Migration from full-head mask to "open-face" mask for immobilization of patients with head and neck cancer

Randomized self-controlled study comparing open-face vs. closed immobilization masks in fractionated cranial radiotherapy

PURPOSE

To compare patient discomfort and immobilisation performance of open-face and closed immobilization masks in cranial radiotherapy.

MATERIAL AND METHODS

This was a single-center randomized self-controlled clinical trial. At CT simulation, an open-face and closed mask was made for each patient and treatment plans with identical dose prescription were generated for each mask. Patients were randomised to start treatment with an open-face or closed mask. Masks were switched halfway through the treatment course; every patient was their own control. Patients self-reported discomfort, anxiety and pain using the visual analogue scale (VAS). Inter- and intrafraction set-up variability was measured with planar kV imaging and a surface guided radiotherapy (SGRT) system for the open-face masks.

RESULTS

30 patients with primary or metastatic brain tumors were randomized - 29 completed radiotherapy to a median total dose of 54 Gy (range 30-60 Gy). Mean discomfort VAS score was significantly lower with open-face masks (0.5, standard deviation 1.0) vs. closed masks (3.3, standard deviation 2.9), P < 0.0001. Anxiety and pain VAS scores were significantly lower with open-face masks (P < 0.0001). Closed masks caused more discomfort in infraorbital (P < 0.001) and maxillary (P = 0.02) areas. Two patients and 27 patients preferred closed or open-face masks, respectively. Interfraction longitudinal shifts and roll and yaw rotations were significantly smaller and lateral shifts were significantly larger with closed masks in combination with the laser system (P < 0.05) compared to open masks in combination with a SGRT system. Intrafraction variability did not differ between the masks.

CONCLUSIONS

Open-face masks are associated with decreased patient discomfort without compromising patient positioning and immobilisation accuracy.

Patient Education Materials for Immobilisation Masks in Radiation Therapy for Adult Head and Neck Cancer Patients: A Scoping Review

Immobilisation masks (IMs) are used for people with head and neck cancer (HNC) undergoing radiation therapy (RT) treatment to ensure accuracy and reproducibility between treatments. Claustrophobia-related mask anxiety in HNC patients is common and can compromise treatment due to patient distress. This scoping review aimed to describe the content of publicly available Patient Education Materials (PEMs) for people with HNC undergoing RT. Three search engines (Bing, Yahoo, and Google) were systematically searched using standard terms. PEMs in audio-visual or written formats were eligible for inclusion if the target readership was adults with HNC and included content on IMs for RT. Content was appraised using the Patient Education Materials Assessment Tool for Printable and Audio-Visual Materials to assess understandability and actionability. In total, 304 PEMs were identified of which 20 met the inclusion criteria. Sixteen PEMs were webpages, three were PDF format, and one was a standalone video. The understandability and actionability of PEMs ranged between 47 to 100% and 0 to 80%, respectively. PEMs authored by Foundations/Organisations scored higher in understandability (80-100%) and were more likely to discuss mask anxiety coping strategies. In comparison, News sites and IM manufacturers published PEMs with the lowest understandability scores (20-80%). The significant variations in the quality of IM PEMs identified suggest that some sources may be more effective at informing patients about IMs. Although multiple aspects of the PEMs were consistent across the reviewed materials, many PEMs lacked information, and a stronger focus on understandability and actionability is required.

Setup and intra-fractional motion measurements using surface scanning in head and neck cancer radiotherapy- A feasibility study

Background and purpose

Surface-guided radiotherapy (SGRT) is applied to improve patient set-up and to monitor intra-fraction motion. Head and neck cancer (H&N) patients are usually fixated using 5-point thermoplastic masks, that are experienced as uncomfortable or even stressful. Therefore, the feasibility of irradiating H&N patients without a mask by using SGRT was examined.

Material and methods

Nineteen H&N patients were included in a simulation study. Once a week, before the standard treatment, a maskless treatment was simulated, using SGRT for setup and intrafraction motion monitoring. Initial patient setup accuracy and intrafraction motion was determined using ConeBeam CT (CBCT) images as well as SGRT before and after the (simulated) treatment. The clinical target volume to planning target volume (CTV-PTV) margin for intrafraction motion was calculated. Using patient questionnaires, the patient-friendliness H&N irradiation with and without mask was determined.

Results

Maskless setup with SGRT and CBCT was as accurate as with a mask. SGRT showed that intrafraction motion was gradual during the treatment. The CTV-PTV margin correcting for intrafraction motion was 1.7 mm for maskless treatment without interventions, and 1.2 mm if corrected for motions > 2 mm. For 19 % of fractions, the intrafraction motion, as detected by both SGRT and CBCT, was larger than 2 mm in at least one direction. Sixteen patients preferred maskless treatment, while 3 worried they would move too much.

Conclusions

Using SGRT and a standard head rest resulted in a patient-friendly treatment with accurate patient setup and acceptably small intrafraction motion for H&N patients.

Surface-guided radiotherapy overview: Technical aspects and clinical applications

In radiotherapy, patient positioning has long been ensured by ionizing imaging (kV or MV). Over the past ten years, surface-guided radiotherapy has appeared in radiotherapy departments. It is a continuous three-dimensional acquisition of the surface of the patient, based on the use of several optical cameras. The acquired surface is compared to an expected surface (usually taken from the planning scanner). Operators can constantly appreciate poor position, anatomical deformity or patient shift. Thus, the system allows an aid to the positioning of the patient, possibly without tattooing, but also a follow-up of the patient during the duration of the session. The most obvious contribution of the system concerns the treatment of the breast. In fact, for this location, the bone registration is not ideal and the target is visible in surface-guided radiotherapy. These systems also make it possible to treat in deep inspiration breath hold. But several other locations can benefit from it (pelvis, thorax, etc.).

Evaluation of the accuracy of a six-degree-of-freedom robotic couch using optical surface and cone beam CT images of an SRS QA phantom

Purpose:

To assess the accuracy of the Varian PerfectPitch six-degree-of-freedom (6DOF) robotic couch by using a Varian SRS QA phantom.

Methods:

The stereotactic radiosurgery (SRS) phantom has five tungsten carbide BBs each with 7·5 mm in diameter arranged with the known geometry. Optical surface images and cone beam CT (CBCT) images of the phantom were taken at different pitch, roll and rotation angles. The pitch, roll, and rotation angles were varied from −3 to 3 degrees by inputs from the linac console. A total of 39 Vision RT images with different rotation angle combinations were collected, and the Vision RT software was used to determine the rotation angles and translational shifts from those images. Eight CBCT images at most allowed rotational angles were analysed by in-house software. The software took the coordinates of the voxel of the maximum CT number inside a 7·5-mm sphere surrounding one BB to be the measured position of this BB. Expected BB positions at different rotation angles were determined by multiplying measured BB positions at zero pitch and roll values by a rotation matrix. Applying the rotation matrix to 5 BB positions yielded 15 equations. A linear least square method was used for regression analysis to approximate the solutions of those equations.

Results:

Of the eight calculations from CBCT images, the maximum rotation angle differences (degree) were 0·10 for pitch, 0·15 for roll and 0·09 for yaw. The maximum translation differences were 0·3 mm in the left–right direction, 0·5 mm in the anterior–posterior direction and 0·4 mm in the superior–inferior direction.

