Intraoperative Radiation Therapy for Colorectal Cancer
Sudha R. Amarnath
Perioperative Considerations
Indications
Intraoperative radiation therapy (IORT) can be used for patients being treated surgically in the definitive or recurrent setting who are at risk of close or positive margins at the time of resection (R0/R1 resection).
IORT is not appropriate for patients with gross residual tumor at the time of resection (R2 resection).
Typical areas at risk include tumors that are very close to the circumferential resection margin, pelvic sidewall (vessels, ureter), sacrum (presacral vessels/nerves and bone), and other organs (prostate, vagina, bladder without invasion) where further surgical resection for negative margins would lead to significant morbidity.
Patients who have received prior external beam radiation therapy to the pelvis may receive IORT, but dosing should be chosen cautiously to minimize long-term toxicities.
Patient positioning
IORT is delivered after the resection of the primary tumor, and therefore, patient positioning (supine vs prone) is determined by the colorectal surgeon based on the surgical technique being used.
The surgical technique to be used as well as the area(s) deemed most likely to be at high risk for close or positive margins at the time of surgery should be discussed with the radiation oncologist in advance to ensure that IORT can be delivered at the time of resection and planned accordingly.
Some IORT devices require specialized operating rooms (ORs) (ie, Intraop Mobetron)—cases requiring IORT should be scheduled accordingly.
Approach and equipment
At CCF, a Zeiss Intrabeam 50-kV unit is used for IORT applications.1
Power source
Lead aprons and thyroid shields for personnel remaining in OR during IORT delivery
Mobile lead shields for essential personnel to sit/stand behind during IORT delivery
Radiation safety signs to place on the doors to the OR
Geiger counter
Sterile draping for the Intrabeam device arm
Flexible lead sheets with sterile bags to help shield internal organs as needed
Applicators (Fig. 28-1)
Spherical (1.5-5 cm in diameter): intracavitary tumor bed applications such as circumferential resection margin (post-total mesorectal excision), presacral hollow
Flat/surface (1-6 cm in diameter): surgically exposed surface applications such as the pelvic sidewall
Recommend having a wide range of applicators available at the time of IORT so that the most appropriate size and shape applicator can be selected for the tumor bed/surface to be treated.
 FIGURE 28-1 ▪ Zeiss applicators that can be used for intraoperative radiation therapy. Clockwise from top left: flat applicator, needle applicator (not commonly used for colorectal applications), surface applicator, and spherical applicator. |
Technique
All patients who are deemed to be possible candidates for IORT should undergo consultation with a radiation oncologist for a full discussion of the risks and benefits of treatment and to sign informed consent prior to surgery. This also facilitates treatment planning and appropriate scheduling of resources.
On the day of the planned IORT, the radiation physics team should calibrate the IORT device early in the day so that it is ready for use when needed (Fig. 28-2).
FIGURE 28-2 ▪ The Intrabeam device should be calibrated prior to intraoperative radiation therapy treatment and should be handled with care to avoid the need for re-calibration in the operating room.
After resection of the tumor, the surgeon using clinical judgment and/or results of frozen section assessment from pathology determines whether margins are close or positive and if there is a need for IORT. If IORT is deemed necessary, the radiation team is called to the OR for setup and treatment delivery (Fig. 28-3).
The surgeon and radiation oncologist both should evaluate the area(s) at risk to determine the optimal applicator size and shape, as well as the best approach for placement of the applicator.Related posts:
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