beam energy. The detector may be located and may be kept on the lobe. From surface dose in either case, one has to apply conversion factor (available from Nuclear Medicine literature) to arrive at the actual thyroid dose in mGy Then one can apply the tissue weighting factor (ICRP value) for thyroid (0.03) to arrive at the effective dose to the whole body in mSv.
One may also use the Rando human phantom for getting a rough estimate of the thyroid dose.
Thank you, Dr.Radu, I had already modified my answer!