Conclusions:

The uncertainties of the 6-DOF couch were examined with the methods of optical surface imaging and CBCT imaging of the SRS QA phantom. The rotational errors were less than 0·2 degree, and the isocentre shifts were less than 0·8 mm.

Advances and potential of optical surface imaging in radiotherapy

This article reviews the recent advancements and future potential of optical surface imaging (OSI) in clinical applications as a four-dimensional (4D) imaging modality for surface-guided radiotherapy (SGRT), including OSI systems, clinical SGRT applications, and OSI-based clinical research. The OSI is a non-ionizing radiation imaging modality, offering real-time 3D surface imaging with a large field of view (FOV), suitable for in-room interactive patient setup, and real-time motion monitoring at any couch rotation during radiotherapy. So far, most clinical SGRT applications have focused on treating superficial breast cancer or deep-seated brain cancer in rigid anatomy, because the skin surface can serve as tumor surrogates in these two clinical scenarios, and the procedures for breast treatments in free-breathing (FB) or at deep-inspiration breath-hold (DIBH), and for cranial stereotactic radiosurgery (SRS) and radiotherapy (SRT) are well developed. When using the skin surface as a body-position surrogate, SGRT promises to replace the traditional tattoo/laser-based setup. However, this requires new SGRT procedures for all anatomical sites and new workflows from treatment simulation to delivery. SGRT studies in other anatomical sites have shown slightly higher accuracy and better performance than a tattoo/laser-based setup. In addition, radiographical image-guided radiotherapy (IGRT) is still necessary, especially for stereotactic body radiotherapy (SBRT). To go beyond the external body surface and infer an internal tumor motion, recent studies have shown the clinical potential of OSI-based spirometry to measure dynamic tidal volume as a tumor motion surrogate, and Cherenkov surface imaging to guide and assess treatment delivery. As OSI provides complete datasets of body position, deformation, and motion, it offers an opportunity to replace fiducial-based optical tracking systems. After all, SGRT has great potential for further clinical applications. In this review, OSI technology, applications, and potential are discussed since its first introduction to radiotherapy in 2005, including technical characterization, different commercial systems, and major clinical applications, including conventional SGRT on top of tattoo/laser-based alignment and new SGRT techniques attempting to replace tattoo/laser-based setup. The clinical research for OSI-based tumor tracking is reviewed, including OSI-based spirometry and OSI-guided tumor tracking models. Ongoing clinical research has created more SGRT opportunities for clinical applications beyond the current scope.

Intrafractional monitoring of patients using four different immobilization mask systems for cranial radiotherapy

Background and purpose

Patients receiving cranial radiotherapy are immobilized with a thermoplastic mask to restrict patient motion. Depending on the target volume margins and treatment dose, different mask systems are used. Intrafractional movements can be monitored using stereoscopic X-ray imaging. The aim of the present work was to compare the magnitudes of intrafractional deviation for different mask systems.

Material and methods

Four different head mask systems (open face mask, open mask, stereotactic mask, double mask) used in the treatment of 40 patients were investigated. In total 487 treatment fractions and 3708 X-ray images were collected. Deviations were calculated by comparison of the acquired X-ray images with digitally reconstructed radiographs. The results of intrafractional X-ray deviations for translational and rotational axes were compared between the different mask systems.

Results

Deviations were below 0.6 mm for translations and below 0.6° for rotations for all mask systems. Along the lateral and longitudinal directions the stereotactic mask was superior, while along the vertical direction the double mask showed the lowest deviations. For low rotational deviations the double mask is the best amongst all other mask systems.

Conclusion

As expected, the lowest movement was shown using cranial stereotactic mask systems. The results have shown deviations lower than 0.6 mm and 0.6° using any of the four thermoplastic mask systems.

Clinical validation of an AI-based motion correction reconstruction algorithm in cerebral CT

OBJECTIVES

To evaluate the clinical performance of an artificial intelligence (AI)-based motion correction (MC) reconstruction algorithm for cerebral CT.

METHODS

A total of 53 cases, where motion artifacts were found in the first scan so that an immediate rescan was taken, were retrospectively enrolled. While the rescanned images were reconstructed with a hybrid iterative reconstruction (IR) algorithm (reference group), images of the first scan were reconstructed with both the hybrid IR (motion group) and the MC algorithm (MC group). Image quality was compared in terms of standard deviation (SD), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), the mean squared error (MSE), peak signal-to-noise ratio (PSNR), structural similarity index (SSIM), and mutual information (MI), as well as subjective scores. The diagnostic performance for each case was evaluated accordingly by lesion detectability or the Alberta Stroke Program Early CT Score (ASPECTS) assessment.

RESULTS

Compared with the motion group, the SNR and CNR of the MC group were significantly increased. The MSE, PSNR, SSIM, and MI with respect to the reference group were improved by 44.1%, 15.8%, 7.4%, and 18.3%, respectively (all p < 0.001). Subjective image quality indicators were scored higher for the MC than the motion group (p < 0.05). Improved lesion detectability and higher AUC (0.817 vs 0.614) in the ASPECTS assessment were found for the MC to the motion group.

CONCLUSIONS

The AI-based MC reconstruction algorithm has been clinically validated for reducing motion artifacts and improving diagnostic performance of cerebral CT.

KEY POINTS

• An artificial intelligence-based motion correction (MC) reconstruction algorithm has been clinically validated in both qualitative and quantitative manner. • The MC algorithm reduces motion artifacts in cerebral CT and increases the diagnostic confidence for brain lesions. • The MC algorithm can help avoiding rescans caused by motion and improving the efficiency of cerebral CT in the emergency department.

End to end comparison of surface-guided imaging versus stereoscopic X-rays for the SRS treatment of multiple metastases with a single isocenter using 3D anthropomorphic gel phantoms

INTRODUCTION

Two end-to-end tests evaluate the accuracy of a surface-guided radiation therapy (SGRT) system (CRAD Catalyst HD) for position verification in comparison to a stereoscopic x-ray imaging system (Brainlab Exactrac ) for single-isocenter, multiple metastases stereotactic radiosurgery (SRS) using 3D polymer gel inserts.

MATERIALS AND METHODS

A 3D-printed phantom (Prime phantom, RTsafe PC, Athens, Greece) with two separate cylindrical polymer gel inserts were immobilized in open-face masks and treated with a single isocentric, multitarget SRS plan. Planning was done in Brainlab (Elements) to treat five metastatic lesions in one fraction, and initial setup was done using cone beam computed tomography. Positional verification was done using orthogonal X-ray imaging (Brainlab Exactrac) and/or a surface imaging system (CRAD Catalyst HD, Uppsala, Sweden), and shift discrepancies were recorded for each couch angle. Forty-two hours after irradiation, the gel phantom was scanned in a 1.5 Tesla MRI, and images were fused with the patient computed tomography data/structure set for further analysis of spatial dose distribution.

RESULTS

Discrepancies between the CRAD Catalyst HD system and Brainlab Exactrac were <1 mm in the translational direction and <0.5° in the angular direction at noncoplanar couch angles. Dose parameters (DMean% , D95% ) and 3D gamma index passing rates were evaluated for both setup modalities for each planned target volume (PTV) at a variety of thresholds: 3%/2 mm (Exactrac≥93.1% and CRAD ≥87.2%), 5%/2 mm (Exactrac≥95.6% and CRAD ≥94.6%), and 5%/1 mm (Exactrac≥81.8% and CRAD ≥83.7%).

