Richard Terrill

TOLERANCE OF' PERIPHERAL NERVE TO INTRAOPERATIVE RADIOTHERAPY (IORT): CLINICAL AND EXPERIMENTAL STUDIES

In our clinical experience combining wide excision and intraoperative radiotherapy (IORT), five patients have developed clinical signs of lumbosacral or sciatic neuropathy within 9 months of receiving IORT to a dose of 20-25 Gy. Three patients showed recovery of nerve function over several months while two patients have shown no recovery and have near complete loss of extremity function. In an attempt to investigate this clinical observation further, the lumbosacral plexus and sciatic nerve of American foxhounds were surgically exposed and received a single dose of IORT ranging from 20-75 Gy. An approximate linear relationship between radiation dose and time to onset of hind limb paresis is found with 19 of 21 irradiated dogs showing clinical signs of nerve injury within an interval of 1-19 months. No recovery of nerve function is seen in these dogs. Histological study of the irradiated nerves demonstrates a loss of nerve fibers, particularly those of the large myelinated type without evidence of vascular occlusion or thrombosis. These studies suggest that peripheral nerve may be a dose-limiting normal tissue in clinical studies of IORT.

Tolerance of retroperitoneal structures to intraoperative radiation.

In conjunction with the clinical development of intraoperative radiotherapy, a study was undertaken in dogs to define the tolerance of normal anatomic structures in the retroperitoneum to radiation delivered during operation. Twenty adult dogs were subjected to laparotomy and intraoperative 11 MeV electron irradiation in single doses ranging from 0 to 5000 rad. Animals were followed regularly with clinical observation, blood count, serum chemistries, pyelography, and angiography. Animals were sacrificed and autopsied at regular intervals up to 12 months following treatment to assess radiation-induced complications or tissue damage. Irradiation field in all dogs consisted of a 4 x 15 cm rectangle extending in the retroperitoneum from the level of the renal vessels to the bifurcation of aorta and vena cava. The field included aorta, vena cava, inferior portion of left kidney, and distal portion of left ureter. No complications or histologic changes occurred in any animal given doses of 2000 rad, with a follow-up in excess of 18 months. A dose of 3000 rad was well tolerated, except for left ureteral occlusion in one animal. Mild vascular fibrosis was present in the aorta and vena cava, and significant ureteral fibrosis developed by six months after doses of 4000 or 5000 rad. All animals that received 5000 rad died of radiation-related complications, including ureteral obstruction and rectal perforation. It was concluded that major vessels tolerate intraoperative irradiation well up to and including 3000 rad and that no clinically significant vascular problems develop after 4000 and 5000 rad, although some fibrosis does occur. The ureter and kidney appear to be the most radiosensitive structures in the retroperitoneum, showing progressive changes at 3000 rad or greater and showing the potential for serious complications after doses of 4000 rad or more.

Threshold dose for peripheral neuropathy following intraoperative radiotherapy (IORT) in a large animal model

Radiation injury to peripheral nerve is a dose-limiting toxicity in the clinical application of intraoperative radiotherapy, particularly for pelvic and retroperitoneal tumors. Intraoperative radiotherapy-related peripheral neuropathy in humans receiving doses of 20-25 Gy is manifested as a mixed motor-sensory deficit beginning 6-9 months following treatment. In a previous experimental study of intraoperative radiotherapy-related neuropathy of the lumbro-sacral plexus, an approximate inverse linear relationship was reported between the intraoperative dose (20-75 Gy range) and the time to onset of hind limb paresis (1-12 mos following intraoperative radiotherapy). The principal histological lesion in irradiated nerve was loss of large nerve fibers and perineural fibrosis without significant vascular injury. Similar histological changes in irradiated nerves were found in humans. To assess peripheral nerve injury to lower doses of intraoperative radiotherapy in this same large animal model, groups of four adult American Foxhounds (wt 20-25 kg) received doses of 10, 15, or 20 Gy to the right lumbro-sacral plexus and sciatic nerve using 9 MeV electrons. The left lumbro-sacral plexus and sciatic nerve were excluded from the intraoperative field to allow each animal to serve as its own control. Following treatment, a complete neurological exam, electromyogram, and nerve conduction studies were performed monthly for 1 year. Monthly neurological exams were performed in years 2 and 3 whereas electromyogram and nerve conduction studies were performed every 3 months during this follow-up period. With follow-up of greater than or equal to 42 months, no dog receiving 10 or 15 Gy IORT shows any clinical or laboratory evidence of peripheral nerve injury. However, all four dogs receiving 20 Gy developed right hind limb paresis at 8, 9, 9, and 12 mos following intraoperative radiotherapy. These experimental data suggest that intraoperative doses of less than 20 Gy may not result in clinically significant peripheral nerve injury with follow-up of 3.5 years. Longer (5 yrs) follow-up with planned sacrifice of the remaining dogs is scheduled to assess any late peripheral nerve damage.

