82Rubidium chloride positron emission tomography discrimination of recurrent intracranial malignancy from radiation necrosis.

Background: Accurate identification and discrimination of post treatment changes from recurrent disease remains a challenge for patients with intracranial malignancies despite advances in molecular and magnetic resonance imaging. We have explored the ability of readily available Rubidium-82 chloride (RbCl) positron emission tomography (PET) to identify and distinguish progressive intracranial disease from radiation necrosis in patients previously treated with radiation therapy.

Methods: Six patients with a total of 9 lesions of either primary (N.=3) or metastatic (N.=6) intracranial malignancies previously treated with stereotactic radiation surgery (SRS) and persistent contrast enhancement on MRI underwent brain RbCl PET imaging. Two patients with arteriovenous malformations previously treated with SRS, also had brain RbCl PET imaging for a total of 11 lesions studied. Histological confirmation via stereotactic biopsy/excisional resection was obtained for 9 lesions with the remaining 2 classified as either recurrent tumor or radiation necrosis based on subsequent MRI examinations. RbCl PET time activity curve analysis was performed which comprised lesion SUVmax, contralateral normal brain SUVmax, and tumor to background ratios (TBmax).

Results: RbCl demonstrates uptake greater than normal brain parenchyma in all lesions studied. Time activity curves demonstrated progressive uptake of RbCl in all lesions without evidence of washout. While recurrent disease demonstrated a greater mean SUVmax compared to radiation necrosis, no statistically significant difference between lesion SUVmax nor TBmax was found (P>0.05).

Conclusions: RbCl PET produces high-contrast uptake of both recurrent disease and radiation necrosis compared to normal brain. However, no statistically significant difference was found between recurrent tumor and radiation necrosis.