Dr. Michael Zelefsky, a radiation oncologist, is Professor of Radiation Oncology, Chief of the Brachytherapy Service, and Co-Leader of the Genitourinary Disease Management Team at Memorial Sloan Kettering Cancer Center in New York City.
Prostatepedia recently spoke with him about how advances in imaging have impacted radiation therapy. Subscribe to read the entire conversation.
What role does imaging now play in radiation therapy?
Dr. Zelefsky: Radiation therapy has been linked to imaging for many years. In the late 1970s and early 1980s with the advent of the CAT scan, those images were used in the treatment planning process to provide greater accuracy for targeting the radiation. Over the ensuing 20-30 years, there have been significant advances in imaging, from CAT scanning to MRI, and from multiparametric MRI to molecular imaging. These advances in diagnostic imaging continue to be linked to radiation treatment. We use multiparametric MRI imaging to target radiation to the prostate with exquisite precision. Just as importantly, we use these technologies to understand the geometry and anatomy of the surrounding normal tissues. For the prostate, that could mean the bladder, rectum, bowels, and even specific anatomic regions like the bladder neck and the neurovascular bundles that control erectile function.
Advances in imaging have allowed us to visualize these normal tissue structures, and this information is incorporated into treatment planning, giving us a way to deliver the radiation with a precision we’ve never had before.
What sorts of changes do you think are on the horizon as we develop better imaging techniques?
Dr. Zelefsky: We have successfully moved from CT-based imaging to MR-based imaging. Now, we commonly use MRI and fuse those images with the CAT scan. At Memorial Sloan Kettering, we have moved to the next step, which is pure MRI-based planning. This means we don’t need the intermediary step of a CT scan anymore. We can plan directly off the MRI, and we map everything out from these sets of specific We’ve also moved beyond MRI to what we call multiparametric MRI. We look at different sequences and formats of the MRI, including dynamic contrast enhanced imaging, and diffusion-weighted imaging to give us further information about the location of the disease within the prostate, which is called the dominant intraprostatic lesion (DIL). This dominant intraprostatic lesion is an important area to target because recurrences after radiation stem from regrowth of disease from that initial site of disease in the prostate.
Radiation oncologists are recognizing that there may be opportunities to intensify the focus of the radiation to the DIL to improve the tumor control rates with radiation. We have moved from CT-based to MR-based radiation therapy to pure MRI-based planning, and now we incorporate important information from multiparametric imaging. In the future, we’ll also incorporate molecular imaging, which comes from advanced nuclear medicine studies.