Detecting a Geometric Miss by Dynamic Contrast-enhanced Magnetic Resonance Imaging

Abstract

Purpose/Objective(s)To investigate the potential of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in determining the margins of the radiation fields through a half-tumor irradiation model.Materials/MethodsMurine prostate TRAMP-C1 tumors were i.m. inoculated C57BL/6J mice in the thigh. When the tumors had achieved a size of 8 mm, the distal half of the tumors were irradiated for a total dose of 15 Gy in either a single fraction or 5 fractions (n = 6 for each group) by a Radiosurgery System with a 2-cm cone. The quantitative parameters of the DCE-MRI by a 7 Tesla MR scanner were derived using the extended Kety model in a voxel-wise manner. After the last MR scanning, the mice were euthanized and tumors were examined with immunochemical staining.ResultsThe Monte Carlo simulation and film analysis suggested that the dose fall-off from 80% to 20% was less than 3 mm in this system. The effects of the half-tumor irradiation were demonstrated by a decrease of the tumor microvascular density and an aggregation of giant cells at the irradiated site, which is compatible with the whole-tumor irradiation model. However, there were no differences between the non-irradiated and irradiated sites on the conventional T1 weighted MR images. Interestingly, tumors with single-fraction irradiation showed increased K-trans values on the irradiated site after the fourth day of radiation. The K-trans results on the sixth day post-radiation were well correlated with the histological findings. In addition, similar effects were observed in tumors with 5-fraction irradiation.ConclusionsThis half-tumor irradiation model provides a self-control system to study the radiation effects on the tumor microenvironments. Although the dose fall-off in clinical situations should not be as sharp as that in this model, our results suggest that functional MRIs could be used for the early detection a geometric miss during radiation therapy. Purpose/Objective(s)To investigate the potential of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in determining the margins of the radiation fields through a half-tumor irradiation model. To investigate the potential of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in determining the margins of the radiation fields through a half-tumor irradiation model. Materials/MethodsMurine prostate TRAMP-C1 tumors were i.m. inoculated C57BL/6J mice in the thigh. When the tumors had achieved a size of 8 mm, the distal half of the tumors were irradiated for a total dose of 15 Gy in either a single fraction or 5 fractions (n = 6 for each group) by a Radiosurgery System with a 2-cm cone. The quantitative parameters of the DCE-MRI by a 7 Tesla MR scanner were derived using the extended Kety model in a voxel-wise manner. After the last MR scanning, the mice were euthanized and tumors were examined with immunochemical staining. Murine prostate TRAMP-C1 tumors were i.m. inoculated C57BL/6J mice in the thigh. When the tumors had achieved a size of 8 mm, the distal half of the tumors were irradiated for a total dose of 15 Gy in either a single fraction or 5 fractions (n = 6 for each group) by a Radiosurgery System with a 2-cm cone. The quantitative parameters of the DCE-MRI by a 7 Tesla MR scanner were derived using the extended Kety model in a voxel-wise manner. After the last MR scanning, the mice were euthanized and tumors were examined with immunochemical staining. ResultsThe Monte Carlo simulation and film analysis suggested that the dose fall-off from 80% to 20% was less than 3 mm in this system. The effects of the half-tumor irradiation were demonstrated by a decrease of the tumor microvascular density and an aggregation of giant cells at the irradiated site, which is compatible with the whole-tumor irradiation model. However, there were no differences between the non-irradiated and irradiated sites on the conventional T1 weighted MR images. Interestingly, tumors with single-fraction irradiation showed increased K-trans values on the irradiated site after the fourth day of radiation. The K-trans results on the sixth day post-radiation were well correlated with the histological findings. In addition, similar effects were observed in tumors with 5-fraction irradiation. The Monte Carlo simulation and film analysis suggested that the dose fall-off from 80% to 20% was less than 3 mm in this system. The effects of the half-tumor irradiation were demonstrated by a decrease of the tumor microvascular density and an aggregation of giant cells at the irradiated site, which is compatible with the whole-tumor irradiation model. However, there were no differences between the non-irradiated and irradiated sites on the conventional T1 weighted MR images. Interestingly, tumors with single-fraction irradiation showed increased K-trans values on the irradiated site after the fourth day of radiation. The K-trans results on the sixth day post-radiation were well correlated with the histological findings. In addition, similar effects were observed in tumors with 5-fraction irradiation. ConclusionsThis half-tumor irradiation model provides a self-control system to study the radiation effects on the tumor microenvironments. Although the dose fall-off in clinical situations should not be as sharp as that in this model, our results suggest that functional MRIs could be used for the early detection a geometric miss during radiation therapy. This half-tumor irradiation model provides a self-control system to study the radiation effects on the tumor microenvironments. Although the dose fall-off in clinical situations should not be as sharp as that in this model, our results suggest that functional MRIs could be used for the early detection a geometric miss during radiation therapy.