To frame or not to frame? Cone‐beam CT‐based analysis of head immobilization devices specific to linac‐based stereotactic radiosurgery and radiotherapy

PurposeIn stereotactic radiosurgery (SRS) with single‐isocentric treatments for brain metastases, rotational setup errors may cause considerable dosimetric effects. We assessed the dosimetric effects on HyperArc plans for single and multiple metastases.MethodsFor 29 patients (1–8 brain metastases), HyperArc plans with a prescription dose of 20–24 Gy for a dose that covers 95% (D95%) of the planning target volume (PTV) were retrospectively generated (Ref‐plan). Subsequently, the computed tomography (CT) used for the Ref‐plan and cone‐beam CT acquired during treatments (Rot‐CT) were registered. The HyperArc plans involving rotational setup errors (Rot‐plan) were generated by re‐calculating doses based on the Rot‐CT. The dosimetric parameters between the two plans were compared.ResultsThe dosimetric parameters [D99%, D95%, D1%, homogeneity index, and conformity index (CI)] for the single‐metastasis cases were comparable (P > 0.05), whereas the D95% for each PTV of the Rot‐plan decreased 10.8% on average, and the CI of the Rot‐plan was also significantly lower than that of the Ref‐plan (Ref‐plan vs Rot‐plan, 0.93 ± 0.02 vs 0.75 ± 0.14, P < 0.01) for the multiple‐metastases cases. In addition, for the multiple‐metastases cases, the Rot‐plan resulted in significantly higher V10Gy (P = 0.01), V12Gy (P = 0.02), V14Gy (P = 0.02), and V16Gy (P < 0.01) than those in the Ref‐plan.ConclusionThe rotational setup errors for multiple brain metastases cases caused non‐negligible underdosage for PTV and significant increases of V10Gy to V16Gy in SRS with HyperArc.

Section: Discussionmentioning

confidence: 99%

Dosimetric effect of rotational setup errors in stereotactic radiosurgery with HyperArc for single and multiple brain metastases

Sagawa

Ohira

Ueda

et al. 2019

“…[2][3][4][5][6][7] Non-invasive options use one of or a combination of thermoplastic masks, bite blocks, cradles, and optical surface tracking imaging systems to localize and immobilize the brain. 8 In this study, we compared two commercially available devices used in our clinic: Aktina PinPoint™ (non-invasive) 8 and TALON Cranial SRS frame (invasive). 9 Both intra-fraction and inter-fraction setup errors were evaluated.…”

Section: Discussionmentioning

confidence: 99%

“…Thus no treatment margin beyond the treated target is needed . Non‐invasive options use one of or a combination of thermoplastic masks, bite blocks, cradles, and optical surface tracking imaging systems to localize and immobilize the brain . While the invasive devices can often offer sub‐millimeter positional accuracy, the invasive nature limits their acceptance by patients and deters fractionated treatments.…”

Section: Introductionmentioning

confidence: 99%

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Residual setup errors in cranial stereotactic radiosurgery without six degree of freedom robotic couch: Frameless versus rigid immobilization systems

