A feasibility study of multislice X-ray CT imaging of gel dosimeters using the "zero scan" method.

Muhammad B Kakakhel,Tanya Kairn,Jamie V Trapp,Paul Charles

doi:10.1120/jacmp.v15i4.4360

Abstract

This study extends the ‘zero scan’ method for CT imaging of polymer gel dosimeters to include multislice acquisitions. Multislice CT images consisting of 24 slices of 1.2 mm thickness were acquired of an irradiated polymer gel dosimeter and processed with the zero scan technique. The results demonstrate that zero scan‐based gel readout can be successfully applied to generate a three‐dimensional image of the irradiated gel field. Compared to the raw CT images, the processed figures and cross‐gel profiles demonstrated reduced noise and clear visibility of the penumbral region. Moreover, these improved results further highlight the suitability of this method in volumetric reconstruction with reduced CT data acquisition per slice. This work shows that 3D volumes of irradiated polymer gel dosimeters can be acquired and processed with X‐ray CT.PACS number: 87.57.Q‐, 87.57.nf, 87.55.‐x

Highlights

Radiotherapy dose verification is an integral part of the cancer treatment chain
The zero scan method introduced by Kakakhel et al[10] and previously demonstrated for a single two-dimensional CT slice, has been used for the three-dimensional volumetric reconstruction of a multislice irradiated gel, while reducing the number of CT scans required for high-contrast imaging
A PAGAT gel dosimeter according to the recipe of Venning et al[3] was prepared with increased concentration (8 mM) of Tetrakis phosphonium chloride (THPC) for improved stability, as suggested by Khoei et al in their investigation of the pre-irradiation temporal stability of PAGAT gel dosimeter.[11]. The gel was poured into a cylindrical polyethylene terephthalate (PET) container and stored at 4°C for 15 hours prior to irradiation

Summary

Introduction

Radiotherapy dose verification is an integral part of the cancer treatment chain. Polymer gel dosimeters offering 3D dose verification capabilities have been developed[1] for the verification of complex radiotherapy treatments.Readout of dose information from polymer gel dosimeters can be undertaken with imaging techniques, such as magnetic resonance imaging (MRI)(2-4) and optical computed tomography (CT),(5-7) though these modalities are not available at all radiation oncology clinics. Polymer gel dosimeters offering 3D dose verification capabilities have been developed[1] for the verification of complex radiotherapy treatments. The zero scan method introduced by Kakakhel et al[10] and previously demonstrated for a single two-dimensional CT slice, has been used for the three-dimensional volumetric reconstruction of a multislice irradiated gel, while reducing the number of CT scans required for high-contrast imaging The ‘zero scan’ method generates a new image as follow: 1) repeat a number of CT scans of the irradiated gel phantom; 2) due to the massive number of CT scans, the absorbed dose will increase, which gives an increased Hounds field number (HU) with increasing number of scans; 3) a function is fitted on a pixelby-pixel basis for the fractional increase in the gel density with each scan; 4) the intercept value of the fit for each pixel forms the new image (i.e., the ‘zero scan’).

Methods

Results

Conclusion