The reduced canine pancreas to study the effects of intra-operative radiotherapy

Radioprotective effects of α2-adrenergic receptor agonist dexmedetomidine on X-ray irradiation-induced pancreatic islet cell damage

Comprehensive epidemiological analyses conducted in the last 30 years have revealed a link between radiation and DM. We aimed to determine the effects of dexmedetomidine pretreatment on radiation-induced pancreatic islet cell damage. Twenty-four rats were divided into three groups: group 1 (control group), group 2 (only X-ray irradiation group), and group 3 (X-ray irradiation + dexmedetomidine). We observed necrotic cells with vacuoles accompanying loss of cytoplasm in the islets of Langerhans, extensive edematous areas, and vascular congestions in group 2. In group 3, we observed a decrease in necrotic cells in the islets of Langerhans, and edematous areas and vascular congestion was also reduced. We determined a decrease in β-cells, α-cells, and D-cells in the islets of Langerhans in group 2 compared to the control group. In group 3, β-cells, α-cells, and D-cells were elevated compared to group 2. Ionizing radiation may induce DM. Dexmedetomidine appears to exert a radioprotective effect.

Normal tissue tolerance to intraoperative radiotherapy

Much experimental evidence has been accumulated assessing the tolerance of various tissues to IORT, and much of the tolerance data have resulted from the use of canine models. Guidelines of IORT tissue tolerance established in experimental models have been used in the clinical application of IORT at numerous institutions. Although the radiotolerance of differing tissues can vary among species, sufficient clinical experience has accumulated to validate the canine tissue tolerance model as representative of human tissue responses to IORT. Cellular effects from radiation principally stem from direct damage to DNA, and thus proliferating tissues are among the most radiosensitive, with arrested or abnormal cell division. These tissues can manifest striking early toxicity, reflecting the rate of cell division that is affected by the radiation. Irradiation of nonproliferating or slowly proliferating tissues may show little or no early toxicity, but late effects can be manifested to considerable and varying degrees. In much of this late toxicity, pathologic changes develop from progressive ischemia, brought about by the gradual obliteration of small blood vessels. Irradiated endothelium often becomes replaced by a thickened fibrous layer, which, in small vessels, leads to occlusion and ischemic necrotic changes in the supplied tissue. In larger vessels, fibrosis can lead to wall weakening and aneurysmal dilatation, rupture, or thrombosis. The common denominator, then, of radiation damage to many tissues is related to vascular effects. Although the tolerance to IORT-induced toxicity can vary considerably among tissues, doses ranging to 25 Gy can generally be tolerated without significant toxicity. Vital areas where IORT dose must be carefully monitored include critical vasculature, gastrointestinal viscera, ureter, significant motor or sensory nerve trunks, and central nervous system structures. Higher doses can generally be delivered safely to anatomic areas at risk for tumor that are at a distance from sensitive organs or tissues. The general principle providing the rationale of IORT should always be practiced: maximize the radiation dose to the tumor and tumor-harboring tissues while minimizing dose exposure to surrounding normal tissues.

Intraoperative radiotherapy for pancreatic carcinoma

Intraoperative radiotherapy (IORT) with an electron beam is a therapeutic modality employed predominantly in tumours with a high risk of local recurrence. In this department 35 patients with proven adenocarcinoma of the pancreas underwent surgery and IORT, while 41 patients underwent surgery only. Irradiated patients suffered more serious postoperative complications (21 per cent versus 7 per cent), spent more time in hospital (32 days versus 26 days) and did not show a survival advantage (median of 326 days versus 366 days for two patients with curative resection). Anastomotic breakdown (twp patients), abscess formation (two patients) and pancreatitis in the pancreatic remnant (one patient) occurred only in this group. It is concluded that IORT may increase the risk of postoperative complications. As, on the basis of experimental data, an additional serious long-term risk is to be expected, application of IORT should be limited to well controlled study conditions.

Intraoperative irradiation of the canine pancreas: short-term effects

Intraoperative electron beam radiotherapy (IORT) is clinically used as a potential adjunctive treatment to surgery of locally advanced pancreatic and gastric cancer. The tolerance of the pancreas to IORT was studied in 15 adult beagles, divided in 3 groups of 5 beagles in which 25, 30 or 35 Gy IORT was delivered through a 6-7 cm circular lucite cone with 6-8 MeV electrons to the pancreas and medial wall of the duodenum. The dogs were followed for endocrine and exocrine pancreatic insufficiency. Two dogs (13%) developed radiation-induced morbidity which consisted of a common bile duct stenosis and an enterocolic fistula, as was confirmed at autopsy after 8 and 18 months, respectively. After a follow-up of 1 year, none of the dogs had developed pancreatitis, diabetes or exocrine insufficiency. There was a significant reduction in serum insulin levels and glucose clearance rates without overt diabetes for 30 Gy and 35 Gy (p < 0.05). No significant changes were found for 25 Gy. This study suggests that 25 Gy IORT to the pancreas may be used clinically, and that higher IORT doses may induce endocrine pancreatic insufficiency in the long-term.