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

Abstract

Introduction: Linac-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.

Methods: Twenty-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.

Results: The 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).

Conclusion: Our 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.

Keywords: Brain metastasis; Edema; SRS; Steroids; Tumor shifts.

Fig. 1

Example of patient who received the day before the MRD one gift of dexamethasone and continued dexamethasone intake hereafter (2dd4mg). The MRRT was made 8 days later and the tumor contours overlaid on sagittal (left) and coronal (right) view of the MRRT T1w + c image. The pink contour is the reference contour from the MRD examination, whereas the green contour is delineated on the data from the MRRT examination. The red lines in the left image represent the positive distances between the two tumor surfaces. The right image shows a 3-dimentional depiction of these tumor contours. Here, the MRRT tumor volume which is shifted outside the MRD tumor volume is indicated in green. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

Schematic 2D view of the distances D^CoM and D^MRD-MRRT. D^CoM represents the shift of the Centre of Mass of the tumor on the MRD (in grey) and MRRT (in white), whereas D^MRD-MRRT is the maximal perpendicular distance between the two tumor delineations on the MRD and MRRT. We did correct for possible tumor volume changes as explained in the material and methods (but this is not schematically represented in this graph).

Fig. 3

D^CoM as function of absolute volume change of oedema. The group ‘difference in oedema >6.6 cc’ is split up in patients with a decrease and increase of oedema. For the whole group a significant Spearman correlation of r² = 0.640 (p < 0.001) is found. For 2 patients no oedema is seen on MRD. For patients with multiple metastases, only the tumor with largest D^CoM is included resulting in a cut off of 6.6 cc.

Fig. 4

D^MRD-MRRT as function of absolute volume change of oedema. The group ‘difference in oedema >6.6 cc’ is split up in patients with a decrease and increase of oedema. For the whole group no significant Spearman correlation is found (r² = 0.405 (p = 0.040)). For 2 patients no oedema is seen on MRD. For patients with multiple metastases, only the tumor with largest D^CoM is included resulting in a cut off of 6.6 cc.