5.2.5\ Brachytherapy Seeds

5.2.5.1\ Discussion

Local radiation therapy can be administered for treatment of brain tumors via brachytherapy (interstitial) seed implantation. The seeds contain radioactive isotopes, such as I-125, and can

a

c

be implanted temporarily (for approximately 1 week) or permanently. Temporary seeds are typically introduced and removed using plastic catheters passed through burr holes, while permanent seeds are implanted in the tumor/surgical bed. The seeds appear as tiny metallic cylinders on CT or signal voids on MRI (Fig. 5.29).

b

Fig. 5.29  Brachytherapy seeds. The patient has a history of metastatic sarcoma to the right frontal lobe and is status post right frontal craniotomy, gross total tumor resection, and placement of I-125 interstitial radiation seeds. Axial

CT image (a) demonstrates numerous metallic interstitial seeds each measuring a few millimeters in length within the surgical cavity. On both T2-weighted (b) and T1-weighted (c) MRI, the seeds are of low signal intensity

5.2.6\ GliaSite Radiation

Therapy System

5.2.6.1\ Discussion

The GliaSite radiation therapy system is used to administer intracranial brachytherapy for brain tumor treatment. The system is a catheterbased device that consists of an infusion port on one end and a double balloon on the other. Positioning markers are also included along the length of the catheter. The balloon, which contains the radioactive isotope solution, is

a

positioned within the surgical cavity. The filled balloon is hyperattenuating on CT and displays fluid signal on MRI (Fig. 5.30). Normally, there can be enhancement in the tissues surrounding the balloon. The catheter and its position markers are also visible on both modalities. However, the balloon and surrounding tissues are better assessed on MRI, particularly when there is tumor recurrence. Perfusion MRI is especially helpful for evaluating enhancing lesions in the tumor bed, whereby elevated rCBV suggests recurrence of high-grade tumor.

b

Fig. 5.30  GliaSite system. The patient has a history of right frontal glioblastoma, status post resection. Axial CT (a) and axial T2-weighted (b) and T1-weighted (c) MR images that show the fluid-filled GliaSite radiation therapy system balloon at the end of the low signal intensity catheter with positioning markers. Pre- (d) and

post-contrast (e) T1-weighted images and CBV map (f) obtained 1 year later show an enhancing nodule with corresponding increased perfusion adjacent to the catheter in the surgical bed, consistent with recurrent tumor (arrows). Illustration of the GliaSite Radiation Therapy system (g)