Stereotactic Radiosurgery for Gynecologic Cancer

The overall goal of this stereotactic body radiosurgery procedure is to deliver radiation that sterilizes gynecologic cancer targets. First, women lie on the flat tabletop and have cross plane radiographic imaging equipment and the target localizing system track soft tissue fiducials. The second step is to confirm that the fiducials are in the expected cancer target location.

Next, if automatic registration indicates soft tissue fiducials have shifted beyond predefined six degree tolerances, treatment is automatically paused. Patient repositioning then occurs. Once all of the tracking systems can confirm patient positioning, stereotactic body radiosurgery radiation is delivered to the cancer target.

Ultimately, stereotactic body radiosurgery is used to ablate cancer targets with submillimeter Precision CyberKnife radiosurgery involves the use of a linear accelerator mounted on an industrial robotic arm similar to those machines used to make automobiles. The robotic arm moves the linear accelerator in three dimensional space around a patient as it progresses through multiple beam stops for beam delivery. Cross plane X-rays are obtained during treatment to verify the patient is in a correct treatment position.

Since treatment beam delivery is not restricted to a two dimensional plane, the system further enhances the ability to deliver concentrated radiation doses to cancer targets while minimizing the radiation dose to critical skin and visceral organ structures. Treating physicians and patients must appreciate that stereotactic body radiotherapy may result in possible tanning and reding of skin fatigue, infrequent nausea and diarrhea, rare visceral organ injury, muscle nerve, and bone injury, and very small risk of second cancer. However, iatric radiosurgery permits the use of a reduced number of ablative radiation doses to cancer targets usually refractory to chemotherapy and conventional radiation.

Women being treated for persistent or recurrent gynecologic cancers may be candidates for SBRT After the decision to perform the surgery has been made. The first step is the operative or CT guided placement of at least three single 1.6 by three millimeter gold soft tissue fiducials. Fiducials are placed at varying tissue depths around the radiosurgical target and must be separated by two centimeters or more.

Fiducials are positioned within four to six centimeters of the target. It is important to note that surgical clips placed at the time of prior surgery are not of sufficient density to be used as radiosurgical fiducials and that surgical clips do not interfere with radiosurgical targeting because of the density discrepancy. At least one week after fiducial placement when healing has occurred and fiducial movement is minimized, the patient undergoes CT guided SBRT treatment simulation.

In this program. Two pin localized evacuated vacuum bag pelvic immobilization is used. First orient the patient in a supine position on the CyberKnife RADIOSURGICAL flat tabletop.

The patient is then immobilized by evacuated vacuum bag immobilization to reduce infraction motion during radiation dose delivery. Next, perform non contrasted contiguous axial CT high resolution imaging. After CT imaging, conventional F 18 FDG PET CT imaging is performed on the patient while in the same SBRT treatment position.

Alternatively, conventional contrasted pelvic magnetic resonance imaging may be used after all scans are complete. Import the images from high resolution CT and F 18 FDG PET CT to MultiPlan 3.5 0.2 treatment planning system for inverse radiation treatment planning. Both a radiation oncologist and gynecologic oncologist then contour cancer, target clinical target volumes or CTVs.

Other disease at risk. Tissue is contoured and is included in CTVs nearby normal tissue structures such as the small bowel rectum, bladder, liver, kidneys, lungs, bilateral proximal femurs, vagina, and sacral nerve roots are contoured. The final prepar preparative step is to calculate the radiation dose to be administered during stereotactic CyberKnife radiosurgery.

A radiation prescription dose of three by 800 centigrade equal to 2, 400 centigrade commonly to the 70%isod dose line has been selected. Here in a 200 centigrade biological equivalent dose calculation, nearly 6, 100 are delivered with this prescription, assuming an alpha beta ratio of 10 for tumor, normal organs have a tolerance of radiation and use of dose volume. Histogram Parameters for normal tissue constraint during ablative stereotactic radiosurgery are listed in this table.

First, ensure that the patient is positioned correctly for radiosurgery. Engage the radiographic imaging equipment and target localizing system to track soft tissue fiducials by cross plane radiographic imaging and confirm that the fiducials are in the expected target location before and during CyberKnife radio surgery. Fiducials are tracked in three and up to six degrees of freedom.

Images generated by the TLS are automatically registered and compared with digitally reconstructed radiographs generated from the initial treatment planning CT scan. If the results of automatic registration indicate that fiducials have shifted beyond predefined tolerances in any one of the six degrees of freedom, treatment is automatically paused. Patient repositioning then occurs if the target is likely to move with respiratory motion.

The synchrony respiratory tracking subsystem is used. Light emitting diodes are affixed to a vest around the patient's thorax and mounted camera tracks the movement of the LEDs. Together with the fiducial location information obtained from cross plane x-rays, the synchrony system builds a correlation model with the external data and the internal data.

This correlation model allows the robotic arm to follow any respiratory induced motion of the target during the delivery of any and all treatment beams. Once all of the tracking systems are set up and it is confirmed that the patient is positioned correctly, stereotactic body radiosurgery radiation may be administered. Treatment may entail 100 to 150 deliverable treatment positions of the robotic arm and treatments may last 30 to 90 minutes as shown by the blue vectors in this figure.

SBRT may involve many individual radiation beams that converge on single or multiple closely associated clinical radiation targets. Here a transverse image of patient undergoing treatment on a pelvic relapse of a chemo refractory ovarian cancer target is shown. The clinical target appears red.

The 2, 400 centi guy area is shaded orange and the critical organ at risk. The small bowel is shaded blue here. 131 beams were used to treat on the pelvic relapse of a chemo refractory ovarian cancer target over 42 minutes.

SBRT prescribed to the 80%isod dose line rendered 100%clinical target volume coverage with a conformity index of 1.94 for a total dose of 2, 400 tiga in three daily 800 centi guy fractions. This figure shows the dose volume histograms for the clinical target shown in red and for the critical structures of rectum in brown bladder in yellow small bowel in light blue sacral nerves in tan and hips in orange. After its development.

This radiation delivery technique paved the way for clinical investigations in the field of gynecologic radiation oncology to explore stereotactic body radiosurgery in women with persistent or recurrent gynecologic cancer. After watching this video, you should have a good understanding of how to deliver stereotactic body radiosurgery with an intent to sterilize gynecologic cancers by fiducial tracking, patient positioning and radiosurgical dose delivery. Don't forget that delivering ablative radiation doses can lead to consequential short and long-term radiation related side effects and caution should be taken by treating physicians in the appropriate selection of women with gynecologic cancers.

For this radiosurgical procedure.