Session Item

Brain metastases (BM) are considered a serious problem regarding the nature of oncological diseases. Radiotherapy, either alone or after surgery, remains the mainstay of treatment for brain metastases. Whole brain radiotherapy (WBRT), stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) could be an option. SRT can be performed with Gamma knife, Cyberknife, tomotherapy and linear accelerator. Modern linear accelerators with integrated image guided radiotherapy (IGRT) solutions such as cone beam computed tomography (CBCT) enabled the extensive use of SRT in the management of BMs. The aim of our work is to demonstrate the role of image guidance and volumetric imaging in stereotactic radiotherapy (SRT) of brain metastases. 

Between 2018 and 2020, 106 patients underwent intracranial stereotactic radiotherapy. 10 patients with metastatic brain tumors treated with SRT were randomly selected and included in our study model. Patients were scanned pre- and post-treatment with cone beam CT. This is used to determine the translational and rotational deviations. Rotation values can be corrected up to 2.9°, and for values above 3° the patient must be repositioned. Translational values are corrected to 10 mm, above that the patient needs to be repositioned. Immediately post-treatment, another HR 3D CBCT is performed to assess the intra-fractional displacements. Total of 100 verifications of 50 stereotactic treatments were performed and analyzed.

Our analysis compared the results of 50 pre-treatment and 50 post-treatment verification CBCT measurements in 10 patients. Population mean X, Y, Z values were -0.13 cm, -0.04 cm, -0.03 cm, respectively, rotation values 0.81°, 0.51°, 0.46°, respectively. Systematic error components for translational displacements pre corrections were as follows: 0.14 cm for X, 0.13 cm for Y and 0.1 cm for Z. Systematic error components of the post-treatment HR 3D CBCTs were as follows: 0.01 cm for X, 0.06 cm for Y and 0.04 cm for Z. 

Frameless immobilization allows fractionation of the treatments but requires a very high degree of accuracy and reproducibility in patient positioning. In our study we evaluated the patient positioning and inter-fractional accuracy of our frameless system. Population mean values close to 0 confirmed that there is no systematic variation in our system and the accuracy of our equipment and tools is reliable. HR 3D CBCT scans performed pre SRTs further refine patient and target volume setting, support medical decision making and eliminate the possibility of gross error.