#Shift all peaks inmr trial#

#Shift all peaks inmr trial#

The feasibility of SMART was shown in a prospective trial demonstrating improved PTV coverage and/or simultaneous organs at risk (OARs) sparing for abdominal malignancies. Therefore, stereotactic MR-guided online adaptive radiation therapy (SMART) has been suggested to overcome the limitations of low soft-tissue contrast IGRT by combining daily MR based treatment adaptation and replanning with MR based target localization and continuous real-time tracking of the moving target.

However, low soft tissue contrast combined with slow image acquisition relative to breathing motion do not allow accurate visualization of the hepatic metastases themselves and upper abdominal organs at risk. Ĭone-beam based image-guided radiation therapy (IGRT) strategies have substantially improved the accuracy of SBRT in liver SBRT. Both intra-fraction respiratory motion and physiologic organ alterations have been identified as critical factors influencing treatment accuracy. This may translate in reduced local control if a minimum BED of 100 Gy cannot be achieved. Especially when treating abdominal malignancies, such as liver metastases, the dose of SBRT is often limited by the proximity of gastrointestinal organs and PTV compromises are necessary to minimize the risk of radiation-induced gastrointestinal toxicity. SBRT requires maximum accuracy in treatment delivery to ensure that the high irradiation doses are precisely administered to the target structures while simultaneously sparing surrounding normal tissues. High rates of local control in various disease sites including hepatic metastases have been observed, as long as high biologically effective (BED) doses could be delivered. The implementation of stereotactic body radiation therapy (SBRT) was an important milestone in local treatment for oligometastatic and medically inoperable cancers. Only marginal improvements in target coverage were observed for target distant to critical OARs, indicating that these patients do not benefit from daily adaptive replanning. MR-guided online replanning SBRT improved target coverage and OAR sparing for liver metastases with a distance from the edge of the PTV to the nearest luminal OAR < 2 cm. No acute grade 3 treatment-related toxicities were observed. RP significantly improved PTV coverage (V100%) for metastases within close proximity to an OAR by 4.0% (≤ 0.2 cm distance from the edge of the PTV to the edge of the OAR n = 7 p = 0.01), but only by 0.2% for metastases farther away from OAR (> 2 cm distance n = 7 p = 0.37). SBRT with RP improved PTV coverage (V100%) for 47/75 of the fractions and reduced doses to the most proximal OARs (D1cc, Dmean) in 33/75 fractions compared to sBP. Median pre-treatment GTV and PTV were 14.9 cc (interquartile range (IQR): 7.7–32.9) and 62.7 cc (IQR: 42.4–105.5) respectively. After extraction of DVH parameters for GTV, planning target volume (PTV), and OARs (stomach, duodenum, bowel, liver, heart) plans were compared on a per-patient basis. A reoptimized plan (RP) and a rigidly shifted baseline plan (sBP) without re-optimization were generated for each fraction. Gross tumor volume (GTV) and organs at risk (OARs) were adapted to the anatomy-of-the-day. Methodsįifteen patients assigned to SBRT for oligometastatic liver metastases underwent daily MR-guided target localization and on-table treatment plan re-optimization. To assess the effects of daily adaptive MR-guided replanning in stereotactic body radiation therapy (SBRT) of liver metastases based on a patient individual longitudinal dosimetric analysis.