A Smart Setup for Craniospinal Irradiation

Peterson, Jennifer L.,Vallow, Laura A.,Kim, Siyong,Casale, Henry E.,Tzou, Katherine S. Korean Society of Medical Physics 2013 의학물리 Vol.24 No.4

Our purpose is to present a novel technique for delivering craniospinal irradiation in the supine position using a perfect match, field-in-field (FIF) intrafractional feathering, and simple forward-optimization technique. To achieve this purpose, computed tomography simulation was performed with patients in the supine position. Half-beam, blocked, opposed, lateral, cranial fields with a collimator rotation were matched to the divergence of the superior border of an upper-spinal field. Fixed field parameters were used, and the isocenter of the upper-spinal field was placed at the same source-to-axis distance (SAD), 20 cm inferior to the cranial isocenter. For a lower-spinal field, the isocenter was placed 40 cm inferior to the cranial isocenter at a constant SAD. Both gantry and couch rotations for the lower-spinal field were used to achieve perfect divergence match with the inferior border of the upper-spinal field. A FIF technique was used to feather the craniospinal and spinal-spinal junction daily by varying the match line over 2 cm. The dose throughout the target volume was modulated using the FIF simple forward optimization technique to obtain homogenous coverage. Daily, image-guided therapy was used to assure and verify the setup. This supine-position, perfect match craniospinal irradiation technique with FIF intrafractional feathering and dose modulation provides a simple and safe way to deliver treatment while minimizing dose inhomogeneity.

A Smart Setup for Craniospinal Irradiation

Jennifer L. Peterson,Laura A. Vallow,Siyong Kim,Henry E. Casale,Katherine S. Tzou 한국의학물리학회 2013 의학물리 Vol.24 No.4

To present a novel technique for delivering craniospinal irradiation in the supine position using a perfect match,field-in-field (FIF) intrafractional feathering, and simple forward-optimization technique. Computed tomographysimulation was performed with patients in the supine position. Half-beam, blocked, opposed, lateral, cranialfields with a collimator rotation were matched to the divergence of the superior border of an upper-spinal field. Fixed field parameters were used, and the isocenter of the upper-spinal field was placed at the samesource-to-axis distance (SAD), 20 cm inferior to the cranial isocenter. For a lower-spinal field, the isocenterwas placed 40 cm inferior to the cranial isocenter at a constant SAD. Both gantry and couch rotations for thelower-spinal field were used to achieve perfect divergence match with the inferior border of the upper-spinalfield. A FIF technique was used to feather the craniospinal and spinal-spinal junction daily by varying the matchline over 2 cm. The dose throughout the target volume was modulated using the FIF simple forward optimizationtechnique to obtain homogenous coverage. Daily, image-guided therapy was used to assure and verify the setup. Our supine-position, perfect match craniospinal irradiation technique with FIF intrafractional feathering and dosemodulation provided a simple and safe way to deliver treatment while minimizing dose inhomogeneity.

Use of Flattening Filter Free Photon Beams for Off-axis Targets in Conformal Arc Stereotactic Body Radiation Therapy

Smith, Ashley,Kim, Siyong,Serago, Christopher,Hintenlang, Kathleen,Ko, Stephen,Vallow, Laura,Peterson, Jennifer,Hintenlang, David,Heckman, Michael,Buskirk, Steven Korean Society of Medical Physics 2014 의학물리 Vol.25 No.4

