Thomas Jefferson University adds to body frame track record
Radiotherapy using Elekta's Stereotactic Body Frame® is giving hope to Thomas Jefferson University (TJU) patients who cannot tolerate additional standard radiotherapy to control the pain or progression of their lung or pelvic malignancies. Stereotactic Body Frame®'s ability to precisely immobilize patients, with precise target positioning, enables safe hypofractionated reirradiation courses with a greatly reduced risk of toxicity. While TJU focuses on Stereotactic Body Frame® reirradiation presently, plans are underway to use Stereotactic Body Frame® in conjunction with curative radiotherapy and to investigate IMRT's potential for improving Stereotactic Body Frame® - assisted body radiotherapy.
Clinicians at TJU's Kimmel Cancer Center at Jefferson Medical College are zeroing in on tumors and minimizing normal tissue exposure by virtue of Stereotactic Body Frame®'s precise patient immobilization combined with daily pre-treatment target localization by CT. TJU treated its first patient using Elekta's Stereotactic Body Frame® in May 1999, and at press time had used the body frame in a total of 32 reirradiation cases, involving mostly lung and pelvic malignancies.
A recent 24-patient study led by Department of Radiation Oncology Director of Clinical Operations, Maria Werner-Wasik, M.D., concluded that hypofractionated 3-D radiotherapy using Stereotactic Body Frame®, with CT-based isocenter verification, is a safe and effective tool for tumor reirradiation, when given for symptom palliation and tumor control in selected patients with recurrent malignancies.
"Among 13 symptomatic patients, the presenting symptoms of pain or bleeding resolved completely in five, partially resolved in four patients suffering pain or dyspnea and were unchanged in another four," Dr. Werner-Wasik notes. "Radiographically, there was a complete response in one patient, partial response in three, stable disease in eight and progression of disease in three."
The largest subset of the patients was a group of 10 with locally progressive or metastatic lung malignancies. Reirradiation of the lung has become somewhat of a specialty at the Cancer Center, which has a history of non-Stereotactic Body Frame® - assisted lung reirradiations employing multiple non-coplanar fields to enable 3-D conformal radiotherapy. "Many radiation oncologists think that once a lung tumor is irradiated it cannot be reirradiated," she says. "Our experience challenges that opinion. We reirradiate lung cancers routinely in specific circumstances, such as regrowth of a local tumor that begins to cause problems like hemoptysis, airway compression or SVC syndrome. Since we've done this type of treatment before, we didn't shy away from attempting it again with Stereotactic Body Frame® with larger fraction sizes."
The median fraction size of 4 Gy used in the 24-patient Stereotactic Body Frame® study is twice that used in conventional radiotherapy, enabling clinicians to use a hypofractionated RT regimen employing a median fraction number of just six (range: 3-14), delivered 3-5 times per week. A representative fraction size and number for conventional lung radiotherapy is 2 Gy X 30.
James Galvin, D.Sc.
Maria Werner-Wasik, M.D.
Jay Reiff, Ph.D.
The key to hypofractionation is the ability to plan tighter than conventional margins around the tumor, enabling radiation oncologists to boost fraction size. The body frame also improves the patient's general comfort, so that more non-coplanar beams can be added to decrease the dose to normal tissue falling in the path of the beams. This is especially important in advanced lung cancer stages involving normal midline anatomy that may have already reached initial treatment tolerances, such as the esophagus and spinal cord. Treating advanced stage lung cancer also risks inducing pneumonitis as more normal lung parenchyma is typically involved.
"If we're confident that Stereotactic Body Frame® will immobilize the patient sufficiently, we can use smaller margins around the tumor," Dr. Werner-Wasik observes. "That, theoretically, allows us to be more bold in using hypofractionated regimens with larger fraction sizes - we obviously will minimize normal tissue exposure by using smaller margins."
In conjunction with Stereotactic Body Frame®, the group at Jefferson uses a CT simulator for daily isocenter verification, the FOCUS 3-D Treatment Planning System, and its Elekta Precise Treatment System™ (6 MV, 18 MV). To track and correct deviations between fractions, Cancer Center clinicians take daily variation measurements comparing the coordinates of the pre-treatment isocenter to those of the original isocenter on the treatment planning CT. |
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"We had displacement in the x, y and z dimensions," she says. "In the AP dimension, for example, we found that 63 percent of all deviations were less than 2 mm and 76 percent less than 3 mm. In the longitudinal and lateral dimensions we have 52 percent within 2 mm. Taking into account all dimensions, we found 35 percent of deviations were less than 1 mm, 21 percent between 1 mm and 2 mm, and 16 percent between 2 mm and 3 mm. That is, 71 percent of all deviations were within 3 mm. Only 13 percent were more than 5 mm.