CONCLUSION

Dose metrics for a setup with surface imaging was found to be consistent with setup using x-ray imaging, demonstrating high accuracy and reproducibility for treatment delivery. Results indicate the feasibility of using surface imaging for position verification at noncoplanar couch angles for single-isocenter, multiple-target SRS using end-to-end quality assurance (QA) testing with 3D polymer gel dosimetry.

AAPM task group report 302: Surface guided radiotherapy

The clinical use of surface imaging has increased dramatically with demonstrated utility for initial patient positioning, real-time motion monitoring, and beam gating in a variety of anatomical sites. The Therapy Physics Subcommittee and the Imaging for Treatment Verification Working Group of the American Association of Physicists in Medicine commissioned Task Group 302 to review the current clinical uses of surface imaging and emerging clinical applications. The specific charge of this task group was to provide technical guidelines for clinical indications of use for general positioning, breast deep-inspiration breath-hold (DIBH) treatment, and frameless stereotactic radiosurgery (SRS). Additionally, the task group was charged with providing commissioning and on-going quality assurance (QA) requirements for surface guided radiation therapy (SGRT) as part of a comprehensive QA program including risk assessment. Workflow considerations for other anatomic sites and for computed tomography (CT) simulation, including motion management are also discussed. Finally, developing clinical applications such as stereotactic body radiotherapy (SBRT) or proton radiotherapy are presented. The recommendations made in this report, which are summarized at the end of the report, are applicable to all video-based SGRT systems available at the time of writing. Review current use of non-ionizing surface imaging functionality and commercially available systems. Summarize commissioning and on-going quality assurance (QA) requirements of surface image-guided systems, including implementation of risk or hazard assessment of surface guided radiotherapy as a part of a total quality management program (e.g., TG-100). Provide clinically relevant technical guidelines that include recommendations for the use of SGRT for general patient positioning, breast DIBH, and frameless brain SRS, including potential pitfalls to avoid when implementing this technology. Discuss emerging clinical applications of SGRT and associated QA implications based on evaluation of technology and risk assessment. This article is protected by copyright. All rights reserved.

Innovative Non-Irradiating and Non-Invasive Per Fraction Control System in Radiotherapy: Surface-Guided Radiation Therapy Experience of Casablanca Cancer Center

Purpose: Evaluation of the added value of radiotherapy guided by the cutaneous   surface in the positioning and monitoring of the radiotherapy   Patients and Methods: This study included 21 consecutive patients treated with an   accelerator dedicated to "True Beam®" stereotactic radiotherapy whose sessions were   monitored by an Optical Surface Monitoring System: "OSMS®". Excluded from our   study were treatments controlled exclusively by radiological imaging (IGRT).   Positioning variabilities were compared between conventional imaging and skin   surface infrared (OSMS) monitoring. Conventional imaging was in the form of   standard radiography (KV) performed during the treatment session or three-   dimensional by a series of Cone Beam computerized tomography (CBCT) scanned   images made at the beginning and end of The total time of the session and   the positioning variability’s in the 3 planes were   14   Results: The results of our study show that the cutaneous surface monitoring allowed   to obtain a faster alignment of the patient with an improvement in the overall time of   the session with a mean at 32% [14.5-49.27%], likewise a sub-millimeter positioning   quality for all locations with a median longitudinal distance of 0.02 cm [0-0.66], 01   cm verticality [0-0.32] and laterality 0.02 cm [0-0.77] This benefit is significantly   greater for cerebral and Head and neck’s localizations   21   Conclusion: Optical Surface Monitoring System (OSMS®) is a non-invasive and non-   irradiating means that allows reliable and fast  

Uncertainty in the positioning of patients receiving treatment for brain metastases and wearing surgical mask underneath thermoplastic mask during COVID-19 crisis

Thermoplastic masks, used along with surgical masks, enable immobilization methods to reduce the risk of infection in patients undergoing intracranial stereotactic radiosurgery and stereotactic radiotherapy (SRS/SRT) during the COVID‐19 crisis. The purpose of this study was to investigate the feasibility of thermoplastic mask immobilization with a surgical mask using an ExacTrac system. Twelve patients each with brain metastases were immobilized using a thermoplastic mask and a surgical mask and only a thermoplastic mask. Two x‐ray images were acquired to correct (XC) and verify (XV) the patient’s position at a couch angle of 0°. Subsequently, the XC and XV images were acquired at each planned couch angle for non‐coplanar beams. When the position errors were detected after couch rotation for non‐coplanar beams, the errors were corrected at each planned couch angle until a clinically acceptable tolerance was attained. The position errors in the translational and rotational directions (vertical, lateral, longitudinal, pitch, roll, and yaw) were retrospectively investigated using data from the ExacTrac system database. A standard deviation of XC translational and rotational position errors with and without a surgical mask in the lateral (1.52 vs 2.07 mm), longitudinal (1.59 vs 1.87 mm), vertical (1.00 vs 1.73 mm), pitch (0.99 vs 0.79°), roll (1.24 vs 0.68°), and yaw (1.58 vs 0.90°) directions were observed at a couch angle of 0°. Most of patient positioning errors were less than 1.0 mm or 1.0° after the couch was rotated to the planned angle for non‐coplanar beams. The overall absolute values of the translational and rotational XV position errors with and without the surgical mask were less than 0.5 mm and 0.5°, respectively. This study showed that a thermoplastic mask with a surgical mask is a feasible immobilization technique for brain SRS/SRT patients using the ExacTrac system.

Occupational therapy for people with mask anxiety undergoing radiotherapy

INTRODUCTION

Up to one third of people with head and neck cancer undergoing radiation therapy experience mask anxiety. However, there is limited literature guiding the role of health professionals, including occupational therapists, in managing mask anxiety. This study aimed to explore the content of occupational therapy interactions with people who have identified mask anxiety.

METHODS

A cohort of 20 participants with identified mask anxiety engaged in semi-structured interviews with occupational therapists. Theoretical thematic analysis and the framework provided by the Canadian Model of Occupational Performance and Engagement (CMOP-E) were employed to explore the content of occupational therapy interactions with people experiencing mask anxiety.

RESULTS

Theoretical thematic analysis identified 13 relevant themes with 49 codes relating to the interaction between participants and occupational therapists. Analysis of these interactions identified the occupational therapy role to be holistic and multifaceted. The cognitive, affective, and institutional components of the CMOP-E were dominantly explored by the occupational therapists with participants. Occupation, spirituality, and the cultural environment were either not addressed or minimally discussed with participants.

CONCLUSION

The management of mask anxiety during radiation therapy is a novel area of practice for occupational therapists. The results of this study suggest that the occupational therapy profession explores a range of factors with the person undergoing radiation therapy with mask anxiety, and that the CMOP-E model can be used to guide these interactions. Future research is required to further define this role and its efficacy in managing mask anxiety.

Comparison of treatment position with mask immobilization and standard diagnostic setup in intracranial MRI radiotherapy simulation

PURPOSE

This study aims to compare the quality of images resulting from magnetic resonance imaging of patients who underwent intracranial MRI simulation using two different setups (treatment position with mask immobilization and standard diagnostic setup). Due to a larger number of channels and lack of mask immobilization in the standard diagnostic setup, we would like to evaluate whether this is an appropriate technique for MRI treatment planning.

