Intensity-Modulated Radiation Therapy:
Fighting Prostate Cancer With Precision

Quick and painless, external-beam radiation therapy has long been used to destroy cancer cells. The latest method—intensity-modulated radiation therapy (IMRT)—uses state-of-the-art technology to deliver more intense radiation directly to prostate cancer tumors while sparing nearby healthy tissue.

For patients, this means

• more effective treatment focused on cancer cells,
• less radiation exposure to normal tissue,
• potentially fewer and milder side effects, and
• the ability to treat some tumors that couldn’t previously be treated by radiation.

While IMRT can treat a wide variety of malignancies, it is most commonly used to eradicate prostate cancer. Since the prostate is located near the bladder, bowels, and anus, physicians traditionally limited the amount of external-beam radiation delivered close to these sensitive organs. Still, healthy tissue is often damaged when less precise methods are used. Unlike cancerous cells, normal ones can adapt and survive, but unnecessary radiation exposure can still lead to incontinence and bowel problems. While some of these side effects may manifest immediately, others develop over time. By increasing radiation exposure to malignant cells and decreasing it to healthy tissue, IMRT may reduce such complications.

Clinical studies conducted at Memorial Sloan Kettering Cancer Center indicate that higher dose rates delivered with IMRT significantly improve local tumor control while reducing some of the complications caused by damage to normal tissue.^1,2 While IMRT may be used in conjunction with other treatments, it may also offer an noninvasive, outpatient alternative to surgery for some patients.

How IMRT Works

SightLine is developing IMRT clinics using state-of-the-art technology usually unavailable at most freestanding outpatient clinics. The process begins with detailed treatment planning. Patients first undergo computed tomography and potentially a magnetic resonance imaging scan. Working with these images, radiation oncologists use powerful treatment planning software to calculate precise beam angles, shapes, and exposure times tailored to each tumor.

SightLine facilities also incorporate image-guided radiation therapy (IGRT) into treatment planning. Tumors can shift between treatments, so IGRT employs a variety of digital technologies to capture detailed images before each session. This allows our radiologists to adjust IMRT beam shaping and dosage to make cancer treatment even more precise.

The radiation is delivered by a medical linear accelerator, which generates X-rays or photon radiation. The linear accelerator moves, so the patient lies comfortably without being repositioned during treatment.

A dynamic multileaf collimator provides the “modulated” part of IMRT. This device precisely shapes thousands of tiny beams that minutely vary the radiation dose depending on the type and density of targeted tissue.

Patients typically undergo fifteen- to thirty-minute treatments five days a week for seven or eight weeks.

¹ Zelefsky MJ, Chan H, Hunt M, et al, Long-term outcome of high dose intensity modulated radiation therapy for patients with clinically localized prostate cancer, Journal of Urology, 2006 Oct;172(4 Pt 1):1415-9.

² Zelefsky MJ , Fuks Z, Hunt M, et al, High-dose intensity modulated radiation therapy for prostate cancer: Early toxicity and biochemical outcome in 772 patients, International Journal of Radiation Oncology • Biology • Physics , 2002 Aug 1;53(5):1111-6.