ABSTRACT
Background: Due to abscopal effect, cell damage may occur outside of the radiation field and the quantification of this effect is one of the most challenging debates in radiation therapy. The aim of this study was to estimate the abscopal effect induced in non-irradiated tumors quantitatively by means of biological effective dose [BED]
Materials and Methods: Breast tumors using 4T1 and MC4-L2 cells, were induced into the flank region of Balb/c mice. When palpable, the tumor on one side of the body was irradiated with dose of 28Gy in 14 fractions and 2 Gy per fraction, 5 fractions per week. The tumor on the other side of the body was shielded with a lead plate. BED was estimated based on tumor volume. H and E staining and TUNEL assay were performed to assess histological changes and apoptosis in irradiated and non-irradiated tumors
Results: The effect of radiation on non-irradiated tumors was more than that on irradiated ones. The BED was 4.49 and 6.74 in 4T1 and MC4-L2 tumors, respectively. The ratio of the tumor volume in the last fraction to that in the first fraction for irradiated 4T1 tumors was 2.32 and in non-irradiated was 1.50. This ratio in irradiated and non- irradiated MC4-L2 tumors was 2.64 and 1.98, respectively. The number of apoptotic cells was higher in non-irradiated tissues
Conclusion: Results indicate that the occurrence of abscopal effect is highly depends on the type of tumor. By means of the abscopal effect, more radiation dose can be delivered to the tumor and metastatic sites
ABSTRACT
Nowadays, Imaging of the myocardial perfusion [MPI] using the single photon emission tomography [SPET] in the diagnosis of coronary artery disease, especially myocardial ischemia, is of great importance. In contrast to the coronary artery angiography, MPI is non-invasive, less expensive and more physiological. Unfortunately, this image is affected by the some artifacts. These artifacts lead to decrease image diagnostic accuracy and increase false positive cases. One of the most important effective artifacts is due to attenuation. These attenuation artifacts are caused by the left breast tissue in women, diaphragm in men and the chest wall in both sexes. Because of the inherent non- uniform attenuation map in the thorax region, this problem is very complex. The aim of this study is to correct attenuation artifact with a simple method that is available and very easy to use. In this study we used transmission scanning by 99mTc in the sequential views and an attenuation map was created. After attenuation correction of the original images with attenuation map, non corrected and corrected images were compared with angiography results to apply attenuation correction based on functional findings. Results show that new artifacts are created and experiences of physicians in the impression of the images is critical. Finally, the sensitivity of images increased from 86.20% to 96.42%, the specificity decreased from 85.71% to 54.54% and the diagnostic accuracy decreased from 86% to 78%. Attenuation correction can produce new artifacts, which can influence the way scans are interpreted. It seems that attenuation correction of the images, need special experience. Lack of enough experience in attenuation correction techniques, can comprise the diagnostic accuracy of images