METHODS

In total, 70 patients who underwent MR imaging of the brain at 1.5T were included in the study (48 for 6‑channel flex coil, 22 for 24-channel HNU face bill coil). Contrast-enhanced 3D T1w and T2 FLAIR images were acquired. Images were subjectively compared for artifact appearance and general image quality by three radiographers. Objective comparison of contrast rate, contrast-to-noise ratio, and signal-to-noise ratio was also performed.

RESULTS

FLAIR and contrast-enhanced 3D T1w images showed various artifacts, such as susceptibility and movement artifacts. There were no statistically significant differences regarding the evaluation of movement artifacts between two coils and two different immobilization methods. There were also no statistically significant differences (p > 0.05) between the 6‑channel flex coil and 24-channel HNU face bill coil regarding qualitative general image quality and objective measures.

CONCLUSION

There were no statistically significant differences between the occurrence of movement artifacts, overall image quality, and objective image quality in treatment position with mask immobilization and standard diagnostic setup. Based on this result, we can conclude that a standard diagnostic setup is also applicable in intracranial MRI treatment planning with no loss to image quality. Registration of the imaging plans was not performed in this study; therefore, it might still be necessary to perform measurements of tumor delineation matching and geometrical accuracy acceptance in our institution.

Accuracy of surface-guided patient setup for conventional radiotherapy of brain and nasopharynx cancer

Purpose

To evaluate the accuracy of surface‐guided radiotherapy (SGRT) in cranial patient setup by direct comparison between optical surface imaging (OSI) and cone‐beam computed tomography (CBCT), before applying SGRT‐only setup for conventional radiotherapy of brain and nasopharynx cancer.

Methods and Materials

Using CBCT as reference, SGRT setup accuracy was examined based on 269 patients (415 treatments) treated with frameless cranial stereotactic radiosurgery (SRS) during 2018‐2019. Patients were immobilized in customized head molds and open‐face masks and monitored using OSI during treatment. The facial skin area in planning CT was used as OSI region of interest (ROI) for automatic surface alignment and the skull was used as the landmark for automatic CBCT/CT registration. A 6 degrees of freedom (6DOF) couch was used. Immediately after CBCT setup, an OSI verification image was captured, recording the SGRT setup differences. These differences were analyzed in 6DOFs and as a function of isocenter positions away from the anterior surface to assess OSI‐ROI bias. The SGRT in‐room setup time was estimated and compared with CBCT and orthogonal 2D kilovoltage (2DkV) setups.

Results

The SGRT setup difference (magnitude) is found to be 1.0 ± 2.5 mm and 0.1˚±1.4˚ on average among 415 treatments and within 5 mm/3˚ with greater than 95% confidence level (P < 0.001). Outliers were observed for very‐posterior isocenters: 15 differences (3.6%) are >5.0mm and 9 (2.2%) are >3.0˚. The setup differences show minor correlations (|r| < 0.45) between translational and rotational DOFs and a minor increasing trend (<1.0 mm) in the anterior‐to‐posterior direction. The SGRT setup time is 0.8 ± 0.3 min, much shorter than CBCT (5 ± 2 min) and 2DkV (2 ± 1 min) setups.

Conclusion

This study demonstrates that SGRT has sufficient accuracy for fast in‐room patient setup and allows real‐time motion monitoring for beam holding during treatment, potentially useful to guide radiotherapy of brain and nasopharynx cancer with standard fractionation.

Commissioning of optical surface imaging systems for cranial frameless stereotactic radiosurgery

Purpose

This study aimed to evaluate and compare different system calibration methods from a large cohort of systems to establish a commissioning procedure for surface‐guided frameless cranial stereotactic radiosurgery (SRS) with intrafractional motion monitoring and gating. Using optical surface imaging (OSI) to guide non‐coplanar SRS treatments, the determination of OSI couch‐angle dependency, baseline drift, and gated‐delivered‐dose equivalency are essential.

Methods

Eleven trained physicists evaluated 17 OSI systems at nine clinical centers within our institution. Three calibration methods were examined, including 1‐level (2D), 2‐level plate (3D) calibration for both surface image reconstruction and isocenter determination, and cube phantom calibration to assess OSI‐megavoltage (MV) isocenter concordance. After each calibration, a couch‐angle dependency error was measured as the maximum registration error within the couch rotation range. A head phantom was immobilized on the treatment couch and the isocenter was set in the middle of the brain, marked with the room lasers. An on‐site reference image was acquired at couch zero, the facial region of interest (ROI) was defined, and static verification images were captured every 10° for 0°–90° and 360°–270°. The baseline drift was assessed with real‐time monitoring of the motionless phantom over 20 min. The gated‐delivered‐dose equivalency was assessed using the electron portal imaging device and gamma test (1%/1mm) in reference to non‐gated delivery.

Results

The maximum couch‐angle dependency error occurs in longitudinal and lateral directions and is reduced significantly (P < 0.05) from 1‐level (1.3 ± 0.4 mm) to 2‐level (0.8 ± 0.3 mm) calibration. The MV cube calibration does not further reduce the couch‐angle dependency error (0.8 ± 0.2 mm) on average. The baseline drift error plateaus at 0.3 ± 0.1 mm after 10 min. The gated‐delivered‐dose equivalency has a >98% gamma‐test passing rate.

Conclusion

A commissioning method is recommended using the 3D plate calibration, which is verified by radiation isocenter and validated with couch‐angle dependency, baseline drift, and gated‐delivered‐dose equivalency tests. This method characterizes OSI uncertainties, ensuring motion‐monitoring accuracy for SRS treatments.

Quantifying false positional corrections due to facial motion using SGRT with open-face Masks

Purpose

Studies have evaluated the viability of using open‐face masks as an immobilization technique to treat intracranial and head and neck cancers. This method offers less stress to the patient with comparable accuracy to closed‐face masks. Open‐face masks permit implementation of surface guided radiation therapy (SGRT) to assist in positioning and motion management. Research suggests that changes in patient facial expressions may influence the SGRT system to generate false positional corrections. This study aims to quantify these errors produced by the SGRT system due to face motion.

Methods

Ten human subjects were immobilized using open‐face masks. Four discrete SGRT regions of interest (ROIs) were analyzed based on anatomical features to simulate different mask openings. The largest ROI was lateral to the cheeks, superior to the eyebrows, and inferior to the mouth. The smallest ROI included only the eyes and bridge of the nose. Subjects were asked to open and close their eyes and simulate fear and annoyance and peak isocenter shifts were recorded. This was performed in both standard and SRS specific resolutions with the C‐RAD Catalyst HD system.

Results

All four ROIs analyzed in SRS and Standard resolutions demonstrated an average deviation of 0.3 ± 0.3 mm for eyes closed and 0.4 ± 0.4 mm shift for eyes open, and 0.3 ± 0.3 mm for eyes closed and 0.8 ± 0.9 mm shift for eyes open. The average deviation observed due to changing facial expressions was 1.4 ± 0.9 mm for SRS specific and 1.6 ± 1.6 mm for standard resolution.

Conclusion

The SGRT system can generate false positional corrections for face motion and this is amplified at lower resolutions and smaller ROIs. These errors should be considered in the overall tolerances and treatment plan when using open‐face masks with SGRT and may warrant additional radiographic imaging.

A phantom study to evaluate three different registration platform of 3D/3D, 2D/3D, and 3D surface match with 6D alignment for precise image-guided radiotherapy

Purpose

To evaluate two three‐dimensional (3D)/3D registration platforms, one two‐dimensional (2D)/3D registration method, and one 3D surface registration method (3DS). These three technologies are available to perform six‐dimensional (6D) registrations for image‐guided radiotherapy treatment.

