Custom 3D Printed Boluses Increase Efficacy of Radiation Therapy

As a cancer survivor, I can tell you that radiation is a stressful process. It’s nothing like what I would have imagined, which is not surprising because the sum total of all of my knowledge prior to diagnosis was what I had gleaned from watching grainy black and white movies in which a person/insect was exposed to a beam of radiation and then became a superhero/enormous carnivorous creature. Radiation actually works by being very specifically targeted to the area needing treatment.

During the therapy, the radiation kills the cancerous cells by doing irreparable damage to their DNA. The radiation itself can either come from a focused beam outside of the body (external-beam radiation therapy) or from the placement of radioactive materials near the cancer cells (internal radiation therapy or brachytherapy). Because radiation is damaging and because it is important to direct it so that the full brunt of its strength is received by cancer cells, a device known as a bolus is used in order to “shape” the radiation treatment to the specifics of the body of the recipient.

Dr. James Robar

Traditionally, the bolus has been made out of a material called Superflab, a rubbery material that can shaped to match the contour of the patient’s body. Unfortunately, it isn’t always an exact fit, as Dalhousie University’s Dr. James Robar explained:

“The Superflab doesn’t always conform to the surface very well. This may cause air gaps, which inadvertently decreases the dose of radiation to the surface.”

As a result, many locations that offer radiation resort to fashioning their own boluses with wax, plaster, string, and whatever other materials seem to lend themselves to the case at hand. This means that there are inconsistencies introduced by the human hand, as well as other problems such as those identified by Dr. Robar:

“If you tour a clinic like this, you’ll see rooms that look like arts and crafts studios, where radiation therapists are trying to be sculptors essentially and build things for the patients. There are a few consequences of that approach. It has limited accuracy in many cases, and can take a lot of time. It’s not only a time-sink for the patient, but also for the radiation therapists and other staff.”

For these reasons, Dr. Robar decided it was time to set about finding a new way to create the necessary bolus. Having heard of the precision and facility with which 3D printing was working to assist in the medical industry, he decided to investigate the potential the technology held for his purpose. With the help of a grant from Springboard Atlantic, his team purchased a 3D printer and set about to create four different devices that would assist with a variety of issues associated with radiation administration.

The first product was a bolus designed to be used in the administration of electron beam therapy. This type of radiation therapy is used when the tumor to be treated is close to the surface. For a bolus to be effective in this case, its depth must be printed in relationship to the distance between the surface of the patient’s body and the contour of the tumor itself. The algorithm that was used in order to create the 3D model was developed by a student of Dr. Robar’s, Shiqin Su of the Dal Medical Physics graduate program.

Chest wall bolus.

The second type of device was meant for use in photon beam therapy to deliver a powerful dose of radiation, over 100 times that delivered by an X-ray, to a surface area requiring treatment. It was during the creation of the bolus for this particular type of treatment for a patient with a tumor in his nasal septum. The tumor had been removed, but had since recurred and imaging from his previous surgery was used to create the bolus.

“The patient hadn’t been to our clinic before but he had a previous CT imaging for diagnoses and follow-up with his surgery,” Dr. Robar said. “We put topical anesthetic on it, and it fit his nose perfectly. We could verify that because he had to have a CT scan that day. It worked really well. He had 30 treatments with this device and by the end of his treatment course, he would hop on the treatment bed, grab his 3D printed nose bolus, insert it himself, snap it together and he was ready to go.”

The third creation to come out of the research team’s investigations was for a device to immobilize flexible tissue. This is particularly useful in the performance of radiation on intact breasts the movement of which from treatment to treatment can cause inconsistencies in the radiation dosage. The bolus in this case was printed in order to create a stiff, cast like impression that would conform the breast to the exact same form each time radiation was to be administered.

Finally, the team decided to address issues arising during the administration of internal radiation therapy. The current method for delivering the internal dose is to affix something called a Freiburg Flap, a sheet of beads through which catheters pass the radiation to the destination. The difficulty with this technique is in forcing the flap to conform to the surface of any particular patient’s body. Here again, 3D printing was able to provide an advantage by being used to print a custom applicator.

The products developed through this research are the basis for the startup company 3D Bolus and the technology is being used in clinics in Ireland and Israel. Further research versions are undergoing testing in Chicago, San Francisco, and Halifax. The next step for the product is the process of testing and further development, with the ultimate goal being FDA approval. Dr. Robar discussed his vision for the product:

“The hope is for this to become the standard model of treatment. In order to achieve that, we have to make this as practical and reliable as possible, otherwise we’re not going to meet that goal. Delivery of radiotherapy involves extremely busy clinicians who need to use these tools, and they can’t resemble a research project. It has to be an entirely turn-key solution. It’s getting very close to being at that point.”

It is exactly this customizable, patient-specific ability that has made 3D printing such a powerful tool in the medical community. From the creation of prosthetics to building up models for surgical preparation to the printing of cell grafts, 3D printing offers the perfect combination of accessibility and precision that has kept it in the news and in an increasing number of medical facilities with onsite 3D printing services.

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