TITLE:
In-Vivo Dosimetry Method for Measuring Peak Surface Dose Using Radiochromic Films during Computed Tomography Scanning of the Sinus
AUTHORS:
Khaled Soliman, Salman Altimyat, Abdullah Alrushoud, Ahmed Alenezi, Mohammed Alkhorayef
KEYWORDS:
Radiochromic Films, Sinus CT, In-Vivo Dosimetry, CTDI(Vol), Entrance Surface Dose
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.7 No.2,
May
7,
2018
ABSTRACT: Purpose:
During computed tomography (CT) helical scanning mode the patient surface dose
distribution is assumed to be non-uniform, therefore point dose measurement
methods may lead to imprecise estimation of the radiation dose received by the
patient skin in particular. We have used XRQA2 films as in-vivo dosimeters to measure the entrance skin dose during sinus exams. Methods:
The films were placed under the patient head rest in order to sample the
entrance surface dose in-vivo. We have performed in-vivo film
irradiation on 23 patients in this study to verify the clinical suitability of
the method and were found adequate. Results: The measured average ESD in
the sinus exam was 11.7 ± 1.0 mGy, the PSD was 15.7 ± 1.7 mGy and the CTDI(vol) was 13.3 ± 0.1 mGy. The ratio of ESD/CTDI(vol) and PSD/CTDI(vol) was 0.88 and 1.18 respectively. The results indicate
that the scanner registered CTDI(vol) underestimates the PSD and in the same time it overestimates the ESD by 18% and
13.6% respectively. Conclusion: The observed differences between the
ESD, PSD and CTDI(vol) although
seem small for the radiation dose range measured during CT of the sinus [13.2 - 13.4] mGy, but important for
the medical physicist to know, since monitoring of patients’ doses from CT
examinations is becoming more mandatory. The use of radiochromic film as in-vivo dosimeter does not interfere with the clinical radiological exam and
does not produce any image artifacts. The method can be used to study other CT
examinations specially the ones with large beam width, high pitch factor
and high dose exams. The method allows measurement of the peak skin dose,
examination of the CT dose profile and the 2D dose distribution in the XZ plan.