Harmful spillover radiation to the bowels, stomach and liver has soured many cancer physicians
on using conventional radiation concurrently with chemotherapy or surgery for treating gastrointestinal (GI) cancers.
But the lesser side effects of highly targeted proton radiation may dramatically change the negative perceptions about using radiation for GI cancers.
“Conventional radiation treatments for GI cancers have definitely been marginalized in pancreatic cancer, gastric cancer and rectal cancer,” says John Plastaras, M.D., a GI cancer specialist at the Roberts Proton Therapy Center and associate professor of radiation oncology at the Perelman School of Medicine at the University of Pennsylvania, part of Penn Medicine in Philadelphia, Pennsylvania. “They’ve been marginalized because their toxicities and perceived toxicities are so great.”
“But with protons,” Plastaras continues, “we can potentially make the treatments less toxic and easier on the patients, hopefully improving their quality of life and getting them to additional chemotherapy or through surgery, which is usually a big, big procedure.”
According to the World Health Organization, about 4 million people worldwide are diagnosed with GI cancer every year, including more than 144,000 Americans.
Plastaras says combination therapy using both protons and chemo is a very powerful weapon against GI cancers, especially when treatments need to be intensified locally. But many medical oncologists are unaware that protons can be as effective at killing cancer cells as photon radiation therapy, albeit with far fewer troubling side effects.
“GI cancers tend to hang around the bowel,” Plastaras says. “So whether that’s anal cancer, rectal cancer, pancreaticobiliary cancers or gastric cancers, the unintended radiation dose to the bowel tends to be what drives the toxicity. The dose that really correlates to Grade 3 and higher GI toxicity seems to be in the 15 to 20 Gray range. And that range is really easy to reduce with proton therapy compared to IMRT [intensity-modulated radiation therapy].”
Grade 3 radiation toxicities include diarrhea, nausea and/or weight loss greater than 15 percent, for which intravenous treatments or hospitalization are needed. Treating Grade 3 and more severe Grade 4 toxicities often require patients to suspend their cancer treatments for a while. Less severe Grade 2 toxicities can usually be treated at home with medications.
If we can reduce the dose to the bowel using proton therapy, we may be able to decrease those short-term toxicities,” says Plastaras, “whether that’s diarrhea or nausea or vomiting. And we’ll be able to show our medical oncology colleagues that we can actually deliver the same treatment with all the local-regional control benefits that we get from conventional radiation — without putting the patient in the hospital with acute side effects.”
Using pencil-beam scanning, Plastaras and his associates at Penn Medicine have treated rectal cancer patients with proton therapy and compared treatment side effects with a similar group of patients treated using concurrent IMRT-based chemo-radiation. “We saw significant decreases in Grade 2 and higher diarrhea,” he says.
Those findings was presented by Plastaras at the American Society of Clinical Oncology’s GI Cancers Symposium earlier this year.