A Model-Based Method for Assessment of Salivary Gland and Planning Target Volume Dosimetry in Volumetric-Modulated Arc Therapy Planning on Head-and-Neck Cancer

Honglai Zhang; Yijian Cao; Jeffrey Antone; Adam C Riegel; Maged Ghaly; Louis Potters; Abolghassem Jamshidi

doi:10.4103/jmp.JMP_19_19

A Model-Based Method for Assessment of Salivary Gland and Planning Target Volume Dosimetry in Volumetric-Modulated Arc Therapy Planning on Head-and-Neck Cancer

J Med Phys. 2019 Jul-Sep;44(3):201-206. doi: 10.4103/jmp.JMP_19_19.

Authors

Honglai Zhang¹, Yijian Cao^{1

2}, Jeffrey Antone¹, Adam C Riegel^{1

2}, Maged Ghaly^{1

2}, Louis Potters^{1

2}, Abolghassem Jamshidi^{1

2}

Affiliations

¹ Department of Radiation Medicine, Northwell Health Cancer Institute, Lake Success, New York, USA.
² Zucker School of Medicine at Northwell/Hofstra, Hempstead, New York, USA.

Abstract

This study examined the relationship of achievable mean dose and percent volumetric overlap of salivary gland with the planning target volume (PTV) in volumetric-modulated arc therapy (VMAT) plan in radiotherapy for a patient with head-and-neck cancer. The aim was to develop a model to predict the viability of planning objectives for both PTV coverage and organs-at-risk (OAR) sparing based on overlap volumes between PTVs and OARs, before the planning process. Forty patients with head-and-neck cancer were selected for this retrospective plan analysis. The patients were treated using 6 MV photons with 2-arc VMAT plan in prescriptions with simultaneous integrated boost in dose of 70 Gy, 63 Gy, and 58.1 Gy to primary tumor sites, high-risk nodal regions, and low-risk nodal regions, respectively, over 35 fractions. A VMAT plan was generated using Varian Eclipse (V13.6), in optimization with biological-based generalized equivalent uniform dose (gEUD) objective for OARs and targets. Target dose coverage (D ₉₅, D _max, conformity index) and salivary gland dose (D _mean and D _max) were evaluated in those plans. With a range of volume overlaps between salivary glands and PTVs and dose constraints applied, results showed that dose D ₉₅ for each PTV was adequate to satisfy D ₉₅ >95% of the prescription. Mean dose to parotid <26 Gy could be achieved with <20% volumetric overlap with PTV₅₈ (parotid-PTV₅₈). On an average, the D _mean was seen at 15.6 Gy, 21.1 Gy, and 24.2 Gy for the parotid-PTV₅₈ volume at <5%, <10%, and <20%, respectively. For submandibular glands (SMGs), an average D _mean of 27.6 Gy was achieved in patients having <10% overlap with PTV₅₈, and 36.1 Gy when <20% overlap. Mean doses on parotid and SMG were linearly correlated with overlap volume (regression R ² = 0.95 and 0.98, respectively), which were statistically significant (P < 0.0001). This linear relationship suggests that the assessment of the structural overlap might provide prospective for achievable planning objectives in the head-and-neck plan.

Keywords: Generalized equivalent uniform dose optimization; head-and-neck cancer; radiotherapy; salivary gland sparing; volumetric-modulated arc therapy plan.