Dose Sculpting with IMRT
At What Cost?
"IMRT is the biggest breakthrough in radiation therapy in the last 40 years."
- Donald B. Fuller M.D.,
Radiation Medical Group, San Diego, Ca
The World Health Organization shows prostate cancer is gaining on lung and stomach cancer as the most prevalent cancer among men globally - with over half a million cases diagnosed in the year 2000 alone. More recently, the American cancer Society (ACS) states that in the U.S. in 2003 there were over 220,000 new cases, and an estimated 28,900 deaths.
Prostate Cancer has grown in public visibility since 1992 when former U.S. Senator Bob Dole went public with his ordeal. Since then many public figures including, U.K. footballer Denis Law, former South African President Nelson Mandela, former NYC Mayor Rudolph Giuliani, golf legend Arnold Palmer, and Ret. General Norman Schwarzkopf have helped raise public awareness about this killer. Beyond the surgical indication, the use of radiation for cancer treatment has been a constant over the years. Controlled radiation doses are a viable way of killing the cancer cells. But the question commonly asked is "at what cost?"
Radiation strong enough to kill cancerous tumors also kills healthy cells. Recently a technique has been introduced that significantly improves physician's odds of using radiation to destroy the invading cancer while saving the healthy tissue - it's called intensity modulated radiation therapy (IMRT).
What is IMRT?
IMRT is one of the most technologically advanced cancer treatment methods available in external beam radiation therapy. Simply put, IMRT uses a computer program to design a precise dose distribution plan that conforms closely to the shape of the target volume (the tumor) and a computer controlled, beam-shaping multileaf collimator (MLC) to deliver that plan. The result is a modulation of radiation intensity across the target volume with the highest dose going to the tumor and the lowest dose to the surrounding healthy tissues.
"IMRT allows you to give a higher dose of radiation because you're treating less collateral tissue with the full dose. You're shaping the treatment volume to much more closely match the target volume," says Dr. Donald Fuller of Radiation Medical Group, San Diego, California. "For the first time ever it gives us the ability to wrap a high dose of radiation around any target that we choose. We've covered some highly irregular volumes with it. You can really make any shape radiation dose you want."
Applications for Prostate Cancer
"Dose escalation is the name of the game in prostate cancer," says Dr. Wingate F. Clapper, Director of Radiation Oncology at Waukesha and Oconomowoc Memorial Hospitals in Wisconsin. There are several studies that show the higher the dose, the higher the cure rate. But you can't go to those high doses without limiting your rectal dose." IMRT now allows doctors to limit that dose.
Localize and Conform
Administering effective radiation therapy relies on two key elements: the ability to localize the target (in this case the prostate with tumor) and the ability to conform or shape the beam to that target area.
Logical Next Step
Dr. Carl R. Bogardus writes in IMRT: An Overview (special supplement to Oncology Issues March/April 2003 vol.18, number 2), "IMRT takes radiation therapy one step further by using computer programs to design the dose distribution, control the radiation therapy treatment delivery system, and allow the collimator leaves to move during treatment. The motion of the leaves stops and starts the beam while the treatment is given, varying the beam's intensity so the radiation dose to the tumor is different than the radiation dose to surrounding normal tissue. This dramatically reduces side effects at higher radiation doses."
"Now we can give very high doses of radiation," says Dr. Donald Fuller, "that prior to this technology we wouldn't even dream of giving because we would simply destroy all the normal tissue adjacent to the target volume."
Introducing the Pinnacle Algorithm
IMRT cannot be accomplished without a computer program that is the basis for treatment planning and administration, and Philips Radiation Oncology Systems' Pinnacle3 treatment planning system is a leading player in this field. As a result of design integration and clinically efficient planning tools, Pinnacle3 is now being clinically utilized for IMRT in over 300+ clinical sites worldwide.
A Teamwork Approach (Continuum of Care)
"To implement IMRT requires teamwork. For each radiation treatment you need the skills of a physician for contouring, a physicist for planning and QA, and a therapist for daily treatment. If you have one weak link in the whole chain then you are not going to treat with IMRT successfully."
- Dr. Haoran Jin PhD., Director of Physics,
Radiation Medical Group, San Diego, CA
Every step in the IMRT continuum of care must be executed flawlessly. In its simplest breakdown the key steps look like this:
Consult - Patient consultation is conducted to review options and determine treatment approach
Image - A CT scan is ordered in the treatment position with skin reference marks (MRI or PET may also be used to determine if the cancer has metastasized)
Define - A target volume is defined through a process called "contouring" and appropriate radiation dosage is suggested
Create - A treatment plan is created based on prescribed radiation dose
Confirm - Testing and verifying the treatment plan through a rigorous QA process confirms its viability
Treat - Therapy begins
Each team member has a critical role in the process. And each team member depends upon the other for success.
