The objective of this work is to study the influence of the patient size and geometry on CBCT Hounsfield Unit and the accuracy of calibration Hounsfield Unit to electron density (HU-ED) using patient specific HU-ED mapping method for dose calculation. Two clinical cases, namely nasopharyngeal carcinoma (NPC) case and prostate case for 4 patients with different size and geometry were enrolled to assess the impact of size and geometry on CBCT Hounsfield Unit. The accuracy of the patient specific HU-ED mapping method was validated by comparing dose distributions based on planning CT and CBCT, dose-volume based indices and the digitally reconstructed radiograph (DRR) by analyzing their line profile plots. Significant differences in Hounsfield unit and line profile plots were found for NPC and prostate cases. The doses computed based on planning CT data sets and CBCT datasets for both clinical cases agree to within 1% for planning target volumes and 3% for organs at risk. The data shows that there are high dependence of HU on patient size and geometry; thus, the use of one CBCT HU-ED calibration curve made of one size and geometry will not be accurate for use with a patient of different size and geometry.
Interventional cardiology (IC) procedures are known to give high radiation doses to patients and cardiologists as they involve long fluoroscopy times and several cine runs. Patients' dose measurements were carried out at the cardiology department in a local hospital in Penang, Malaysia, using Gafchromic XR-RV2 films. The dosimetric properties of the Gafchromic film were first characterised. The film was energy and dose rate independent but dose dependent for the clinically used values. The film had reproducibility within ± 3% when irradiated on three different days and hence the same XR-RV2 dose-response calibration curve can be used to obtain patient entrance skin dose on different days. The increase in the response of the film post-irradiation was less than 4% over a period of 35 days. For patient dose measurements, the films were placed on the table underneath the patient for an under-couch tube position. This study included a total of 44 patients. Values of 35-2442 mGy for peak skin dose (PSD) and 10.9-344.4 Gy cm(2) for dose-area product (DAP) were obtained. DAP was found to be a poor indicator of PSD for PTCA procedures but there was a better correlation (R(2) = 0.7344) for CA + PTCA procedures. The highest PSD value in this study exceeded the threshold dose value of 2 Gy for early transient skin injury recommended by the Food and Drug Administration.
Pumping air through a soft tissue which acts as a membrane is a relatively easy and quick method to collect and measure radon/thoron and its daughter nuclides in air. Analysis of the activity of the radionuclides can be calculated using an alpha counter which has been calibrated. In this method the activity of radon/thoron cannot be separated from the activity of radionuclides already present in the aerosol or dust particles.
Estimation of the surface dose is very important for patients undergoing radiation therapy. The purpose of this study is to investigate the dose at the surface of a water phantom at a depth of 0.007 cm as recommended by the International Commission on Radiological Protection and International Commission on Radiation Units and Measurement with radiochromic films (RFs), thermoluminescent dosemeters and an ionisation chamber in a 6-MV photon beam. The results were compared with the theoretical calculation using Monte Carlo (MC) simulation software (MCNP5, BEAMnrc and DOSXYZnrc). The RF was calibrated by placing the films at a depth of maximum dose (d(max)) in a solid water phantom and exposing it to doses from 0 to 500 cGy. The films were scanned using a transmission high-resolution HP scanner. The optical density of the film was obtained from the red component of the RGB images using ImageJ software. The per cent surface dose (PSD) and percentage depth dose (PDD) curve were obtained by placing film pieces at the surface and at different depths in the solid water phantom. TLDs were placed at a depth of 10 cm in a solid water phantom for calibration. Then the TLDs were placed at different depths in the water phantom and were exposed to obtain the PDD. The obtained PSD and PDD values were compared with those obtained using a cylindrical ionisation chamber. The PSD was also determined using Monte Carlo simulation of a LINAC 6-MV photon beam. The extrapolation method was used to determine the PSD for all measurements. The PSD was 15.0±3.6% for RF. The TLD measurement of the PSD was 16.0±5.0%. The (0.6 cm(3)) cylindrical ionisation chamber measurement of the PSD was 50.0±3.0%. The theoretical calculation using MCNP5 and DOSXYZnrc yielded a PSD of 15.0±2.0% and 15.7±2.2%. In this study, good agreement between PSD measurements was observed using RF and TLDs with the Monte Carlo calculation. However, the cylindrical chamber measurement yielded an overestimate of the PSD. This is probably due to the ionisation chamber calibration factor that is only valid in charged particle equilibrium condition, which is not achieved at the surface in the build-up region.
