Significant tumor shift in patients treated with stereotactic radiosurgery for brain metastasis

Abstract

IntroductionLinac-based stereotactic radiosurgery (SRS) for brain metastases may be influenced by the time interval between treatment preparation and delivery, related to risk of anatomical changes. We studied tumor position shifts and its relations to peritumoral volume edema changes over time, as seen on MRI.MethodsTwenty-six patients who underwent SRS for brain metastases in our institution were included. We evaluated the occurrence of a tumor shift between the diagnostic MRI and radiotherapy planning MRI. For 42 brain metastases the tumor and peritumoral edema were delineated on the contrast enhanced T1weighted and FLAIR images of both the diagnostic MRI and planning MRI examinations. Centre of Mass (CoM) shifts and tumor borders were evaluated. We evaluated the influence of steroids on peritumoral edema and tumor volume and the correlation with CoM and tumor border changes.ResultsThe median values of the CoM shifts and of the maximum distances between the tumor borders obtained from the diagnostic MRI and radiotherapy planning MRI were 1.3 mm (maximum shift of 5.0 mm) and 1.9 mm (maximum distance of 7.4 mm), respectively. We found significant correlations between the absolute change in edema volume and the tumor shift of the CoM (p < 0.001) and tumor border (p = 0.040). Patients who received steroids did not only had a decrease in peritumoral edema, but also had a median decrease in tumor volume of 0.02 cc while patients who did not receive steroids had a median increase of 0.06 cc in tumor volume (p = 0.035).ConclusionOur results show that large tumor shifts of brain metastases can occur over time. Because shifts may have a significant impact on the local dose coverage, we recommend minimizing the time between treatment preparation and delivery for Linac based SRS.

MRI appearance change during stereotactic radiotherapy for large brain metastases and importance of treatment plan modification during treatment period

“…The timing of steroid administration was the predictive factor of tumor reduction, displacement and shape change. The correlation between the shift of center of PTV and change in edema volume was mentioned in previous report [13]. As steroid administration reduced the surrounding edema [14], displacement and shape change might have been caused.…”

“…This study reported MRI appearance changes during linac-based SRT for large brain metastases, and analyzed the lesions necessitating treatment plan modification. Some studies reported about tumor changes in a short period between planning MRI and STI start, such as tumor size and shift [12, 13]. However, there were few studies mentioned about the detail changes of tumor during SRT periods [9, 10].…”

MR-guidance in clinical reality: current treatment challenges and future perspectives

“…Specific entities are metastases, primary brain tumors (low-grade gliomas, anaplastic astrocytomas, oligodendrogliomas, glioblastomas), extra-axial tumors such as meningioma, and other benign entities including pituitary adenomas and vestibular schwannomas. A MRI-based planning workflow could potentially be both, cost- and time-saving while reducing uncertainties associated with CT-MRI registration [4]. MRI already represents the gold-standard imaging method for brain tumor diagnosis and the assessment of treatment response [5].…”

“…However, a crucial difference emerges: the MRL systems enable a rapid adaptation, immediate target volume delineation [6] and quick tumor response assessment. An example is the treatment of a resection cavity, which can change significantly in shape and size between the simulation MRI and the initiation of treatment [4]. Furthermore, if hypofractionated stereotactic radiosurgery (SRS) is applied, the resection cavity could also change during the treatment course of 3–5 fractions, which would be visible using MRgRT.…”

Does an immobilization mask have added value during planning magnetic resonance imaging for stereotactic radiotherapy of brain tumours?

“…The CT scan provides electron density information necessary for dose calculations in the currently commercially available treatment planning systems. The MRI is used for anatomical information (especially tumour extent) and is usually acquired shortly before RT delivery as progression and shifting of the lesions over time has been shown to occur in patients with brain metastasis [1] . A contrast-enhanced T1-weighted sequence is the recommended MRI simulation reference image for intracranial stereotactic radiotherapy (SRT) [2] .…”