Methods

Fiducial markers were asymmetrically placed on the surfaces of an anthropomorphic head phantom (n = 13) and a body phantom (n = 8), respectively. The point match (PM) solution to the six‐dimensional (6D) transformation between the two image sets [planning computed tomography (CT) and cone beam CT (CBCT)] was determined through least‐square fitting of the fiducial positions using singular value decomposition (SVD). The transformation result from SVD was verified and was used as the gold standard to evaluate the 6D accuracy of 3D/3D registration in Varian’s platform (3D3DV), 3D/3D and 2D/3D registration in the BrainLab ExacTrac system (3D3DE and 2D3D), as well as 3DS in the AlignRT system. Image registration accuracy from each method was quantitatively evaluated by root mean square of target registration error (rmsTRE) on fiducial markers and by isocenter registration error (IRE). The Wilcoxon signed‐rank test was utilized to compare the difference of each registration method with PM. A P < 0.05 was considered significant.

Results

rmsTRE was in the range of 0.4 mm/0.7 mm (cranial/body), 0.5 mm/1 mm, 1.0 mm/1.5 mm, and 1.0 mm/1.2 mm for PM, 3D3D, 2D3D, and 3DS, respectively. Comparing to PM, the mean errors of IRE were 0.3 mm/1 mm for 3D3D, 0.5 mm/1.4 mm for 2D3D, and 1.6 mm/1.35 mm for 3DS for the cranial and body phantoms respectively. Both of 3D3D and 2D3D methods differed significantly in the roll direction as compared to the PM method for the cranial phantom. The 3DS method was significantly different from the PM method in all three translation dimensions for both the cranial (P = 0.003–P = 0.03) and body (P < 0.001–P = 0.008) phantoms.

Conclusion

3D3D using CBCT had the best image registration accuracy among all the tested methods. 2D3D method was slightly inferior to the 3D3D method but was still acceptable as a treatment position verification device. 3DS is comparable to 2D3D technique and could be a substitute for X‐ray or CBCT for pretreatment verification for treatment of anatomical sites that are rigid.

A review of Image Guided Radiation Therapy in head and neck cancer from 2009-201 - Best Practice Recommendations for RTTs in the Clinic

Radiation therapy (RT) is beneficial in Head and Neck Cancer (HNC) in both the definitive and adjuvant setting. Highly complex and conformal planning techniques are becoming standard practice in delivering increased doses in HNC. A sharp falloff in dose outside the high dose area is characteristic of highly complex techniques and geometric uncertainties must be minimised to prevent under dosage of the target volume and possible over dosage of surrounding critical structures. CTV-PTV margins are employed to account for geometric uncertainties such as set up errors and both interfraction and intrafraction motion. Robust immobilisation and Image Guided Radiation Therapy (IGRT) is also essential in this group of patients to minimise discrepancies in patient position during the treatment course. IGRT has evolved with increased 2-Dimensional (2D) and 3-Dimensional (3D) IGRT modalities available for geometric verification. 2D and 3D IGRT modalities are both beneficial in geometric verification while 3D imaging is a valuable tool in assessing volumetric changes that may have dosimetric consequences for this group of patients. IGRT if executed effectively and efficiently provides clinicians with confidence to reduce CTV-PTV margins thus limiting treatment related toxicities in patients. Accumulated exposure dose from IGRT vary considerably and may be incorporated into the treatment plan to avoid excess dose. However, there are considerable variations in the application of IGRT in RT practice. This paper aims to summarise the advances in IGRT in HNC treatment and provide clinics with recommendations for an IGRT strategy for HNC in the clinic.

Quantifying the impact of optical surface guidance in the treatment of cancers of the head and neck

Surface guided radiation therapy (SGRT) is increasingly being adopted for use in radiation treatment delivery for Head and Neck (H&N) cancer patients. This study investigated the improvement of patient setup accuracy and reduction of setup time for SGRT compared to a conventional setup. A total of 60 H&N cancer patients were retrospectively included. Patients were categorized into three groups: oral cavity, oropharynx and nasopharynx/sinonasal sites with 20 patients in each group. They were further separated into two (2) subgroups, depending on whether they were set up with the aid of SGRT. The Align‐RT™ system was used for SGRT in this work. Positioning was confirmed by daily kV‐kV imaging in conjunction with weekly CBCT scans. Translational and rotational couch shifts along with patient setup times were recorded. Imaging setup time, which was defined as the elapsed time from the acquisition of the first image set to the end of the last image set, was recorded. Average translational shifts were larger in the non‐SGRT group. Vertical shifts showed the most significant reduction in the SGRT group for both oropharynx and oral cavity groups. Pitch corrections were significantly higher in the SGRT group for oropharynx patients and higher pitch corrections were also observed in the SGRT groups of oral cavity and nasopharynx/sinonasal patients. The average setup time when SGRT guidance was employed was shorter for all three treatment sites although this did not reach statistical significance. The largest time reduction between the SGRT and non‐SGRT groups was seen in the nasopharynx/sinonasal group. This study suggests that the use of SGRT decreases the magnitude of translational couch shifts during patient setup. However, the rotational corrections needed were generally higher with SGRT group. When SGRT was employed, a definite reduction in patient setup time was observed for nasopharynx/sinonasal and hypopharynx cancer patients.

Head Motion Correction Based on Filtered Backprojection in Helical CT Scanning

Head motion may unexpectedly occur during a CT scan. It thereby results in motion artifacts in a reconstructed image and may lead to a false diagnosis or a failure of diagnosis. To alleviate this motion problem, as a hardware approach, increasing the gantry rotation speed or using an immobilization device is usually considered. These approaches, however, cannot completely resolve the motion problem. Hence, motion estimation (ME) and compensation for it have been explored as a software approach instead. In this paper, adopting the latter approach, we propose a head motion correction algorithm in helical CT scanning, based on filtered backprojection (FBP). For the motion correction, we first introduce a new motion-compensated (MC) reconstruction scheme based on FBP, which is applicable to helical scanning. We then estimate the head motion parameters by using an iterative nonlinear optimization algorithm, or the L-BFGS. Note here that an objective function for the optimization is defined on reconstructed images in each iteration, which are obtained by using the proposed MC reconstruction scheme. Using the estimated motion parameters, we then obtain the final MC reconstructed image. Using numerical and physical phantom datasets along with simulated head motions, we demonstrate that the proposed algorithm can provide significantly improved quality to MC reconstructed images by alleviating motion artifacts.

A comparative study between open-face and closed-face masks for head and neck cancer (HNC) in radiation therapy

Aim

To determine the setup reproducibility in the radiation treatment of Head and Neck (HN) patients using open face head and shoulder masks (OHSM) with customized headrest (CHR) versus standard closed head and shoulder masks (CHSM) and to determine the patient's level of comfort and satisfaction for both masks.

Methods

Forty patients were prospectively randomized into two groups using simple random sampling. Group 1 was assigned with CHSMs, immobilized with a standard HR (SHR) while Group 2 was assigned with OHSMs, and immobilized with CHR. Cone beam computed tomography (CBCT) was taken the first 3 days, followed by weekly CBCT (prior treatment) with results registered to the planning CT to determine translational and rotational inter-fraction shifts and to verify accuracy. Mean (M) and standard deviation (SD) of the systematic and random setup errors of the 2 arms in the translational and rotational directions were analyzed, using Independent t-test and Mann-Whitney U test. Patient comfort was measured using a Likert questionnaire.

