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Altered Fractionation for Head and Neck Cancer

Altered Fractionation for Head and Neck Cancer

Dr. Garden, an internationally known
expert in the field of head and neck radiation oncology, has written an
excellent article that clarifies the biological rationales for
hyperfractionation and accelerated fractionation treatment programs. His article
appearing in this month’s issue of ONCOLOGY provides a thorough review of the
literature by examining the randomized trials that have been performed in this
area. Dr. Garden establishes strong biological and clinical evidence that dose
escalation (via hyperfractionation) and shortening of the overall treatment time
(by accelerated fractionation) can improve local control of head and neck
cancer.

Remaining Problems

The question now is this: How can radiation oncologists
improve on these results? Most accelerated fractionation regimens use
large-volume radiation treatment portals that are not designed with an eye
toward sparing normal tissue. The other major problem is that, since treatments
are separated by 6 hours, these regimens require the patient to come to the
clinic more than once a day. This schedule translates into increased costs and
inconvenience for the patient.

Advances in Treatment Delivery

A technological advance called intensity-modulated radiation
therapy (IMRT) has become available in the last 10 years, resulting in
improvements in the delivery of radiation.[1-7] The radiation oncologist has
historically worked via a trial and error method—placing radiation treatment
portals on the patient and then looking at the dose distribution. If the dose
distribution is not acceptable, new portals are placed, and the process
continues until an acceptable dose distribution is obtained.

In contrast, IMRT breaks the large portal into multiple small
beamlets that are no more than 1 × 1 cm² in size. Instead of two or three large
portals being used to treat the patient, the potential for millions of beamlets
exists. The radiation oncologist defines where he wants the dose distribution,
and the computer determines how to meet that prescription most effectively—ie,
where the best beamlets are and what their contribution in intensity should be.

The chosen beamlet pattern is also based on the dose
avoidance pattern that the radiation oncologist wishes to achieve. While dose
deposition patterns are established to encompass primary tumors and areas at
risk for microscopic disease, dose avoidance patterns cover normal tissues, such
as the spinal cord, parotid gland, retina, and optic chiasm.

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