Passively Scattered Proton Stereotactic Body Radiation Therapy for Spine Metastasis: A Dosimetric Analysis

Abstract

calibrations were constructed for all the tube voltages. All HU images and direct ED images were imported into a treatment planning system, where all HU images were assigned the corresponding CT calibration curves while all direct ED images were assigned a linear CT calibration curve. A cylindrical planning target volume of 5 cm in diameter was planned to receive full prescription dose from 9 coplanar beams on all images. Gamma analysis was performed to demonstrate dosimetric change quantitatively. Results: The deviation of ED obtained from the direct ED images was -0.4%AE1.7% from the true values for all inserts, slightly better than that from the HU images, which was determined to be -0.7%AE1.8%. Gamma analysis on intercomparison between the direct ED images and the HU images acquired at the same tube voltage indicated negligible difference with lowest passing rate at 99.9%. Gamma analysis on cross-comparison among the direct ED images acquired at various voltages indicated negligible inherent variation with lowest passing rate at 99.1%, slightly better than the lowest passing rate of 99.0% scored on cross-comparison among the HU images acquired at various tube voltages. Conclusion: Direct ED images require no CT calibration while showing equivalent dosimetry, regardless of tube voltages, compared to that obtained from standard HU images. The ability of acquiring direct ED images simplifies the current practice at a safer level by eliminating CT calibration and HU conversion from commissioning and treatment planning, respectively. Furthermore, it unlocks a wider range of tube voltages in CT scanner for better imaging quality while maintaining similar dosimetric accuracy.Purpose/Objective(s): Traditional radiation therapy inverse planning relies on the weighting factors to subjectively balance the conflicting criteria for different structures. The resulting manual trial-and-error determination of the weighting factors has long been recognized as the most timeconsuming part of treatment planning. The purpose of this work is to develop a novel inverse planning framework that parameterizes the dosimetric tradeoff among the structures with physically more meaningful quantities to simplify the search for a clinically sensible plan.Materials/Methods: A permissible dosimetric uncertainty is introduced for each of the structures to balance their conflicting dosimetric requirements. For simplicity, the uncertainty of a structure is extracted from a library of previous cases that possess similar anatomy and prescription. The inverse planning is then formulated into a convex feasibility problem with the goal of generating plans with acceptable dosimetric uncertainties. A sequential procedure (SP) is derived to simultaneously tune and solve the model. In SP, the feasibility problem is reduced to 3 submodels to contain the uncertainty in the planning target volume (PTV), the critical structures, and all other structures to spare, respectively. The proposed technique is applied to plan a liver case and a head-and-neck case in...

Is proton beam therapy ready for single fraction spine SBRS? – a feasibility study to use spot-scanning proton arc (SPArc) therapy to improve the robustness and dosimetric plan quality

“…Additionally, compared to the photon treatment, IMPT alone cannot provide high dose conformity and sharp dose fall-off, which is critical to SBRS/ SBRT due to the large lateral penumbra from each individual proton spot [12][13][14]. As a result, only passive-scattering proton beam therapy using a collimator system was occasionally used in spine SBRT proton treatment cases through five or more fractions instead of a newer technique, PBS [15,16].…”

Hybrid Therapy for Metastatic Disease

“…14 Using this treatment methodology, large centers have reported local control rates of up to 96%, regardless of primary tumor radiosensitivity. 13,24 Proton-based therapies are less commonly described in the literature 31 as the technology is much newer and is less widely available. Potential advantages of proton beam therapy are higher biological effectiveness and lower whole-body radiation doses, however these advantages have yet to be established.…”

“…Proton-based therapies are less commonly described in the literature31 as the technology is much newer and is less widely available. Potential advantages of proton beam therapy are higher biological effectiveness and lower whole-body radiation doses, however these advantages have yet to be established.…”