Jenny Gorgisyan1, Per Munck Af Rosenschold2, Rosalind Perrin3, Gitte F Persson4, Mirjana Josipovic2, Maria Francesca Belosi3, Svend Aage Engelholm4, Damien C Weber5, Antony J Lomax6. 1. Center for Proton Therapy, Paul Scherrer Institute, Villigen PSI, Switzerland; Department of Oncology, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark; Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark. Electronic address: jenny.gorgisyan@psi.ch. 2. Department of Oncology, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark; Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark. 3. Center for Proton Therapy, Paul Scherrer Institute, Villigen PSI, Switzerland. 4. Department of Oncology, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark. 5. Center for Proton Therapy, Paul Scherrer Institute, Villigen PSI, Switzerland; Department of Radiation Oncology, University Hospital of Zürich, Zürich, Switzerland. 6. Center for Proton Therapy, Paul Scherrer Institute, Villigen PSI, Switzerland; Department of Physics, ETH Zürich, Zürich, Switzerland.
Abstract
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.
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 NSCLCpatients 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 NSCLCpatients, 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.
Authors: Lydia A den Otter; Renske M Anakotta; Menkedina Weessies; Catharina T G Roos; Nanna M Sijtsema; Christina T Muijs; Margriet Dieters; Robin Wijsman; Esther G C Troost; Christian Richter; Arturs Meijers; Johannes A Langendijk; Stefan Both; Antje-Christin Knopf Journal: Med Phys Date: 2020-07-09 Impact factor: 4.071