3-D dose distribution for organ dose measurement in CT thoracic exams using Gafchromic™ XR-QA2 films

Abstract

A: The patient dose in radiodiagnostic is currently monitored through an ionizing radiation exposure index named Volume Computed Tomography Dose Index (CTDI vol ) and the Dose-Length Product (DLP), displayed by CT scanner and measurable through a 100 mm long pencil ionization chamber, inserted in a homogeneous cylindrical PMMA phantom. The phantom is 14 cm long and has a diameter of 16 (32) cm that represents the adult head (body). One of the main flaws of such a method is that it does not return any information on the dose distribution to organs, and the average absorbed dose value, due to the material and dimensions of both the phantom and the ionization chamber, might be either underestimated or overestimated depending upon the patient size. With the aim to obtain complementary information, this work presents a method to estimate organ dose in the thoracic area of an anthropomorphic woman phantom in CT, by employing Gafchromic TM XR-QA2 and computational 3-D reconstruction methods. Lungs, heart, and spinal cord have been chosen as a dosimetry case study. XR-QA2 films have been placed between the phantom slabs in the thoracic area and scanned with a multi-slice CT scanner. 2-D and 3-D absorbed dose distributions for each organ have been analyzed, by means of a custom code in Matlab ® . Critical aspects in the dose distributions have been found for the spinal-cord case (serial organ) where the dose distribution is non normal and the maximum dose value is ∼ 30 mGy while a maximum dose value between 26 and 28 mGy has been measured elsewhere. K: Dosimetry concepts and apparatus; Computerized Tomography (CT) and Computed Radiography (CR); Medical-image reconstruction methods and algorithms, computer-aided diagnosis 1Corresponding author.

CT-Dose Measurement of the Spinal Cord Region Using XR-QA2 Radiochromic Films and TLD 100H Dosimeters

“…The radiochromic films image acquisition was performed before the irradiation and 72 h after the irradiation [11,13], using an Epson Expression 10,000 XL flatbed scanner. The scanner that we employed has a negligible sensitivity variation in the central region that is used for the reading.…”

“…The scanner that we employed has a negligible sensitivity variation in the central region that is used for the reading. This was set up using the reflective mode because of the film opaque property [2,10,14], an RGB image with a resolution of 72 dpi in 48-bit and no color corrections was applied [11,15]. The image analysis was performed in the red channel and the pixel-by-pixel background fog subtraction method was applied [11,16] using ImageJ software (available at https://imagej.net).…”

“…The Gafchromic TM XR-QA2 is the most recent radiochromic film used to carry out measurements of CT dose distribution [3]. In general, the XR-QA model allows high-resolution slice-by-slice dose distribution measurements inside an organ volume, as well as spatial-and punctual-dose measurements, providing a potential tool to perform 2D-and 3D-CT dosimetry [2,11].…”