Energy as well as applicator size and shape utilized in over 200 intraoperative electron beam procedures

Energy and applicator size and shape used in over 800 intraoperative electron beam therapy fields

Intraoperative radiotherapy is a treatment option for some patients with locally advanced malignancies. This report updates the Mayo Clinic experience in more than 800 patients by analyzing the use of electron energy and cone size and shape by disease site between 1981 and 1996.

Intraoperative radiation therapy in gynecologic cancer: update of the experience at a single institution

PURPOSE

To update the Mayo Clinic experience with intraoperative radiation therapy (IORT) in patients with gynecologic cancer.

METHODS AND MATERIALS

Between January 1983 and June 1991, 39 patients with recurrent or locally advanced gynecologic malignancies received intraoperative radiation therapy with electrons. The anatomical area treated was pelvis (side walls or presacrum) or periaortic nodes or a combination of both. In addition to intraoperative radiation therapy, 28 patients received external beam irradiation (median dose, 45 Gy; range, 0.9 to 65.7 Gy), and 13 received chemotherapy preoperatively. At the time of intraoperative radiation therapy and after maximum debulking operation, 23 patients had microscopic residual disease and 16 had gross residual disease up to 5 cm in thickness. Median follow-up for surviving patients was 43.4 months (range, 27.1 to 125.4 months).

RESULTS

The 5-year actuarial local control with or without central control was 67.4%, and the control within the IORT field (central control) was 81%. The risk of distant metastases at 5 years was 52% (82% in patients with gross residual disease and 33% in patients with only microscopic disease postoperatively). Actuarial 5-year overall survival and disease-free survival was 31.5 and 40.5%, respectively. Patients with microscopic disease had 5-year disease-free and overall survival of 55 and 50%, respectively. Grade 3 toxicity was directly associated with IORT in six patients (15%).

CONCLUSION

Patients with local, regionally recurrent gynecologic cancer may benefit from maximal surgical debulking and IORT with or without external beam irradiation, especially those with microscopic residual disease.

Field homogeneity of bevelled intraoperative electron beam cones: the influence of virtual focus surface distance

Field flatness of bevelled intraoperative electron therapy cones were evaluated from dose profiles, taken at dmax, both in the longitudinal plane (long axis direction) and the transversal plane (short axis direction), and were found to depend strongly on the setting of the x-ray collimators. Dose gradients in the longitudinal plane of 10-12% were found for collimator settings of 5 mm larger than the cone diameter for low energies, while the dose gradient were smaller for higher energies, both decreasing with larger collimator setting. The dose increase, relative to the central dose, of the hot spots observed in the profile of the transversal plane were in the range of 5-10% for high energies and large collimator settings, decreasing to less than 3% for low electron beam energies and smaller collimator setting. A decrease in virtual focus to surface distance (VFSD) was found to accompany the increasing dose gradient in the longitudinal plane with decreasing collimator setting, this due to increased scatter of electrons at collimator level. Increasing scatter with smaller collimator setting is also indicated by the increase in photon contamination ranging from 1-2.5% for low energies and 3.5-5% for high energies.