Patient Consultation
(Physician)
A prostate cancer patient has an initial consultation with their physician (typically a radiation oncologist). Options are discussed as to whether surgery, seed implants or external beam therapy is most appropriate. Today, as IMRT becomes more accepted, it is often the treatment of choice. Dr. Donald B. Fuller of the Radiation Medical Group says, "Before IMRT the only way you could get a dose to the prostate that satisfied me was seed implant. But now I think we can achieve that same biologically effective dose with external beam radiation through IMRT."
Imaging Studies
(Physician)
"The fundamental imaging study that drives all radiation treatment planning is the CT scan," states Dr. Fuller. "So every patient gets a CT scan in the treatment position with skin reference marks." Other studies such as MRI and PET can be acquired to provide additional insight.
Defining the Target
(Physician supported by the Physicist)
Once the imaging studies are complete they are imported into a treatment planning system such as the Philips Pinnacle3. Here, the SmartSim CT simulation process allows multiple imaging modalities to be fused together for accurate target localization. At this point it is up to the physician to draw "contours" around the rectum, bladder, seminal vesicles and prostate. The seminal vesicles and the prostate define the target. Once the target is defined, the physician determines the radiation dose and beam configuration he feels has the best chance of killing the cancerous tumor.
Creating the Plan
(Physicist and Dosimetrist supported by the Physician)
The most time consuming part of the process is the creation and testing of the plan proposed by the physician. It is the physicist's and dosimetrist's responsibility to develop a workable plan based on the objectives posed by the physician.
The planner must establish the fundamental gantry positions for the radiation beams, and determine the optimum dose distribution for each beam. This is usually an iterative process. Using tools such as the Philips P3IMRT inverse planning software, they must calculate a distribution pattern that delivers maximum dose to the target volume, while sparing the surrounding tissue. Using the patient CT and an established protocol for beam placement/dose, Chief medical physicist at Greenwich hospital, Dr. Delli Carpini makes necessary modifications to the protocol based on the planning target volume indicated by the physician. He then takes this optimized plan and transfers it to a phantom dummy in Pinnacle to confirm its viability. The process is repeated as needed. Dr. Delli Carpini comments on the reliability of the Pinnacle3 product, "As a Unix-based system, Windows-based system, Pinnacle3 is extremely powerful. It's got excellent 3D rendering capabilities and its algorithm is extremely precise. If there's any discrepancy, what usually happens is that Pinnacle3 is right and in our calculations we have made some little mistake or omission."
Once the program is created and approved by the physician, it must be thoroughly tested.
Quality Assurance
(Physicist)
The approved plan is tested on the linear accelerator (linac) irradiating a phantom in exactly the same way the patient would be irradiated. A phantom is a testing device that can simulate the patient. In essence all the computational steps are tested to verify that the treatment will be accurately delivered to the patient.
The approved plan is also tested on the computer using the stored phantom images and the results compared to the measured results. "The Pinnacle3 product is so easy to use for quality assurance," claims Eric Hendee, Chief physicist at Waukesha and Oconomowoc Memorial Hospitals, "It uses a familiar toolbox approach and there's not anything that I've wanted to do planning-wise that I haven't been able to achieve. I'm never limited by Pinnacle3."
Therapy
(Therapist supported by Physician and Physicist)
After as much as two weeks of preparation following the patient's initial visit, the treatment plan is ready to be administered by the therapist. As all aspects of the plan have been rigorously tested, nothing is left to chance and radiation is delivered to the patient via multiple MLC field shapes as specified by the computer. An entire course of treatment can run up to 40 days depending on the tumor size.
Optimum Results
"We were able to show in our preliminary studies that the dose distribution was better with IMRT than the old way we were doing it."
- Dr. Domenico Delli Carpini, Chief Medical Physicist,
Greenwich Hospital, Greenwich, CT
Teamwork and technology combine successfully in IMRT to provide prostate cancer patients with a better cure rate than conventional treatments. "With IMRT I can give more dose to a smaller region," concludes Dr. Delli Carpini. "So if I'm irradiating a smaller region I increase the dose. If I increase the dose, I increase the probability of cure."
Says Dr. Daniel Fass, Director of Radiation Oncology, Greenwich Hospital, Greenwich, CT, "Clearly the evidence would suggest that improved dose distribution from intensity modulated radiation leads to better patient outcomes particularly in prostate cancer."