Manufacturing technology
Robar, professor at Dalhousie University and chief of medical physics at Nova Scotia Health, is both to “wrap a very high radiation dose around a tumour” and to “control that radiation dose so it falls off to a very low level as quickly as possible outside the boundaries of that tumour”.
Keeping momentum in treatment The location, size and shape of the tumour, which may be irregular, can all add to the difficulty in addressing the problem. There have, however, been developments that make it easier to avoid damage to healthy tissue. Radiation is now commonly delivered by linear accelerators, which approach that irregular tumour from different angles, using different beams. In doing so, they create a three- dimensional distribution of the radiation dose, matching the radiation beams very carefully to the shape of the tumour.
While this is generally highly effective in protecting the surrounding tissue, the success rate can drop in cases where the cancer is not localised. Patients with head and neck, oesophageal, gastrointestinal and rectal cancers are more likely to develop mucositis, with some stopping treatment as a result. Another difficulty arises with the need to make sure the tumour itself receives the correct radiation dose. When radiation is directed at the top layers of the patient’s skin – for example, in post-mastectomy patients where the surgical scar is being treated, or in patients with head and neck cancers or malignant melanoma – the maximum dose typically occurs over a centimetre deep below the skin, rather than on the skin itself. In these cases, clinicians use a bolus: a device made with material with properties similar to those of human tissue, which is placed over the site of the tumour to make sure that the tumour itself receives the correct radiation dose. A bolus can also be used to modify a dose subdermally.
There are technical challenges to designing a bolus, however. As Robar points out, the surfaces are often “complex”, and sometimes they are “treating around surgical deficits, where surgery has been done previously”. One of the materials traditionally used to make a bolus is wax, which is inefficient and has limited accuracy, as well as being uncomfortable for the patient.
Creating devices tailored to the individual
The turning point came in 2013, says Robar, when many of the patents on 3D-printing technology expired. In 3D printing, or additive manufacturing, a digital image is used to create three-dimensional objects from the bottom up by adding a layer of
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Around 50% of cancer patients will undergo radiotherapy as part of their treatment. During the procedure, patients are required to wear a bolus, but current off-the-shelf iterations leave spaces between the device and patient’s anatomy, which can result in cancerous cells receiving a lower dose than what’s necessary, as well as healthy tissue receiving a higher dose than what’s desirable. Medical personnel don’t always have to spend individualising each bolus to patient specifications, so 3D Systems developed an alternative 3D-printing workflow, which it calls VSP Bolus. The process works by clinicians submitting a patient’s CT scan data, which is segmented and used as a basis for a custom bolus designed via its DICOM To Print (D2P) software. Once ready, the device is sent for production at one of 3D Systems’ certified medical instrument manufacturing facilities. The technology arrived on the scene in April 2022 and is currently the only design and production service for a bolus based on a patient’s treatment plan.
material at a time. It is a particularly useful technology when an individual, tailored device is needed. Researchers recognised the high-resolution CT scans that cancer patients undergo could also be used to create algorithms that would instruct a 3D printer to make a bolus tailored exactly to the anatomy of an individual patient.
This meant, as well as making sure the patient received the right dosage to the skin, the bolus could be shaped so it matched the shape of the tumour exactly. In a trial of 16 post-mastectomy patients, Robar and his colleagues found that the ability of the 3D-printed bolus to fit the patient was significantly improved and the air gaps diminished. Adaptiiv, the company Robar set up with his colleagues to market the technology, has now partnered with HP to offer an on-demand service, whereby clinicians use the software to design the bolus in their clinic and then have it printed remotely and delivered three days later. Although Adaptiiv was one of the first companies to offer 3D-printed boluses, others have since followed suit.
“Researchers recognised that the high- resolution CT scans that cancer patients undergo could also be used to create algorithms that would instruct a 3D printer to make a bolus tailored exactly to the anatomy of an individual patient.”
Adaptiiv also markets Modulated Electron Bolus (MEB) software. While X-ray photons are normally used in radiotherapy, sometimes in the treatment of superficial tumours such as skin cancer, modulated electron radiation therapy (MERT) is used instead. Using an electron beam, says Robar, it is possible to “mirror the shape of the tumour with the shape of the 3D printed bolus to allow selective absorption of that electron beam. The end result is the distal or deep boundary of the radiation will match the
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