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IORT involves the delivery of radiation during exposure of a tumor or tumor bed at the time of a planned operative procedure. In its broadest sense, IORT includes brachytherapy with temporary or permanent implantation of radioactive seeds.[177] Radiation therapy plays a major role in the management of many malignant diseases. The usual method by which radiation is delivered is external beam treatment with high-energy photons. The external beam doses required to achieve local tumor control can exceed the radiation tolerance of some normal organs and other structures of the body.[178] IORT with variable-energy electrons can be effectively used as a supplemental boost to external beam treatments. By delivering the radiation therapy during surgery, it is possible to remove normal structures away from the radiation beam or to shield them with lead.[179]
This method of treatment is appealing, particularly for locally advanced malignant lesions when conventional modalities are unlikely to produce local tumor control. Theoretical advantages over conventional external radiotherapy are the ability to increase the tumor dose with less damage to adjacent healthy tissues and more accurate localization of the radiation field. Disadvantages of this technique are that an operation is needed, optimal dose combinations of external beam radiation and IORT are complex to calculate,[177] and complications are not infrequent. Such complications include pain, nausea and vomiting, bowel dysfunction, ureteral obstruction, neuropathy, abscesses, and delayed wound healing. [180] All patients treated with IORT at the Mayo Clinic are specifically told about possible nerve-related side effects.[181] In most patients treated by IORT, surgery alone would not achieve local control, and the external radiation doses needed for local control would exceed normal tissue tolerance.[182] Tumors treated with IORT have included locally advanced colorectal cancer, retroperitoneal sarcomas, limb sarcomas, gynecologic malignancies, and pediatric malignancies.[180] [183] [184] [185] [186]
Most of the advances in the use of radiation have been achieved by an improved dose distribution and better differentiation of the dose delivered to tumor and normal tissue. Delivering the radiation during the surgical procedure permits direct observation of tumor size and density and the tissues at risk for microscopic spread of tumor. Shielding of nearby sensitive structures from the intense local radiation field is possible by surgical manipulation.[187] By moving normal and noninvolved tissue out of the path of the electrons, the radiation is confined to the cancer to the greatest possible extent, and the therapeutic ratio can be maximized.[188] Patient selection for IORT should include no contraindications to surgery and the belief that surgical intervention alone will not result in local tumor control. The tumor should be a localized focus of disease, and no distant metastasis should be apparent.[177] IORT is seen as potentially curative.[187]
Ideally, anesthesia, incision, radiation, and closure occur in a single dedicated IORT room. At the Mayo Clinic, both the operative procedure and delivery of IORT are performed in a dedicated IORT room within the operating suite. A dedicated IORT room has the advantage of allowing surgery and radiation therapy to be accomplished in a single setting without moving the patient through a nonsterile environment with the wound protected by drapes. Other advantages of a dedicated IORT room within the surgical suite include the close proximity of other ancillary facilities (e.g., blood bank) and the immediate availability of additional anesthesia and surgical personnel and equipment.
Alternatively, induction of anesthesia, surgical incision, and tumor isolation can be accomplished in a modified operating room within the radiation oncology area.[189] This alternative allows the linear accelerator room to be used without interruption for treating other patients while the patient who is to undergo IORT is being prepared. After preparation, the anesthetized and surgically draped patient is transported a short distance to the accelerator treatment room. Once radiation treatment is completed, the patient is returned to the modified operating room for closure of the incision. This situation would be subject to the limitations of all procedures requiring anesthesia in non-operating room settings.
Patients typically receive a conventional general anesthetic regimen with endotracheal intubation. Standard monitors are used, as well as additional monitors as dictated by the patient's condition and the surgical procedure planned. After surgical incision and exploration, the tumor is exposed and isolated. A sterile Lucite cylinder is then inserted to cover the tumor mass, define the radiation beam, and displace normal structures outwardly circumferentially around its perimeter ( Fig. 69-2 ). Radiation therapy may then be focused directly on the isolated tumor.
During IORT, the patient is ventilated automatically. Throughout the actual radiation treatment period, all personnel must leave the treatment room to avoid high radiation exposure, and the patient, anesthesia equipment, and monitors are observed continuously by closed-circuit television ( Fig. 69-3 ). After treatment, the patient is transported to the recovery room.
Patients who undergo IORT may present special challenges to anesthesiologists. The patient's physical status may be compromised by the malignant disease process or by chemotherapy, and surgery may involve advanced resection of tumor and considerable blood loss.[190] Nutritional support is important in these patients, many of whom will have lost 20% or more of their body weight because of the malignant disease and may have been subjected to multiple operations. A percutaneous feeding tube is frequently inserted selectively during the IORT procedure to facilitate nutritional support during convalescence. Perioperative deaths from intraoperative cerebrovascular accidents, postoperative hemorrhage, hepatorenal syndrome, and aspiration have been reported.[190] [191]
Figure 69-2
Intraoperative radiation therapy room. A sterile Lucite
cylinder is used to isolate the tumor mass and displace normal tissues to limit the
radiation dose. (From Mackenzie RA, Southorn PA, Stensrud PE: Anesthesia
at remote locations. In Miller RD [ed]: Anesthesiology,
5th ed. Philadelphia, Churchill Livingstone, 2000, p 2261.)
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