A round-up of some recent international patent applications in radiation therapy.

Silicon photomultipliers line up for Cerenkov-guided radiotherapy

Cerenkov emission during external-beam radiotherapy provides a useful quality assurance tool and potential for online tracking of tumours during treatment. However, molecular probing of the cancer status during delivery has not been developed — mainly due to the limited sensitivity of current photodetectors for Cerenkov emission and a lack of tools to fit into the complex treatment delivery environment. Silicon photomultipliers (SiPMs) offer the high sensitivity of photomultiplier tubes, with a similar a form factor to silicon photodiodes, allowing for improved flexibility in device design. In patent application WO/2018/208775, University of Michigan researchers present a SiPM array-based multispectral optical probe. They assess the feasibility of using SiPMs to detect Cerenkov emission and interrogate physiological information during radiotherapy.

Dose calculations compensate for inhomogeneous tissue

Particle therapy of inhomogeneous tissues such as lungs, which include an irregular pattern of air cavities, is difficult as the structure of such tissue affects the trajectory of the ions and can cause errors. Raysearch Laboratories has developed ion radiotherapy dose calculations that compensate for tissue in which voxels may be inhomogeneous in density, by approximating a portion of the voxel as an air cavity (WO/2018/189364). Each dose voxel is inscribed in a 3D grid comprising a number of cells, preferably in such a way that the voxel overlaps at least one cell fully. Each cell comprises one portion representing the density of tissue and a second representing the density of air, the first and second portions forming a cell pattern. The propagation of ions through the voxel is then calculated based on the cell pattern in any cells overlapping the voxel.

Compact system delivers gantry-less particle therapy

A team from Massachusetts General Hospital has published details of a gantry-less particle therapy system (WO/2018/204579). The described methods can be used to treat patients in the same room as the particle therapy system by positioning the treatment area inward from the system’s beam track. Charged particles are extracted from an ion source and accelerated in a beam transport system. This transport system has an annular portion that extends in one plane and circumscribes a volume, an arcuate portion in a second plane, and a transition portion that connects the two. The arcuate portion terminates at a beam nozzle that extends radially inward from the annular portion to deliver an ion beam to a treatment area within the volume defined by the annular portion.

Motion target volume accounts for shape changes

Elekta has devised a way to generate a motion target volume that represents changes in the shape of the target in a patient during radiotherapy delivery (WO/2018/208390). At least one computer system is configured to receive a series of medical images that include the target region, with each image taken at a different time point. The computer defines a 3D volume containing the target in each image; this 3D volume may be different in at least two of the images due to differences in the shape of the target region. The system then co-registers the 3D volumes and generates the motion target volume, which encompasses each of the 3D volumes.

Dermatology system delivers fast skin treatments

Sensus Healthcare has invented a dermatological radiotherapy system with a hybrid imager that can be used to diagnose, treat and verify treatment of skin cancers or lesions (WO/2018/187619). The system provides a means to deliver the required radiation dose to the patient in a significantly shorter period of time — for example, less than 1 min as opposed to more than 5 min — by increasing the flow of photons emitted from a radiotherapy treatment device. This is achieved by shortening the removable applicator of the radiotherapy device, and using either relatively thick filters with normal dose rates (less than 1000 cGy/min), or thin filters with relatively high dose rates (above 1000 cGy/min).