SU‐E‐T‐481: Treatment Plans of Brain Metastasis with Cutting Edge Radiation Therapy Techniques: A Dosimetric Comparison Study of 3D Conformational Radiotherapy, Intensity Modulation Radiation Therapy, Dynamic Stereotactic Radiation Therapy and Contrast‐En

Purpose: Contrast‐enhanced stereotactic synchrotron radiation therapy (SSRT) is an innovative technique based on localized dose‐enhancement effects obtained by reinforced photoelectric absorption in the target using medium energy monochromatic x‐rays (50–100 keV). The purpose of this study is to compare three cutting edge radiation therapy techniques with conventional 3D conformational radiotherapy: intensity modulated radiation therapy (IMRT), dynamic stereotactic arctherapy and contrast enhanced SSRT. Methods: A patient bearing a single parenchymal brain metastasis has received two helical 3D CT scans, the head being immobilized by a stereotactic frame. The fisrt scan is performed without contrast injection for high energy radiotherapy dosimetry. The second scan is performed 15 min after the injection of 200 mL of iodinated contrast agent contrast‐enhanced SSRT dosimetry. 3D conformational radiotherapy, IMRT, dynamic arctherapy contrast enhanced dosimetry plans have been performed on dedicated treatment planing softwares (Eclipse, IPlan and Isogray, respectively). The objective of each plans is such as the 100% of the prescribed dose is delivered at the beams isocentre and that the 70% isodose should contain all the target volume. The volume of the 70% isodose and the average and maximal dosed delivered to the organs at risk (brainstem, optical nerves, chiasma, eyes, skull bone and healthy brain parenchyma) are compared for each technique. Results: Among all high energy techniques, the stereotactic dynamic arctherapy gave the best results in terms of dose conformation and organs at risk sparing effect. However contrast enhanced SSRT provide a serious added value in terms of dosimetry by significantly reducing the dose delivered to the brainstem and the brain parenchyma. Conclusion: This study validates the dosimetric advantages of contrast enhanced SSRT for treating brain metastasis. This is another crucial step toward SSRT clinical trials.