Physics Contribution On the Need for Comprehensive Validation of Deformable Image Registration, Investigated With a Novel 3-Dimensional Deformable Dosimeter Q10 Titania Juang, BS,* ,y Shiva Das, PhD, y John Adamovics, PhD, z Ron Benning, z and Mark Oldham, PhD y Q1 *Medical Physics Graduate Program and y Department of Radiation Oncology Physics, Duke University Medical Center, Durham, North Carolina; and z Department of Chemistry and Biology, Rider University, Lawrenceville, New Jersey Q2 Received Dec 3, 2012, and in revised form May 15, 2013. Accepted for publication May 27, 2013 Summary Accurate deformable image registration (DIR) is essential to achieving full potential for adaptive radiation therapy and treatment response assessment. The lack of comprehensive methods for verifying DIR algorithms is currently limiting clinical implementation. This study introduces a novel deform- able 3D dosimetry system (Presage-Def/Optical-CT) and its application to the verification of a commercial DIR algorithm. Results demonstrate substantial errors may occur and high- light the critical need for DIR validation before clinical implementation. Purpose: To Q3 introduce and evaluate a novel deformable 3-dimensional (3D) dosimetry system (Presage-Def/Optical-CT) and its application toward investigating the accuracy of dose defor- mation in a commercial deformable image registration (DIR) package. Methods and Materials: Presage-Def is a new dosimetry material consisting of an elastic poly- urethane matrix doped with radiochromic leuco dye. Radiologic and mechanical properties were characterized using standard techniques. Dose-tracking feasibility was evaluated by comparing dose distributions between dosimeters irradiated with and without 27% lateral compression. A checkerboard plan of 5-mm square fields enabled precise measurement of true deformation using 3D dosimetry. Predicted deformation was determined from a commercial DIR algorithm. Results: Presage-Def exhibited a linear dose response with sensitivity of 0.0032 DOD/(Gy∙cm). Mass density is 1.02 g/cm 3 , and effective atomic number is within 1.5% of water over a broad (0.03-10 MeV) energy range, indicating good water-equivalence. Elastic characteristics were close to that of liver tissue, with Young’s modulus of 13.5-887 kPa over a stress range of 0.233-303 kPa, and Poisson’s ratio of 0.475 (SE, 0.036). The Presage-Def/Optical-CT system successfully imaged the nondeformed and deformed dose distributions, with isotropic resolution of 1 mm. Comparison with the predicted deformed 3D dose distribution identified inaccuracies in the commercial DIR algorithm. Although external contours were accurately deformed (submillimeter accuracy), volumetric dose deformation was poor. Checkerboard field posi- tioning and dimension errors of up to 9 and 14 mm, respectively, were identified, and the 3D DIR-deformed dose g passing rate was only g 3%/3 mm Z 60.0%. Conclusions: The Presage-Def/Optical-CT system shows strong potential for comprehensive investigation of DIR algorithm accuracy. Substantial errors in a commercial DIR were found in the conditions evaluated. This work highlights the critical importance of careful validation of DIR algorithms before clinical implementation. Ó 2013 Elsevier Inc. Reprint requests to: Mark Oldham, PhD, Duke University Medical Center, Room 04216 Red Zone, Duke Clinics, Durham, NC 27710. Tel: (919) 668-0349; E-mail: mark.oldham@duke.edu This work was supported by National Institutes of Health Grant R01CA100835. J.A. is president of Heuris Inc, which commercializes Presage. Conflict of interest: none. AcknowledgmentdThe authors thank Patrick McGuire of the Duke University Mechanical Engineering and Materials Science Department for his help with tensile measurements. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 FLA 5.2.0 DTD  ROB21611_proof  26 June 2013  12:54 pm  ce Int J Radiation Oncol Biol Phys, Vol. -, No. -, pp. 1e8, 2013 0360-3016/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.ijrobp.2013.05.045 Radiation Oncology International Journal of biology physics www.redjournal.org g s s g m