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A Pencil Beam Precision Q and A

The precision benefits of proton therapy are well documented and pencil beam scanning, a more complex form of proton radiation, takes this specificity to new levels to treat complicated, irregular tumors.

Proton therapy is different than standard radiation because it uses heavy, positively charged atomic particles, instead of standard X-rays used in conventional radiation therapy, which results in fewer negative side effects.

Protons can be calibrated to release the bulk of their energy at certain depths inside the body. This level of precision helps specialists place more radiation exactly at the spot of the tumor while sparing nearby healthy tissue and represents the primary difference between proton radiation and standard radiation.

“By virtue of sparing more normal tissues in certain cases, quality of life can be preserved,” says William Hartsell, MD, medical director of the Northwestern Medicine Proton Center.

Pencil beam scanning builds on these benefits and enhances the shaping abilities of proton radiation technology by using a beam that is much smaller than those used in common proton treatments. To better understand the extent of this technology, Dr. Hartsell answered a few questions about pencil beam scanning.

How does pencil beam scanning work?

Pencil beam scanning (PBS) technology uses protons like paint on the tip of a brush. It’s like painting on a canvas, using a brush tip approach as opposed to broad strokes. Protons and their energy are dotted on, and into, a tumor within the body. This technology allows us to treat all types of tumors, regardless of shape, size or location in the body.

What makes pencil beam scanning a breakthrough treatment?

PBS represents a breakthrough in our ability to deliver proton radiation to any tumor shape and size to better reduce the collateral radiation exposure to the normal tissues in the body. Unlike standard proton therapy that relies on devices called compensators and apertures to conform the proton beam to the edges and depths of a patient’s tumor, PBS technology delivers protons in small, controlled beams. The breakthrough reduction of side effects seen with proton therapy is provided to more patients through the enhanced precision of PBS.

Who can benefit from pencil beam scanning?

Many proton therapy patients can benefit from PBS, but patients with tumor targets that are irregularly shaped or in close proximity to significant normal tissues will experience the greatest benefit.

Patients with head and neck cancers especially can have very irregular targets and can benefit in particular from PBS. Primary tumors in head and neck cases tend to be in the mouth, nasal passages, sinus cavities and throat. Shaping the proton radiation to these areas to prevent normal tissue exposure is difficult even with prior proton delivery techniques and pencil beam scanning delivers radiation to these hard to reach spots while minimizing exposure to other parts of the body.

Where is pencil beam scanning administered?

While PBS can be administered in a fixed beam room, as it has been at Northwestern Medicine Proton Center since 2014, the addition of PBS to the 360-degree gantry room at the center allows this proton modality to be delivered around the patient from an infinite amount of positions and angles. The gantry now enables the care team to treat more complex cancers such as head and neck, esophageal, brain, lung, breast and pediatric cancers. This technology provides the community with truly the full spectrum of capabilities to treat any tumor shape, size or location in the body.

William F. Hartsell, MD
William F. Hartsell, MD
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