Proton Therapy: How it works and helps cancer patients

Among the most common treatments for cancer patients, radiation therapy or radiotherapy uses ionizing radiation, typically x-rays, to damage the DNA of cancer cells. When radiated, these cancer cells would gradually be killed. But conventional X-ray radiotherapy has side effects. Proton therapy, another type of radiotherapy, is said to be less damaging, which makes this treatment especially beneficial for certain patients.

While not really a new development in radiation oncology, proton therapy machines have been getting better in the past few years, according to Dr. Lee Kuo Ann, a senior consultant and radiation oncologist at Mount Elizabeth Novena Hospital in Singapore.

X-rays have to traverse normal tissues from the skin to reach the tumor. After passing through the tumor, X-rays continue on till they exit the body on the other side, causing radiation injury to normal tissues on both sides of the tumor.

“Proton therapy is like playing basketball or golf. By shooting the proton particle at the correct direction and speed, it will land in the tumor and stop there, with no radiation coming out the other side. So we reduce radiation injury to the normal tissues on the way in and especially on the way out,” Dr. Lee explained.

“So that’s the main attraction to proton therapy. It effectively reduces the radiation exposure to the patient maybe by about a third. And that’s expected to reduce side effects both in the short term as well as in the long run,” he added.

Arguably, almost any patient undergoing radiotherapy can receive a proton therapy treatment as well, according to Dr. Lee. But the benefits would differ from one patient to another. “Some patients will expect to see more benefit than others,” he said.

Dr. Lee considered that children and young adults generally, can benefit more from proton therapy, as many of the side effects such as radiation-induced malignancy could appear late or years after.

Proton therapy can also be helpful for patients with large tumors, said Dr. Lee. Treating large tumors with radiotherapy would involve large radiation fields, thus side effects could be worse. Whereas, with proton therapy, given it reduces exposure of normal tissues to radiation, patients with large tumors can expect less side effects.

The treatment could also help patients with a tumor located within sensitive organs like the liver. Dr. Lee shared that for patients with large liver tumors, it is hard to deliver a large dose of x-rays without unacceptable injury to the organ. “But with proton therapy, we are now able to give that same dose of radiation safely,” he said.

Dr. Lee also said that proton therapy could potentially be beneficial to patients who already went through radiation. “If we give a second round of radiation, the injury to the tissues would exceed what is safe. With proton therapy, we might be able to reduce radiation exposure to nearby tissues,” he said.

“Having said that, proton therapy for re-radiation cases still has to be very carefully done, and not everyone is a candidate,” Dr. Lee also noted. “Because if the recurrence is located in a critical organ, you have to deliver the high dose to the tumor at the critical organ. And no matter what radiation technique you’re using, including proton therapy, there will be a high dose to that organ and hence will still be risky and dangerous.”

Mount Elizabeth now has a newly available Proton Therapy Centre added to its array of machines for cancer treatments.

“This is the newest state-of-the-art compact proton radiotherapy machine, and it will be installed at Mount Elizabeth Novena Hospital,” Dr. Lee said. “The cases that we’ll be allowed to treat will be dictated and guided by the Singapore Ministry of Health rules, which are actually online.”

“We are quite excited to be able to firstly, have all the tools at our disposal. Previously, with the highest-end x-ray radiotherapy machines, and now our newest addition of a proton therapy machine,” he added.

Mount Elizabeth Novena Hospital’s Proton Therapy Centre has started operations this month.

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