Evaluation of Intraoperative Radiotherapy for Gastric Carcinoma

Discussion

Each surgical procedure that does not achieve a complete local excision of the primary tumor in all 3 dimensions (length, width, aboral, and depth of tumor) and of the area of lymphatic drainage is, according to the UICC classification of D1 or D2 resection (i.e.,a resection leaving residual microscopic or macroscopic tumor) considered to be a “palliative resection”. In addition to procedures that leave the entire tumor in situ, any type of operation that leaves residual macroscopic or microscopic tumor at the resection margin, tumor bed, or in the lymphatic drainage area must also be considered to be a palliative procedure.

The rationale for IORT is to increase the irradiation dose to the tumor without exceeding critical normal tissue tolerance. IORT used as neoadjuvant therapy, can increase the 5-YSR of advanced gastric carcinoma patients. Special linear accelerators have been used for the application of high single-dose radiation to the tumor bed.^[1,2] Abe et al.^[3] reported the treatment of 115 gastric cancer patients by IORT. Survival of patients in stages II through IV treated by IORT increased by nearly 10% to 20% at 5 years. No difference in the survival of patients with stage was observed for the 2 groups. IORT did not afford benefit if the lymph node metastases were limited with n₁ group or serosal invasion was not found. On the other hand, the 5-YSR for patients who were treated by IORT increased by nearly 10% when the serosal invasion was observed, and by nearly 18% when n₂ and n₃ lymph node metastases were found. Ogata et al.^[4] reported that the 5-YSR and 8-YSR for 58 cases treated by IORT were both 100%, the control group was 60% and 48% in stage I cancer; the 8-YSR of stage III cancer cases treated by IORT was 55% and the control group was 35%. But these results were controversial, as Coquard et al.^[5] reported that the 5-YSR of patients with gastrectomy and local lymph node resection combined with IORT was the same as single expanded lymph node resection. However the postoperation complications and mortality were lower than that in a group having only a gastrectomy operation. Our results showed that an operation combined with IORT is beneficial for patients in stage II and stage III cancer with a survival advantage of 14.4% to 20% at 5 years. However, this procedure was ineffective for patients with stage I and stage IV cancer. With D2 lymphadenectomy combined with IORT, 5-YSR of stage II cancer patients was improved as compared with D2 lymphadenectomy only, the former increased 60.0%, the later was 35.7%. With D3 lymphadenectomy combined with IORT, the 3 and 4-YSR were improved, but it was ineffective for the 1,2 and 5-YSR.

The radiation target area in the region of the upper abdomen includes potential microscopic tumor extensions and known or suspected macroscopic disease. In order to reduce the injury of irradiation to the normal tissue near the stomach, the target area is restricted to the gastric bed. The inferior field border is generally at the level of the L3 to L4 vertebrae, but this depends on the location of the carcinoma and the position of the stomach before treatment. The target area includes the proximal and regional lymphatics, the right and left cardiac nodes, the nodal chains of the lesser and greater curvatures, the suprapyloric and infapyloric chains, the splenic chains, and the lymph nodes along the hepatic artery. For tumors of the cardiac, upper extension of the field to the terminal esophagus and paraesophageal lymph nodes is recommended. If the tumor is unresectable or if, after surgery, macroscopic disease remains, the total irradiation dose can be increased in a coned-down volume, which is restricted to the area of gross disease.

With regard to the optimization of IORT, we developed a new technique that provides a wider irradiation field for patients undergoing total gastrectomy. In these patients with total gastrectomy, splenectomy, removal of the pancreas capsule, and extended lymph node dissection including the nodes along the splenic artery were performed. Then the tail and body of the pancreas were moved up to the right side margin of the abdominal aorta and the superior mesenteric vein. These maneuvers provided a much wider irradiation field, which included the paraaortic lymph nodes. After irradiation, the pancreas was returned to its normal position and an esophagoenterostomy was performed. This method was performed only in patients without cancer invasion of the pancreas or metastases in the lymph nodes along the splenic artery. The advantage of this method is that it produces a wide irradiation field including paraaortic lymph nodes and does not increase the complications and mortality. Meanwhile, one must be careful to protect the duodenum and jejunum before irradiation as those organs must be shielded from the irradiation field.

With regard to special radiotherapeutic techniques that include the potential of relatively high biologically effective doses, gastric cancer has some of the most convincing indications for intraoperative irradiation. Special linear accelerators have been used for the application of high single doses ( 15 to 35 Gy) to the tumor bed. One problem with IORT is to correctly cover tumor sites outside the midline area or under the left hemidiaphgragm. In addition, the maximum tolerable dose administered in one session is limited from 15 to 35 Gy. Abe et al.^[3] reported that doses of irradiation selected were dependent on the radicality achieved by the operation. In general, the irradiation doses from 15-30 Gy were applied in curative situations and 30 to 35 Gy in palliative situations. We selected the doses of IORT according to the residual tumor volume, including clinically undetectable lesions (10-15 Gy), microscopic residual (20 Gy), macroscopic residual (25 Gy), or noncurative surgery (30 Gy). No serious complications occurred in these cases. Our data strongly support the efficacy of IORT for local tumor control.