Recently in AAPM Annual Meeting 2008 Category

Tom Dellinger, medical physicist at Pardee Hospital (Hendersonville, NC) had something to smile about today. He was the lucky winner of medicalphysicsweb's prize draw, and will be heading home from AAPM in possession of a brand new iPod nano (in medicalphysicsweb blue, of course).

Smile: Tom Dellinger at the IOP Publishing booth

And we'll be heading home soon too, swapping the Houston heat for Bristol drizzle. I hope that you've enjoyed reading this blog, and be sure to check out the main site for AAPM follow-up coverage in the next week or two.

I've spent a busy few days pacing the AAPM exhibition show floor. There's just not room here to include all the new products that I've seen, but here are a few more releases that caught my eye:

• Modus Medical Devices of Ontario, Canada unveiled a neat system for turning a standard Catphan phantom into a breathing phantom. Its QUASAR Catphan Shaker can be programmed with patient-specific breathing data (from a Varian RPM) to simulate respiratory motion for quality assurance before treatment. 

The Shaker comes with software for displaying, editing and running motion waveforms

According to the data sheet, the Shaker offers an amplitude of up to 30mm for RPM input; or it can move sinusoidally with speeds from four to 60 breaths per minute at 40 mm amplitude. 

• Standard Imaging (Middleton, WI) had a whole host of new products to promote. First up, MIMI - a new phantom for testing the isocentricity of imaging modalities. The MIMI (multiple imaging modality isocentricity) platform can be used for QA of optical positioning systems, kV cone-beam CT, on-board imaging and laser systems.

Next up, new versions of the company's IMSure QA and PIPSpro software packages. IMSure version 3.1 offers features including Cyberknife verification, support for .decimal compensators and the ability to import DICOM structure sets. Version 4.2 of PIPSpro comes with automated cone-beam CT testing and improved stereotactic accuracy.

Standard Imaging also unveiled its new SuperMAX - a two-channel electrometer with a colour touch-screen interface - as well as an upgraded version of the MAX 4000 electrometer and three new inserts for its Lucy phantom.

• The big push at the Siemens' booth was ARTISTE, a linac for adaptive radiotherapy. According to Siemens, the system's key selling point is its "ultimate flexibility", which gives clinicians control over how to treat each patient each day.

The ARTISTEs were all tied up, so Siemens brought a big photo instead

ARTISTE features a 160-leaf MLC, claimed to be the fastest on the market with a leaf movement speed of 4 cm/s. "The more leaves you have and the finer resolution, the better you can conform to the tumour and the better you can deliver the dose," Siemens' product manager Brett Evans told me.

Using this collimator in tandem with the company's new IM-Confident Plan treatment planning system enables IMRT treatment time to be reduced to less than five minutes, he explained.

One company that caught my eye on the show floor was Aktina Medical, a Congers, NY-based manufacturer of radiation oncology accessories and treatment systems. Aktina was demonstrating a scheme for performing frameless radiosurgery. The company's pin.point localization and fixation system boasts sub-millimetre positioning accuracy for cranial and head-and-neck treatments.

"Previously, people didn't want to move away from using frames because nothing else could provide the same accuracy," Nick Zacharopoulos, Aktina's vice president, told me. "But we can do just as well as an invasive frame."

Pin.point works by using a moulded mouthpiece, vacuum attached to the roof of the patient's mouth and fixed within a Perspex frame. This frame contains metal rods that can be visualized via CT imaging, thus providing accurate information as to the patient's position. The company also offers a software package for autoregistration.

The pin.point system showing the mouthpiece (blue) within the perspex frame

"The therapist can determine the accuracy based on the vacuum pressure," Zacharopoulos explained. "If you see a good vacuum, you know the patient is set-up with sub-millimetre accuracy."

Aktina expects FDA clearance for pin.point early next month.

