Hippocampal Sparing in Stereotactic Radiotherapy for Multiple Brain Metastases: A Comparison of Intensity-modulated Arc Therapy, CyberKnife, and Helical Radiotherapy

OBJECTIVE In this study, we performed a plan study to evaluate brain and hippocampal doses with hippocampal sparing in the treatment of multiple brain metastases with stereotactic radiosurgery (SRS). For this purpose, treatment plans prepared using intensity-modulated arc therapy (IMAT), CyberKnife radio surgery, and helical tomotherapy techniques. The results were compared and evaluated according to their superiority to each other.METHODS Fifteen patients with multiple brain metastases who had a tumor diameter of <3.5 cm were included in this study. IMAT, CK, and HT plans were separately created for each patient. The dose prescription was defined as 18 Gy in the single fraction.RESULTS The D40% of hippocampal (in Gy) averaged 1.63, 1.69, and 0.52 for IMAT, CyberKnife, and Tomotherapy, respectively. The median hippocampal Dmax (in Gy) averaged 2.81, 4.63, and 1.98, respectively. Some plans were statically different in terms of critical organ doses, but the results were clinically acceptable. The mean values of V12 (cc) were found to be 12.6, 38.23, and 37.46 for IMAT, CyberKnife, and Tomotherapy, respectively, when evaluating the doses taken by healthy brain tissue.CONCLUSION Brain radiotherapy is a treatment modality for primary and metastatic lesions. However, after radiotherapy (even with SRS) damage especially in the hippocampus may cause cognitive impairment and a decrease in patients' quality of life. Therefore, when the hippocampus is outlined as organs of risk, it can be protected without compromising PTV coverage. We saw this result in all of three treatment platforms used in this study

Complete Response Evaluation of Locally Advanced Rectal Cancer to Neoadjuvant Chemoradiotherapy Using Textural Features Obtained from T2 Weighted Imaging and ADC Maps

Background: The prediction of pathological responses for locally advanced rectal cancer using magnetic resonance imaging (MRI) after neoadjuvant chemoradiotherapy (CRT) is a challenging task for radiologists, as residual tumor cells can be mistaken for fibrosis. Texture analysis of MR images has been proposed to understand the underlying pathology. Objective: This study aimed to assess the responses of lesions to CRT in patients with locally advanced rectal cancer using the first-order textural features of MRI T2-weighted imaging (T2-WI) and apparent diffusion coefficient (ADC) maps. Methods: Forty-four patients with locally advanced rectal cancer (median age: 57 years) who underwent MRI before and after CRT were enrolled in this retrospective study. The first-order textural parameters of tumors on T2-WI and ADC maps were extracted. The textural features of lesions in pathologic complete responders were compared to partial responders using Student's t- or Mann-Whitney U tests. A comparison of textural features before and after CRT for each group was performed using the Wilcoxon rank sum test. Receiver operating characteristic curves were calculated to detect the diagnostic performance of the ADC. Results: Of the 44 patients evaluated, 22 (50%) were placed in a partial response group and 50% were placed in a complete response group. The ADC changes of the complete responders were statistically more significant than those of the partial responders (P = 0.002). Pathologic total response was predicted with an ADC cut-off of 1310 x 10(-6) mm(2)/s, with a sensitivity of 72%, a specificity of 77%, and an accuracy of 78.1% after neoadjuvant CRT. The skewness of the T2-WI before and after neoadjuvant CRT showed a significant difference in the complete response group compared to the partial response group (P = 0.001 for complete responders vs. P = 0.482 for partial responders). Also, relative T2-WI signal intensity in the complete response group was statistically lower than that of the partial response group after neoadjuvant CRT (P = 0.006). Conclusion: As a result of the conversion of tumor cells to fibrosis, the skewness of the T2-WI before and after neoadjuvant CRT was statistically different in the complete response group compared to the partial response group, and the complete response group showed statistically lower relative T2-WI signal intensity than the partial response group after neoadjuvant CRT. Additionally, the ADC cut-off value of 1310 x 10(-6) mm(2)/s could be used as a marker for a complete response along with absolute ADC value changes within this dataset