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.
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 methodplacing 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 effectivelyie, 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.