Youssef Ben Bouchta1, Karen Goddard2, M Peter Petric3, Alanah M Bergman4. 1. Department of Medical Physics, British Columbia Cancer - Vancouver Center, Vancouver, BC, Canada; Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada. 2. Department of Radiation Oncology, British Columbia Cancer - Vancouver Center, Vancouver, BC, Canada. 3. Department of Medical Physics, British Columbia Cancer - Vancouver Center, Vancouver, BC, Canada. 4. Department of Medical Physics, British Columbia Cancer - Vancouver Center, Vancouver, BC, Canada. Electronic address: abergman@bccancer.bc.ca.
Abstract
PURPOSE: To assess the effect of flattening-filter-free (FFF) and 10 MV radiation therapy beams on the peripheral dose received by a population of pediatric patients undergoing volumetric modulated arc therapy (VMAT). METHODS AND MATERIALS: Twenty-six previously delivered 6 MV flattened VMAT pediatric radiation therapy treatments plans were replanned with 6 MV flattened, 6 MV FFF, and 10 MV FFF VMAT. Monte Carlo simulation code EGSnrc was used in conjunction with a measurement-based model to obtain 3-dimensional dose distributions. Peripheral dose delivered by FFF beams was compared with that delivered by 6 MV flattened beams. A statistical analysis was performed to determine whether certain clinical factors (eg, target volume, location) were associated with a change in integral relative radiation dose. Neutron dose measurements assessed the neutron contribution from the 6 MV flattened and 10 MV FFF x-ray beams. RESULTS: Both the 6 MV FFF and 10 MV FFF beams delivered significantly lower peripheral radiation doses than 6 MV flattened (P < .01). The dose reduction was of 3.9% (95% confidence interval [CI] 2.1-5.7) and 9.8% (95% CI, 8.0-11.6) at 5 cm from the PTV and 21.9% (95% CI, 13.7-30.1) and 25.6% (95% CI, 17.6-33.6) at 30 cm for 6 MV FFF and 10 MV FFF beams, respectively. The clinical factors examined did not have a significant effect on the relative magnitude of the peripheral dose reduction. The upper limit on the neutron dose was determined to be 203 μSv for the 6 MV flattened and 522 μSv for the 10 MV FFF beam. CONCLUSIONS: Both FFF beams significantly (P < .01) reduced the peripheral dose. 10 MV FFF was more effective at reducing peripheral dose at distances <5 cm from the PTV edge. The neutron doses delivered by all beams were <1% compared with the photon doses. 10 MV FFF should be used to minimize peripheral dose.
PURPOSE: To assess the effect of flattening-filter-free (FFF) and 10 MV radiation therapy beams on the peripheral dose received by a population of pediatric patients undergoing volumetric modulated arc therapy (VMAT). METHODS AND MATERIALS: Twenty-six previously delivered 6 MV flattened VMAT pediatric radiation therapy treatments plans were replanned with 6 MV flattened, 6 MV FFF, and 10 MV FFF VMAT. Monte Carlo simulation code EGSnrc was used in conjunction with a measurement-based model to obtain 3-dimensional dose distributions. Peripheral dose delivered by FFF beams was compared with that delivered by 6 MV flattened beams. A statistical analysis was performed to determine whether certain clinical factors (eg, target volume, location) were associated with a change in integral relative radiation dose. Neutron dose measurements assessed the neutron contribution from the 6 MV flattened and 10 MV FFF x-ray beams. RESULTS: Both the 6 MV FFF and 10 MV FFF beams delivered significantly lower peripheral radiation doses than 6 MV flattened (P < .01). The dose reduction was of 3.9% (95% confidence interval [CI] 2.1-5.7) and 9.8% (95% CI, 8.0-11.6) at 5 cm from the PTV and 21.9% (95% CI, 13.7-30.1) and 25.6% (95% CI, 17.6-33.6) at 30 cm for 6 MV FFF and 10 MV FFF beams, respectively. The clinical factors examined did not have a significant effect on the relative magnitude of the peripheral dose reduction. The upper limit on the neutron dose was determined to be 203 μSv for the 6 MV flattened and 522 μSv for the 10 MV FFF beam. CONCLUSIONS: Both FFF beams significantly (P < .01) reduced the peripheral dose. 10 MV FFF was more effective at reducing peripheral dose at distances <5 cm from the PTV edge. The neutron doses delivered by all beams were <1% compared with the photon doses. 10 MV FFF should be used to minimize peripheral dose.