A comparison of patient position displacements from body surface laser scanning and cone beam CT bone registrations for radiotherapy of pelvic targets

A feasibility study of tumor motion monitoring for SBRT of lung cancer based on 3D point cloud detection and stacking ensemble learning

PURPOSE

To construct a tumor motion monitoring model for stereotactic body radiation therapy (SBRT) of lung cancer from a feasibility perspective.

METHODS

A total of 32 treatment plans for 22 patients were collected, whose planning CT and the centroid position of the planning target volume (PTV) were used as the reference. Images of different respiratory phases in 4DCT were acquired to redefine the targets and obtain the floating PTV centroid positions. In accordance with the planning CT and CBCT registration parameters, data augmentation was accomplished, yielding 2130 experimental recordings for analysis. We employed a stacking multi-learning ensemble approach to fit the 3D point cloud variations of body surface and the change of target position to construct the tumor motion monitoring model, and the prediction accuracy was assess using root mean squared error (RMSE) and R-Square (R2).

RESULTS

The prediction displacement of the stacking ensemble model shows a high degree of agreement with the reference value in each direction. In the first layer of model, the X direction (RMSE =0.019 ∼ 0.145mm, R2 =0.9793∼0.9996) and the Z direction (RMSE = 0.051 ∼ 0.168 mm, R2 = 0.9736∼0.9976) show the best results, while the Y direction ranked behind (RMSE = 0.088 ∼ 0.224 mm, R2 = 0.9553∼ 0.9933). The second layer model summarizes the advantages of unit models of first layer, and RMSE of 0.015 mm, 0.083 mm, 0.041 mm, and R2 of 0.9998, 0.9931, 0.9984 respectively for X, Y, Z were obtained.

CONCLUSIONS

The tumor motion monitoring method for SBRT of lung cancer has potential application of non-ionization, non-invasive, markerless, and real-time.

Characterization of the IDENTIFYTM surface scanning system for radiation therapy setup on a closed-bore linac

PURPOSE

In radiation therapy, surface guidance can be used for patient setup and intra-fraction motion monitoring. The surface guided radiation therapy (SGRT) system from Varian Medical systems, IDENTIFYTM, consists of three pods, including cameras and a random pattern projector, mounted on the ceiling. The information captured by the cameras is used to make a reconstruction of the surface. The aim of the study was to assess the technical performance of this SGRT system on a closed-bore linac.

METHODS

Phantom measurements were performed to assess the accuracy, precision, reproducibility and temporal stability of the system, both in align and in load position. Translations of the phantoms in lateral, longitudinal, and vertical direction, and rotations around three axes (pitch, roll and yaw) were performed with an accurate, in-house built, positioning stage. Different phantom geometries and different surface colors were used, and various ambient light intensities were tested.

RESULTS

The accuracy of the IDENTIFYTM system at the closed-bore linac was 0.07 mm and 0.07 degrees at load position, and 0.06 mm and 0.01 degrees at align position for the white head phantom. The precision was 0.02 mm and 0.02 degrees in load position, and 0.01 mm and 0.02 degrees in align position. The accuracy for the Penta-Guide phantom was comparable to the white head phantom, with 0.06 mm and 0.01 degrees in align position. The system was slightly less accurate for translations of the CIRS lung phantom in align position (0.20 mm, 0.05 degrees). Reproducibility measurements showed a variation of 0.02 mm in load position. Regarding the temporal stability, the maximum drift over 30 min was 0.33 mm and 0.02 degrees in load position. No effect of ambient light level on the accuracy of the IDENTIFYTM system was observed. Regarding different surface colors, the accuracy of the system for a black phantom was slightly worse compared to a white surface, but not clinical relevant.

CONCLUSION

The IDENTIFYTM system can adequately be used for motion monitoring on a closed-bore linac with submillimeter accuracy. The results of the performed measurements meet the clinical requirements described in the guidelines of the AAPM and the ESTRO.

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.).

Development of a new coordinate calibration phantom for a light-section-based optical surface monitoring system

A calibration phantom made of Derlin requires manual translational and rotational adjustments when calibrating a light-section-based optical surface monitoring system (VOXELAN) with a phantom material that insufficiently reflects the red-slit laser of the system. This study aimed to develop a new calibration phantom using different materials and to propose a procedure that minimizes setup errors. The new phantom, primarily made of PET100, which exhibits good reflectivity without scattering or attenuating the red-slit laser at the phantom surface, was shaped in a manner similar to that of previous designs. The detection accuracy and stability were evaluated using six different regions of interest (ROIs) and compared with previous phantom designs. The coordinate coincidence between the machine and VOXELAN was compared for both phantom designs. The detection accuracy and stability of the new phantom in the reference ROI setting were found to be better than those of previous phantoms. In the lateral, longitudinal, and vertical directions, the coordinate coincidences in translational directions for the previous phantom were obtained at 1.07 ± 0.66, 1.46 ± 0.47, and 0.26 ± 0.83 mm, whereas those for the new phantom were obtained at 0.28 ± 0.21, 0.18 ± 0.30, and - 0.30 ± 0.29 mm, respectively. The rotational errors of the two phantoms were identical. The new phantom exhibited improved detection stability because of its good reflectivity. Additionally, the new placement procedure was linked to the six-degrees-of-freedom couch. A combination of the new phantom and its new placement procedure is suitable for coordinate calibration of VOXELAN.

