Proton therapy lowers risk of side effects in cancer

Proton therapy leads to significantly lower risk of side effects for cancer patients when compared with traditional radiation, researchers have found.

For the findings, published in the journal JAMA Oncology, researchers from University of Pennsylvania analysed if the cancer patients going through radiation therapy alongside chemotherapy faced severe side effects in a span of 90 days.

They found proton therapy reduces the relative risk of these side effects by two-thirds.

"This is exciting because it shows that proton therapy offers a way for us to reduce the serious side effects of chemo-radiation and improve patient health and wellbeing without sacrificing the effectiveness of the therapy," said the study's lead author Brian Baumann from the University of Pennsylvania in the US.

Proton therapy has a few key differences from traditional photon radiation.

Photon radiation typically uses multiple x-ray beams to deliver radiation to the tumour target but unavoidably deposits radiation in the normal tissues beyond the target, potentially damaging those tissues as the beam exits the body.

For this study, researchers evaluated side effects including pain or difficulty swallowing, difficulty breathing, nausea, or diarrhea, among others.

Researchers focused on grade-three effects or higher, defined as side effects severe enough for patients to be hospitalised.

They evaluated data on 1,483 cancer patients receiving radiation and chemotherapy at the same time.

Of these, 391 patients received proton therapy, while 1,092 underwent photon treatment.

All patients had non-metastatic cancer and were undergoing treatment intended to be curative.

Patients with brain cancer, head and neck cancer, lung cancer, gastrointestinal cancer, and gynecologic cancer treated with concurrent chemo-radiation were included.

The primary outcome was whether or not patients experienced adverse side effects that were grade-three or higher within 90 days of treatment.

In the proton group, only 11.5 per cent of patients (45) did, compared to 27.6 per cent of patients (301) in the photon group.

A weighted analysis of both patient groups, which controlled for other factors that may have led to differences between the patient groups, found that the relative risk of a severe toxicity was two-thirds lower for proton patients compared to photon patients.

Importantly, overall survival and disease-free survival were similar between the two groups, suggesting that the reduction in toxicity seen with proton therapy did not come at the cost of reduced effectiveness.

Researchers said these results hint at the promise of proton therapy as a way to deliver intensified systemic therapy and/or higher dose radiation therapy more safely, which could improve survival outcomes.

In fact, data showed that while older patients with more comorbidities were more likely to receive proton therapy, they experienced fewer side effects, the researchers said.

"This tells us proton therapy may allow older patients to receive the most effective combined treatments, and that older, sicker patients can more safely be included in clinical trials that use proton therapy," Baumann said.