Dynamic conformal arc therapy (DCAT) and flattening-filter-free (FFF) beams are commonly adopted for efficient conformal dose delivery in stereotactic body radiation therapy (SBRT). Off-axis geometry (OAG) may be necessary to obtain full gantry rotation without collision, which has been shown to be beneficial for peripheral targets using flattened beams. In this study dose distributions in OAG using FFF were evaluated and the effect of mechanical rotation induced uncertainty was investigated. For the lateral target, OAG evaluation, sphere targets (2, 4, and 6 cm diameter) were placed at three locations (central axis, 3 cm off-axis, and 6 cm off-axis) in a representative patient CT set. For each target, DCAT plans under the same objective were obtained for 6X, 6FFF, 10X, and 10FFF. The parameters used to evaluate the quality of the plans were homogeneity index (HI), conformality indices (CI), and beam on time (BOT). Next, the mechanical rotation induced uncertainty was evaluated using five SBRT patient plans that were randomly selected from a group of patients with laterally located tumors. For each of the five cases, a plan was generated using OAG and CAG with the same prescription and coverage. Each was replanned to account for one degree collimator/couch rotation errors during delivery. Prescription isodose coverage, CI, and lung dose were evaluated. HI and CI values for the lateral target, OAG evaluation were similar for flattened and unflattened beams; however, 6FFF provided slightly better values than 10FFF in OAG. For all plans the HI and CI were acceptable with the maximum difference between flattened and unflattend beams being 0.1. FFF beams showed better conformality than flattened beams for low doses and small targets. Variation due to rotational error for isodose coverage, CI, and lung dose was generally smaller for CAG compared to OAG, with some of these comparisons reaching statistical significance. However, the variations in dose distributions for either treatment technique were small and may not be clinically significant. FFF beams showed acceptable dose distributions in OAG. Although 10FFF provides more dramatic BOT reduction, it generally provides less favorable dosimetric indices compared to 6FFF in OAG. Mechanical uncertainty in collimator and couch rotation had an increased effect for OAG compared to CAG; however, the variations in dose distributions for either treatment technique were minimal.

Use of Flattening Filter Free Photon Beams for Off-axis Targets in Conformal Arc Stereotactic Body Radiation Therapy

Ashley Smith,Siyong Kim,Kathleen Hintenlang,Stephen Ko,Laura Vallow,Jennifer Peterson,David Hintenlang,Michael Heckman,Steven Buskirk 한국의학물리학회 2014 의학물리 Vol.25 No.4

Dynamic conformal arc therapy (DCAT) and flattening-filter-free (FFF) beams are commonly adopted for efficientconformal dose delivery in stereotactic body radiation therapy (SBRT). Off-axis geometry (OAG) may benecessary to obtain full gantry rotation without collision, which has been shown to be beneficial for peripheraltargets using flattened beams. In this study dose distributions in OAG using FFF were evaluated and the effectof mechanical rotation induced uncertainty was investigated. For the lateral target, OAG evaluation, sphere targets(2, 4, and 6 cm diameter) were placed at three locations (central axis, 3 cm off-axis, and 6 cm off-axis) ina representative patient CT set. For each target, DCAT plans under the same objective were obtained for 6X,6FFF, 10X, and 10FFF. The parameters used to evaluate the quality of the plans were homogeneity index (HI),conformality indices (CI), and beam on time (BOT). Next, the mechanical rotation induced uncertainty wasevaluated using five SBRT patient plans that were randomly selected from a group of patients with laterally locatedtumors. For each of the five cases, a plan was generated using OAG and CAG with the same prescription andcoverage. Each was replanned to account for one degree collimator/couch rotation errors during delivery. Prescription isodose coverage, CI, and lung dose were evaluated. HI and CI values for the lateral target, OAGevaluation were similar for flattened and unflattened beams; however, 6FFF provided slightly better values than10FFF in OAG. For all plans the HI and CI were acceptable with the maximum difference between flattened andunflattend beams being 0.1. FFF beams showed better conformality than flattened beams for low doses andsmall targets. Variation due to rotational error for isodose coverage, CI, and lung dose was generally smallerfor CAG compared to OAG, with some of these comparisons reaching statistical significance. However, thevariations in dose distributions for either treatment technique were small and may not be clinically significant. FFF beams showed acceptable dose distributions in OAG. Although 10FFF provides more dramatic BOTreduction, it generally provides less favorable dosimetric indices compared to 6FFF in OAG. Mechanicaluncertainty in collimator and couch rotation had an increased effect for OAG compared to CAG; however, thevariations in dose distributions for either treatment technique were minimal.