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Evaluation of motion mitigation using abdominal compression in the clinical implementation of pencil beam scanning proton therapy of liver tumors
Author(s) -
Lin Liyong,
Souris Kevin,
Kang Minglei,
Glick Adam,
Lin Haibo,
Huang Sheng,
Stützer Kristin,
Janssens Guillaume,
Sterpin Edmond,
Lee John A.,
Solberg Timothy D.,
McDonough James E.,
Simone Charles B.,
BenJosef Edgar
Publication year - 2017
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.12040
Subject(s) - proton therapy , pencil beam scanning , nuclear medicine , radiation treatment planning , dosimetry , beam (structure) , proton , cone beam computed tomography , pencil (optics) , materials science , radiation therapy , biomedical engineering , medicine , radiology , physics , optics , computed tomography , quantum mechanics
Purpose To determine whether individual liver tumor patients can be safely treated with pencil beam scanning proton therapy. This study reports a planning preparation workflow that can be used for beam angle selection and the evaluation of the efficacy of abdominal compression ( AC ) to mitigate motion. Methods Four‐dimensional computed tomography scans (4 DCT ) with and without AC were available from 10 liver tumor patients with fluoroscopy‐proven motion reduction by AC , previously treated using photons. For each scan, the motion amplitudes and the motion‐induced variation of water‐equivalent thickness (Δ WET ) in each voxel of the target volume were evaluated during treatment plan preparation. Optimal proton beam angles were selected after volume analysis of the respective beam‐specific planning target volume ( BSPTV ). M ⊥80 and Δ WET 80 derived from the 80th percentiles of perpendicular motion amplitude (M ⊥ ) and Δ WET were compared with and without AC . Proton plans were created on the average CT to achieve target coverage similar to that of the conventional photon treatments. 4D dynamic dose calculation was performed postplan by synchronizing proton beam delivery timing patterns to the 4 DCT phases to assess interplay and fractionation effects, and to determine motion criteria for subsequent patient treatment. Results Selected coplanar beam angles ranged between 180° and 39°, primarily from right lateral (oblique) and posterior (oblique) directions. While AC produced a significant reduction in mean Liver‐GTV dose, any reduction in mean heart dose was patient dependent and not significant. Similarly, AC resulted in reductions in M ⊥ , Δ WET , and BSPTV volumes and improved dose degradation (ΔD 95 and ΔD 1 ) within the CTV . For small motion (M ⊥80 < 7 mm and Δ WET 80 < 5 mm), motion mitigation was not needed. For moderate motion (M ⊥80 7–10 mm or Δ WET 80 5–7 mm), AC produced a modest improvement. For large motion (M ⊥80 > 10 mm or Δ WET 80 > 7 mm), AC and/or some other form of mitigation strategies were required. Conclusion A workflow for screening patients’ motion characteristics and optimizing beam angle selection was established for the pencil beam scanning proton therapy treatment of liver tumors. Abdominal compression was found to be useful at mitigation of moderate and large motion.