The design was unveiled in a scientific session on Sunday morning, as the weeklong marathon of the RSNA annual meeting got under way. Paul Keall, PhD, professor of medical physics and director of the Radiation Physics Laboratory at University of Sydney Medical School, described the project. In addition to the University of Sydney, the 13 members of the team are affiliated with Prince of Wales Hospital, Liverpool Hospital, the University of New South Wales, the University of Newcastle, and the University of Wollongong.
Radiotherapy is underutilized around the world and varies widely among countries. Published peer-review literature has suggested that approximately 50% to 53% of all cancer patients should have radiotherapy included as part of their treatment regimen. The utilization range in developed countries is 20% to 55%. In countries with underdeveloped or developing economies, radiotherapy is provided to no more than 25% of cancer patients, and in some countries, it is not available at all.
Australia is in the middle of the range, with a utilization rate of 38% in 2009. It offers a ratio of one radiotherapy center for every 250,000 residents, which the International Atomic Energy Agency (IAEA) considers acceptable.
"However, there is a global shortfall of an estimated 10,000 radiotherapy machines," Keall said, citing the 2010 IAEA Programme of Action for Cancer Therapy (PACT) report. "Many countries cannot afford the complex radiotherapy equipment being sold, often at a cost of over $4 million. There is a need to reduce the cost of radiotherapy machines without compromising on technology."
The Nano-X system is being designed to meet this need. It utilizes engineering and space-efficient designs to potentially reduce not only the cost of the equipment, but also the overall system costs.
"We based the design of the Nano-X on three criteria," Keall said. "We knew we needed to take a minimal cost approach in the design parameters that we could control, such as its hardware engineering and the building size. We needed to design a system that would deliver the current standard of care in radiotherapy systems, including image-guided intensity-modulated radiotherapy and volumetric modulated arc therapy. And we wanted the Nano-X to be able to accommodate the future standard of care, such as having the ability to enable real-time adaptive radiotherapy."
To meet these criteria, the team calculated the building size and required shielding for a Nano-X system. The calculations were compared with comparable values for existing commercial linear accelerators that are compact in size.
The team designed a system that shares many components of a standard gantry-mounted linac system. A fixed linac eliminates the need for primary shielding for the walls and ceiling of the treatment room. The system's compact design requires less space and less building material. Everything is geared toward achieving economy without sacrificing treatment quality.
Keall explained that the minimum internal bunker space requirement is 3 m (L) x 3.7 m (W) x 3 m (H). By comparison, the space requirement for a conventional compact rotating gantry linac system is nearly double, at 6.7 m (L) x 6.1 m (W) x 3 m (H).
The concrete volume required for the construction of a bunker to house the Nano-X system is 80 m3, compared with 160 m3 for a conventional compact linac.
The team also considered a lower standard leakage factor for the linac head. By reducing this factor from 10-3 to 10-5, the bunker footprint could be reduced to 17 m2 and a concrete volume of 35 m3.
The challenge to the design team is the patient rotation system, which may cause discomfort or problems for patients who get vertigo or are susceptible to claustrophobia. The team is currently working on anatomic reproducibility with rotation, developing methods to account for changes, and developing procedures to quantify the level of patient acceptance for the patient rotation systems. After this work is finalized, the next step is to build a prototype.
"There is a great need to reduce global disparity among countries with respect to being able to offer radiotherapy treatment to their patients who have cancer," Keall said. "The Nano-X addresses the need to reduce the cost of radiotherapy treatment by building a cheaper and equally effective treatment system. "
"The Nano-X will utilize one-third to one-half less space and construction materials as current commercially available linacs," he said. "Additionally, as a result of our focus on simpler engineering, it will have fewer moving parts, resulting in being cheaper and operating with greater reliability."