Radiation therapy for breast cancer can be a double-edged sword. The treatment is usually given to destroy any stray cancer cells that may have been left behind after a breast tumor is surgically removed. But if there is evidence the disease has spread locally — to the chest wall and nearby lymph nodes — the chest and multiple nodes must be targeted while minimizing the dose to the lungs and heart.
This is a challenging task, even with an advanced method like intensity-modulated radiation therapy, or IMRT, which targets tumors using multiple beams at different angles and intensities. Too much radiation to the lungs can cause an inflammatory condition known as pneumonitis, while in the heart it can cause thickening and stiffness of muscle tissue and connecting arteries, increasing the risk of heart disease.
The standard IMRT approach, which uses three to five beams, has provided somewhat patchwork coverage. While it helps preserve heart and lung function, the uneven radiation levels create “hot” and “cold” pockets that increase the risk of missing microscopic disease that could spread.
“If you’re targeting the chest wall and multiple nodes, it gets very complicated to design a way to treat the entire area safely,” says Memorial Sloan Kettering radiation oncologist Alice Y. Ho. “In addition, an increasing percentage of breast cancer patients are having reconstructive surgery and receiving implants, which present a technical challenge to work around.”
Expanding Coverage with Additional Beams
Dr. Ho, in collaboration with Radiation Oncology Department Chair Simon Powell, decided to investigate whether spreading the radiation dose over a larger number of beams would make it possible to cover the area more thoroughly without endangering the patient. Working with medical physicists Ase Ballangrud-Popovic and Guang Li, they developed a treatment plan using eight to 12 beams that targeted potential disease sites while sculpting the radiation around multiple obstacles in the anatomy.
The approach leaves less margin for error around the targets — being even a few millimeters off can miss cancer cells and greatly undermine results. “This technique has a very steep dosage fall-off, meaning that the radiation drops right off at the edge of the treatment area,” Dr. Ballangrud-Popovic says. “Because of this, we have to make certain the patient is positioned more accurately than with standard therapy.”
To accomplish this, the team employed a new 3D surface imaging system called Align RT®, which uses three cameras to track the position of the patient in relation to the radiation beam. The system continuously monitors any movement during treatment so adjustments can be made. The Align RT surface images are used in combination with conventional x-ray images that rely on bones as landmarks.
The combination of the new IMRT planning approach and the Align RT imaging system was recently tested in a pilot study involving 106 breast cancer patients who were given the treatment following surgery. Each patient received 25 radiation doses, with some getting chemotherapy as well. The results show conclusively that the method, while covering a larger area, does not increase detectable side effects to the heart or lungs.
The study also suggests the new method may provide some unexpected cosmetic benefits. Because the higher number of beams provides a more evenly spread dose, there are fewer pockets of high radiation that cause red or dark spots in the breast skin. Fibrosis — a scarring and stiffness in the breasts of women with implants — may also be minimized or avoided.
A new study is now planned to look specifically at the question of whether the new IMRT approach produces better results than conventional therapy in women with implants. “It will be significant if we improve the cosmetic appearance of women with implants,” Dr. Ho says. “It has become clear that this is a major concern for patients, so this benefit alone would be very important.”
This blog entry is part of a larger feature about advances in radiation oncology published in the October 2013 issue of Center News.