Late Effects of Intraoperative Radiation therapy on Retroperitoneal Tissues, Intestine, and Bile Duct in a Large Animal Model.

PURPOSE The late histopathological effects of intraoperative radiotherapy (IORT) on retroperitoneal tissues, intestine, and bile duct were investigated in dogs. METHODS AND MATERIALS Fourteen adult foxhounds were subjected to laparotomy and varying doses (0-45 Gy) of IORT (11 MeV electrons) delivered to retroperitoneal tissues including the great vessels and ureters, to a loop of defunctionalized small bowel, or to the extrahepatic bile duct. One control animal received an aortic transection and reanastomosis at the time of laparotomy; another control received laparotomy alone. This paper describes the late effects of single-fraction IORT occurring 3-5 years following treatment. RESULTS AND CONCLUSION Dogs receiving IORT to the retroperitoneum through a 4 x 15 cm portal showed few gross or histologic abnormalities at 20 Gy. At doses ranging from 30-45 Gy, radiation changes in normal tissues were consistently observed. Retroperitoneal fibrosis with encasement of the ureters and great vessels developed at doses > or = 30 Gy. Radiation changes were present in the aorta and vena cava at doses > or = 40 Gy. A 30 Gy dog developed an in-field malignant osteosarcoma at 3 years which invaded the vertebral column and compressed the spinal cord. A 40 Gy animal developed obstruction of the right ureter with fatal septic hydronephrosis at 4 years. Animals receiving IORT through a 5 cm IORT portal to an upper abdominal field which included a defunctionalized loop of small bowel, showed a few gross or histologic abnormalities at a dose of 20 Gy. At 30 Gy, hyaline degeneration of the intestinal muscularis layer of the bowel occurred. At a dose of 45 Gy, internal intestinal fistulae developed. One 30 Gy animal developed right ureteral obstruction and hydronephrosis at 5 years. A dog receiving 30 Gy IORT through a 5 cm portal to the extrahepatic bile duct showed diffuse fibrosis through the gastroduodenal ligament. These canine studies contribute to the area of late tissue tolerance to IORT.

Response of the mediastinal and thoracic viscera of the dog to intraoperative radiation therapy (IORT)

IORT may be a potentially useful adjunctive treatment combined with surgery and/or external beam irradiation in treating locally advanced lung and esophageal tumors. To begin investigation of this modality, the tolerance of intact mediastinal structures to IORT was studied using adult American Foxhounds (wt. 25-30 kg). Groups of six animals received IORT to doses of 20, 30, or 40 Gy to two separate intrathoracic ports, using 9 MeV electrons to treat a portion of the collapsed right upper lobe, and 12 MeV electrons to treat the mediastinal structures. A group of three dogs received thoracotomy with sham irradiation. Two dogs from each treatment dose group, as well as one sham-irradiated control, were sacrificed electively at 1, 3, and 12 months following IORT. There were no acute nor late IORT related mortalities. Post-operative weight loss was minimal (average 4.5% of pre-operative weight) for all dogs. Serial esophagrams showed no inflammation or ulceration. No cardiac nor pulmonary changes were noted clinically. At autopsy, the irradiated lung showed evidence of acute pneumonitis at 1 month with progressive fibrosis at 3 months and 1 year. Esophageal reactions were minimal, with only two dogs (one 30 Gy and one 40 Gy) demonstrating histologically confirmed esophagitis at 1 month. Tracheal changes were minimal. Cardiac damage was evident in the right atrial tissues. In several dogs, this cardiac damage ranged from myocardial vascular changes to frank ischemic necrosis noted at 1 and 3 months, and dense fibrosis at 1 year. The phrenic nerves showed normal function, but had evidence of perineural fibrosis. The large vessels demonstrated only mild histologic evidence of irradiation. The results of this large animal study suggest that intact mediastinal structures will tolerate small volume IORT to doses of 20 Gy without significant clinical sequellae. Although the histologic changes in the right atrium and contralateral lung are worrisome, no cardiac nor pulmonary problems arose over the 1 year follow-up. Irradiation of the contralateral lung and other sensitive structures can be reduced by careful selection of electron beam energy and use of custom lead shielding.

