Heavy ion therapy could provide a safer and more effective way to deal with a rare type of cancer known as melanoma than existing radiation treatment, Japanese researchers have found.

The National Institutes for Quantum and Radiological Science and Technology (QST) said heavy ion therapy can treat malignant melanoma on the mucous membrane in the nose, throat, mouth and elsewhere in the head and neck to the same extent as surgical operations. But unlike surgery, the therapy does not change the appearance of patients.

The results were obtained during joint research involving four institutions in Japan, including the QST’s National Institute of Radiological Sciences, and have been published in the U.S. journal International Journal of Radiation Oncology, Biology, Physics.

Based on an analysis of 260 melanoma cases reported between 2003 and 2014, the scientists estimated the non-recurring ratio in treated areas was 84 percent two years after therapy and 72 percent five years after.

Taking into account recurrences in untreated areas and other factors, the survival rates were 69 percent after two years and 45 percent after five years.

The five-year survival rate was comparable to that for surgery, the standard method to treat mucosal melanoma, and much higher than the ratio for X-ray-based radiation therapy.

Although loss of eyesight and other serious side effects were reported in some cases of heavy ion therapy, the ratio of those instances was only 2.7 percent, well below that for radiation therapy.

Around 100 to 200 people in Japan develop malignant mucosal melanoma in the head and neck each year.

It is difficult to find mucosal melanoma when the tumor develops deep inside the mouth, nose, throat and elsewhere.

Even if surgery can resect the tumor, a significant part of bones in the jaws and face of the patient must be removed. Some patients are reluctant to undergo the operation out of concerns that their appearance will drastically change.

Conventional radiation therapy has proved less effective than surgical operations.