The symptoms of radiation necrosis are varied depending upon the area of the brain involved, but common symptoms include headache, drowsiness, memory loss (especially if the temporal lobe is involved), personality changes, and seizures. Whole-brain radiation therapy, as is commonly done for treating lymphoma, can result in a diffuse encephalopathy.

The problem with diagnosing radiation necrosis of the brain is that it is difficult to distinguish tumor recurrence versus radiation necrosis. This distinction is especially difficult with glioblastoma multiforme which often may have a palisading pattern of necrosis. Brain MRI perfusion scanning can be helpful in differentiating because in radiation necrosis there is often a lack of T2 flair usually involving the white matter but is commonly present with tumors. MR spectroscopy typically shows low choline and creatine and NAA in radiation necrosis. FDG-PET scanning typically shows lower activity in radiation necrosis, while recurrent tumors typically have increased metabolic activity. Conventional imaging can be misleading and ultimately surgical biopsy may be necessary to distinguish whether the lesion is from radiation necrosis or recurrence of cancer.[6]

The approach to the treatment of patients with radiation necrosis should be divided into patients who are asymptomatic and symptomatic. In the asymptomatic patients, it would be reasonable to do serial MRI scans to follow the area of suspected necrosis and see if it further evolves or consider the possibility of tumor recurrence. A lesion biopsy ultimately may be necessary to determine whether it is radiation necrosis versus tumor recurrence, especially if the lesion continues to grow. It is very important to establish the diagnosis of radiation necrosis versus tumor recurrence so that the appropriate therapy may be rendered to the patient. If the patient is having neurologic symptoms or increased intracranial pressure, then surgical options, steroids, anticoagulation therapy, and even hyperbaric oxygen therapy will need to be considered. A novel treatment for radiation necrosis using bevacizumab has been studied with just class one evidence available for its efficacy but is not yet considered standard therapy.[7]

Hyperbaric oxygen therapy (HBO2) has no double-blind placebo-controlled trials to prove its efficacy, but many case studies and prospective studies demonstrate some benefit. HBO2 promotes tissue healing by improved angiogenesis that results in better tissue perfusion. Hyperbaric oxygen therapy also can reduce tissue edema and enhance collagen synthesis by fibroblasts which activity is crucial for the healing of damaged tissue. Radiation necrosis is in part caused by a coagulative and ischemic process which leads to cellular death; this is, in essence, an ischemia-reperfusion injury phenomenon. HBO2 helps to restore normal cellular functions to aid the repair of the ischemic damaged tissue. It is important to note that the angiogenesis that occurs with hyperbaric oxygen therapy produces a vascular supply to the radiation damage tissue that is more robust than the telangiectasia that sometimes occurs as a part of the radiation necrosis.[8][9]

HBO2 usually is delivered at a dose of 2 to 2.4 atmospheres absolute for 90 to 120 minutes daily and may take 20 to 30 treatments before significant angiogenesis occurs with the improvement of the neurologic symptoms. The major disadvantage of hyperbaric oxygen therapy is that it is expensive, time-consuming, and universally not readily available, although this later problem is becoming less of a concern as more facilities are built. More studies on the use of hyperbaric oxygen therapy alone and in conjunction with other therapies, such as concomitant steroids and surgery, are needed to determine the best treatment practices.[10] An interesting study using bevacizumab (which inhibits VEGF) and HBO2 (which enhances VEGF) in combination would be interesting to do.[11] This would be helpful to elucidate some of the other mechanisms by which the HBO2 is working.

The main differential diagnosis of radiation necrosis is tumor recurrence that can be differentiated on the basis of imaging findings described under "Evaluation."

Small retrospective studies have shown high rate of stability and improvement in 70-80% of treated patients.[12]

• Ear barotrauma
• Dyspnea and pneumothorax
• Chest tighntess due to oxygen toxicity

The patient should be educated regarding the treatment, its complications, and that he/she may have to lie in the chamber till the therapy is over.

HBO2 does have undesirable side effects which include enhancement of cataracts; ear barotrauma; pneumothorax formation with pressure changes during the treatment, which can become life-threatening; hypoglycemia in diabetic patients, especially if taking insulin and/or oral hypoglycemic agents; and oxygen associated seizures. Because the patient is being treated in an environment with 100% oxygen under pressure, there is always the risk of fire and failure of the chamber. The risk of hyperbaric oxygen treatment is relatively low, and the benefit of the therapy generally outweighs the risk. It is important that safety precautions are followed and strongly recommended that the facility considered for treatment have appropriate certification.

The diagnosis and management of radiation-induced brain necrosis are complex and best done with an interprofessional team including neurology nurses. There is no optimal treatment for this pathology and recently HBO has been advocated. However, there are no good randomized trials on the use of HBO for radiation-induced brain necrosis. Some reports indicate positive results but the recovery is prolonged. One should not forget that HBO therapy is not benign and is also associated with a number of complications that may adversely affect outcomes.