Reproducibility of the lung anatomy under active breathing coordinator control: Dosimetric consequences for scanned proton treatments

Purpose The treatment of moving targets with scanned proton beams is challenging. For motion mitigation, an Active Breathing Coordinator (ABC) can be used to assist breath‐holding. The delivery of pencil beam scanning fields often exceeds feasible breath‐hold durations, requiring high breath‐hold reproducibility. We evaluated the robustness of scanned proton therapy against anatomical uncertainties when treating nonsmall‐cell lung cancer (NSCLC) patients during ABC controlled breath‐hold. Methods Four subsequent MRIs of five healthy volunteers (3 male, 2 female, age: 25–58, BMI: 19–29) were acquired under ABC controlled breath‐hold during two simulated treatment fractions, providing both intrafractional and interfractional information about breath‐hold reproducibility. Deformation vector fields between these MRIs were used to deform CTs of five NSCLC patients. Per patient, four or five cases with different tumor locations were modeled, simulating a total of 23 NSCLC patients. Robustly optimized (3 and 5 mm setup uncertainty respectively and 3% density perturbation) intensity‐modulated proton plans (IMPT) were created and split into subplans of 20 s duration (assumed breath‐hold duration). A fully fractionated treatment was recalculated on the deformed CTs. For each treatment fraction the deformed CTs representing multiple breath‐hold geometries were alternated to simulate repeated ABC breath‐holding during irradiation. Also a worst‐case scenario was simulated by recalculating the complete treatment plan on the deformed CT scan showing the largest deviation with the first deformed CT scan, introducing a systematic error. Both the fractionated breath‐hold scenario and worst‐case scenario were dosimetrically evaluated. Results Looking at the deformation vector fields between the MRIs of the volunteers, up to 8 mm median intra‐ and interfraction displacements (without outliers) were found for all lung segments. The dosimetric evaluation showed a median difference in D98% between the planned and breath‐hold scenarios of −0.1 Gy (range: −4.1 Gy to 2.0 Gy). D98% target coverage was more than 57.0 Gy for 22/23 cases. The D1 cc of the CTV increased for 21/23 simulations, with a median difference of 0.9 Gy (range: −0.3 to 4.6 Gy). For 14/23 simulations the increment was beyond the allowed maximum dose of 63.0 Gy, though remained under 66.0 Gy (110% of the prescribed dose of 60.0 Gy). Organs at risk doses differed little compared to the planned doses (difference in mean doses <0.9 Gy for the heart and lungs, <1.4% difference in V35 [%] and V20 [%] to the esophagus and lung). Conclusions When treating under ABC controlled breath‐hold, robustly optimized IMPT plans show limited dosimetric consequences due to anatomical variations between repeated ABC breath‐holds for most cases. Thus, the combination of robustly optimized IMPT plans and the delivery under ABC controlled breath‐hold presents a safe approach for PBS lung treatments.

[1]  A. Berman,et al.  An in-silico comparison of proton beam and IMRT for postoperative radiotherapy in completely resected stage IIIA non-small cell lung cancer , 2013, Radiation oncology.

[2]  Antje-Christin Knopf,et al.  Scanned proton radiotherapy for mobile targets—the effectiveness of re-scanning in the context of different treatment planning approaches and for different motion characteristics , 2011, Physics in medicine and biology.

[3]  E W Korevaar,et al.  An automated, quantitative, and case-specific evaluation of deformable image registration in computed tomography images , 2018, Physics in medicine and biology.

[4]  Max A. Viergever,et al.  elastix: A Toolbox for Intensity-Based Medical Image Registration , 2010, IEEE Transactions on Medical Imaging.

[5]  U Oelfke,et al.  Worst case optimization: a method to account for uncertainties in the optimization of intensity modulated proton therapy , 2008, Physics in medicine and biology.

[6]  Kevin Souris,et al.  Evaluation of motion mitigation using abdominal compression in the clinical implementation of pencil beam scanning proton therapy of liver tumors , 2017, Medical physics.

[7]  Radhe Mohan,et al.  Robust optimization of intensity modulated proton therapy. , 2012, Medical physics.

[8]  S van de Water,et al.  Tumour tracking with scanned proton beams: assessing the accuracy and practicalities , 2009, Physics in medicine and biology.

[9]  A J Lomax,et al.  Online image guided tumour tracking with scanned proton beams: a comprehensive simulation study , 2014, Physics in medicine and biology.

[10]  Christoph Bert,et al.  Quantification of interplay effects of scanned particle beams and moving targets , 2008, Physics in medicine and biology.

[11]  Richard Symonds-Tayler,et al.  The use of the Active Breathing Coordinator throughout radical non-small-cell lung cancer (NSCLC) radiotherapy. , 2011, International journal of radiation oncology, biology, physics.

[12]  Gudrun Goitein,et al.  The clinical potential of intensity modulated proton therapy. , 2004, Zeitschrift fur medizinische Physik.

[13]  M. V. van Herk,et al.  Precise and real-time measurement of 3D tumor motion in lung due to breathing and heartbeat, measured during radiotherapy. , 2002, International journal of radiation oncology, biology, physics.

[14]  Michael B Sharpe,et al.  Significant reductions in heart and lung doses using deep inspiration breath hold with active breathing control and intensity-modulated radiation therapy for patients treated with locoregional breast irradiation. , 2003, International journal of radiation oncology, biology, physics.

[15]  David Sarrut,et al.  Nonrigid registration method to assess reproducibility of breath-holding with ABC in lung cancer. , 2004, International journal of radiation oncology, biology, physics.

[16]  A J Lomax,et al.  Intensity modulated proton therapy and its sensitivity to treatment uncertainties 2: the potential effects of inter-fraction and inter-field motions , 2008, Physics in medicine and biology.

[17]  Anders Forsgren,et al.  Minimax optimization for handling range and setup uncertainties in proton therapy. , 2011, Medical physics.

[18]  D. Collins,et al.  First MRI application of an active breathing coordinator , 2015, Physics in medicine and biology.

[19]  Damien Charles Weber,et al.  Improving 4D plan quality for PBS-based liver tumour treatments by combining online image guided beam gating with rescanning , 2015, Physics in medicine and biology.

[20]  Radhe Mohan,et al.  Intensity-modulated proton therapy reduces the dose to normal tissue compared with intensity-modulated radiation therapy or passive scattering proton therapy and enables individualized radical radiotherapy for extensive stage IIIB non-small-cell lung cancer: a virtual clinical study. , 2010, International journal of radiation oncology, biology, physics.

[21]  Harald Paganetti,et al.  Relative biological effectiveness (RBE) values for proton beam therapy. , 2002, International journal of radiation oncology, biology, physics.

[22]  Francesca Albertini,et al.  Robustness of the Voluntary Breath-Hold Approach for the Treatment of Peripheral Lung Tumors Using Hypofractionated Pencil Beam Scanning Proton Therapy. , 2016, International journal of radiation oncology, biology, physics.

[23]  Harald Paganetti,et al.  Motion mitigation for lung cancer patients treated with active scanning proton therapy. , 2015, Medical physics.

[24]  Keisuke Usui,et al.  Limited Impact of Setup and Range Uncertainties, Breathing Motion, and Interplay Effects in Robustly Optimized Intensity Modulated Proton Therapy for Stage III Non-small Cell Lung Cancer. , 2016, International journal of radiation oncology, biology, physics.

[25]  Martin O. Leach,et al.  Lung volume reproducibility under ABC control and self‐sustained breath‐holding , 2017, Journal of applied clinical medical physics.