A single-gradient junction technique to replace multiple-junction shifts for craniospinal irradiation treatment Austin Hadley, B.A., and George X. Ding, Ph.D. Department of Radiation Oncology, Vanderbilt University School of Medicine, Nashville, TN ARTICLE INFO Article history: Received 21 January 2014 Received in revised form 21 April 2014 Accepted 6 May 2014 Keywords: Craniospinal irradiation Field junctions Gradient-dose junction IMRT ABSTRACT Craniospinal irradiation (CSI) requires abutting fields at the cervical spine. Junction shifts are conven- tionally used to prevent setup error–induced overdosage/underdosage from occurring at the same location. This study compared the dosimetric differences at the cranial-spinal junction between a single- gradient junction technique and conventional multiple-junction shifts and evaluated the effect of setup errors on the dose distributions between both techniques for a treatment course and single fraction. Conventionally, 2 lateral brain fields and a posterior spine field(s) are used for CSI with weekly 1-cm junction shifts. We retrospectively replanned 4 CSI patients using a single-gradient junction between the lateral brain fields and the posterior spine field. The fields were extended to allow a minimum 3-cm field overlap. The dose gradient at the junction was achieved using dose painting and intensity-modulated radiation therapy planning. The effect of positioning setup errors on the dose distributions for both techniques was simulated by applying shifts of  3 and 5 mm. The resulting cervical spine doses across the field junction for both techniques were calculated and compared. Dose profiles were obtained for both a single fraction and entire treatment course to include the effects of the conventional weekly junction shifts. Compared with the conventional technique, the gradient-dose technique resulted in higher dose uniformity and conformity to the target volumes, lower organ at risk (OAR) mean and maximum doses, and diminished hot spots from systematic positioning errors over the course of treatment. Single-fraction hot and cold spots were improved for the gradient-dose technique. The single- gradient junction technique provides improved conformity, dose uniformity, diminished hot spots, lower OAR mean and maximum dose, and one plan for the entire treatment course, which reduces the potential human error associated with conventional 4-shifted plans. & 2014 American Association of Medical Dosimetrists. Introduction Irradiation of the craniospinal axis is used in the therapeutic treatment of medulloblastoma and other brain tumors with possible meningeal spread. Owing to the length of the craniospinal axis, multiple radiation fields with distinct isocenters are required to cover the planned target volume (PTV). Field junctions in the neck (craniospinal junction) and possibly a spinal-spinal junction are required, depending on the length of the craniospinal axis. Achieving uniform dose at field junctions is a unique challenge in craniospinal irradiation (CSI). The large dose falloff at these field junctions creates potentially large overdosage or underdosage if the fields are not correctly matched during treatment. Conventional CSI treatment involves weekly junction shifts to “feather” the beam 1-4 to avoid overdosage/underdosage at the junctions. Alternative methods have been suggested to reduce these potential junction dose errors using more modern techniques. South et al. 5 presented a field-in-field technique that uses intra- fraction feathering using a multileaf collimator (MLC). Kusters et al. 6 and others have presented multifield intensity-modulated radiation therapy (IMRT) methods. 7,8 Lee et al. 9 used multiple isocentric volumetric-modulated arc therapy (VMAT), whereas Bedford et al. 10 proposed a helical VMAT technique. The advantages of proton therapy in CSI have been presented by St. Clair et al. 11 Helical tomotherapy has also been explored for CSI treatment. 12 Although each method provides unique advantages over the conventional treatment, each introduces other disadvantages. Intrafraction shifts reduce the magnitude of dose overlap or underlap because of setup journal homepage: www.meddos.org Medical Dosimetry http://dx.doi.org/10.1016/j.meddos.2014.05.004 0958-3947/Copyright Ó 2014 American Association of Medical Dosimetrists Reprint requests to: George Ding, Ph.D., Department of Radiation Oncology, Vanderbilt University School of Medicine, 2220 Pierce Ave, Preston Research Building, Basement Room B-1003, Nashville, TN 37232-5671. E-mail: george.ding@vanderbilt.edu Medical Dosimetry ] (2014) ]]]–]]]