Intensity Modulated Radiation Therapy at UCSF

Intensity Modulated Radiation Therapy

Intensity modulated radiation therapy (IMRT) is an advanced radiation technique that has been used at UCSF since 1997, giving us more experience with IMRT than many centers across the world.

IMRT uses recent innovations in imaging and computer technology to adjust the shape and intensity of individual radiation beams, customizing radiation delivery to the shape of each tumor. This allows for higher, more effective doses of radiation to be delivered while minimizing exposure to surrounding healthy tissue.

With this treatment, the radiation oncologist starts by creating 3D digital datasets of a patient’s brain, combining data from scans like CT, MRI, and PET. Using the patient’s individualized 3D dataset, the radiation oncologists can plan out the best way to target the tumor while minimizing damage to healthy tissue. The computer program optimizes a treatment plan that is carefully designed for each patient with selected radiation beam directions, shapes, and intensities.

Over the course of weeks, the patient will come in for daily radiation sessions (except for weekends) that typically last between 5 or 15 minutes. Dividing the radiation treatment into smaller doses over a few weeks helps reduce damage to the healthy tissue around the tumor, and weekend rest breaks allow normal cells to recover. However, the total dose of radiation and number of treatments a patient receives depends on the size, location and type of the tumor, in addition to the patient's general health and other factors. While patients may experience general side effects from the radiation (like nausea or fatigue), IMRT itself is a painless, non-invasive procedure.

During each IMRT session, the patient lies down on a flat platform, carefully positioned by the radiation oncologist. Typically, radiation will be delivered by a device that rotates around the patient’s head to position the radiation beams at specific angles. A computer-optimized program controls the direction, shape, and intensity of each radiation beam. This ensures that each radiation beam is targeted to align with the tumor’s shape, limiting radiation in the healthy tissue surrounding the tumor. Although each radiation beam has to pass through healthy tissue to reach the tumor, the highest dose of radiation is limited to the tumor itself. Each radiation beam is positioned at a different angle, so that the highest, effective dose of radiation is concentrated where the beams intersect. Adjusting the direction, shape, and intensity of the beams allows the radiation oncologists to concentrate the radiation in the exact 3D volume of the tumor. This precision allows high doses of radiation to be delivered to the tumor while minimizing the radiation (and potential damage) to healthy tissue.

A similar treatment option, 3D Conformal Radiation Treatment (3DCRT) uses the same techniques to shape (or “conform”) the radiation beams into alignment with the tumor’s shape. IMRT offers the additional customization of being able to adjust the intensity (or strength) of the radiation beams as well.

Because IMRT (like 3DCRT) efficiently concentrates radiation throughout the tumor volume and minimizes damage to surrounding healthy structures, it is widely accepted as an excellent treatment option for many brain tumors.


This content was reviewed by UCSF neurosurgeon Michael McDermott, MD and UCSF radiation oncologist David Raleigh MD, PhD.