Memorial Sloan Kettering has long been recognized as a pioneer in the treatment of cancer with radiation. The collaboration of radiation oncologists and medical physicists has produced the development and clinical implementation of new therapies that are “beyond the standard approaches and definitely not out of the textbook,” in the words of Radiation Oncology Department Chair Simon N. Powell.
Evolving technologies and novel enhancements, many of which were developed by Memorial Sloan Kettering medical physicists, have spurred a number of new clinical initiatives led by radiation oncologists investigating more-effective approaches. Memorial Sloan Kettering has particular expertise in the use of intensity-modulated radiation therapy (IMRT), which targets tumors with multiple beams at different angles and intensities.
The SHARP Advantage
Memorial Sloan Kettering’s extensive experience working with IMRT has served as an important foundation for the development of new approaches to treat prostate cancer. With the help of sophisticated image guidance and global positioning system (GPS) techniques, radiation oncologists are now able to offer prostate cancer patients a more focused approach to delivering higher doses of radiation more accurately and in less time than with IMRT.
Using a form of radiosurgery called stereotactic hypofractionated accelerated radiation to the prostate (SHARP), physicians can deliver ultrahigh doses of radiation in only five treatment sessions, compared with close to 50 sessions over ten weeks using the conventional approach.
GPS markers called ferromagnetic transponders are implanted by a urologist into the patient’s prostate gland. The beacons act as homing devices, sending out electromagnetic signals of the prostate’s exact location that can be used to guide the linear accelerator, which delivers high-energy radiation to the prostate over several minutes. If the prostate moves outside of a very tight margin, the radiation treatment can be stopped and adjustments made.
“This kind of missile technology helps us and our medical physics colleagues localize the target with an accuracy akin to the sharpness of a surgeon’s scalpel, sculpt a high dose of radiation around the prostate, and effectively minimize the amount of normal tissue that’s included in that margin,” says radiation oncologist Michael J. Zelefsky. “In this way, we can safely give the entire course of radiation in only five treatment sessions with fewer side effects.”
Memorial Sloan Kettering is the only hospital in Manhattan currently offering this treatment approach and one of only a few academic medical centers in the world doing it within the context of an ongoing clinical trial. Despite the application of high radiation doses, the more than 100 patients with disease confined to the prostate who have been treated with SHARP have tolerated the treatment well. After treatment, patients are closely followed with MRIs and a prostate biopsy.
“SHARP will likely replace the standard way of delivering external radiation therapy for prostate cancer if continued research and patient follow-up show that it is equally or more effective,” says Dr. Zelefsky.
Improving Brachytherapy with Intraoperative Image Guidance
Over the past 15 years, Memorial Sloan Kettering has established long-term success rates using brachytherapy — the placement of radioactive seeds into the prostate gland to deliver an extraordinarily high dose of radiation to the tumor.
Brachytherapy delivery has been improved by the incorporation of advanced imaging techniques that are commonly used for diagnostic procedures and treatment planning prior to treatment. In fact, it built the only state-of-the-art intraoperative imaging suite in the country dedicated solely to brachytherapy procedures.
One unique feature of the suite is a portable intraoperative CT unit called the O-Arm, which allows physicians to obtain real-time snapshots of the prostate that are fused with ultrasound images to target and confirm the accuracy of radioactive seed placement during the procedure. Memorial Sloan Kettering is currently the only center in the world routinely using this system during brachytherapy.
Marco Zaider, Head of Brachytherapy Physics, and Gikas S. Mageras, Chief of the Computer Service, led a team that developed a unique, patent-pending computer program that enhances the precision of the procedure by enabling physicians to receive instantaneous feedback about exactly where the seeds should be placed within the prostate gland and giving them the opportunity to make corrections on the spot. Being able to obtain and act on this information while a patient is asleep during the procedure in the operating room reduces the possibility that physicians will have to make adjustments later.
“Another advantage is that we can now safely re-treat patients with prostate tumors that have recurred years after treatment with other modalities by using this pinpointed seed implant approach, presenting a treatment option for these patients that didn’t exist before,” says Dr. Zelefsky, who is Chief of the Brachytherapy Service.
Memorial Sloan Kettering’s intraoperative imaging suite also offers MRI, which shows soft tissue differentiation, and PET/CT, which provides detailed anatomical images. Plans are under way to integrate these tools into a computer navigation system that could be used to further refine seed placement during brachytherapy. This unique combination of advanced imaging tools will enhance treatment planning and delivery as well as tumor assessment after treatment, allowing for more-adaptive therapy in which treatment changes can be made based upon tumor response.
“What makes the prostate program at Memorial Sloan Kettering unique is the availability of this comprehensive package of options we can offer our patients,” says Dr. Zelefsky. “Our expertise and this array of options at our disposal enable us to tailor radiation therapy based on the characteristics and location of the tumor, as well as important physical, emotional, and psychological factors that take the entire individual and his quality of life into account.”
This blog entry is part of a larger feature about advances in radiation oncology published in the October 2013 issue of Center News.