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Title: SU-E-T-581: A Comparative Study of Standard IMRT and VMAT Planning Techniques for Unilateral and Bilateral Head and Neck Irradiation

Purpose: To compare dosimetric properties and monitor units (MU) of IMRT plans with several VMAT head and neck (H and N) plans. Methods: Seventeen unilateral H and N (UHN) and five bilateral H and N (BHN) patients initially treated with IMRT were replanned with VMAT. Several arc arrangements were studied for each patient: 1)for UHN, two 360° arcs, two 260° arcs, two 210° arcs, two 360° arcs with contralateral avoidance sectors, and 2)for BHN, two 360° arcs, two 360° arcs with bilateral avoidance sectors, two 360° arcs with bilateral avoidance sectors and a third arc limited to the upper neck. Optimization constraints were adjusted for each patient and plan. All plans were normalized to achieve the same highest-dose PTV coverage. Percent differences (IMRT-VMAT)/VMAT in MU, dose homogeneity (HI=maximum point dose/prescription dose), and organ-at-risk (OAR) metrics are reported and statistical significance evaluated (p<0.05; paired Student t-test). Results: Average reduction in MU with VMAT was 28% for UHN (p<0.0001) and 63% for BHN (p<0.0001). Average HI for UHN IMRT and 360° arc VMAT plans was 1.08 and for plans with arcs <360° average HI=1.10. Average HI for BHN IMRT was 1.07, for three-arc VMAT 1.08, and for two-arc VMAT 1.11. For UHN,more » two 210° arcs achieved lower contralateral parotid max (−2.6 Gy, p<0.02) and mean (−1.2 Gy, p=0.06) dose. For BHN two-arc plans, contralateral parotid mean dose increased (3.3 Gy, p<0.04) and larynx max dose increased (2.9 Gy, p<0.02) with no change in larynx mean dose. Conclusion: For UHN, 360degree arc VMAT consistently produced plans dosimetrically comparable to IMRT with the benefit of lower MU. VMAT with arcs <360degrees produced plans inferior to IMRT in dose homogeneity and without significantly improved OAR sparing. For BHN, three-arc plans were dosimetrically comparable to IMRT with lower MU, while two-arc plans were inferior to IMRT in HI and OAR dose. Research supported in part by a Kaye Family Award.« less
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  1. Dana-Farber Cancer Institute/Brigham and Women's Hospital, Boston, MA (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 41; Journal Issue: 6; Other Information: (c) 2014 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States