Program Information
Whole Abdominopelvic Treatment of Desmoplastic Small Round Cell Tumor Using Multi-Isocenter Volumetric Modulated Arc Therapy
C Abing1*, P Conway2 , (1) Gundersen Lutheran Medical Center, La Crosse, WI, (2) Gundersen Health System, La Crosse, WI
Presentations
PO-BPC-Exhibit Hall-19 (Saturday, March 7, 2015) Room: Exhibit Hall
Purpose:
To treat whole abdominopelvic irradiation using a multi-isocenter volumetric modulated arc therapy (VMAT) technique. This technique will be utilized to lower the mean kidney, liver and pelvic bone dose, respectively. This will demonstrate a dosimetrically superior plan when compared to a conventional anteroposterior technique.
Methods:
A three-isocenter VMAT plan was created using the Eclipse treatment planning system with the analytic anisotropic dose calculation algorithm. Each isocenter shared the same anteroposterior and lateral position but were separated by 12.5cm longitudinally. Each isocenter contained two to three VMAT fields, each with 359.8 degrees of rotation, thus making the entire plan composed of 8 VMAT arcs. The target was the entire abdominopelvic cavity and the organs at risk (OAR) were the bilateral kidneys, liver and pelvic bones. Because of the unique physical length and complexity of this treatment, special care was taken to ensure the patient was not rotated prior to treatment. This VMAT plan was compared with a conventional treatment plan with two opposed fields, an anterior field with partial transmission block over the liver and a posterior field with partial transmission blocks over the kidneys.
Results:
The three-isocenter VMAT plan gave lower bilateral mean kidney dose (12.8Gy vs 14.3Gy) and a lower mean pelvic bone dose (15.2Gy vs. 20Gy). The liver was optimized to give a mean dose of 24Gy, this would not have been achievable with the conventional plan. Although treatment time for the VMAT plan was longer than conventional, it was kept to 9 minutes of “beam on†time, with a total treatment time mean and standard deviation of 30 minutes and 13 minutes, respectively.
Conclusion:
This methodology proved to be effective and efficient when compared to a conventional field arrangement. Proper care must be taken to ensure accurate isocenter separation and patient rotation.
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