Estimation of Absorbed Dose Distribution in Different Organs during the CT Scan: Monte Carlo Study

Special Article - Therapeutic Radiology

Austin J Radiol. 2017; 4(1): 1063.

Estimation of Absorbed Dose Distribution in Different Organs during the CT Scan: Monte Carlo Study

Kara U¹* and Huseyin Ozan Tekin²

¹Medical Imaging, Suleyman Demirel University, Turkey

²Department of Radiotherapy, Uskudar University, Turkey

*Corresponding author: Kara1 U, Suleyman Demirel University, Vocational School of Health Services, Medical Imaging, 32100, Isparta, Turkey

Received: March 08, 2017; Accepted: March 30, 2017; Published: April 04, 2017

Abstract

This work aimed to validate the accuracy of a Monte Carlo source model of the Ge Lightspeed CT scanner using organ doses measured in specific human adult phantoms. The x-ray output of the Ge Lightspeed multidetector CT scanner was simulated within the Monte Carlo code. The resulting source model was able to perform various real simulated scan model helical Computed Tomography (CT) scans of varying scan parameters such as kVp, mAs, filtration, pitch, and beam collimation. This work has been performed by using real Computed Tomography (CT) protocols to patients in public hospitals in Turkey. We used Monte Carlo simulation methods with real height and weight of patients and Computed Tomography (CT) scanners real parameters. Absorbed organ doses have been calculated by using Monte Carlo simulation. The results showed that changes in mAs value are significantly important for obtaining the risk of cancer from dose rates. Additionally, the dose received by each organ has been calculated and the results showed that Monte Carlo is a strong and effective tool in radiological investigations.

Keywords: CT scan; Absorbed dose; Monte carlo simulation

Introduction

Diagnostic radiology is a significant tool for clinical diagnosis and includes general x rays, Computed Tomography (CT), Magnetic Resonance Imaging (MRI), ultrasound, mammography, etc. Diagnostic radiology is part of medicine that uses medical imaging facility and technology to diagnose disease and helps define the structures inside in human body. Diagnostic radiology uses the imaging technologies of X-rays radiography, computed tomography, magnetic resonance imaging, ultrasound, mammography, etc. Common classifications of CT scans are abdominal, bone, head and vascular system. CT scanning is the one of most used units in diagnostic radiology and these units combine the use of X-rays and computer processing to generate tomographic images of the body. The use of CT in radiology and medical imaging has been growing in the world. CT is useful as it allows the radiologist, to view a crosssectional picture of the entire body. CT is painless, fast, and accurate and CT scan uses x-ray equipment and computers to produce medical images that often can make more detailed image than conventional radiography. CT scans use ionizing radiation as used in other x-rays units. In clinical, the benefits of a correct diagnosis preponderance to the risk of exposure to ionizing radiation during the body scan. In diagnostic radiology, it is relevant to see the absorbed doses in organs, particularly those that receive the highest radiation doses. Absorbed radiation doses are estimated using standardized reference. The Monte Carlo (MC) simulation has been widely adopted to medical physics and medical imaging. In a medical physics simulation estimated image of the conditions is modeling to a computer program, which then authorizes imaginary radiation particles, waves and simulates interactions with the program tools. Although there are a variety of methods by which one can estimate patient organ doses from CT examinations, Monte Carlo simulations have been reported to be the most accurate, reliable, and versatile in accomplishing this task [1-8].

In the Monte Carlo method, the patient and CT scanner are simulated using a computational anatomic model of the patient and an x-ray source model representing the scanner’s beam output. However, to ensure the accuracy of these calculations, these CT source models must be benchmarked and validated against actual experimental measurements made on the scanners they simulate. In the past, most validation studies were accomplished using standard CT Dose Index (CTDI) phantoms, but in recent years, anthropomorphic phantoms have been increasingly utilized [9,10]. Mathematical phantoms or MIRD phantoms have been produced [11] which were the first models of human phantoms to be widely used in dosimetry studies involving X-ray exposure by the Monte Carlo method.

However, the organs in these phantoms are described by mathematical equations with limited representation of the actual structure of a human body and its chemical and physical characteristics [12]. Voxel-based phantoms created from tomography images present a geometry which adequately represents a patient, including internal organ, displacements, and deformations. These phantoms are recommended for dosimetric studies with the Monte Carlo method because more consistent results are obtained with adult reference computational phantoms, as described in ICRP 110 [13,14]. This study aimed to investigate the using availability of Monte Carlo technique during the calculation of absorbed dose amounts by different organs and make an assessment on cancer risk by considering dose magnitudes.

Materials and Methods

A General Electric (GE) Lightspeed multidetector CT scanner was used as the base for the Monte Carlo code model as well as for all radiation dose and organ absorbed dose measurements. The GE Lightspeed multidetector CT scanner was measured with real protocols to patients in public hospitals and used Monte Carlo simulation methods with the real height and weight of patients and the CT scanner’s actual parameters (Table 1). Absorbed organ doses were then calculated based on these Monte Carlo results. Monte Carlo simulation in the CT scanner containing 64 rows of detectors, scan mode helical, total collimation 40.0 mm, table height 133.00mm, pitch 1.53, filter 10.0 mm Al 7 Deg Tungsten, mean spectral energy 64.9 keV, helical scan table increment 6 cm, number of rotations 6, source-to-iso-centre distance 53.9 cm, total field size at iso-centre 57.3 cm x 36.0 cm, beam width at iso-centre 4cm, scanlength 36cm (Table 2).