A Dosimetric Analysis of Single Fraction Lattice Radiotherapy as a Boost for the Palliative Treatment of Bulky Head and Neck Tumors

Abstract

<h3>Purpose/Objective(s)</h3> This study investigates the dosimetry achieved in VMAT/IMRT-planned lattice radiotherapy (LRT) for bulky, palliative head and neck tumors. LRT allows for the delivery of higher radiation doses without dramatically increasing toxicity by using high-dose spheres within the tumor while directing high dose away from OAR's. Our objective was to analyze LRT using 3 dose levels as a boost for palliative treatment of bulky head and neck tumors. The clinical goal of LRT boost would be to increase the effectiveness of treatment while minimizing the burden of care for patients requiring a quick palliation of symptoms associated with bulky tumors. <h3>Materials/Methods</h3> Six bulky palliative head and neck cases were used for this study. A 3D lattice of 0.75 cm spheres spaced 0.85 cm apart was applied to the planning scan and restricted to the area inside the lattice inward contour (GTV was contracted by 0.5 mm). Each case was planned with three different dose prescriptions (15 Gy, 20 Gy and 25 Gy in a single fraction) to the lattice of spheres. In addition, a standard IMRT plan was also created to deliver a uniform 20 Gy in 5 fractions to a defined PTV. The margins (CTV + PTV expansions) used were between 0.5 to 1 cm. A total of 7 plans were created for each case, which included the three single fraction doses, the five fractions of standard treatment, and a combination of the single and five fraction plans. <h3>Results</h3> The average planned tumor volume was 209.77 mL (range 137.80 – 411.01). The number of spheres used in the LRT plan ranged from 13 to 41. The median maximum dose (Dmax) and dose statistics achieved are listed in Table 1. The median ipsilateral carotid dose was high for the 25 Gy (single fraction) plan, so our results suggest that a neoadjuvant LRT boost with of a single fraction of 20 Gy would likely be safe. <h3>Conclusion</h3> Lattice radiotherapy is a viable treatment option for bulky head and neck cases treated with palliative intent. We were able to achieve acceptable dosimetric plans in both the 15 and 20 Gy boosts (single fraction) followed by 20 Gy in 5 fractions, a combination that would be expected to provide more favorable tumor control and symptom relief than traditional palliative regimens of 20-30 Gy. A clinical application with prospective dose escalation trial is under consideration.