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  • Updated 08.06.2021
  • Released 03.24.1999
  • Expires For CME 08.06.2024

Radiation: CNS complications

Introduction

Overview

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

In recent years, a number of novel methods to prevent radiation toxicity have been investigated and the results published. NRG Oncology CC001 showed that hippocampal-sparing whole brain radiation therapy decreases neurocognitive injury compared to conventional whole brain radiation therapy. Treatment modalities like proton therapy and FLASH radiation therapy may mitigate the risk of radiation injury without compromising tumor control.

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 may be permanent.

The incidence and severity of radiation-induced CNS complications varies with the radiation dose, volume of tissue irradiated, fractionation scheme, and potentially target radiotherapy location; degree of edema; 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 with the risk of progressive or recurrent disease.

Historical note and terminology

Most historic cancer therapies were nonspecifically cytotoxic. This was especially true of radiation therapy. 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 (16). 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. The incidence of radiation-related nervous system side effects appears to be increasing as conventional radiation therapy techniques are being applied more aggressively, new radiation delivery approaches such as stereotactic radiotherapy, intensity modulated radiation therapy (IMRT), volumetric modulated arc radiation therapy (VMAT) or particle therapy are becoming commonplace, and patients are surviving longer.

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