Feasibility of Pencil Beam Scanned Intensity Modulated Proton Therapy in Breath-hold for Locally Advanced Non-Small Cell Lung Cancer

International Journal of Radiation Oncology • Biology • Physics, Elsevier, ISSN 1879-355X

Volume 99, 5, 2017

DOI:10.1016/j.ijrobp.2017.08.023, Dimensions: pub.1091340877, PMID: 28964587,



  1. (1) Rigshospitalet, grid.475435.4, Capital Region
  2. (2) University of Copenhagen, grid.5254.6, KU
  3. (3) Paul Scherrer Institute, grid.5991.4
  4. (4) University Hospital of Zurich, grid.412004.3
  5. (5) ETH Zurich, grid.5801.c







PURPOSE: We evaluated the feasibility of treating patients with locally advanced non-small cell lung cancer (NSCLC) with pencil beam scanned intensity modulated proton therapy (IMPT) in breath-hold. METHODS AND MATERIALS: Fifteen NSCLC patients who had previously received 66 Gy in 33 fractions with image guided photon radiation therapy were included in the present simulation study. In addition to a planning breath-hold computed tomography (CT) scan before the treatment start, a median of 6 (range 3-9) breath-hold CT scans per patient were acquired prospectively throughout the radiation therapy course. Three-field IMPT plans were constructed using the planning breath-hold CT scan, and the four-dimensional dose distributions were simulated, with consideration of both patient intra- and interfraction motion, in addition to dynamic treatment delivery. RESULTS: The median clinical target volume receiving 95% of the prescribed dose was 99.8% and 99.7% for the planned and simulated dose distributions, respectively. For 3 patients (20%), the dose degradation was >5%, and plan adjustment was needed. Dose degradation correlated significantly with the change in water-equivalent path lengths (P<.01) in terms of the percentage of voxels with 3-mm or more undershoot on repeat CT scans. The dose to the organs at risk was similar for the planned and simulated dose distributions. Three or fewer breath-holds per field would be required for 12 of the 15 patients, which was clinically feasible. CONCLUSIONS: For 9 of 15 NSCLC patients, IMPT in breath-hold was both dosimetrically robust and feasible to deliver regarding the treatment time. Three patients would have required plan adaption to meet the dosimetric criteria. The change in water-equivalent path length is an indicator of plan robustness and should be considered for the selection of patients for whom the plan would require adaptation.

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