ABSTRACT
Purpose@#The present study was conducted to compare dosimetric parameters for the heart and left lung between free breathing (FB) and deep inspiration breath hold (DIBH) and determine the most important potential factors associated with increasing the lung dose for left-sided breast radiotherapy using image analysis with 3D Slicer software. @*Materials and Methods@#Computed tomography-simulation scans in FB and DIBH were obtained from 17 patients with left-sided breast cancer. After contouring, three-dimensional conformal plans were generated for them. The prescribed dose was 50 Gy to the clinical target volume. In addition to the dosimetric parameters, the irradiated volumes and both displacement magnitudes and vectors for the heart and left lung were assessed using 3D Slicer software. @*Results@#The average of the heart mean dose (Dmean) decreased from 5.97 to 3.83 Gy and V25 from 7.60% to 3.29% using DIBH (p < 0.001). Furthermore, the average of Dmean for the left lung was changed from 8.67 to 8.95 Gy (p = 0.389) and V20 from 14.84% to 15.44% (p = 0.387). Both of the absolute and relative irradiated heart volumes decreased from 42.12 to 15.82 mL and 8.16% to 3.17%, respectively (p < 0.001); however, these parameters for the left lung increased from 124.32 to 223.27 mL (p < 0.001) and 13.33% to 13.99% (p = 0.350). In addition, the average of heart and left lung displacement magnitudes were calculated at 7.32 and 20.91 mm, respectively. @*Conclusion@#The DIBH is an effective technique in the reduction of the heart dose for tangentially treated left sided-breast cancer patients, without a detrimental effect on the left lung.
ABSTRACT
Ordered subset expectation maximization [OSEM], is an effective iterative method for SPECT image reconstruction. The aim of this study is the evaluation of the role of system matrix in OSEM image reconstruction method using four different physical beam radiation models with three detection configurations. SPECT was done with an arc of 180 degree in 32 projections after injection of 2 mCi of [99m]Tc-pertechnetate in a heart phantom by a Siemens E.Cam gamma camera equipped with LEHR collimator and data were transferred to a PC computer for reconstruction of the images with Mathlab software. The system or probability matrixes were firstly calculated using radiation fraction of pixels for three different detection models with linear, rectangular and divergent FOV, and reduction coefficient of photons from pixels to detectors in four different radiation models of distance independent [DID], inverse distance dependence [IDD] [= 1/R], inverse square distance dependence [ISDD],[= 1/R[2]] and inverse exponential distance dependence[IEDD], [= exp-R]. In these calculations the detector was assumed at a distance of 842 mm from the phantom center and pixel size was 6.638 mm. The divergent angle in divergent field of view was 2.08 degree. 12 Images of the phantom were reconstructed using system matrixes of 4 different radiation and 3 detection models. Qualities of the images were compared using universal image quality index, UIQI. The results shows negligible although statistically significant difference between contrast and brightness of the images, but it is possible in the organs with constant absorption coefficients such as brain, to use the system matrix with mathematical IEDD radiation model for attenuation correction in SPECT images. It is shown that variation in distance weighting factors in mathematical IEDD radiation model changes the system matrix so that the weights of deeper data decrease in image reconstruction process. Therefore, by this method contrast of the image at different depth can be controlled. Applying different beam radiation models and detection configurations in system matrix has no significant improvements on the image quality. However image contrast at different depth can be controlled by using system matrix derived from different distance weighting factor in mathematical IEDD radiation model
Subject(s)
Radiographic Image Enhancement , Image Processing, Computer-AssistedABSTRACT
Attenuation correction is a useful process for improving myocardial perfusion SPECT and is dependent on activity and distribution of attenuation coefficients in the body [attenuation map]. Attenuation artifacts are a common problem in myocardial perfusion SPECT. The aim of this study was to compare the effect of attenuation correction using different attenuation maps and different activities in a specially designed heart phantom. The SPECT imaging for different activities and different body contours were performed by a phantom using tissue-equivalent boluses for making different thicknesses. The activity was ranged from 0.3-2mCi and the images were acquired in 180 degree, 32 steps. The images were reconstructed by OSEM method in a PC computer using Matlab software. Attenuation map were derived from CT images of the phantom. Two quality and quantity indices, derived from universal image quality index have been used to investigate the effect of attenuation correction in each SPECT image. The result of our measurements showed that the quantity index of corrected image was in the range of 3.5 to 5.2 for minimum and maximum tissue thickness and was independent of activity. Comparing attenuation corrected and uncorrected images, the quality index of corrected image improved by increasing body thickness and decreasing activity of the voxels. Attenuation correction was more effective for images with low activity or phantoms with more thickness. In our study, the location of the pixel relative to the associated attenuator tissues was another important factor in attenuation correction. The more accurate the registration process [attenuation map and SPECT] the better the result of attenuation correction