Difference Between Neutron Radiation & IMRT

It may seem an unlikely ally, but ionizing radiation can often be a potent weapon in the fight against cancer. Over the past few decades, the technology available to radiation oncologists has become increasingly sophisticated; new techniques like intensity-modulated radiation therapy (IMRT) offer doctors the ability to increase the dose of radiation to the tumor while sparing healthy tissue. Other approaches like neutron therapy try to kill more cancer cells by using different kinds of radiation.

Types

• The most basic difference between intensity-modulated radiation therapy (IMRT) and neutron therapy lies in the type of radiation they use. IMRT attacks the tumor with X-rays (electromagnetic radiation), while neutron therapy bombards it with a stream of subatomic particles called neutrons. Linear energy transfer (LET) measures the rate at which radiation delivers energy. Neutron therapy has higher LET, meaning that neutron therapy is able to inflict more damage on tumor cells, although by the same token it's also able to inflict more damage on healthy cells.

Function

• IMRT uses computer-controlled X-ray accelerators to shape beams of X-rays and deliver them from different angles, maximizing the dose to the target while minimizing damage to healthy tissue. Modern fast-neutron therapy relies on multileaf collimators--toothed devices with adjustable "leaves" made out of heavy metal that can absorb particles--to shape the neutron beam; radiation is typically delivered from multiple angles in these systems as well.

Effects

• The great advantage of IMRT lies in the ability to maximize the dose to the tumor. Damage to healthy tissue had traditionally limited the amount of radiation oncologists could apply; while increasing the intensity would kill more cancer cells, it would also harm other cells as well. IMRT affords greater precision and enables oncologists to use doses that will kill as many cancer cells as possible. Neutron therapy is advantageous in that the fast neutrons are more lethal to the cancer, but they also have the potential to cause more side effects.

Significance

• The first experiments with neutron therapy resulted in severe toxicity and side effects. While modern techniques offer a greater degree of precision, neutron therapy has yet to become widespread. According to the Seattle Cancer Care Alliance, neutron therapy is currently offered at only three centers in the United States. It's been shown to be effective against salivary gland tumors and certain other cancers; a 2008 commentary on Medical Physics Web, however, notes that "there now remain very few advocates for fast-neutron therapy." IMRT, on the other hand, has enjoyed growing popularity ever since its advent in the late 1990s and is currently offered by many cancer treatment centers.

Considerations

• While IMRT has increased precision compared to traditional radiation therapy, mistakes still can sometimes occur. A January 2010 article in the "New York Times" recounted a number of cases in which patients had suffered massive radiation overdose with IMRT, usually due to human error or poor training. The article noted that these kinds of serious errors are rare, but reminded readers that the potential for error exists even with advanced computer-controlled systems like those now in common use.

Potential

• Both neutron therapy and IMRT have advantages that may make them more appropriate to treat certain tumors or conditions. If you have questions about which therapy will achieve better results for you, the best person to consult is your oncologist or your doctor.