Partial-Arc VMAT Planning Solution for Craniospinal Irradiation
J Setianegara1*, J Rolfingsmeier2, T Zhang1, T Zhao1, S Perkins1, F Reynoso1, (1) Department of Radiation Oncology, Washington University in St. Louis, St. Louis, MO 63110; (2) Department of Radiation Oncology, Barnes-Jewish Hospital, St. Louis, MO 63110.
Presentations
TU-J430-BReP-F3-3 (Tuesday, 7/12/2022) 4:30 PM - 5:30 PM [Eastern Time (GMT-4)]
Exhibit Hall | Forum 3
Purpose: To propose a multi-isocenter auto-feathered partial-arc VMAT solution for craniospinal irradiation (CSI).
Methods: Six patient plans (ages 5-58) where made using a 2-3 isocenters depending on target length with 7-11 total arcs using 6MV photon beams and a dose prescription of 3600cGy in twenty fractions. The brain was treated with 3 full-arcs while the lower and upper spine were treated with four posterior 60° partial-arcs. The isocenters were auto-feathered via optimization and strategically placed for longitudinal shifts only reducing the likelihood of setup errors. Plan quality was compared with other published VMAT CSI techniques and our clinical proton techniques.
Results: The average V95%, CI and HI of the PTV coverage were 99.05±0.41%, 0.86±0.03 and 0.11±0.02 respectively. The OAR Dmean[Dmax] are 7.69±1.06Gy[15.99±5.35Gy] to parotids, 3.93±0.87Gy[15.20±5.47Gy] to heart, 7.5±2.39Gy[30.96±5.89Gy] to lungs, 9.88±2.19Gy[23.28±4.65Gy] to esophagus and 3.95±1.09Gy[15.98±5.07Gy] to kidneys with average D0.03cc of the lenses being 8.54±1.46Gy. Comparing with similar techniques available in the literature, we attained lower average Dmean values to the heart, parotids, esophagus and kidneys with the latter 3 OARs also having lower Dmax values. In addition, the average D0.03cc of the lenses were also lower than reported in literature. Proton techniques offer a further decrease in the average Dmean to the heart, lungs, esophagus and kidneys at the expense of higher Dmax values to all OARs and a higher Dmean to the parotids.
Conclusion: The VMAT CSI technique presented achieved similar coverage with improved OAR sparing at the expense of a higher lung Dmean. Compared to our proton techniques the VMAT plans achieved markedly lower parotid dose, similar mean doses to kidneys and esophagus, but higher mean dose to heart and lungs. The technique described is a good alternative to proton CSI techniques in the event where protons are not available.
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