Clinical Investigation: Gastrointestinal Cancer Adaptive Liver Stereotactic Body Radiation Therapy: Automated Daily Plan Reoptimization Prevents Dose Delivery Degradation Caused by Anatomy Deformations Suzanne M. Leinders, MSc,* ,y Sebastiaan Breedveld, MSc,* Alejandra Me ´ndez Romero, MD, PhD,* Dennis Schaart, PhD, y Yvette Seppenwoolde, PhD,* and Ben J.M. Heijmen, PhD* *Erasmus Medical Center-Daniel den Hoed Cancer Center, Rotterdam, The Netherlands, and y Delft University of Technology, Delft, The Netherlands Received May 6, 2013, and in revised form Aug 1, 2013. Accepted for publication Aug 6, 2013 Summary Dose distributions for liver stereotactic body radiation therapy can be improved with daily reoptimization of the treatment plan to account for anatomy deformations. With adaptive strategies, violation of organs at risk could often be avoided. For patients with restricted tumor dose in the planning phase, fraction doses could be increased due to more favorable anatomy throughout the treatment. This study demonstrated that replanning based on daily computed tomography scans can improve liver stereo- tactic body radiation therapy dose delivery. Purpose: To investigate how dose distributions for liver stereotactic body radiation therapy (SBRT) can be improved by using automated, daily plan reoptimization to account for anatomy deformations, compared with setup corrections only. Methods and Materials: For 12 tumors, 3 strategies for dose delivery were simulated. In the ﬁrst strategy, computed tomography scans made before each treatment fraction were used only for patient repositioning before dose delivery for correction of detected tumor setup errors. In adaptive second and third strategies, in addition to the isocenter shift, intensity modulated radiation therapy beam proﬁles were reoptimized or both intensity proﬁles and beam orientations were reoptimized, respectively. All optimizations were performed with a recently published algorithm for automated, multicriteria optimization of both beam proﬁles and beam angles. Results: In 6 of 12 cases, violations of organs at risk (ie, heart, stomach, kidney) constraints of 1 to 6 Gy in single fractions occurred in cases of tumor repositioning only. By using the adaptive strategies, these could be avoided (<1 Gy). For 1 case, this needed adaptation by slightly underdosing the planning target volume. For 2 cases with restricted tumor dose in the planning phase to avoid organ-at-risk constraint violations, fraction doses could be increased by 1 and 2 Gy because of more favorable anatomy. Daily reoptimization of both beam proﬁles and beam angles (third strategy) performed slightly better than reoptimization of proﬁles only, but the latter required only a few minutes of computation time, whereas full reoptimization took several hours. Conclusions: This simulation study demonstrated that replanning based on daily acquired computed tomography scans can improve liver stereotactic body radiation therapy dose delivery. Ó 2013 Elsevier Inc. Reprint requests to: Yvette Seppenwoolde, PhD, Division of Medical Physics, Department of Radiation Oncology, ErasmusMC/Daniel den Hoed Cancer Center, Groene Hilledijk 301, 3075 EA Rotterdam, The Netherlands. Tel: (31) 10-7041131; E-mail: y.seppenwoolde@erasmusmc.nl Conﬂicts of interest: none. AcknowledgmentsdWe thank Eliana Vasquez-Osorio, Luiza Bondar, and Mischa Hoogeman for useful discussions. Int J Radiation Oncol Biol Phys, Vol. 87, No. 5, pp. 1016e1021, 2013 0360-3016/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.ijrobp.2013.08.009 Radiation Oncology International Journal of biology physics www.redjournal.org