Author: Kenny Guida, Daniel Johnson, Wesley Tucker 👨🔬
Affiliation: University of Kansas Medical Center, Department of Radiation Oncology, University of Kansas Medical Center 🌍
Purpose: Intensity modulated proton therapy (IMPT) has emerged as a standard of care for unilateral head and neck (HN) cancers due to superior OAR sparing. With the increase of proton centers nationally, patients have greater access to care. However, for cases of insurance denial, machine downtime, or inaccessibility to IMPT, high-quality VMAT plans are necessary. The goal of this study is to drive automated planning through the use of an in-house knowledge-based planning (KBP) model to produce unilateral HN VMAT plans that are dosimetrically comparable to IMPT.
Methods: 10 unilateral HN IMPT cases were retrospectively planned with VMAT using an in-house KBP model. Plans involved 2-3 target volumes with hierarchal prescription dose schemes (range 50-70Gy) delivered in 30-35 fractions. IMPT cases were planned with Raystation v2023B and utilized three beams. VMAT cases were planned with three partial arcs in Eclipse v18.0 with RapidPlan for plan optimization. Dosimetric scorecards, based on departmental standards, were used to compare IMPT and VMAT plan quality.
Results: IMPT plans scored higher than VMAT, on average, (90.8% to 84.7%, p=6.2e-06). CTV coverages were comparable between the IMPT and VMAT (p=0.11), scoring 97.6% and 95.7%, respectively. Differences in metrics for brain, cochlea_contra, cochlea_ipsi, esophagus, larynx, and trachea sparing were unremarkable (p>0.1 for all). VMAT plans reduced parotid_ipsi Dmean (average: 44Gy versus 51Gy, p<0.05). IMPT delivered near-negligible dose to OARs outside of the beam path; however, VMAT reduced OAR dose to well within clinical standards, as in the case of contralateral parotid and submandibular glands, which achieved Dmean of 5.6Gy and 6.3Gy, respectively.
Conclusion: This study demonstrated the potential of a well-constructed KBP model in planning unilateral HN cases. For instances when IMPT is unavailable, clinicians would benefit from a KBP model that ensures that a high level of plan quality remains achievable.