Aug 4, 2006
Radiotherapy sensor has extra dimensions
Better-targeted radiotherapy regimes have prompted demands for similarly sophisticated dosimetry systems. Swedish start-up ScandiDos AB is responding with a high-end sensor module capable of 3D and 4D dose verification in a single step.
ScandiDos' Delta4 device has been designed to improve quality assurance (QA) during intensity-modulated radiotherapy (IMRT). IMRT involves using a multileaf collimator with around 80 moving fingers to "paint" radiation on the region-of-interest. This allows the highest doses of radiation to be targeted more directly at the tumour - i.e. surrounding healthy tissue and vital organs are likely to receive much less radiation than during conventional radiotherapy.
IMRT regimes should ideally be verified using 3D volume measurements prior to treatment, says Görgen Nilsson, president and CEO of ScandiDos. To date, however, the only systems available for IMRT quality control have worked in 2D. "With 2D systems, you split the treatment into several parts and verify each part separately, whereas with Delta4 you verify the whole treatment at once. This not only saves time, but it also increases the accuracy of the verification, and hence the QA of the treatment."
Nilsson says the advanced functionality of Delta4 is thanks to three core elements: a next-generation solid-state detector; new electronics (including a tailor-made application-specific integrated circuit); and sophisticated application software. The detector technology was developed with the Tyndall National Institute (Cork, Ireland) and the Clatterbridge Centre for Oncology (Wirral, UK) as part of the European Union-funded INVORAD project.
Radiation is monitored using 1069 p-Si semiconductor diodes arranged in two orthogonal 2D arrays. The diodes measure the accelerator pulses individually (typically 300-400 pulses per second). This configuration means that all data required for 3D treatment evaluation can be acquired in a single detector run, explains Aleksandar Jaksic, who led the INVORAD project from the Tyndall Institute. Time-resolved measurements add the fourth dimension to radiotherapy QA.
The Delta4 design also means speedier problem-solving if deviations from the planned dose are found, says Jaksic. The significance of the error can be determined quickly, and the cause identified from analysis of individual beams and sub-beams without the need for repeat measurements.
The small p-Si detectors, which combine high efficiency and sub-millimetre spatial resolution with dose-per-pulse independence, are ideal for working with the IMRT's steep field gradients, says Jaksic. "The directional and energy response of the detectors are significantly improved over the existing commercial detectors. Recalibration frequency is substantially reduced, and when recalibration is needed, it can be performed in less than 60 minutes."
ScandiDos is now marketing its advanced radiotherapy QA solution in earnest. Delta4 received 510k clearance from the US Food and Drug Administration in January 2006, and has also been granted a CE Mark by European regulatory authorities. Nilsson reckons initial demand is likely to be greatest in the US, where favourable reimbursement policies mean that 70-80% of cancer treatment clinics use IMRT.
IMRT is much rarer in Europe and Asia, though uptake is increasing. Nilsson claims that conventional radiotherapy clinics may still benefit from Delta4's ability to analyse differences between planned and delivered dosages. The system will also suit still-more sophisticated approaches that are coming on-stream, including tumour-tracking and image-guided radiotherapy.
Nilsson added: "Looking to the future and the newer treatment techniques, this is what has been the real focus for us. We are quite confident that we have the right product for these emerging therapies."
About the author
Paula Gould is a contributing editor on medicalphysicsweb.