Liu

Yang

Neylon

et al. 2020

Purpose and Objectives This IRB‐approved study was to compare the residual inter‐fractional setup errors and intra‐fractional motion of patients treated with cranial stereotactic radiosurgery without a 6 degree of freedom (DoF) couch. We evaluated both frameless non‐invasive vacuum‐suction immobilization (Aktina PinPoint) and TALON rigid screw immobilization. Materials and Methods Twenty consecutive patients treated by Varian TrueBeam STX or Tomotherapy were selected for data collection. The dose and number of fractions received by each patient ranged from 18 Gy in 1 fraction (SRS) to 25 Gy in 5 fractions (SRT). Twelve patients were immobilized using PinPoint, a frameless suction system (Aktina Medical, New York) and eight patients were immobilized using the TALON rigid screw system. Customized head cushions were used for all patients. Six Atkina patients received pre‐ and post‐treatment cone‐beam CT (CBCT) to evaluate the intra‐fractional motion of the Aktina system. The intra‐fractional motion with the TALON rigid screw system has been reported to be negligible and was not repeated in this study. All patients received pre‐treatment CBCT or megavoltage CT (MVCT) to assess inter‐fractional setup accuracy. Shifts to the final treatment position were determined based on matching bony anatomy in the pre‐treatment setup CT and the planning CT. Setup CT and planning CT were registered retrospectively based on bony anatomy using image registration software to quantify rotational and translational errors. Results For the frameless Aktina system, mean and standard deviation of the intra‐fractional motion were −0.5 ± 0.7 mm (lateral), 0.1 ± 0.9 mm (vertical), −0.5 ± 0.6 mm (longitudinal), −0.04 ± 0.18°(pitch), −0.1 ± 0.23°(yaw), and −0.03 ± 0.17°(roll) indicating negligible intra‐fractional motion. Inter‐fractional rotation errors were −0.10 ± 0.25° (pitch), −0.08 ± 0.16° (yaw), and −0.20 ± 0.41° (roll) for TALON rigid screw immobilization versus 0.20 ± 0.69° (pitch), 0.34 ± 0.56° (yaw), 0.35 ± 0.82° (roll) for frameless vacuum‐suction immobilization showing that the rigid immobilization setup is more reproducible than the frameless immobilization. Without rotational correction by a 6 DoF couch, residual registration error exists and increases with distance from the image fusion center. In a 3D vector space, a tumor located 5 cm from the center of image fusion would require a 0.9 mm margin with the TALON system and a 2.1 mm margin with Aktina. Conclusions With image‐guided radiotherapy, translational setup errors can be corrected by image registration between pre‐treatment setup CT and planning CT. However, rotational errors cannot be accounted for without a 6 DoF couch. Our study showed that the frameless Aktina immobilization system provided negligible intra‐fractional motion. The inter‐fractional rotation setup error using Aktina was larger than rigid immobilization with the TALON system. To treat a single lesion far from the center of image registration or for multiple lesions in a single plan, additional mar...

“…The frameless technique typically involves 1-3 mm planning target volume (PTV) margin. [11][12][13] In particular, rotational errors for targets at distances away from the isocenter would negatively affect the treatment delivery accuracy unless an additional margin is added due to the less effective immobilization and setup with a nonrigid mask system. [14][15][16] Also, accurately positioning the patient for treatment setup for all treatment couch angles becomes the challenge for this approach since multiple targets are treated with one isocenter.…”

mentioning

confidence: 99%

Frame‐based radiosurgery of multiple metastases using single‐isocenter volumetric modulated arc therapy technique

Ahn

Yenice

Koshy

et al. 2019

Single-isocenter volumetric modulated arc therapy (VMAT) technique can provide stereotactic radiosurgery (SRS) treatment with improved delivery efficiency for treating multiple metastases. Nevertheless, planning is time consuming and verification of frame-based SRS setup, especially at noncoplanar angles, can be challenging. We report on a single-isocenter VMAT technique with a special focus on improving treatment workflow and delivery verification to exploit the minimized patient motion of the frame-based SRS. We developed protocols for preplanning and verification for VMAT and evaluated them for ten patient cases. Preplans based on MRI were used to generate comparable treatment plans using CT taken on the day of treatment after frame placement. Target positioning accuracy was evaluated by stereoscopic in-room kV imaging. Dosimetric accuracy of the noncoplanar plan delivery was validated using measurement-guided 3D dose reconstruction as well as film-based end-to-end test with a Rando phantom. Average absolute differences of homogeneity indices, conformity indices, and V12Gy between MR preplans and CT-based plans were within 5%. In-room imaging positioning accuracy of 0.4 mm was verified to be independent of the distance to the isocenter. For treatment verification, average local and global passing rates of the 3D gamma (1 mm, 3%) were 86% and 99%, respectively. D99 values were matched within 5% for individual target structures (>0.5 cc). Additional film analysis confirmed dosimetric accuracy for small targets that had large verification errors in the 3D dose reconstruction. Our results suggest that the advantages of frame-based SRS and noncoplanar single-isocenter VMAT technique can be combined for efficient and accurate treatment of patients with multiple metastases. K E Y W O R D S frame-based SRS, multiple metastases, single-isocenter volumetric modulated arc therapy, VMAT SRS 1 | INTRODUCTION Brain metastases are the most common intracranial neoplasms that require precise treatment modalities to achieve high local control. Previous clinical studies validated the effectiveness of stereotactic radiosurgery (SRS) in the treatment of brain metastases and showed that various commercially mature solutions could deliver cranial SRS with a high level of geometrical and dosimetric