Results

The vertical, lateral, longitudinal and Z/roll rotational shifts were not significantly different between the two masks. X/yaw and Y/pitch rotational shifts were significantly greater in Group 2 versus Group 1, for both systematic (p = 0.009 and 0.046, respectively) and random settings (p = 0.016 and 0.020) but still within three degrees. Patients reported higher neck and shoulder comfort (p = 0.020) and overall satisfaction (p = 0.026) using the OHSM with the CHR versus the CHSM with the SHR during CT simulation.

Conclusion

Open masks provide comparable yet comfortable immobilization to closed masks for HN radiotherapy.

Does an immobilization mask have added value during planning magnetic resonance imaging for stereotactic radiotherapy of brain tumours?

BACKGROUND AND PURPOSE

When using an immobilization mask, a magnetic resonance imaging (MRI) head receive coil cannot be used and patients may experience discomfort during the examination. We therefore wish to assess the added value of an immobilization mask during all MRI scans intended for cranial stereotactic radiotherapy (SRT) planning.

MATERIALS AND METHODS

An MRI was acquired with and without a thermoplastic immobilization mask in ten patients eligible for SRT. A planning computed tomography (CT) scan was also made, to which the two MRIs were independently registered. Additionally, the MRI without immobilization was registered to the MRI in mask. On each sequence, gross tumour volume (GTV), the right eye, brain stem and chiasm were delineated. The absolute differences in centre-of-gravity coordinates and Dice coefficients of the volumes of the delineated structures between the two MRIs were compared.

RESULTS

Differences in GTV volume between the two MRIs were low, with median Dice coefficients between 0.88 and 0.91. Similarly, the median absolute differences in centre-of-gravity coordinates between the GTVs, organs at risk and landmarks delineated on the two MRIs were within 0.5 mm. The 95% confidence intervals of the median absolute differences in the three GTV coordinates was within 1 mm, which corresponds to the target volume safety margin used to account for possible errors during the SRT treatment chain.

CONCLUSIONS

The effect of scanning a patient without the immobilization mask falls within acceptable bounds of error for the geometrical accuracy of the SRT treatment chain. Consequently, placing the head in treatment position during all MRI scans for patients undergoing radiotherapy of brain metastasis is deemed unnecessary.

Assessment of the use of different imaging and delivery techniques for cranial treatments on the Halcyon linac

Purpose

In this work, we investigated the effect on the workflow and setup accuracy of using surface guided radiation therapy (SGRT) for patient setup, megavoltage cone beam CT (MVCBCT) or kilovoltage cone beam CT (kVCBCT) for imaging and fixed IMRT or volumetric‐modulated arc therapy (VMAT) for treatment delivery with the Halcyon linac.

Methods

We performed a retrospective investigation of 272 treatment fractions, using three different workflows. The first and second workflows used MVCBCT and fixed IMRT for imaging and treatment delivery, and the second one also used SGRT for patient setup. The third workflow used SGRT for setup, kVCBCT for imaging and VMAT for delivery. Workflows were evaluated by comparing the number of fractions requiring repeated imaging acquisitions and the time required for setup, imaging and treatment delivery. Setup position accuracy was assessed by comparing the daily kV‐ or MV‐ CBCT with the planning CT and measuring the residual rotational errors for pitch, yaw and roll angles.

Results

Without the use of SGRT, the imaging fields were delivered more than once on 11.1% of the fractions, while re‐imaging was necessary in 5.5% of the fractions using SGRT. The total treatment time, including setup, imaging, and delivery, for the three workflows was 531 ± 157 s, 503 ± 130 s and 457 ± 91 s, respectively. A statistically significant difference was observed when comparing the third workflow with the first two. The total residual rotational errors were 1.96 ± 1.29°, 1.28 ± 0.67° and 1.22 ± 0.76° and statistically significant differences were observed when comparing workflows with and without SGRT.

Conclusions

The use of SGRT allowed for a reduction of re‐imaging during patient setup and improved patient position accuracy by reducing residual rotational errors. A reduction in treatment time using kVCBCT with SGRT was observed. The most efficient workflow was the one including kVCBCT and SGRT for setup and VMAT for delivery.

Quantifying the dosimetric impact of organ-at-risk delineation variability in head and neck radiation therapy in the context of patient setup uncertainty

The purpose of this study was to quantify the potential dosimetric impact of delineation variability (DV) in head and neck radiation therapy (RT) when inherent patient setup variability (SV) is also considered. The impact of DV was assessed by generating plans with multiple structure sets, cross-evaluating them, including SV, across sets, and determining P _PQM: the probability of achieving organ-specific plan quality metrics (PQM). DV was incorporated by: (1) using multiple organ at risk (OAR) structure sets delineated by independent manual observers; and (2) randomly perturbing manually generated OARs to generate alternatives with varying levels of uncertainty (low, medium, and high DV). For each structure set, independent VMAT plans were auto-generated to meet clinical PQMs. Each plan was cross-evaluated using OARs from multiple structure sets with simulated SV including per-fraction random (σ _s) and per-treatment-course systematic (Σ_s) setup errors. The dosimetric impact of DV was assessed by examining P _PQM with and without SV/DV. Clinically significant differences were defined by those that exceeded differences caused by a  +2% output variation. Without including SV, simulated DV at the medium level reduced P _PQM by an average of 5.5% for all OARs with D _max PQMs. This reduction decreased to 2.8% for SV  =  2 mm and 2.4% for SV  =  4 mm (the average P _PQM reduction due to 2% output errors was 2.7%). For OARs with D _mean PQMs, the average P _PQM reduction was 0.9% for SV  =  0 and  ⩽0.1% for SV  ⩾  2 mm. The effect of DV was larger for OARs that directly abutted a target volume than for those that did not. These trends were also observed with real DV from multi-observer delineations. The dosimetric impact of DV appeared to decrease when random and systematic SV was considered. Sensitivity to DV was affected by OAR objective type (i.e. D _mean versus D _max objectives) as well as distance from the target volume.

Whole-brain radiation therapy without a thermoplastic mask

The aim of the study was to investigate the clinical feasibility of whole-brain radiation therapy without a thermoplastic mask. Positioning and intra-fractional motion monitoring were performed using optical surface scanning. The motion threshold was 3 mm/3 degrees. The group mean vector deviation was 1.1 mm. The roll was larger compared to pitch and rotation. Two patients out of 30 were not able to lie still. All other patients completed their treatment successfully without a mask. With a probability of success of 93%, we concluded that irradiation without a mask is a clinically feasible method.

An evaluation of the consistency of shifts reported by three different systems for non-coplanar treatments

Treatment of intra-cranial lesions sometimes requires a non-coplanar beam configuration. One of the most commonly used IGRT modalities, kV conebeam CT, cannot typically be used when large couch rotations are introduced. However, multiple other systems allow for imaging/tracking the patient for such situations. This work compares shift consistency from three independent systems, namely Varian's Advanced Imaging, Brainlab's Exactrac and Varian's OSMS, all installed on the same linear accelerator. After a phantom was first positioned using conebeam CT, the three systems were used to determine shifts at different couch positions. This was done with and without intentional shifts inserted in the original phantom position. Results show that the difference in shifts between the three systems was never more than 0.7 mm (average of 0.2 mm, standard deviation of 0.2 mm). These results confirm that all three systems are equivalent to within 1 mm and may potentially be uses interchangeably, especially in cases where the PTV margin is on the order of 1 mm.

