Feasibility of pencil beam scanned Intensity Modulated Proton Therapy in breath-hold for locally-advanced non-small cell lung cancer

Publication date: Available online 24 August 2017
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Jenny Gorgisyan, Per Munck af Rosenschold, Rosalind Perrin, Gitte F. Persson, Mirjana Josipovic, Maria Francesca Belosi, Svend Aage Engelholm, Damien C. Weber, Antony J. Lomax
PurposeThe 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 has been evaluated.Methods and MaterialsFifteen NSCLC patients previously treated to 66 Gy in 33 fractions with image-guided photon radiation therapy were included in this simulation study. In addition to a planning breath-hold CT scan prior to treatment start, six (median, range: 3-9) breath-hold CT scans per patient were acquired prospectively, throughout the course of the radiation therapy. Three field IMPT treatment plans were constructed based on the planning breath-hold CT scan and the 4D dose distributions were simulated, taking both the intra- and inter-fractional motion of the patient into account, in addition to the dynamic treatment delivery.ResultsThe median clinical target volume (CTV) V95% (the volume receiving 95% of the prescribed dose) was 99.8% and 99.7% for the planned and simulated dose distributions, respectively. For three patients (20%), the dose degradation was more than 5% and plan adjustment was needed. Dose degradation was significantly correlated to the change in water-equivalent path lengths (WEPL) (p<0.01) in terms of percentage of voxels with 3 mm undershoot on repeat CTs. The dose to the organs at risk was similar for planned and simulated dose distributions. Three or less breath-holds per field would be required for 12/15 patients, which is clinically feasible.ConclusionsFor 9/15 NSCLC patients, IMPT in breath-hold was both dosimetrically robust and feasible to deliver regarding the treatment time. Three patients would require plan adaption to meet the dosimetric criteria. WEPL is an indicator of plan robustness and should be considered for selection of patients for which the plan would require adaptation.



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