Purpose: We developed an intensity-modulated arc therapy (IMAT) technique for the treatment of women with high-risk endometrial malignancies. In the context of multimodality therapy, nodal and tumor bed irradiation was delivered while respecting tolerance doses for critical structures.
Methods and materials: Five patients were planned and treated with the IMAT technique after hysterectomy. Computed tomographic (CT) scans for treatment planning were acquired with the tumor bed contoured as the clinical target volume (CTV(tumor_bed)) and the iliac and presacral vessels contoured as the gross tumor volume (GTV). In 2 patients the lower para-aortic nodes were included into the GTV. The small bowel, iliac crests, femoral heads, bladder, and rectum were contoured as critical organs. For the nodes, a CTV(nodes) was generated with a 7-10-mm margin around the vessels, and the planning target volume (PTV(nodes)) was generated by a further 5-mm expansion. For the tumor bed, the PTV(tumor_bed) was generated with a margin of 7-10 mm around CTV(tumor_bed). Planning constraints included adequate coverage of the tumor bed (>95% receiving > or =45 Gy) and nodes (> or =95% receiving > or =40 Gy). Arc combinations with different extents were tested, and the final plan was generated based on the balance between complexity (number of arcs), PTV coverage, and critical structure sparing. Conventional and 8-field intensity-modulated radiation therapy (IMRT) plans were generated for each patient for comparison purposes. All patients were treated with IMAT.
Results: We found that two anterior intensity-modulated arcs (300 degrees to 30 degrees and 330 degrees to 60 degrees ) adequately treated the PTVs. Furthermore, this IMAT technique allowed sparing of small bowel and the iliac crests (marrow space) to a similar degree as the 8-field IMRT. The 8-field IMRT yielded better dose uniformity than IMAT in the target volumes; however, neither technique was as uniform as the conventional plan. In the 5 patients, IMAT treatment was well tolerated and completed as planned.
Conclusions: We successfully piloted an optimized intensity-modulated arc technique to treat 5 high-risk endometrial cancer patients undergoing multimodality treatment. This allowed a significant reduction in dose to bone marrow and small bowel compared with conventional techniques and was simpler to deliver than multifield IMRT.