Tolerance of canine anastomoses to intraoperative radiation therapy

Radiation has been given intraoperatively to various abdominal structures in dogs, using a fixed horizontal 11 MeV electron beam at the Armed Forces Radiobiologic Research Institute. Animals were irradiated with single doses of 2000, 3000 and 4500 rad to a field which extended from the bifurcation of the aorta to the rib cage. All animals were irradiated during laparotomy under general anesthesia. Because the clinical use of intraoperative radiotherapy in cancer treatment will occasionally require irradiation of anastomosed large vessels and blind loops of bowel, the tolerance of aortic anastomoses and the suture lines of blind loops of jejunum to irradiation were studied. Responses in these experiments were scored at times up to one year after irradiation. In separate experiments both aortic and intestinal anastomoses were performed on each animal for evaluation of short term response. Response was graded by arteriography, gastrointestinal roentgenography, blind loop bursting pressure, and pathologic findings at autopsy and microscopic evaluation. The dogs with aortic anastomoses showed adequate healing at all doses with no evidence of suture line weakening. On long-term follow-up one animal (2000 rad) had stenosis at the anastomosis and one animal (4500 rad) developed an arteriovenous fistula. Three of the animals that had an intestinal blind loop irradiated subsequently developed intussusception, with the irradiated loop acting as the lead point. One week after irradiation, bursting pressure of an intestinal blind loop was normal at 3000 rad, but markedly decreased at 4500 rad. No late complications were noted after the irradiation of the intestinal anastomosis. Thus, it appears that adequate healing can take place with minimal risk of suture line breakdown even after a high single dose of irradiation (up to 3000 rad) to an anastomotic site. No late complications were observed after irradiation of intestinal anastomoses, but one needs to be cautious with regards to possible late stenosis at the site of an irradiated vascular anastomosis.

Isolated lung perfusion with tumor necrosis factor: a swine model in preparation of human trials.

Isolated lung perfusion with tumor necrosis factor (TNF) potentially could deliver high doses of drug and avoid systemic toxicity in patients with unresectable lung cancer or metastases. We investigated the feasibility of isolated lung perfusion with TNF in a pig model. Eleven animals had left-sided isolated lung perfusion with no TNF (n = 3), 40 micrograms/kg TNF (n = 2), 80 micrograms/kg TNF (n = 3), and 40 micrograms/kg TNF at moderate (39.5 degrees C) hyperthermia (n = 3). Hemodynamic monitoring and measurement of systemic and pulmonary circuit TNF levels were performed. Surviving animals were electively sacrificed a minimum of 6 months after isolated lung perfusion. All sham-perfused pigs survived. Isolated lung perfusion elevated pulmonary artery pressure, decreased cardiac output, and had minimal effects on mean pressure (15 +/- 0 versus 32 +/- 8 mm Hg, 4.5 +/- 1.1 versus 3.03 +/- 0.03 L/min, 67 +/- 11 versus 61 +/- 2 mm Hg; before versus after 90 minutes of isolated lung perfusion). Both 40 micrograms/kg animals and 2 of the 3 hyperthermic perfusion pigs survived, with 1 requiring pneumonectomy. Of the three 80 micrograms/kg animals, 1 survived, 1 died, and 1 required pneumonectomy. Survivors, compared with dying animals, had lower systemic/pulmonary TNF ratios and lower peak systemic TNF levels. All surviving pigs were electively sacrificed. These data justify phase I human protocols of isolated lung perfusion with TNF and hyperthermia; however, intraoperative leak rates must be monitored to ensure pulmonary isolation because systemic TNF levels may dictate treatment morbidity/mortality.