Minimal mask immobilization with optical surface guidance for head and neck radiotherapy

PURPOSE

Full face and neck thermoplastic masks provide standard-of-care immobilization for patients receiving H&N IMRT. However, these masks are uncomfortable and increase skin dose. The purpose of this pilot trial was to investigate the feasibility and setup accuracy of minimal face and neck mask immobilization with optical surface guidance.

METHODS

Twenty patients enrolled onto this IRB-approved protocol. Patients were immobilized with masks securing only forehead and chin. Shoulder movement was restricted by either moldable cushion or hand held strap retractors. Positional information, including isocenter location and CT skin contours, were imported to a commercial surface image guidance system. Patients typically received standard-of-care IMRT to 60-70 Gy in 30-33 fractions. Patients were first set up to surface markings with optical image guidance referenced to regions of interest (ROIs) on simulation CT images. Positioning was confirmed by in-room CBCT. Following six-dimensional robotic couch correction, a new optical real-time surface image was acquired to track intrafraction motion and to serve as a reference surface for setup at the next treatment fraction. Therapists manually recorded total treatment time as well as couch shifts based on kV imaging. Intrafractional ROI motion tracking was automatically recorded by the optical image guidance system. Patient comfort was assessed by self-administered surveys.

RESULTS

Setup error was measured as six-dimensional shifts (vertical/longitudinal/lateral/rotation/pitch/roll). Mean error values were -0.51 ± 2.42 mm, -0.49 ± 3.30 mm, 0.23 ± 2.58 mm, -0.15 ± 1.01o , -0.02 ± 1.19o , and 0.06 ± 1.08o , respectively. Average treatment time was 21.6 ± 8.4 mins). Subjective comfort during surface-guided treatment was confirmed on patient surveys.

CONCLUSION

These pilot results confirm feasibility of minimal mask immobilization combined with commercially available optical image guidance. Patient acceptance of minimal mask immobilization has been encouraging. Follow-up validation, with direct comparison to standard mask immobilization, appears warranted.

Comorbidities in the management of patients with lung cancer

Lung cancer represents a major public health issue worldwide. Unfortunately, more than half of them are diagnosed at an advanced stage. Moreover, even if diagnosed early, diagnosis procedures and treatment can be difficult due to the frequent comorbidities observed in these patients. Some of these comorbidities have a common major risk factor, i.e. smoking, whereas others are unrelated to smoking but frequently observed in the general population. These comorbidities must be carefully assessed before any diagnostic and/or therapeutic decisions are made regarding the lung cancer. For example, in a patient with severe emphysema or with diffuse lung fibrosis, transthoracic needle biopsy can be contraindicated, meaning that in some instances a precise diagnosis cannot be obtained; in a patient with chronic obstructive pulmonary disease, surgery may be impossible or should be preceded by intensive rehabilitation; patients with interstitial lung disease are at risk of radiation pneumonitis and should not receive drugs which can worsen the respiratory insufficiency. Patients who belong to what are called "special populations", e.g. elderly or HIV infected, should be treated specifically, especially regarding systemic treatment. Last but not least, psychosocial factors are of great importance and can vary from one country to another according to health insurance coverage.

Evaluation of a surface imaging system's isocenter calibration methods

AlignRT is a surface imaging system that has been utilized for localizing and tracking patient position during radiotherapy. AlignRT has two calibration procedures that can set the system's isocenter called “Monthly Calibration” (MC) and “Isocentre Calibration” (IC). The MC utilizes a calibration plate. In addition to the calibration plate, the IC utilizes a cubic phantom that is imaged with the linac treatment beam to aid in aligning the AlignRT and treatment‐beam isocenters. This work evaluated the effects of misaligning the calibration plate during the calibration process. The plate was intentionally shifted away from isocenter ±3.0 mm in the longitudinal and lateral directions and ±1.0 mm in the longitudinal, lateral, and vertical directions. A mock stereotactic radiosurgery (SRS) treatment was used to evaluate the effects of the miscalibrations. An anthropomorphic head phantom was placed in an SRS treatment position and monitored with the AlignRT system. The AlignRT‐indicated offsets were recorded at 270°, 315°, 0°, 45°, and 90° couch angles for each intentional misalignment of the calibration plate during the MC. The IC was also performed after each miscalibration, and the measurements were repeated and compared to the previous results. With intentional longitudinal and lateral shifts of ±3.0 mm and ±1.0 mm of the calibration plate, the average indicated offsets at couch rotations of ±90° were 4.3 mm and 1.6 mm, respectively. This was in agreement with the theoretical offset of √2*(shift‐of‐the‐calibration plate). Since vertical shifts were along the rotation axis of the couch, these shifts had little effect on the offsets with changing couch angle. When the IC was applied, the indicated offsets were all within 0.5 mm for all couch angles for each of the miscalibrations. These offsets were in agreement with the known magnitude of couch walkout. The IC method effectively removes the potential miscalibration artifacts of the MC method due to misalignments of the calibration plate.

Prospective treatment plan-specific action limits for real-time intrafractional monitoring in surface image guided radiosurgery

PURPOSE

In surface image guided radiosurgery, action limits are created to determine at what point intrafractional motion exhibited by the patient is large enough to warrant intervention. Action limit values remain constant across patients despite the fact that patient motion affects the target coverage of brain metastases differently depending on the planning technique and other treatment plan-specific factors. The purpose of this work was twofold. The first purpose was to characterize the sensitivity of single-met per iso and multimet per iso treatment plans to uncorrected patient motion. The second purpose was to describe a method to prospectively determine treatment plan-specific action limits considering this sensitivity.

METHODS

In their surface image guided radiosurgery technique, patient positioning is achieved with a thermoplastic mask that does not cover the patient's face. The patient's exposed face is imaged by a stereoscopic photogrammetry system. It is then compared to a reference surface and monitored throughout treatment. Seventy-two brain metastases (representing 29 patients) were used for this study. Twenty-five mets were treated individually ("single-met per iso plans"), and 47 were treated in a plan simultaneously with at least one other met ("multimet per iso plans"). For each met, the proportion of the gross tumor volume that remained within the 100% prescription isodose line was estimated under the influence of combinations of translations and rotations (0.0-3.0 mm and 0.0°-3.0°, respectively). The target volume and the prescription dose-volume were considered concentric spheres that each encompassed a volume determined from the treatment plan. Plan-specific contour plots and DVHs were created to illustrate the sensitivity of a specific lesion to uncorrected patient motion.

RESULTS

Both single-met per iso and multimet per iso plans exhibited compromised target coverage under translations and rotations, though multimet per iso plans were considerably more sensitive to these transformations (2.3% and 39.8%, respectively). Plan-specific contour plots and DVHs were used to illustrate how size, distance from isocenter, and planning technique affect a particular met's sensitivity to motion.

CONCLUSIONS

Stereotactic radiosurgery treatment plans that treat multiple brain metastases using a common isocenter are particularly susceptible to compromised target coverage as a result of uncorrected patient motion. The use of such a planning technique along with other treatment plan-specific factors should influence patient motion management. A graphical representation of the effect of translations and rotations on any particular plan can be generated to inform clinicians of the appropriate action limit when monitoring intrafractional motion.

