TITLE:
Robustness Evaluation of a Novel Proton Beam Geometry for Head and Neck Patients Treated with Pencil Beam Scanning Therapy
AUTHORS:
Sheng Huang, Haoyang Liu, Jiajian Shen, Huifang Zhai, Maura Kirk, Brett Hartl, Alexander Lin, James McDonough, Stefan Both, Haibo Lin
KEYWORDS:
Head and Neck, Robustness, Proton Therapy, Pencil Beam Scanning
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.7 No.3,
July
18,
2018
ABSTRACT: Background: To evaluate the robustness of
head and neck treatment using proton pencil beam scanning (PBS) technique with
respect to range uncertainty (RU) and setup errors (SE), and to establish a
robust PBS planning strategy for future
treatment. Methods and Materials: Ten consecutive patients were planned
with a novel proton field geometry (combination of two posterior oblique fields
and one anterior field with gradient dose match) using single-field uniform
dose (SFUD) planning technique and the proton plans were dosimetrically
compared to two coplanar arc VMAT plans. Robustness of the plans, with
respect to range uncertainties (RU = ± 3% for proton) and setup errors (SE =
2.25 mm for proton and VMAT), in terms of deviations to target coverage (CTV
D98%) and OAR doses (max/mean), were evaluated and compared for each patient
under worst case scenarios. Results: Dosimetrically, PBS plans
provided better sparing to larynx (p = 0.005), oral cavity (p -1.1% ±
1.3 % vs -0.4% ± 0.7% for nodal CTV and -1.4% ±
1.2 vs -0.4% ± 0.5% % for boost CTV). Overall, the
magnitudes of variation of CTV D98% to combined SE and RU were found to be
similar to the impact of the SE on the VMAT plans (-1.6% ±
1.9% vs -1.7% ± 1.4% for nodal CTV and -1.9% ±
1.6% vs -1.3% ± 1.5% for boost CTV). Compared to VMAT, a
larger range of relative dose deviations were found for OARs in proton plans,
but safe doses were maintained for cord (41.8 ± 3.6 Gy for PBS and 41.7 ± 3.9
Gy for VMAT) and brainstem (35.2 ± 8.4 Gy for PBS and 36.2 ± 5.1 Gy for VMAT)
in worst case scenarios. Conclusions: Compared to VMAT, proton plans
containing three SFUD fields with superior-inferior gradient dose matching had
improved sparing to larynx, contralateral parotid and oral cavity, while
providing similar robustness of target coverage. Evaluation of OAR dose
robustness showed higher sensitivities to uncertainties for proton plans, but
safe dose levels were maintained for cord and brainstem.