Tumour Progression or radionecrosis? The role of molecular imaging

Gliomas: The basics● Arises from glial cells● The most common site of gliomas is the brain● Make up ~30% of all brain and central nervous

system tumors and 80% of all malignant brain tumors

● Low-grade gliomas [WHO grade II] are well-differentiated (not anaplastic); these are benign and portend a better prognosis for the patient

● High-grade [WHO grade III–IV] gliomas are undifferentiated or anaplastic; these are malignant and carry a worse prognosis

Prognosis

● Prognosis largely determined by grade● For low grade gliomas, median survival is 12-17

years● Anaplastic astrocytoma (Grade III), median

survival 3 years● Glioblastoma Multiforme (Grade IV), median

survival 14 months (without treatment, 4 months)

Treatment

● Grade IV – debulking with concurrent irradiation and temozolomide, then 6 months of temozolomide

● Grade III – debulking with irradiation. Temozolomide if recurrence

● Low grade – controversial. Debulking. Irradiation if progression? Temozolomide?

● Despite treatment, high grade gliomas often recur

Recurrence or radionecrosis?

● Due to the high risk of recurrence, post-treatment imaging must be able to distinguish between recurrence, pseudo-progression, and radiation necrosis

● Imaging options include MR, PET, and SPECT

MRI

PET

Case Report: 17M with headache, blurred vision, left upper limb weakness

Dx: GBM, 5 months post chemo-rads

FDG-PET/CT

FCH-PET/CT

Sestamibi-SPECT/CT

Sestamibi

● Monovalent lipophilic cation● No tissue specificity● Doesn't cross the BBB● No contrast nephropathy, no NSF, no

significant anaphylaxis risk

Single Photon Emission Computed Tomography (SPECT)

● 3D imaging using a gamma camera● Many different possible radiotracers depending

on the application● For glioma imaging, perfusion agents are

generally used e.g. Sestamibi, Tetrofosmin, Thallium

SPECT

LeJeune et al

● Largest (N=201) MIBI study to date● For all grades, Sn 90%, Sp 91.5%, Accy 90.5%● Path/clinical follow-up as gold standard● False positives in 3 patients - 2 inflammation (?)

1 unknown● False negatives in 5 – intact BBB (?)● SPECT positive earlier than MR

Interpretation

Advantages

● Accuracy comparable to MR Spectroscopy● No risk to the patient (besides radiation)● High inter-observer agreement● Positive earlier than MR● No patient restrictions● Cost ($215.95)

Disadvantages

● Radiation exposure (~4.5 mSv < 2 yrs background radiation)

Fusion Imaging