Comparison of Intrafractional Motion in Head and Neck Cancer Between Two Immobilization Methods During Stereotactic Ablative Radiation Therapy by CyberKnife

Abstract

Purpose: Maintaining immobilization to minimize spine motion is very important during salvage stereotactic ablative radiation therapy (SABR) for recurrent head and neck cancer. This study aimed to compare the intrafractional motion between two immobilization methods. Patients and Methods: With a spine tracking system for image guiding, 9094 records from 41 patients receiving SABR by CyberKnife were obtained for retrospective comparison. Twenty-one patients were immobilized with a thermoplastic mask and headrest (Group A), and another 20 patients used a thermoplastic mask and headrest together with a vacuum bag to support the head and neck area (Group B). The intrafractional motion in the X (superiorinferior), Y (right-left), Z (anterior-posterior) axes, 3D (three-dimensional) vector, Roll, Pitch and Yaw in the two groups was compared. The margins of the planning target volume (PTV) to cover 95% intrafractional motion were evaluated. Results: The translational movements in the X-axis, Y-axis, and 3D vector in Group A were significantly smaller than in Group B. The rotational errors in the Roll and Yaw in Group A were also significantly smaller than those in Group B; conversely, those in the Pitch in Group A were larger. To cover 95% intrafractional motion, margins of 0.96, 1.55, and 1.51 mm in the X, Y and Z axes, respectively were needed in Group A, and 1.06, 2.86, and 1.34 mm, respectively were required in Group B. Conclusion:The immobilization method of thermoplastic mask and head rest with vacuum bag did not provide better immobilization than that without vacuum bag in most axes. The clinical use of 2 mm as a margin of PTV to cover 95% intrafractional motion was adequate in Group A but not in Group B.

Clinical value of styrofoam fixation in intracranial tumor radiotherapy

“…Kang CL et al. ( 19 ) also found that intra-fraction motion increases with increasing treatment duration, especially in the x-axis direction. Also, Kang CL et al.…”

A retrospective study on the investigation of potential dosimetric benefits of online adaptive proton therapy for head and neck cancer

“…Firstly, an investigation on the intra-fractional motion of HN cancer patients with the aid of an immobilization device (e.g., Orfit 5-point mask with shoulder extension and headrest cushion) reported a motion range of within 1 mm translation and 0.7 • rotation. 25 Secondly, an assessment study on the spot position uncertainty of scanning proton pencil beam reported an uncertainty range of within 1 mm for the maximum day-to-day variance for any given spot positions. 26 After simulating the CBCT-guided online APT for every treatment fraction by conducting the steps 3−10 of the proposed workflow,deformable image registration was performed to deform the corrected CBCT images to the planning CT images to accumulate the actual dose of the in-use plan (i.e., either the nominal plan if online adaptation was not triggered yet or the latest new plan) over the entire treatment course.…”

“…Using a smaller setup margin for online adaptation was also suggested in multiple other studies on adaptive radiotherapy 37,38 A recent review paper by Huiskes et al on adaptive proton therapy in HN cancer noted that the majority of online adaption studies did not use any setup margin. 39 We would like to mention that our determina-tion of the 1.5 mm margin size was based on a study on intra-fractional motion of HN cancer patients 25 and a study on spot positioning uncertainty. 26 The optimal margin size for each individual patient needs further investigation in the future with the technology of online APT being in place.…”

Hypofractionation and SABR: 25 years of evolution in medical physics and a glimpse of the future

“…After the introduction of 4DCT and the definition of ITV, the PTV is created with a smaller margin (5 mm) when expanded from the ITV, thus allowing more normal tissue sparing 32 . Nowadays, with advanced immobilization and IGRT techniques, we can confidently reduce the target within a couple of millimeters in the extra‐cranial disease sites such as head neck and spine 33,34 . Such margin reduction, coupled with the advancement in treatment planning optimization and dose calculation algorithm, provides our community a high conformal treatment plan quality and a precise dose deposition.…”

“…32 Nowadays, with advanced immobilization and IGRT techniques, we can confidently reduce the target within a couple of millimeters in the extra-cranial disease sites such as head neck and spine. 33,34 Such margin reduction, coupled with the advancement in treatment planning optimization and dose calculation algorithm, provides our community a high conformal treatment plan quality and a precise dose deposition. With the introduction of multi-leaf collimators in the late 1990s, 35 we are moving from 2D dose calculation by hand [36][37][38] to 3D conformal dose calculation, 39 and now to inverse optimization approach, [40][41][42] offering a superior dosimetric sparing for healthy tissues via the modulation of the fluence map, i.e.…”