Cancer Treatment Today » Imaging

How often to scan the brain after radiosurgery

M Levin, MD — Thu, 22 Nov 2012 15:25:50 +0000

How to follow a patient with brain mets after radiosurgery is becoming a more and more common question becasue treatments that control cancer in the rest of the boady are getting to be more and more effective and patients are living longer before cancer comes back in the brain or in the body. One does not want to overmonitor but also not to miss metastses when they come back. Many patietns remain disease free for many months even years after radiosurgery of the brain. For example, one study reported a median time of 8.8 months to new metastasis becoming visible after radiosurgery. Patients with 3 or more brain metasttses and cancers other than NSCLC were more likely to have future metastasis. Based on these facts, there was a published recommendation for close surveillance with a 3-month interval between magnetic resonance imaging (MRI), in order to identify new metastasis early enough to start treatment. However, much is not known about this. Clearly, more frequent imaigng is warranted soon after radiosurgery and less frequenlty as time goes on. As the most sensitive tests, MRI is the preferred surveillance tool, even though newer methods, such as spectroscopy, diffusion-weighted imaging, and perfusion-weighted imaging are coming to the fore.

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PET for glioblastoma

M Levin, MD — Fri, 24 Aug 2012 18:03:47 +0000

PET is more and more frequently used to visualize brain cancers. However, PET is not medically appropriate to follow glioblastoma because it not supported by credible scientific evidence published in peer-reviewed medical literature generally recognized by the relevant medical community. PET for brain cancer is not included in the NCCN guidelines and CMS does not cover PET for this diagnosis. Occasionally, PET can provide information to differentiate tumor necrosis from tumor progression. Tumor necrosis is when a cancer dies after being treated. The sensitivity of PET for differentiating necrosis and tumor progression is 80%–90% and the specificity is 50%–90%. Causes of false-negative PET results include recent radiation therapy, low grade, and small tumor volume. PET may be false positive in nonmalignant inflammatory processes and subclinical seizure activity. The question of hypermetabolic foci of radiation injury as a cause of false-positive scans requires further investigation. Other issues requiring further study are the optimal timing of PET after radiation and chemotherapy and the accuracy of PET in tumors other than high-grade gliomas.

A 2010 guideline by Laperrier says: “Positron emission tomography (PET) is not recommended for the determination of diagnosis or grading in gliomas. A recommendation cannot be made for or against the use of PET or positron emission tomography/computed tomography (PET/CT) in the assessment of patients with recurrent gliomas because of insufficient evidence. Positron emission tomography (PET) is not recommended for the determination of diagnosis or grading in gliomas. A recommendation cannot be made for or against the use of PET for the assessment of treatment response in gliomas because of insufficient evidence. A recommendation cannot be made for or against the use of PET or positron emission tomography/computed tomography (PET/CT) in the assessment of patients with recurrent gliomas because of insufficient evidence. Positron emission tomography (PET) is not recommended for the determination of diagnosis or grading in gliomas. A recommendation cannot be made for or against the use of PET for the assessment of treatment response in gliomas because of insufficient evidence. A recommendation cannot be made for or against the use of PET or positron emission tomography/computed tomography (PET/CT) in the assessment of patients with recurrent gliomas because of insufficient evidence.”
It is not clinically appropriate in terms of type, frequency, extent, site and duration and considered effective for the condition in question as per literature and guidelines

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Radiologic follow-up of pituitary tumors

M Levin, MD — Fri, 24 Aug 2012 17:53:32 +0000

Pituitary tumors are classified as micoradenomas, sometimes called incidentalomas, because they tend to be asymptomatic and discovered incidentally, or macroadenomas. Microadenomas are small and macroadenomas are larger. BMJ Best Practice (2012) says that there is no consensus about the follow-up duration of patients with non-functional pituitary microadenomas, but recommends a follow-up MRI in 1 year with no further routine imaging study if the tumour is stable, especially in those with a pituitary microadenoma < 6 mm in size, unless the patient develops symptoms or signs suggestive of mass effect.

The risk of tumour growth for pituitary macroadenomas is expected to be higher since the tumour has already shown the propensity to grow. There is no consensus, but a pragmatic approach would be to obtain a follow-up MRI at 6 months and then yearly for 5 years. This can be followed by an imaging study every 2 to 3 years if the pituitary tumor is stable. This recommendation is in line with that of the Endocrine Society and Best Practice.

Biochechemical and laboratory followup is not discussed in this review of radiologic followup.

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