RADIATION INJURY TO THE BRAIN

Radiation treatments  affect all cells that are targeted.  This means where normal healthy cells are targeted along with tumor cells, there will be injury to the healthy cells.  The Merck Manual states the following:

Radiation Injury to the Nervous System:   The nervous system can be damaged by radiation therapy. Acute and subacute transient symptoms may develop early, but progressive, permanent, often disabling nervous system damage may not appear for months to years. The total radiation dose, size of the fractions, duration of therapy, and volume of [healthy brain] nervous tissue irradiated influence the likelihood of injury. Considerable variation in individual susceptibility complicates the effort to predict safe radiation doses. (Source:  The Merck Manual of Diagnosis and Therapy, Section 14, Neurologic Disorders.)

Side-effects of radiation are caused by the radiation treatment’s affect on normal cells with some being minimal and other being permanent.  Additionally, the effects may occur quickly (acute) or months and years after treatment. 

Acute reactions occur during or immediately after radiation.  They are normally caused by swelling and can be easily controlled with medications.  Delayed or late reactions are normally permanent and can be progressive.  They can vary from mild to severe and may include decreased intellect, memory impairment, confusion, personality changes among other changes.  All symptoms would be dependent on the amount of healthy tissue targeted with radiation.

Oncogenesis, the development of another tumor from the radiation treatment to the brain,  is now a recognized, although rare, possible long-term side-effect of radiation to the brain.  When another tumor occurs it is rare, and is most often associated with whole brain radiation or with fractionated radiotherapy.  Each of these target more healthy brain tissue than one-session radiosurgery.

ONE-SESSION RADIOSURGERY:

The most  important component of whether there is radiation injury to the brain is dependent upon the amount of healthy tissue that is targeted.  Additional factors will be the radiation dose that the healthy tissue receives and how it receives it.  The type of instrument that is available to an individual for treatment will be the deciding factor in radiation damage.  Today patients are fortunate in that there are choices for treatment that limit radiation to healthy brain tissue to small amounts or none with one-session radiosurgery.  The most common machine for this type of treatment is the neurosurgical instrument the Gamma Knifeâ.  The Gamma Knifeâ severely restricts the radiation of healthy tissue by targeting exactly where the neurosurgeon directs the radiation to the tumor bed with negligable overlap to healthy tissue.  Where the neurosurgeon can not limit targeting healthy tissue the patient will be told immediately.

FRACTIONATED RADIOTHERAPY:

With fractionated radiotherapy, a larger path of healthy tissue is targeted than with one-session treatments due to limitation with the type of linear accelerator machines utilized.    In the past , it has been felt that some of the healthy cells that are radiated within the brain will have time to heal if the treatments are given over time (fractionated).  Since the brain does not regenerate like other body cells, there is much debate over that value of fractionation within the brain.  Additionally, fractionated radiotherapy may allow the faster growing tumor or cancerous cells within the brain to recover between treatments as tumor cell do regenerate quickly unlike normal brain tissue.  IMRT is a form of fractionated radiotherapy that is more conformal to the tumor area with more overlap that one-session instruments to healthy tissue but less than the older model radiotherapy equipment.  Machines that do fractionated treatments are linear accelerator based.  It should be noted that with daily treatments over time there is less accuracy that with the Gamma Knifeâ as the skull can not be restricted in the same manner.

RADIATION THERAPY:

Whole brain radiation therapy (WBRT) targets wide areas of the brain and was common with metastatic tumors in the past.  We now know that new tumors may ‘seed’ to the brain as soon as the Whole brain radiation is completed.  Thus the treatment only helps for one point in time.

WBRT is the most damaging of all types of radiation treatments and causes the most severe side effects in the long run to patients.  In the past, patients who were candidates for whole brain radiation were selected because they were thought to have limited survival times of less than 1-2 years and other technology did not exist.  Today many physicians question the use of WBRT in most cases as one-session radiosurgery treatment can be repeated for original tumors or used for additional tumors with little or no side effects from radiation to healthy tissues. Increasingly, major studies and research have shown that the benefits of radiosurgery can be as effective as WBRT without the side effects.

SUMMARY:

Where one-session radiosurgery can not be performed, and the patient can not have open skull surgery, fractionated radiation treatments should be the next line of treatment considered.