Well Being — 30 March 2018
Proton therapy takes careful aim at cancer

By Jana Soeldner Danger

City & Shore Magazine

Proton therapy, an advanced form of radiation treatment now offered at the Miami Cancer Institute, a part of Baptist Health South Florida, promises to minimize exposure to healthy tissues and organs compared to conventional radiation therapy.

While radiation is a time-tested method of killing cancer cells, it also damages healthy cells, says Dr. Minesh Mehta, chief of radiation oncology at MCI. Reducing exposure can potentially mean fewer short- and long-term side effects.

When a dose of conventional radiation is delivered, the beam continues to travel into healthy tissue besides the cancer. Protons, however, can be targeted to travel directly to a tumor. Then, when their job of destroying cancer cells is done, they lose their energy instead of continuing on to damage healthy cells.

A Treatment Plan

Doctors first develop a treatment plan using precise images of the patient’s anatomy and the tumor, Dr. Mehta says. These images allow physicians to determine the optimal amount of radiation to deliver – as well as exactly where to place the proton beam – which is about the diameter of a pencil eraser.

Tumor images are then divided so treatment can be administered layer by layer. Larger tumors may have a dozen or more layers, and the deepest layer of the tumor will receive the highest amount of energy, Dr. Mehta says.

Each layer is divided into lines, and the lines are divided into individual spots about the same diameter as the proton beam, with a computer algorithm determining the optimal number of spots. The beam is then directed to each spot on a line. Magnets steer the beam from spot to spot, and the beam then moves down to the next line so radiation is deposited in narrow bands.

Expanded Usage

Until recently, proton therapy was mostly limited to cancers in children and in the brains, spines and prostates of adults, Dr. Mehta says. Now its use is being expanded to more types of tumors. It can be beneficial for women with left-side breast cancer, for example, by minimizing radiation exposure to the heart.

In situations where a high dose of radiotherapy is required, it may be difficult or sometimes even impossible to deliver the dose safely with conventional radiotherapy, Dr. Mehta says, because the dose can exceed the tolerance of surrounding tissues. Proton therapy may permit delivery of the higher dose to a tumor without damaging surrounding tissue.

There are only about 30 centers in the country offering the treatment. Others are being planned or are under construction.

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