Dr. Werner-Wasik admits it's difficult to compare Stereotactic Body Frame®'s localization precision with that of standard radiotherapy's alpha cradle (i.e.: foam cast) immobilization device.
"When you look at standard radiation fields, you compare DRRs to port films. But that's like comparing apples and oranges," she says. "With Stereotactic Body Frame®, we compare the CT-based isocenter to CT-based isocenter. While Stereotactic Body Frame® immobilization isn't at the level of stereotactic brain radiosurgery, it's still pretty good and is probably the best we have for body targets."
In the spring of 2002, Dr. Werner-Wasik will submit a proposal to Jefferson Medical College's Institutional Review Board to use Stereotactic Body Frame® and a hypofractionated radiotherapy regimen as the definitive treatment for selected Stage III and Stage IV patients with lung cancer
Cindi Swanberg, RT., AART
"We have not used Stereotactic Body Frame® for this purpose, because it requires daily CT verification of the isocenter and therefore it is somewhat resource-consuming. But we do want to move on from reirradiation to definitive and primary cases" she says. "We believe Elekta's Stereotactic Body Frame® can help reduce the larger risk of radiation-induced pneumonitis and esophagitis in advanced cases."
On the horizon are the addition of IMRT to create better dose distributions for irregularly-shaped body targets, and the use of Elekta's Active Breathing Coordinator™ for immobilization of breathing motion in patients with lung or upper abdominal malignancies.
Stereotactic Body Frame® shows potential in migrating IMRT to body targets
The physics staff at Kimmel Cancer Center's Department of Radiation Oncology is eager to exploit the benefits of IMRT for extracranial targets other than the now fairly common prostate treatments. A major obstacle for all RT centers wanting to do extracranial IMRT, however, has been the lack of a reliable immobilization device; set-up error and organ movement in the thorax, abdomen and pelvis have proved unpredictable and hard to overcome.
"Physicists and radiation oncologists have concentrated for years on head and neck immobilization, and the stereotactic devices have gotten quite sophisticated. We are presently using IMRT for many of our patients with head and neck tumors, because excellent immobilization is available for treating this part of the body," says James Galvin, D.Sc., Professor and Director of Medical Physics at Jefferson Medical College. "However, because of difficulties with immobilizing other parts of the body, there is concern about using IMRT for anything other than head and neck and prostate malignancies. Certainly, Stereotactic Body Frame® is going to be an important advance in terms of improving immobilization extracranially and we're excited about the possibility of using Stereotactic Body Frame® for IMRT - under carefully controlled studies with Institutional Review Board approval."
Particularly for lung treatments, there are a number of interesting questions that will have to be addressed, Dr. Galvin adds. "In lung radiotherapy, controlling respiratory motion is certainly important, but there is also the issue of accurately correcting for tissue density variations when treating lesions in this part of the body. The performance of inverse planning algorithms in correcting for these tissue heterogeneity changes is not well understood, and has been a contraindication for lung IMRT," he says. "Some inverse planning algorithms are simplified to improve calculation speed. This problem needs to be carefully studied. We're going to evaluate Elekta's Active Breathing Coordinator™ as a more sophisticated alternative to Stereotactic Body Frame®'s diaphragm control in minimizing lung motion, and we are developing inverse planning methods that allow precise calculation algorithms to be used as part of the process."
Obstacles aside, the combination of precise, reproducible immobilization with Stereotactic Body Frame® and IMRT's highly conformal dose distributions creates a powerful synergy for treating body targets. IMRT paints the optimum dose distribution to include the tumor and exclude normal tissue, but its efficacy is clearly maximized by being able to hit targets that can shift spatially on a daily basis, Dr. Galvin says.
The future payoff of a Stereotactic Body Frame® - IMRT combination could be considerable, especially for the lung cancer patients treated at Thomas Jefferson University Hospital, says Jay Reiff, Ph.D., Clinical Associate Professor and Section Chief for Medical Physics at Jefferson Medical College's satellite clinics. "With IMRT, it will be possible to give a higher, more therapeutic dose than ever before to a lung tumor, while conforming the beams to avoid critical structures such as the spinal cord or esophagus. And, Stereotactic Body Frame® will enable us to do that consistently for each of the patient's fractions."
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