Abstract
PurposeTo investigate repositioning accuracy in particle radiotherapy in 6 degrees of freedom (DOF) and intensity-modulated radiotherapy (IMRT, 3 DOF) for two immobilization devices (Scotchcast masks vs thermoplastic head masks) currently in use at our institution for fractionated radiation therapy in head and neck cancer patients.Methods and materialsPosition verifications in patients treated with carbon ion therapy and IMRT for head and neck malignancies were evaluated. Most patients received combined treatment regimen (IMRT plus carbon ion boost), immobilization was achieved with either Scotchcast or thermoplastic head masks. Position corrections in robotic-based carbon ion therapy allowing 6 DOF were compared to IMRT allowing corrections in 3 DOF for two standard immobilization devices. In total, 838 set-up controls of 38 patients were analyzed.ResultsRobotic-based position correction including correction of rotations was well tolerated and without discomfort. Standard deviations of translational components were between 0.5 and 0.8 mm for Scotchcast and 0.7 and 1.3 mm for thermoplastic masks in 6 DOF and 1.2 - 1.4 mm and 1.0 - 1.1 mm in 3 DOF respectively. Mean overall displacement vectors were between 2.1 mm (Scotchcast) and 2.9 mm (thermoplastic masks) in 6 DOF and 3.9 - 3.0 mm in 3 DOF respectively. Displacement vectors were lower when correction in 6 DOF was allowed as opposed to 3 DOF only, which was maintained at the traditional action level of > 3 mm for position correction in the pre-on-board imaging era.ConclusionSetup accuracy for both systems was within the expected range. Smaller shifts were required when 6 DOF were available for correction as opposed to 3 DOF. Where highest possible positioning accuracy is required, frequent image guidance is mandatory to achieve best possible plan delivery and maintenance of sharp gradients and optimal normal tissue sparing inherent in carbon ion therapy.
Highlights
High-precision radiotherapy has raised the interest in positioning systems allowing patient positioning in more than three degrees of freedom (3DOF)
Displacement vectors were lower when correction in 6 degrees of freedom (6 DOF) was allowed as opposed to 3 degrees of freedom (3 DOF) only, which was maintained at the traditional action level of > 3 mm for position correction in the pre-on-board imaging era
Smaller shifts were required when 6 DOF were available for correction as opposed to 3 DOF
Summary
High-precision radiotherapy has raised the interest in positioning systems allowing patient positioning in more than three degrees of freedom (3DOF). Image guidance and subsequent position correction in 6 DOF promise further optimization of patient positioning as opposed to 3 DOF. Various immobilization devices for fractionated radiotherapy have been tested with regard to their repositioning accuracy. Mouthpiece- or bite-platebased masks yield precisions of 0.5 - 1 mm [5,6] Albeit highly precise, these masks are less feasible for patients with head and neck malignancies faced with the often times poor dental status and increasing discomfort caused by radiation-induced mucositis. Results of Zeidan et al [20] could demonstrate residual setup errors in fractionated RT to decrease as frequencies of image guidance increases. As a consequence especially for techniques mandating the highest possible level of positioning accuracy such as particle therapy, frequent image guidance is compulsory
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
