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  • Updated 04.30.2024
  • Released 03.24.1999
  • Expires For CME 04.30.2027

Radiation: CNS complications



Radiation therapy is an effective therapy for many malignancies and benign conditions. However, radiation therapy can potentially cause early and late toxicities in the central nervous system. These include radiation necrosis, cerebrovascular disease, cognitive deficits, endocrinopathies, encephalopathy, myelopathy, plexopathy, radiculopathy, neuropathy, and secondary tumors. This article discusses in detail radiation complications in the central nervous system, prevention of radiation toxicity, and therapeutic options.

With the widespread adoption of conformal intensity modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT), particle therapy, and stereotactic radiation approaches, it has become more possible to limit and prevent radiation toxicity. In recent years, novel methods to prevent radiation toxicity have been reported. NRG Oncology CC001 showed that hippocampal-sparing whole brain radiation therapy decreases neurocognitive injury compared to conventional whole brain radiation therapy. Prospective studies are now investigating the role of sparing other important structures involved in neurocognition, such as the fornix, corpus callosum, and amygdala. Spine stereotactic body radiation therapy (SBRT) has become more prevalent in the treatment of spinal osseous metastases and has been demonstrated to be generally safe, with no difference in toxicity including in rates of myelopathy, when compared with conventionally fractionated radiation therapy in recently published prospective trials.

The diagnosis and treatment of radiation necrosis continues to improve, with more imaging techniques and treatment options available. Advancements in diagnosis include the application of perfusion magnetic resonance imaging (MRI) to determine relative cerebral blood volume (rCBV) and newer imaging modalities like amino acid positron emission tomography (PET). Contemporary treatment options for radiation necrosis include bevacizumab and laser-interstitial thermal therapy (LITT).

Treatment of late cognitive impairment due to central nervous system radiation continues to be an elusive goal.

Key points

• When radiation therapy is used to treat primary or metastatic central nervous system (CNS) diseases, or non-CNS targets located close to neural structures, side effects to the normal neural tissues can occur.

• When practicing within accepted constraints, the acute and subacute complications of radiation therapy are generally mild, transient, or treatable with corticosteroids.

• In contrast, the late complications of radiation therapy are generally progressive and often permanent.

• The incidence and severity of radiation-induced CNS complications varies with the radiation dose, fractionation scheme, volume of tissue irradiated, and target location; patient age; underlying diseases (malignant and nonmalignant); concomitant treatments; comorbidities; and length of survival after completion of radiation treatment.

• In general, the risks of radiation-related CNS side effects are balanced against the risk of progressive or recurrent disease.

Historical note and terminology

Older radiation therapy techniques used to treat primary or metastatic nervous system diseases, or structures adjacent to neural structures, caused damage to the nervous system. The most dramatic example of this type of injury, brain radiation necrosis, was first recognized in 1930, soon after radiation was first used therapeutically for brain tumors (23). Since that time, a spectrum of injuries throughout the central and peripheral nervous system has been identified, and some of the details of specific syndromes have been elucidated. Despite this heightened awareness, the neurologic complications of radiation therapy continue to occur because individual tolerances to radiation are variable, safe radiation thresholds are not precisely known, latency to development of injury range between days to years, and risks are altered by use of chemotherapy, other systemic therapies, or preexisting disease. Conventional and stereotactic radiation treatment cause similar toxicities, though dose per fraction, volume irradiation, location, and other dosimetric factors may affect severity and timing of injury. Despite increasing understanding and ability to prevent CNS radiation toxicity, the incidence of radiation-related nervous system side effects are likely to increase as patients survive longer.

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