Purpose: Stereotactic radiosurgery (SRS) is an established treatment option for patients with a limited number of brain metastases. SRS uses a high dose of radiation to treat tumors. SRS has shown advantages in the increased local control compared with whole brain radiotherapy (WBRT). However, SRS might bring about a risk of radiation induced side effect to be observed months to years after SRS. The current research is to review SRS treated metastases on MR images followed up to 8 years after SRS.
Methods: This is a retrospective imaging study on brain SRS for patients with up to 7 brain metastases. SRS treatment option with a single iso-center technique was offered to the patients with 2 or more brain metastases. The 1- mm magnetic resonance (MR) images with contrast was registered with 1mm-CT images. Identified target volumes were delineated on the registered MR and CT images. A Varian Eclipse version 15.1 treatment planning system was used for treatment planning. Daily image guidance was used for target localization and patient alignment. The treatment was delivered with volumetric modulated arc therapy with 6MV flattened filter free (6MV FFF) mode at a rate of 1400 MU per minute from a Varian TrueBeam linear accelerator.
Results: Followed up MR images in the mean 5 years (ranging from 2 to 8 years) after SRS showed an evolution of metastases (treated volume (TV)). A good control of metastases was seen from months to years after SRS. Some patients had necrosis formed within the treated volume and then degraded with time. Severe side effects from SRS are not observed by reviewing the MR images.
Conclusion: A review of the followed up MR images indicated that both single and multiple iso-center technique are able to achieve similar tumor control. A single iso-center SRS is suggested for multiple metastases.