Defining the Attributes of LINACs, IORT in Pancreatic Cancer Care

Milad Baradaran, PhD, DABR, and his colleagues spoke with CancerNetwork^® about the technical properties of intraoperative radiation therapy (IORT) as a form of care for patients with pancreatic cancer.

After briefly describing how the use of IORT has evolved over time, Baradaran, head of Quality Assurance Operations and assistant professor in the Department of Radiation Oncology, described the potential utility of Mobetron, a mobile self-shielded electron-beam linear accelerator (LINAC) designed to assist with delivering IORT during surgery.

Transcript:

IORT has had a long history in cancer management. The practice of IORT in the United States was started in the late 1970s by Alfred L. Goldson, MD, FACR at Howard University.¹ Back then, the majority of cancer centers used their stationary coalitional linear accelerators, or LINAC, to perform IORT. In that case, the anesthetized patient should be moved from the operating room [OR] to the regional oncology department accompanied by OR personnel to receive treatment. This is technically very difficult and relatively inefficient.

Later on, using a mobile LINAC inside an existing ORs [with reduced shielding requirements] makes the cost and logistics of setting up an IORT program much easier. Therefore, there has been a recent resurgence of interest in IORT. One of the manufacturers of mobile LINACs is IntraOp Medical, which manufactured Mobetron. Mobetron is a kind of linear accelerator that can generate electrons up to 12 MeV, and it can deliver a precise, highly concentrated, doses of radiation to the target, while at the same time sparing normal neighboring tissues.² That is the goal of radiation therapy.

Although there are many similarities between IORT treatments, we have stationary units and mobile units, and [there are] several important considerations unique to mobile units. Mobetron has applicators with a wide variety of sizes from 3 cm to 10 cm diameters; it can even be 8 cm by 20 cm rectangular. This will help us to confine the beam to the volume of interest within the surgical area. A treatment can be performed under sterile conditions with the patient anesthetized, and it can be delivered in a large single fraction. You can also use the modifiers and you can place bolus at the end of the applicator. This will help us to increase target surface dose and, at the same time, decrease penetration depths of the electrons. It helps us spare normal tissue sitting underneath the target.

The Mobetron can generate electrons with energies of 6, 9, and 12 MeV, which, although targets coverage with this sort of subpath for cm, it has a normal dose rate of 1000 monitor units per minute. Then, being on treatment for delivery will only [take] a few minutes per treatment. Moreover, we can have a wide range of motions of the treatment path, which will let us have more flexibility in setting up the patient. This is very user-friendly software for treatment planning software, called Prelude, that we can use to do those calculations as prescribed by our radiation oncologists intraoperatively.

On the other hand, you have some limitations working with mobile LINACs, like concerns of a storage transport, treatment setup, and radiation protection. You’re always asked by an older person, "Is it safe to stay in the same room with Mobetron?" The answer is absolutely yes. Remember, a LINAC doesn’t generate any radiation when it is off. There remain concerns associated with the radiation protection when the machine is on during actual treatment delivery or during treatment quality assurance. Usually, these are self-shielded, they have beam stoppers, and they’re designed primarily for use in an unshielded area. But exposure limits typically restrict our use to the treatment of a small number of patients per day plus the recorded QA and warmup.

In the end, I have to say that based on our experience at Vanderbilt University Medical Center, clear communications among the surgeon, radiation oncologists, and physicists are key for proper patient positioning and successful and efficient treatment delivery.

References

1. Goldson AL. Preliminary clinical experience with intraoperative radiotherapy. J Natl Med Assoc.1978;70(7):493-495. PMCID:PMC2537195.
2. Product Datasheet: Mobetron. IntraOp. Accessed July 1, 2024. https://tinyurl.com/mrxpjxec