Medical and metalworking technologies meld in an effort to heal in Houston, Texas. The two disciplines are working in concert to make cancer "history" at M.D. Anderson's new Proton Therapy Center, located in the heart of the Lone Star State's largest city.
One of only four proton radiation centers in the United States, M.D. Anderson's $125 million facility will serve more patients than any of the other centers, treating 3,500 per year when it reaches full capacity. In order to support such an aggressive treatment schedule, the facility houses its own machine shop that includes four networked CNC vertical machining centers (VMCs).
The primary duty of these machines is to produce two patient-specific components for the center's gantries, or radiation beam delivery devices. One of these components is a brass aperture that receives a window to shape the beam to match a tumor field's outline. The other is an acrylic compensator block into which is machined a cavity to shape the beam to release its energy at the appropriate depth within the patient's body. The ability to manipulate the beam in a way that damages a cancerous tumor without harming nearby healthy tissue is what makes proton therapy such a precise and powerful cancer treatment.
Most hospital-based machine shops are equipped with toolroom-type mills and lathes that are used to produce one-off fixtures or instruments. The shop at M.D. Anderson's proton therapy center does have such equipment for that type of work. However, it is first and foremost a production shop, as John Barr points out. Mr. Barr, the shop's supervisor, selected most of the shop's machine tools and related equipment. Four Mazak Nexus 410 VMCs will bear the brunt of the shop's production work. When the center reaches full capacity, those machines will produce thousands of apertures and compensators each yearMODERN MACHINE SHOP was invited to tour the center and its dedicated shop a few months in advance of the official opening in June 2006. During the visit, Mr. Barr and Paul Wisdom, a deft machinist who is currently "on loan" from M.D. Anderson's nearby instrument shop, explained the role that machining technology plays in support of an effective cancer treatment procedure.
Protons Pack A Punch
The 94,000-square-foot facility is topped by an open, inviting entrance with numerous offices and examination rooms. However, the building is an iceberg of sorts, because 42 feet of it is below ground. Located in this bunker are four proton radiation treatment rooms and the compact machine shop that measures 36 by 44 feet. These rooms are surrounded by 8-foot-thick concrete walls and a ceiling that's 12 feet thick. The subterranean location and beefy enclosure are required to contain stray radiation during treatment.
The apertures and compensators are the final two components in the subatomic beam delivery process. An injector first strips protons from the nucleus of hydrogen atoms and delivers them to a synchrotron, or particle accelerator. The synchrotron, essentially a magnetic "racetrack," accelerates the protons in a vacuum to an energy level approaching 250 million electron volts. The protons then travel at nearly light speed to rotating beam-delivery gantries located in three of the four treatment rooms. Though the huge gantries measure 35 feet in diameter and weigh 190 tons, they rotate smoothly, quietly and precisely 360 degrees around a patient and direct the proton beam to 0.5-mm positioning accuracy. The aperture plates (as many as four identical 2-cm-thick plates may be required) and compensator are inserted into the gantry's snout to shape and focus the beam as it exits the gantry en route to the targeted tumor.
The protons enter the a patient's body at a low energy level, peak their energy level within the tumor and effectively stop there so that surrounding healthy tissue is left unharmed. Apertures and compensators are matched sets specific to each patient and each different beam delivery angle into a patient's body. While no two sets of apertures and compensators are alike, the process for creating these components is the same for all.
Machining From A CAT Scan
The brass aperture plates and acrylic compensator blocks are first squared and face milled to size. The brass is machined dry; the acrylic is machined using high-pressure coolant. One corner of each component receives a notch, which serves as a key to ensure that the components are properly oriented when installed in a gantry snout.
The shapes of the aperture window and compensator cavity are determined by a model of the patient's tumor, which is obtained via a computed tomography scan, or CAT scan. The CAT scan captures the tumor volume one thin 2D slice at a time. The 2D images, taken at discrete depths throughout the tumor, stack together to create what is essentially a 3D model of the tumor. The electronic tumor model is part of each patient's file in the IMPAC treatment planning system, which the shop can access via the network.
Subscribe to:
Post Comments (Atom)
No comments:
Post a Comment