Second cancer induction in the contralateral breast (CB) is an issue of some concern in breast radiotherapy especially for women under the age of 45 years at the time of treatment. The CB dose from 2-field and 3-field techniques in post-mastectomy chest wall irradiations in an anthropomorphic phantom as well as in patients were measured using thermoluminescent dosimeters (TLDs) at the local radiotherapy center. Breast and chest wall radiotherapy treatments were planned conformally (3D-CRT) and delivered using 6-MV photons. The measured CB dose at the surface fell sharply with distance from the field edge. However, the average ratio of the measured to the calculated CB dose using the pencil beam algorithm at the surface was approximately 53%. The mean and median measured internal dose at the posterior border of CB in a phantom was 5.47+/-0.22 cGy and 5.44 cGy, respectively. The internal CB dose was relatively independent of depth. In the present study the internal CB dose is 2.1-4.1% of the prescribed dose which is comparable to the values reported by other authors.
The oxidation of ferrous to ferric ions due to ionizing radiation has been used for chemical dosimetry since 1927. The introduction of metal indicator dye xylenol orange (XO) sensitises the measurement of ferric ion yield. A ferrous sulphate- agarose- xylenol orange (FAX) gel was prepared and the gel then exposed to dose ranging from 0.2 to 10 Gy using various high energy photon and electron beams from a linear accelerator. Some general characteristics of FAX such as energy dependence, optical density (OD)-dose relationship, reproducibility and auto-oxidation of ferrous ions were analysed. The radiation yield G of the gel was calculated for gels prepared in oxygen and in air and the values were 46.3 +/- 2.1 and 40.9 +/- 1.4 Fe3+ per 100 eV for photons respectively. However for stock gel which was kept for 5 days pre-irradiation the G value decreased to 36.6 +/- 1.1. The gel shows linearity in OD-dose relationship, energy independence and reproducibility over the dose range investigated. Auto-oxidation of ferrous ions resulted in optical density changes of less than 1.5% per day.
An optical scanner system, which incorporates a He-Ne laser, photodiode detectors, and a platform for placing film, was built in the laboratory. The laser system operates at the green wavelength of 543.5 nm and functions as a scanning densitometer for measurement of optical changes in a film resulting from irradiation . The central axis electron depth dose of selected electron energies 10,12 and 14 MeV were analysed using Kodak X-Omat and Kodak Extended Dose Range (EDR2) films. The Kodak X-Omat film is routinely used for high-energy electron dose distributions in radiation therapy. The electron depth-dose measured with X-Omat film was found to agree well with standard depth-dose curves in water, obtained using an ion chamber. Conversely, the recently introduced Kodak EDR2 showed an energy dependence for electron beams, the percentage depth-dose curve shifting towards the surface for 12 and 14 MeV electron beams compared to that in water.
One of the factors which influence the spatial resolution of a 2D detector array is the size of the single detector, another the transport of the secondary electrons from the walls into the measuring volume. In this study, the single ion chamber dose response function of an I'mRT MatriXX array was determined by comparison between slit beam dose profiles measured with the array and with EBT2 radiochromic film in a solid water-equivalent phantom at a shallow depth of 0.5cm and at a depth of 5cm beyond the depth dose maximum for a 6 MV photon beam. The dose response functions were obtained using two methods, the best fit method and the deconvolution method. At the shallow depth, a Lorentz function and at 5cm depth a Gaussian function, both with the same FWHM of 7.4mm within limits of uncertainty, were identified as the best suited dose response functions of the 4.5mm diameter single array chamber. These dose response functions were then tested on various dose profiles whose true shape had been determined with EBT2 film and with the IC03 ionization chamber. By convolving these with the Lorentz kernel (at shallow depth) and the Gaussian kernel (at 5cm depth) the signal profiles measured with the I'mRT MatriXX array were closely approximated. Thus, the convolution of TPS-calculated dose profiles with these dose response functions can minimize the differences between calculation and measurement which occur due to the limited spatial resolution of the I'mRT MatriXX detector.
Phantoms are devices that simulate human tissues including soft tissues, lungs, and bones in medical and health physics. The purpose of this work was to investigate the differential dose absorption in several commercially available low-cost materials as substitutes to human tissues using Gafchromic XR-QA2 film. The measurement of absorbed dose by different materials of various densities was made using the film to establish the relationship between the absorbed dose and the material density. Materials investigated included soft board materials, Perspex, chicken bone, Jeltrate, chalk, cow bone, marble, and aluminum, which have varying densities from 0.26 to 2.67gcm-3. The absorbed dose increased as the density and atomic number of the material increased. The absorbed dose to the density can be well represented by a polynomial function for the materials used.