Researchers at the University of Florida (Gainesville, FL) have come up with a new take on proton-therapy dose verification: imaging gamma ray emission during the treatment process. The distribution of gamma rays - produced when high-energy protons interact with nuclei in the patient's tissue - provides a measure of the location and amount of energy delivered during treatment.

"If we have a way to image gamma rays, we can almost do real-time dose verification," said researcher Yuxin Feng, speaking at an AAPM session entitled Innovative frontiers in medical physics.

To detect the gamma rays, Feng and colleagues designed a Compton camera based on LaBr₃, a new scintillation material with high stopping power and good energy resolution. They used pixellated LaBr₃ crystals for both the camera's scattering and absorbing detectors.

The crystal modules in the front (scattering) layer are 2.5x2.5x0.5 cm in size, segmented into 4x4x2 mm on the surface to enhance spatial resolution. The detectors in the rear layer are 2.5x2.5x3.0 cm, segmented into 4x4x10 mm.

"The prototype Compton camera is able to image gamma rays from 0.5 to 2 MeV," said Feng. He noted that this technique could also be used to monitor high-energy photon-based therapies.

The proposed Compton camera offers a potential angular resolution of about 0.3 radians when imaging 511 keV gamma rays, and 0.05 radians or less for gamma rays above 2 MeV. Bench-top tests demonstrated a spatial resolution of 5 mm (at 662 keV) - sufficient to detect the distal fall-off of a proton beam.

Feng says that the Florida team now plans to test the prototype camera in clinical radiotherapy facilities, using both proton and photon beams.

Also in the pipeline: new configurations, such as dense scattering cameras or multiple cameras with a perpendicular set-up; and acceleration of the camera's 3D image reconstruction speed. Ultimately, it's this fast image reconstruction that could make real-time imaging of proton therapy a reality.
 

Treatment planning appears to be one of the recurring themes at this year's AAPM, with BrainLAB of Germany among those highlighting the latest and greatest in radiotherapy planning software. On show at the company's booth were the latest releases of its iPlan packages: iPlan RT image, for contouring and target definition, and iPlan RT Dose, for treatment dose planning.

"From the imaging perspective, the version 4 software integrates a couple of new things: 4D CT integration and the head-and-neck Atlas," iPlan project manager David Brett told me.

The head-and-neck Atlas provides a nifty way to perform automatic segmentation of pre-treatment CT or MRI scans. The Atlas - a series of around 50 predefined anatomical objects - is fused onto the patient data set using elastic image fusion. And it's fast: iPlan takes less than a minute to find these 50 objects, after which the user can tweak the outlines manually, if required.

"There's a lack of consistency in contouring; studies of five doctors will give five different results," Brett said. "The benefit of Atlas-based segmentation is that within one minute you get a consistent outline. BrainLAB's software team works closely with clinical partners to get the ideal contours that fit the greatest percentage of patients".

On the dose planning side, BrainLAB's big announcement is the FDA clearance of its Monte Carlo dose calculation algorithm - an integral part of iPlan RT Dose version 4.

David Brett extols the benefits of BrainLAB's Monte Carlo dose engine

Brett explained that although Monte Carlo algorithms have been used before for treatment planning, clinical implementation tended to be limited by extreme calculation time requirements, or restrictions to planning for a single machine or treatment modality.

"Monte Carlo is considered the gold standard, especially for extra-cranial treatments, because it considers inhomogeneities," he said." With our Monte Carlo algorithm, we can create a complex IMRT case in less than five minutes."

Such a feat, which Brett claims would previously have taken 20 computers running over night to perform, was enabled by designing a Monte Carlo algorithm specifically for radiotherapy needs. What's more, BrainLAB's algorithm supports a multitude of treatment plans, including conformal beam, static and dynamic arc, and IMRT.

"We believe that the release of the BrainLAB Monte Carlo dose calculation algorithm will have a great impact on the field of radiosurgery," said Brett. "We continue to develop software that extends clinicians' treatment precision to cover more extra-cranial cancers, as well as advanced dose calculation possibilities for lung and head-and-neck tumours."