IGRT / IMRT for Prostate Cancer

IMRT Linear Accelerator

Cutaway view of a modern IGRT / IMRT linear accelerator with multi-leaf collimators for beam shaping. Image courtesy of Varian Medical Systems.

State-of-the-art radiation therapy at Genesis Healthcare incorporates intensity-modulated radiation therapy (IMRT) to allow the radiation dose to exactly match the highest cancer cell burden, and image-guided radiation therapy (IGRT) to allow the delivery of each treatment with a very high degree of accuracy.

IGRT / IMRT Background

The major advantage of IGRT / IMRT is that it is adaptable across a wide variety of prostate cancer situations, and as a mature radiation therapy technology, it is recognized for coverage by virtually all insurers. IGRT / IMRT emerges as the preferred treatment option for a wide spectrum of prostate cancer patients.

The Memorial Sloan Kettering Cancer (MSKCC) Group was one of the original clinical developers of IMRT technology for prostate cancer treatment, and recently published their 10-year results, indicating long-term effectiveness on a par with radical prostatectomy. Our IMRT strategy is based on their groundbreaking work, yet incorporates more advanced technology that has since evolved, leading to even greater potential effectiveness and safety.

Briefly, additional improvements that have emerged since the initial development of the IMRT technique described by the MSKCC group include the following:

  • More advanced imaging techniques to better identify and map the specific tumor locations within the prostate for differential dose escalation (advanced MRI prostate imaging protocols). (Illustrated in Figure 1: IGRT Design)
  • More advanced computer treatment planning technology to design a more exact and customized three-dimensional dose pattern. (Also illustrated in Figure 1: IGRT Design)
  • More powerful and flexible medical linear accelerator devices to deliver these patient-customized dose patterns effectively. (Illustrated in Figure 2: IGRT Animation)
  • Sophisticated three-dimensional daily image-guidance (IGRT) techniques that allow these highly conformal treatments to be delivered with a far greater degree of accuracy than previously possible. (Illustrated in Figure 3: IGRT Montage)

IGRT / IMRT Treamtent Process

There are several steps involved in the IGRT / IMRT process, including the following:

1. Radiation Oncologist Consultation:

The original step in the process is a thorough review of the patient's medical records, lab results, imaging studies, and physical examination during a consultation that usually lasts about an hour. At the conclusion of this initial consultation a specific treatment recommendation may be made, or in some cases, further diagnostic testing ordered first. If additional tests are ordered there will then be a second brief visit with the radiation oncologist to review the results of the additional tests and determine a final recommendation. For some patients a clear path of action will be evident, while others may choose to seek consultations from additional specialists before making their final treatment decision.

2.  Fiducials:

In many (but not all) cases, the first step in the treatment planning process will be the implantation of several tiny gold markers, known as fiducials, into the prostate. This is a minimally invasive procedure done under local anesthesia. Fiducials are typically implanted into the prostate of a patient who is receiving radiation therapy as his definitive treatment, whereas patients treated after a radical prostatectomy normally have pre-existing surgical clips that serve the same localization function, such that they typically do not need fiducials. The implanted fiducials (or post-prostatectomy surgical clips) serve as a three-dimensional reference structure for the IGRT process. Fiducial, surgical clip-based and Cone Beam CT-based IGRT are illistrated in Figure 3: IGRT Montage.

3. Simulation:

The next step is the obtaining of CT +/- MRI images of the prostate or surgical prostate bed - a process known as simulation. These images are then imported into the radiation therapy treatment planning computer for detailed anatomic analysis and contouring by the radiation oncologist, followed by three-dimensional treatment planning by our physics/dosimetry staff.  This process represents a patient-specific "medical engineering" project and forms the basis upon which the daily treatments are designed. Figure 1: IGRT Design represents a completed simulation design, constructed from superimposed CT and semi-transparent MRI images.

4. Radiation Therapy Treatment:

Following completion of the simulation process, the scheduled course of daily radiotherapy treatments will begin, typically lasting a total of 6-9 weeks, depending upon the exact situation and course prescribed. The course of treatment is administered over consecutive working days until the prescribed number of treatments has been delivered, such that a 9 week course of treatment will consist of 45 individual treatments. Each treatment session takes 10-15 minutes and consists of two main steps - The IGRT step and the treatment step. The IGRT step consists of stereotactic X-rays of the implanted fiducials or surgical clips, or in the alternative, we may use daily Cone beam CT (CBCT) or ultrasound imaging if fiducials or surgical clips are not done. The treatment itself follows immediately after the IGRT step, during which time the linear accelerator makes one or more full arc sweeps around the targeted area to deliver each daily treatment. This entire process is painless and rapid. Patients remain fully active and may continue working throughout the entire treatment course.

5. Medical Care and follow-up:

During the treatment course, the patient will be checked once per week by the radiation oncologist, primarily to assess and treat side-effects as well as answer any questions from the patient or their family. These weekly MD visits happen right before or after the scheduled radiotherapy treatment and usually add only an extra few minutes to that day's session, though may be longer if the patient's situation call for a more detailed evaluation. After the course of radiotherapy has been completed the patient will be given a follow-up appointment and this is a part of every patient's final day sign-out process. Usually the first follow-up radiation oncologist appointment is 1-3 months after conclusion of treatment and over the longer term, our patients will typically be followed once or twice per year, sometimes more frequently if they are on a clinical trial or have other reasons to require closer attention. Over the very long-term, some patients will be followed by us indefinitely, while others will eventually be discharged back to their referring physician or primary physician, and this decision is individualized to each patient's specific situation and desire. Ultimately we aim to make the treatment and follow-up process as efficient for the patient and family as possible, while maintaining the necessary degree of completeness and attention to detail, until the final outcome of treatment is determined.