INTENSITY MODULATED RADIATION THERAPY (IMRT) TECHNOLOGY
THE PEACOCK SYSTEM
At The Western Pennsylvania Hospital
Last Updated: 2/10/99
The cancer death rate in the United States dropped by nearly 3 percent between 1991 and l995, the first sustained decline since national record keeping began in the 1930s. Early detection is one of the primary reasons. Over the past 30 years, the most significant progress in our battle against cancer has been in diagnostics, fueled by the development of MRI and CT scan technologies.
Now, technology is taking another huge leap forward. This time it is in cancer treatment. Not since the arrival of the powerful linear accelerators in the 1970s has there been such significant advancement in radiation therapy for cancer.
lNTENSITY MODULE RADIATION THERAPY (IMPT):
IMRT is the most sophisticated form of computer-delivered radiation therapy currently available. This
innovative, three-dimensional conformal radiation treatment delivers highly focused radiation with minimal
impact to surrounding tissues. Historically, the maximal dose that could be delivered to a tumor site has
been restricted by the tolerance of nearby tissues. The precision of IMPT technology allows for more finite
definition of the target zone, enabling a higher dose of radiation at the turner site with decreased probability of normal tissue toxicity.
The Western Pennsylvania Hospital Is the only facility to provide IMRT in this region and was one of only six clinical sites in the world selected to develop this cutting-edge technology. This newly FDA-cleared technology promises enhanced outcomes and substantial coat savings compared to related technology.
The Western Pennsylvania Hospital's Division of Radiation Oncology of the Department of Radiology together with The Western Pennsylvania Hospital's Center for Neuro-Oncology have participated In numerous IMRT studies that have resulted in significant advancements in the treatment of brain tumors.
THE IMRT SYSTEM: The IMRT system consists of a computer planning technology that enables clinicians to precisely match a palliative radiation dose to the shape of a tumor target with minimal damage to sensitive structures around it. A rnultileaf intensity modulating collimator enables radiation oncologists to deliver the radiation beam exactly to the tumor sire. In the Division of Radiation Oncology at West Penn Hospital, the Peacock System is used as the IMPT delivery system.
HISTORY Of IMRT:
The Peacock System is the invention of Mark P. Carol, M.D., an expert in stereotactic neurosurgery and
intensity modulated radiation therapy. Dr. Carol holds eight patents in neurosurgery, radiation therapy and
cardiology. Although he developed the initial idea for the Peacock System in 1975, computer technology
could not meet the needs of the idea at that time. Dr. Carol revisited the idea again in 1991, and in 1992
began working on a prototype. The FDA provided final clearance for the hardware system in 1996. In April
1996 the FDA approved the planning software.
HOW IMRT WORKS:
Conforma1 treatments are delivered rotationally in contiguous transverse slices. During rotation, the field shape and intensity of the beam are continuously varied. IMPT has the ability to shape the radiation beam to the target and modulate the intensity of radiation across the target.
The process for the actual planning lakes several days, yet treatment takes no longer than it does for conventional radiotherapy. For planning, a series of 40 to 80 imaging studies are done on a CT scan. These are input into the Emend planning computer. The computer goes through the anatomy, marking as many targets and sensitive structures as necessary. Traditional forms of conventional radiotherapy require that the operator assign the weight of the beam, identify the target zone and then input the information into a computer system for calculation of the radiation dosages. With IMRT clinicians determine and input the optimal dosage for the tumor site into their system. The software simulates the radiation physics and then establishes the optimal treatment plan, including provision of the treatment parameters. During simulation, the planning computer calculates a series of up to 5,000 separate plans, The system is capable of automatically creating and implementing an optimized treatment plan that can target cancerous tissue in almost any size or shape at almost any anatomical location. It can also concurrently plan for and treat multiple targets with the same dose or can give each target a different dose, if desired.
Once the optimal plan is selected the data are transferred onto a floppy disk that is inserted into the IMRT controller on the accelerator and delivers the treatment plan. During treatment, as the IMRT moves around the patient it keeps measuring the angle and adjusts the small vanes that shape the beam.
USES OF IMRT:
IMRT is particularly valuable for intracranial lesions. Because there is no limit to the size of tumor that can treated, IMRT may be used to treat large malignant tumors. It can also be used to treat multiple tumors, such as metastatic lesions, with a single treatment plan. IMRT is especially valuable for treatment of benign tumors, such as meningiomas end acoustic neuromas when the tumor is adjacent to a functional cranial nerve. Because IMRT conforms a high dose to the tumor and a lower dose to sensitive structures, IMRT therapy may also benefit patients who have already received the maximal allowable dose with conventional radiation therapy.
Types Of Tumors Eligible for Treatment:
Since 1994, patients have received treatments at The Western Pennsylvania Hospital for tumors of the brain, head and neck. Future applications will include treatment to the lower spine as well. Improvements in clinical conditions have been achieved without side effects that would have been expected with conventional radiation. These potential side effects include a compromise of visual function, mucositis, spinal cord dysfunction, and xerosomia (Dry mouth resulting from damage to the saliva-producing parotid glands). Many of the patients who have been treated had recurrent cancers or inoperable tumors and had already received the maximal amount of radiation deliverable by conventional means The use of IMRT, as delivered by PEACOCK, allows patients to receive additional radiation safely, in some cases prolonging survival and improving the quality of life.
Patient Selection Criteria: Any patient with a radiation-sensitive tumor occurring anywhere in the central and peripheral nervous system may be a candidate for IMRT: The patient's age, the type of tumor, and the patient's prior history of radiation, eligibility for surgery, and general medical condition must also be considered Based on these factors, the decision is made on a case-by-case basis as to whether or not IMRT would benefit a patient.
|For more information, contact:|
|Robert G. Selker MD|
| Director - Center For Neuro-Oncology|
| Western Pennsylvania Cancer Institute|
| 4800 Friendship Ave|
|Pittsburgh, PA 15221 USA |
| Voice: (412)578-4340|
| Fax: (412)578-4360|