A new nozzle for uniform proton beam scanning

For years now, if proton therapy practitioners wanted to benefit from a uniform dose distribution when using active scanning techniques, they needed their facility to design and develop a uniform scanning dedicated system. In fact, medical physicists at three different proton therapy centers in the world did just that, at considerable time and expense.

But such an enormous R&D investment will no longer be required. A new uniform scanning integrated nozzle has been developed, which will “broaden therapeutic versatility and improve operational efficiencies”, predicts Dr. Jonathan Farr, Chief Medical Physicist at Midwest Proton Radiotherapy Institute (MPRI) in Bloomington, Indiana. MPRI physicists spent more than three years researching and assembling their own uniform scanning system, which was integrated into IBA’s universal nozzle, overcoming incredible challenges along the way.

MPRI’s uniform scanner, developed with the Indiana University Cyclotron Facility, was built especially for complex brain cases, and head and neck cases. But a prostate cancer patient was the first to be treated when the system went online in March 2007. “Uniform Scanning allows you to paint the beam back and forth on the target site,” Farr says. “For patient treatments, we use uniform scanning with dose-layer stacking. The system turns on the beam and treats the deepest layer of the target first. Then the beam is turned off and a combination of range shifters is used to pull the beam range back to the next level. The whole process is iterated until the entire target is covered, like a pancake stack, one layer at a time. The process takes about a minute to complete.”

Farr contends that uniform scanning offers significant advantages over passive beam scattering technologies that have changed little since their inception more than 40 years ago. “Uniform scanning can take us beyond the typical 20-centimeter field size limitation of passive scattering,” says Farr, “and better treat large cancers without the need for field matching—like a pediatric spine case, for example.” Thanks to the uniform scanning integrated nozzle, radiation oncologists and medical physicists can focus more on patient treatments and protocols and less on inventing new technologies.

PBS, the future of proton therapy

A team of researchers, clinicians and physicists from Belgium, Korea, Massachusetts and Florida is working to create the future of proton therapy. Though geographically dispersed, their ideological aim is extremely focused: to develop, test and ultimately deliver a new form of proton therapy to patients: Pencil Beam Scanning (PBS).

Currently, the most prevalent form of proton therapy delivery is double or single scattering. With this technology, the entire volume of a tumor is treated at the same time and with the same intensity using a beam of protons delivered through an aperture adapted to the tumor’s precise size. One of the problems with double scattering is that neutron generation in healthy tissues cannot be avoided before reaching the tumor.

Conversely, proton therapy delivered with PBS allows the doctor to essentially paint, layer by layer, only the volume of the tumor with a precise proton beam, as well as adjust the intensity of the beam. PBS provides a very focused and small beam spot which ensures better precision. Magnets are used to focus the beam and achieve this small spot size at what is called the isocenter, the place where the center of the tumor would be positioned. One of the great strengths of PBS therapy is its adaptability in treating different layers of a tumor with more or less intensity, depending upon clinical need. Instead of giving one constant dose on each layer, it is possible to modulate the beam intensity if there is potentially a hot spot or place on the layer that needs more intense treatment.