Factoring Multidisciplinary Care Into IORT for Pancreatic Cancer
Experts from Vanderbilt University Medical Center emphasize gathering a second opinion to determine if a tumor is resectable in patients with pancreatic cancer.
After reviewing a patient case involving the use of intraoperative radiation therapy (IORT), Kamran Idrees, MD, MSCI, MMHC, FACS; Natalie A. Lockney, MD; and Milad Baradaran, PhD, DABR, spoke with CancerNetwork® about leading multidisciplinary discussions to determine whether patients with pancreatic cancer are eligible to receive this treatment.
The group, all from Vanderbilt University Medical Center, reviewed alternative therapy options for those with potentially unresectable disease. Even in the case of an initially unresectable tumor, however, Idrees emphasized the necessity of receiving a second opinion from other team members who may be capable of resecting a patient’s disease.
Transcript:
Idrees:
This case illustrates that with carefully selected patients and a multidisciplinary team approach, we can offer surgical resection with intraoperative radiation therapy in selected patients with pancreatic cancer. [There] has to be a multidisciplinary team approach to carefully select these patients and [determine] who can benefit from this procedure. Is this a [suitable] procedure for all patients with pancreatic cancer? Certainly not. It has to be carefully selected. Patients [with] either borderline resectable or locally advanced [disease] who receive systemic chemotherapy in a neoadjuvant fashion followed by radiation therapy are then considered to be surgical candidates.
Baradaran:
Having a moment in your accelerator to deploy IORT for these patients can help us treat those patients in just 1 single fraction using high-energy electrons.
Idrees:
Dr Lockney, my question for you is this: what if, at the time of exploration in the operating room, I had determined that this tumor was potentially unresectable? What would have been the options for this patient at that time?
Lockney:
That’s a critical question. That also points to the importance of discussing with a patient prior to surgery [to let them know that] this is a situation we may encounter because we’re left with a patient under anesthesia and have to decide how to proceed. In some scenarios, I would say if you discovered previously unrecognized metastatic disease such as peritoneal tumor deposits or liver metastases, then IORT has the potential for us to deliver some local palliative radiation for the tumor. If the patient is symptomatic from their local tumor symptoms, such as pain or impending gastric outlet obstruction, then we can allow that patient to have a 1-time radiation delivery dose in the operating room [OR] and spare them the 1 to 2 weeks of palliative outpatient radiation they may otherwise receive.
What’s a little bit more difficult to answer is if the patient has localized unresectable disease, what is the best approach at that time? If the patient has already had a course of preoperative external beam radiation, then we still have the option to deliver an IORT boost so that we can try and get some durable local control. Because we know that local symptoms and local progression can contribute to death in these patients and decrease performance status, the ability to tolerate additional chemotherapy, etc. If it’s a patient who has not yet had any prior external beam [radiation], then I would want to have a conversation with the patient beforehand that we maybe wouldn’t deliver intraoperative radiation but may try to target the tumor with a high-dose, ablative external beam approach to try and deliver a high percentage depth dose [PDD] for local tumor control.
Idrees:
Dr Lockney, in the cases that we have [discussed], we found localized disease intraoperatively but no evidence of metastatic disease and gave [those patients] IORT. What do the surgical oncologists or surgeons need to know in terms of [whether] the tumor or radiation is near the head of the pancreas, for example?
Lockney:
Particularly, for those tumors in the head of the pancreas, we have to remember that the duodenum will still be in the radiation field as well as the common bile duct, so we worry about toxicity to the duodenum as well as stricture risks to the bile duct. If 100% of the circumference of the duodenum is going to be in the radiation field of the IORT, we need to reduce the dose. If we’re going to have less than 50% of the duodenum in the field, there will be a gastrointestinal duodenal bypass performed by the surgeon. Then, we can still try to escalate the dose of intraoperative radiation. Having that conversation with a surgeon is key so that you can perform the appropriate [procedure].
Idrees:
That’s what we have done historically in those cases. We perform a prophylactic gastrojejunal bypass in case they do have a subsequent duodenal stricture. What I liked about the intraoperative radiation therapy was that I was able to mobilize the stomach, colon, and small intestine out of the way, and we were able to radiate the area of concern intraoperatively [without an] innocent bystander effect, which would have been the case if the patient had received postoperative radiation therapy.
Lockney: I have a question for Dr Baradaran. If we have a tumor that can’t be resected as Dr Idrees said and we have an intact tumor, we have to think about the maximum tumor depth that we can treat with Mobetron [an electron-beam IORT machine]. Can you comment on your thoughts on that when we look at those PDD curves together in the OR?
Baradaran:
Absolutely. Mobetron can generate electrons at beam energies of up to 6, 9, and 12 MeV. A rule of thumb is that if you divide the energy by 4, it will give you the absolute maximum dose or electron dose distribution. For example, if we are treating a resected tumor and the prescription dose is 1 cm, if we use 6 MeV electrons, divide 6 by 4 for 1.5 cm; we can fully cover that resected region [with] almost 100% of the dose.
Lockney:
If we [needed] to treat an intact tumor that’s greater than 4 cm in depth, then what would our coverage be? For example, [what] if we have a deep tumor, bringing it to a depth of 4.5 cm?
Baradaran:
If you have an intact tumor, using 12 MeV electrons, we can have 90% of the volume receiving 100% of the prescription dose up to a depth of 4 cm. It doesn’t mean that we cannot have more coverage at a deeper depth; you will have just this coverage. For example, we can treat 80% of the isodose line.
Idrees:
Dr Lockney, I have a question for you. If someone gets, for example, 6 months of neoadjuvant chemotherapy and [the tumor is] deemed unresectable when we repeat the cross-sectional imaging but has no evidence of metastatic disease, how would you [treat] that patient?
Lockney:
Typically, I would call you or the treating surgeon to confirm. But yes, if you think there’s no chance of getting that patient to the OR, which is always our preferred first approach to try to achieve a cure, I would instead then try and opt for an ablative approach. When I say ablative, I want to deliver PDD based on alpha/beta 10 of [approximately] 100 Gy to try to get durable local control for that patient. When we need to do that from an external beam approach, I’m trying to deliver up to 75 Gy to as much of the gross tumor as I safely can over 5 weeks of treatment with concurrent capecitabine. That does require a lot of specialized treatment planning and delivery techniques such as breath hold and things like that.
Idrees:
You bring up a valuable point there. For the families and the physicians who are taking care of [patients with] pancreatic cancer, it’s valuable to obtain a second opinion, even if [the tumor is] initially deemed unresectable. What’s unresectable in one surgeon’s hands may be resectable in a different team. We see a lot of patients who have been initially categorized as [having] unresectable pancreatic cancer and come to us for a second opinion. The emphasis on the second opinion cannot be underestimated. When we evaluated those patients, we thought that we were able to resect them with or without intraoperative radiation therapy. That’s another key point: always ask for a second opinion in terms of resectability.
Reference
Product Datasheet: Mobetron. IntraOp. Accessed July 17, 2024. https://tinyurl.com/mrxpjxec