Enhanced Optical Head Tracking for Cranial Radiation Therapy: Supporting Surface Registration by Cutaneous Structures

PURPOSE

To support surface registration in cranial radiation therapy by structural information. The risk for spatial ambiguities is minimized by using tissue thickness variations predicted from backscattered near-infrared (NIR) light from the forehead.

METHODS AND MATERIALS

In a pilot study we recorded NIR surface scans by laser triangulation from 30 volunteers of different skin type. A ground truth for the soft-tissue thickness was segmented from MR scans. After initially matching the NIR scans to the MR reference, Gaussian processes were trained to predict tissue thicknesses from NIR backscatter. Moreover, motion starting from this initial registration was simulated by 5000 random transformations of the NIR scan away from the MR reference. Re-registration to the MR scan was compared with and without tissue thickness support.

RESULTS

By adding prior knowledge to the backscatter features, such as incident angle and neighborhood information in the scanning grid, we showed that tissue thickness can be predicted with mean errors of <0.2 mm, irrespective of the skin type. With this additional information, the average registration error improved from 3.4 mm to 0.48 mm by a factor of 7. Misalignments of more than 1 mm were almost thoroughly (98.9%) pushed below 1 mm.

CONCLUSIONS

For almost all cases tissue-enhanced matching achieved better results than purely spatial registration. Ambiguities can be minimized if the cutaneous structures do not agree. This valuable support for surface registration increases tracking robustness and avoids misalignment of tumor targets far from the registration site.

A prospective evaluation of open face masks for head and neck radiation therapy

PURPOSE

Head and neck (HN) radiation therapy patients are typically immobilized with closed thermoplastic masks that cover the face and may cause discomfort. In this work, we examine the use of open masks for HN radiation therapy.

METHODS AND MATERIALS

Fifty HN patients were prospectively randomized into 2 groups (25 closed masks, 25 open masks). The open-mask group was monitored with surface imaging to evaluate intrafraction motion. Both groups underwent daily volumetric imaging. All daily images were rigidly registered to their respective planning images to evaluate spinal canal and mandible position as a check for interfraction posture change. Posture changes were determined by the amount the spinal canal and mandible contours from the planning images had to be expanded to cover the structures on each daily image set. The vector length (VL) of the intrafraction linear translations, spine, and mandible positions for each open-mask patient were checked for correlation with fraction number using the Pearson r value. All patients were given a weekly survey ranking anxiety and claustrophobia from 0 to 10 (0 = no issue, 10 = extreme issue).

RESULTS

The mean VL for all open-mask patients was 0.9 ± 0.5 mm (1 standard deviation). Only 1 patient showed significant correlation between VL and fraction number. The mean contour expansions to cover the spine and mandible were 1.5 ± 0.9 mm and 1.8 ± 1.3 mm for the closed-mask group, and 1.6 ± 0.8 mm and 1.8 ± 1.1 mm for the open-mask group. Both groups showed similar behavior relative to fraction number. The mean anxiety and claustrophobia scores were 1.63 and 1.44 for the closed-mask group, and 0.81 and 0.63 for the open-mask group. The groups were not significantly different.

CONCLUSIONS

Open masks provide comparable immobilization and posture preservation to closed masks for HN radiation therapy.

Clinical experience with two frameless stereotactic radiosurgery (fSRS) systems using optical surface imaging for motion monitoring

The purpose of this study was to compare two clinical immobilization systems for intracranial frameless stereotactic radiosurgery (fSRS) under the same clinical procedure using cone‐beam computed tomography (CBCT) for setup and video‐based optical surface imaging (OSI) for initial head alignment and intrafractional motion monitoring. A previously established fSRS procedure was applied using two intracranial immobilization systems: PinPoint system (head mold and mouthpiece) and Freedom system (head mold and open face mask). The CBCT was used for patient setup with four degrees of freedom (4DOF), while OSI was used for 6DOF alignment prior to CBCT, post‐CBCT setup verification at all treatment couch angles (zero and nonzero), and intrafractional motion monitoring. Quantitative comparison of the two systems includes residual head rotation, head restriction capacity, and patient setup time in 25 patients (29 lesions) using PinPoint and 8 patients (29 fractions) using Freedom. The maximum possible motion was assessed in nine volunteers with deliberate, forced movement in Freedom system. A consensus‐based comparison of patient comfort level and clinical ease of use is reported. Using OSI‐guided corrections, the maximum residual rotations in all directions were 1.1°±0.5° for PinPoint and 0.6°±0.3° for Freedom. The time spent performing rotation corrections was 5.0±4.1 min by moving the patient with PinPoint and 2.7±1.0 min by adjusting Freedom couch extension. After CBCT, the OSI–CBCT discrepancy due to different anatomic landmarks for alignment was 2.4±1.3 mm using PinPoint and 1.5±0.7 mm using Freedom. Similar results were obtained for setup verification at couch angles (<1.5 mm) and for motion restriction: 0.4±0.3 mm/0.2°±0.2° in PinPoint and 0.6±0.3 mm/0.3°±0.1° in Freedom. The maximum range of forced head motion was 2.2±1.0 mm using Freedom. Both intracranial fSRS immobilization systems can restrict head motion within 1.5 mm during treatment as monitored by OSI. Setting a motion threshold for beam‐hold ensures that head motion is constrained within the treatment margin during beam‐on periods. The capability of 6D setup is useful to improve treatment accuracy. Patient comfort and clinical workflow should play a substantial role in system selection, and Freedom system outperforms PinPoint system in these two aspects.

PACS number: 87.53.Ly, 87.55.D‐, 87.57.Q‐, 87.6s.L‐, 87.85.gi

Development of a novel remote-controlled and self-contained audiovisual-aided interactive system for immobilizing claustrophobic patients

In radiotherapy, only a few immobilization systems, such as open‐face mask and head mold with a bite plate, are available for claustrophobic patients with a certain degree of discomfort. The purpose of this study was to develop a remote‐controlled and self‐contained audiovisual (AV)‐aided interactive system with the iPad mini with Retina display for intrafractional motion management in brain/H&N (head and neck) radiotherapy for claustrophobic patients. The self‐contained, AV‐aided interactive system utilized two tablet computers: one for AV‐aided interactive guidance for the subject and the other for remote control by an operator. The tablet for audiovisual guidance traced the motion of a colored marker using the built‐in front‐facing camera, and the remote control tablet at the control room used infrastructure Wi‐Fi networks for real‐time communication with the other tablet. In the evaluation, a programmed QUASAR motion phantom was used to test the temporal and positional accuracy and resolution. Position data were also obtained from ten healthy volunteers with and without guidance to evaluate the reduction of intrafractional head motion in simulations of a claustrophobic brain or H&N case. In the phantom study, the temporal and positional resolution was 24 Hz and 0.2 mm. In the volunteer study, the average superior–inferior and right–left displacement was reduced from 1.9 mm to 0.3 mm and from 2.2 mm to 0.2 mm with AV‐aided interactive guidance, respectively. The superior–inferior and right–left positional drift was reduced from 0.5 mm/min to 0.1 mm/min and from 0.4 mm/min to 0.04 mm/min with audiovisual‐aided interactive guidance. This study demonstrated a reduction in intrafractional head motion using a remote‐controlled and self‐contained AV‐aided interactive system of iPad minis with Retina display, easily obtainable and cost‐effective tablet computers. This approach can potentially streamline clinical flow for claustrophobic patients without a head mask and also allows patients to practice self‐motion management before radiation treatment delivery.

PACS number: 87.55.Gh