Effects of intraoperative radiotherapy on vascular grafts in a canine model

PURPOSE The effects of intraoperative radiotherapy +/- external beam radiotherapy on prosthetic vascular grafts were investigated in a canine model. METHODS AND MATERIALS In 1986 and 1987, 30 adult beagles underwent laparotomy with transection and segmental resection of the infrarenal aorta followed by immediate reconstruction with a prosthetic graft. Intraoperative radiotherapy at varying doses from 0-30 Gy was then administered to all animals. Half of the dogs received 36 Gy external beam radiotherapy in 10 fractions postoperatively. Animals were sacrificed and necropsied at predetermined intervals and as clinically indicated to assess early (< or = 6 months) and late (> 6 months) effects to the vascular graft and surrounding normal tissue. RESULTS Histopathologic analyses of irradiated vascular structures were performed and correlations were made with the clinical outcome. The most frequent early clinical toxicity was graft thrombosis, occurring in 7 of 10 animals followed for < or = 6 months. Early graft thrombus formation appeared unrelated to radiotherapy dose and probably represented a technical surgical complication. Anastomotic stenosis of varying severity occurred in most animals followed > 6 months. Late (> 6 months) graft stenosis was correlated with intraoperative radiotherapy dose. At < or = 20 Gy of intraoperative irradiation, 3 of 14 animals developed late graft occlusion; at > 25 Gy, five of six animals developed late occlusion. On histopathologic review, increasing intraoperative dose and increasing total radiotherapy dose (intraoperative+external beam) appeared to correspond with increasing severity of graft changes seen after 6 months of follow-up. CONCLUSIONS Thrombus formation is a frequent early complication of vascular graft placement of the infrarenal aorta in our beagle dog model. Intraoperative doses up to 20 Gy appear to contribute minimally to late graft occlusion, while doses > or = 25 Gy contribute to late occlusion with high likelihood. Both intraoperative dose and total radiotherapy dose correlated with late graft occlusion, and with histopathologic changes in the graft and anastomoses.

Isolated hepatic perfusion for lapine liver metastases: Impact of hyperthermia on permeability of tumor neovasculature

BACKGROUND Hyperthermic isolated hepatic perfusion (IHP) has been shown to cause significant regression of advanced unresectable liver metastases in patients. Although there are different agents and treatment modalities used in IHP, the contribution of perfusion hyperthermia is unknown. PURPOSE A large animal model of unresectable liver metastases and a technical standard for IHP in this model were established. This model was used to assess the effects of hyperthermia on vascular permeability of tumors and normal liver tissue during IHP. METHODS Sixty-five New Zealand White rabbits were used in a series of experiments. Disseminated liver tumors were established by direct injection of 1 x 10(6) VX-2 cells into the portal vein by laparotomy in anesthetized animals. Several surgical perfusion techniques were explored to determine a reliable and reproducible IHP model. Vascular permeability in tumor versus liver was then assessed with Evans Blue labeled bovine albumin under normothermic (tissue temperature 36.5 degrees C +/- 0.5 degree C), moderate hyperthermic (39 degrees C +/- 0.5 degree C), or severe hyperthermic (41 degrees C +/- 0.5 degree C) conditions. RESULTS Tumor model and perfusion techniques were successfully established with inflow through the portal vein and outflow through an isolated segment of the inferior vena cava. A gravity driven perfusion circuit with stable perfusion parameters and complete vascular isolation was used. Vascular permeability was higher in tumor than in normal tissues (P = .03) at all time points during IHP. Hyperthermia resulted in a significant (up to 5-fold) increase in permeability of neovasculature; when severe hyperthermia was used, tumor vascular permeability was increased even more than normal liver permeability (P = .01). CONCLUSIONS The VX-2/New Zealand White rabbit system can be used as a reproducible large-animal model for IHP of unresectable liver metastases. It can be used to characterize the contribution and mechanism of action of different treatment parameters used in IHP. Hyperthermia preferentially increases vascular permeability in tumors compared with liver tissue in a dose-dependent fashion, thus providing a mechanism for its presumed benefit during isolated organ perfusion.

Clinical toxicity of peripheral nerve to intraoperative radiotherapy in a canine model

PURPOSE The clinical late effects of intraoperative radiotherapy (IORT) on peripheral nerve were investigated in a foxhound model. METHODS AND MATERIALS Between 1982 and 1987, 40 animals underwent laparotomy with intraoperative radiotherapy of doses from 0-75 Gy administered to the right lumbosacral plexus. Subsequently, all animals were monitored closely and sacrificed to assess clinical effects to peripheral nerve. This analysis reports final clinical results of all animals, with follow-up to 5 years. RESULTS All animals treated with > or = 25 Gy developed ipsilateral neuropathy. An inverse relationship was noted between intraoperative radiotherapy dose and time to neuropathy, with an effective dose for 50% paralysis (ED50) of 17.2 Gy. One of the animals treated with 15 Gy IORT developed paralysis, after a much longer latency than the other animals. CONCLUSIONS Doses of 15 Gy delivered intraoperatively may be accompanied by peripheral neuropathy with long-term follow-up. This threshold is less than that reported with shorter follow-up. The value of ED50 determined here is in keeping with data from other animal trials, and from clinical trials in humans.