Michinori Yamamoto MD, Presenter: Nothing to Disclose

Purpose/Objective;A conditioning regimen with total body irradiation (TBI) is required prior to hematopoietic stem-cell transplant (HSCT) with the purpose of creating space for the transplanted hematopoietic stem-cells, killing any malignant cells, and suppressing the immune system to prevent rejection of the allogeneic HSCT. In past 100 years, numerous techniques have been developed worldwide to perform TBI. However, insufficient customization of the three-dimensional dose distribution is considered the greatest limitation of these methods. Intensity-modulated radiation therapy (IMRT) is the most advanced method of delivering external beam radiotherapy using photon radiation. We conducted a dosimetric study of IMRT for TBI using helical tomotherapy (HT). The purpose of this study is to determine the optimum condition of IMRT for TBI using HT.Material/methods;The CT images from a 64-year old male and a 45-year-old female were used in this study. Both patients had diagnoses of acute myeloid leukemia and underwent allogeneic HSCT in non-myeloablative and myeloablative conditioning regimens, respectively. Both patients’ images covered the body from the top of the head to the thigh. In the non-myeloablative regimen, the body of the patient was contoured. An additional 0.5-cm margin was added to the external contour of the body to account for immobilization uncertainty. This expanded volume was used as the planning target volume (PTV). In the myeloablative regimen, the lung, kidneys, and lenses of the eyes were contoured in addition to the body. The TBI prescription for the non-myeloablative conditioning regimen was 2 Gy in 1 fraction, and for the myeloablative conditioning regimen was 12 Gy in 6 fractions for 3 days to cover 85% of the PTV. The parameters of the slice width, pitch, and modulation factor were assigned as 2.5 cm or 5.0 cm, 0.215 or 0.43, and 2 or 3, respectively. In the myeloablative regimen, planning average doses to the lung, kidneys, and lenses of the eyes did not exceed 8 Gy, 10 Gy, and 6 Gy, respectively. The treatment plan comparison criteria include homogeneity index (HI), and the beam-on times.Results;In non-myeloablative regimen, the beam-on times ranged from 17 to 61 minutes and the HI of the PTV ranged from 0.04 to 0.10. The linear correlating coefficient was - 0.67. In myeloablative regimen, the beam-on times ranged from 18 to 62 minutes and the HI of the PTV ranged from 0.08 to 0.15. The linear correlating coefficient was - 0.76.Conclusion;The HI of the target volume was improved in plans computed by higher intensity-modulation, but these plans required much larger beam-on times. We have to select the most important criterion for the optimal treatment method.

Yamamoto, M, Dosimetric Study of Total Body Irradiation Using Helical Tomotherapy for Patients with Hematopoietic Malignancy Undergoing an Allogeneic Hematopoietic Stem-cell Transplant.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14041372.html