Offering exceptional advantages in precision, dose conformity and patient throughput, Pencil Beam Scanning is poised to be the go-to proton delivery method at new proton therapy centers worldwide.
At 3 millimeters, about the diameter of a smart phone audio plug, the beam spot from Pencil Beam Scanning “is very high quality — meaning, at high energy, it’s very small in size and maintains good quality throughout the energies used for patient treatment,” says Jonathan Farr, Ph.D., Chief Medical Physicist at Westdeutsches Protonentherapiezentrum Essen (WPE), the proton therapy center in Essen, Germany. Farr is helping oversee the first large-scale commercial deployment of Pencil Beam Scanning in the world. Each of WPE’s four patient treatment rooms — three gantry rooms and one fixed-beam room — is equipped for Pencil Beam Scanning. WPE is expected to treat its first patient by the spring of 2011.
“The beam spot primarily defines how sharp the radiation field is,” Farr explains. “So, if you have a tumor abutting the brain stem or rectum or major organs, you want a sharp beam edge to keep to the tumor.” Pencil Beam Scanning also offers a very rapid dose delivery of about two minutes. “Time has a quality and efficiency implication,” Farr says, “because once you have the patient set up and still, you want the fractions to go quickly. And that ensures better patient treatment quality and throughput. So, in many clinical indications, Pencil Beam Scanning is a win-win: high definition, conformity and high efficiency at the same time.”
Pencil Beam Scanning usually omits the need for individualized brass apertures and range compensators that are required for each patient treated with single and double scattering or uniform scanning. “Pencil Beam Scanning doesn’t have anything in the way,” Farr says. “You mostly get pure protons.” Farr predicts Pencil Beam Scanning will enable swift adaptive radiotherapy at WPE, especially since staff will conduct imaging on proton therapy patients every day. “Daily imaging will provide a mountain of data,” says Farr, “allowing us to fine-tune treatments with a Pencil Beam Scanning system. Although new fields should be verified, for beam delivery, it’s a simple change to the computer file. Again, usually there’s no need to make a new brass aperture and compensator.”
Even though Pencil Beam Scanning is an extremely sophisticated tool, treatment plans for it are far less onerous to devise than those for other proton therapy methods, Farr notes. “Treatment plans for scattering treatments are very painstaking to develop,” he says. “They require highly experienced proton treatment planners and take a lot of time to produce. Now, we can look to well qualified radiation therapy personnel in general. Anyone who can devise a good-quality IMRT [intensity-modulated radiation therapy] treatment plan can do a good-quality Pencil Beam Scanning plan with just a little training. Then, the planning workflow can be as efficient as in photon therapy.” Considering the many advantages of Pencil Beam Scanning, “I don’t suppose any new center will be built without Pencil Beam Scanning,” Farr says.