IMRT & IGRT

Quick and painless, external-beam radiation therapy has long been used to destroy cancer cells. The latest methods—Intensity-Modulated Radiation Therapy (IMRT) and Image-Guided Radiation Therapy (IGRT)—provide advanced technology for fighting cancer. Used alone or in conjunction, these therapies allow higher doses of radiation to be delivered with greater precision without destroying surrounding, healthy tissue.

For patients, IMRT/IGRT means:

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

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 cells 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 alone 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 a noninvasive, outpatient alternative to surgery for some patients.

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.

How IMRT Works

[MV1] IMRT is a specialized radiation therapy that uses powerful treatment planning software to calculate precise beam angles, shapes and exposure times tailored to each tumor. The radiation beam can be broken up into many smaller beams and the intensity of each small beam can be adjusted individually. This may allow a higher dose of radiation to be delivered to the tumor with less risk to nearby healthy tissue, potentially decreasing the duration of treatment and increasing the chance of a cure.

How IGRT Works

Image-guided radiation therapy (IGRT) uses frequent imaging during a course of radiation treatment to verify the position of the tumor and improve the precision and accuracy of the treatment delivery. A special on-board imaging system called a cone-beam CT (CBCT) is attached to the treatment machine. After the patient is positioned, images of the tumor are taken and compared with the simulation scans. Necessary adjustments are then made to more precisely target the tumor and avoid surrounding healthy tissue.