|LETTER TO EDITOR
|Year : 2020 | Volume
| Issue : 2 | Page : 416-417
Distinguishing radiation necrosis from tumor recurrence
Paritosh Pandey1, VA Ullas2
1 Department of Neurosurgery, Manipal Hospitals, Bengaluru, Karnataka, India
2 Department of Radiology, Manipal Hospitals, Bengaluru, Karnataka, India
|Date of Submission||22-Mar-2020|
|Date of Decision||29-Apr-2020|
|Date of Acceptance||02-May-2020|
|Date of Web Publication||19-Jun-2020|
Manipal Hospitals, Old Airport Road, Bengaluru, Karnataka
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Pandey P, Ullas V A. Distinguishing radiation necrosis from tumor recurrence. Cancer Res Stat Treat 2020;3:416-7
In the previous issue of the journal, the authors have reported a case of radiation necrosis following whole-brain radiation therapy in a patient with metastatic lung cancer. As highlighted by the authors, even in the best of the situations, it can be very difficult to distinguish between recurrence/relapse and radiation necrosis. The authors have successfully introduced various imaging features to distinguish between tumor recurrence and radiation necrosis, including patterns of contrast enhancement and advanced imaging techniques. Even in the era of advanced imaging techniques, differentiating between the two remains a dilemma, often requiring histopathological confirmation. Hence, in addition to advanced imaging techniques, it is essential to emphasize the review of conventional tumor characteristics in pre- and post-treatment scans, radiation therapy plan, and interval changes on follow-up to aid in the differentiation.
Review of the tumor characteristics for similarity and differences between the pre- and post-treatment scans aids in differentiating recurrence from radiation necrosis. Features that have been suggested to favor radiation necrosis over recurrence include lesions appearing distant from the primary resection site, conversion from a non-enhancing to an enhancing lesion after radiation therapy, periventricular enhancing lesions particularly capping the ventricles or within the corpus callosum, and characteristic patterns of enhancement. On the other hand, multiple enhancing lesions, involvement of the corpus callosum with subependymal spread, and crossing over midline favor recurrence.
Review of the radiation therapy plan will also help in distinguishing radiation necrosis from recurrence, especially in case of extra-axial intracranial malignancies and extracranial head-and-neck malignancies. The key points to note include the location of the primary malignancy, the type of radiation, the radiation portal extent, and the inclusion of normal structures.
On conventional magnetic resonance (MR) images, the presence of a smaller T2-hypointense nodule in relation to a larger peripherally enhancing focus, suggesting a smaller lesion quotient, favors the diagnosis of radiation necrosis over recurrence, given the hypointense appearance of cellular tumors on T2-weighted images.
In a study by Hein et al., diffusion-weighted imaging helped in determining the apparent diffusion coefficient ratio, which was significantly lower in the tumor recurrence group (mean ± standard deviation [SD] =1.43 ± 0.11) than in the non-occurrence group (mean ± SD = 1.82 ± 0.07).
The relative cerebral blood volume at perfusion MR imaging and fluorodeoxyglucose-positron emission tomography (PET) can lead to a false-positive diagnosis of recurrent tumors because of volume averaging with the normal cortex; on the other hand, a mixture of a large percentage of necrosis with limited metastasis can lead to a false-negative diagnosis. An alternative perfusion technique using endogenous proton tracers, i.e., arterial spin-labeling positivity, has been associated with a better pathological diagnosis of tumor progression following stereotactic radiosurgery as compared to PET and single-photon emission computed tomography (SPECT). Arterial spin-labeling (ASL) showed better specificity than other modalities, such as ASL (100%), PET (75%), and SPECT (50%) in a study by Lai et al.
The evolution of a lesion over a period of time also helps in differentiating between tumor recurrence and radiation necrosis. Lesions enhance and enlarge initially as a response to radiation treatment only to become smaller in the follow-up scans as against a recurrent lesion.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Madala RK, Krishnatry R, Noronha V, Patil V, Joshi A, Menon N, Muthuluri H, Prabhash K. Neurological deterioration in a patient with lung cancer and brain metastasis. Cancer Res Stat Treat 2020;3:97-9. [Full text]
Kumar AJ, Leeds NE, Fuller GN, Van Tassel P, Maor MH, Sawaya RE, et al
. Malignant gliomas: MR imaging spectrum of radiation therapy- and chemotherapy-induced necrosis of the brain after treatment. Radiology 2000;217:377-84.
Mullins ME, Barest GD, Schaefer PW, Hochberg FH, Gonzalez RG, Lev MH. Radiation necrosis versus glioma recurrence: Conventional MR imaging clues to diagnosis. AJNR Am J Neuroradiol 2005;26:1967-72.
Shah R, Vattoth S, Jacob R, Manzil FF, O'Malley JP, Borghei P, et al
. Radiation necrosis in the brain: Imaging features and differentiation from tumor recurrence. Radiographics 2012;32:1343-59.
Dequesada IM, Quisling RG, Yachnis A, Friedman WA. Can standard magnetic resonance imaging reliably distinguish recurrent tumor from radiation necrosis after radiosurgery for brain metastases? A radiographic-pathological study. Neurosurgery 2008;63:898-903.
Hein PA, Eskey CJ, Dunn JF, Hug EB. Diffusion-weighted imaging in the follow-up of treated high-grade gliomas: Tumor recurrence versus radiation injury. AJNR Am J Neuroradiol 2004;25:201-9.
Lai G, Mahadevan A, Hackney D, Warnke PC, Nigim F, Kasper E, et al.
Diagnostic accuracy of PET, SPECT, and arterial spin-labeling in differentiating tumor recurrence from necrosis in cerebral metastasis after stereotactic radiosurgery. AJNR Am J Neuroradiol 2015;36:2250-5.
Friedman DP, Morales RE, Goldman HW. MR imaging findings after stereotactic radiosurgery using the gamma knife. AJR Am J Roentgenol 2001;176:1589-95.