Dose coverage and breath-hold analysis of breast cancer patients treated with surface-guided radiotherapy

BACKGROUND

Surface-guided radiotherapy (SGRT) is used to ensure a reproducible patient set-up and for intra-fraction motion monitoring. The arm position of breast cancer patients is important, since this is related to the position of the surrounding lymph nodes. The aim of the study was to investigate the set-up accuracy of the arm of patients positioned using SGRT. Moreover, the actual delivered dose was investigated and an extensive breath-hold analysis was performed.

METHODS

84 patients who received local or locoregional breast radiation therapy were positioned and monitored using SGRT. The accuracy of the arm position, represented by the clavicle position, was studied on the anterior-posterior kV-image. To investigate the effect of changes in anatomy and patient set-up, the actual delivered dose was calculated on cone-beam CT-scans (CBCT). A deformable registration of the CT to the CBCT was applied to deform the structures of the CT onto the CBCT. The minimum dose in percentage of the prescribed dose that was received by 98% of different CTV volumes (D98) was determined. An extensive breath-hold analysis was performed and definitions for relevant parameters were given.

RESULTS

The arm position of 77 out of 84 patients in total was successful, based on the clavicle rotation. The mean clavicle rotation was 0.4° (± 2.0°). For 89.8% of the patients who were irradiated on the whole-breast D98 was larger than 95% of the prescribed dose (D98 > 95%). D98 > 95% applied for 70.8% of the patients irradiated on the chest wall. Concerning the lymph node CTVs, D98 > 95% for at least 95% of the patients. The breath-hold analysis showed a mean residual setup error of - 0.015 (± 0.90), - 0.18 (± 0.82), - 0.58 (± 1.1) mm in vertical, lateral, and longitudinal direction, respectively. The reproducibility and stability of the breath-hold was good, with median 0.60 mm (95% confidence interval (CI) [0.66-0.71] mm) and 0.20 mm (95% CI 0.21-0.23] mm), respectively.

CONCLUSIONS

Using SGRT we were able to position breast cancer patients successfully, with focus on the arm position. The actual delivered dose calculated on the CBCT was adequate and no relation between clavicle rotation and actual delivered dose was found. Moreover, breath-hold analysis showed a good reproducibility and stability of the breath-hold. Trial registration CCMO register NL69214.028.19.

Safely completed radiotherapy in a patient with breast cancer and right axillary vein approach cardiac pacemaker implantation: A case report

Pacemaker implantation is becoming increasingly common in patients with breast cancer. Comprehensive treatment options, such as surgery, chemotherapy, radiation therapy, targeted therapy and immunotherapy, have greatly improved the prognosis of patients with breast cancer. In particular, radiotherapy is an important means of comprehensive breast cancer treatment that can reduce recurrence and prolong survival in high-risk patients who underwent mastectomy. The pacemaker electrical pulse generator is typically implanted subcutaneously in the left subclavian area above the pectoral muscle through the subclavian vein. The present report implemented a new method of 'temporary pacemaker electrode and permanent artificial pacemaker placement' through the right axillary vein in a patient with breast cancer. An electrical pulse generator was placed in the right subcutaneous subclavian tissue. The pacemaker was placed under the right clavicle, and the pacemaker was included as organ at risk (OAR). Dose of planning organ at risk volume (PRV) with additional 6 mm margin to the pacemaker was limited during radiotherapy planning design. This patient with breast cancer, who was also complicated with other underlying comorbidities (such as atrial fibrillation, coronary atherosclerosis, cardiac insufficiency, hypertension, type 2 diabetes mellitus) and implanted with a cardiac pacemaker, was treated with safe (means that the patient has not developed heart disease because of the pacemaker problem) and effective (tumor can be effectively controlled under the condition that the pacemaker does not malfunction) radiotherapy. At present, the patient has successfully completed radiation therapy for breast cancer with no recurrence or metastasis. To the best of our knowledge, the present report is the first to document this application, demonstrating the treatment of a patient with breast cancer and cardiac pacemaker implantation, which is worthy of further study and continuous improvement in clinical practice.

Analysis of a surface imaging system using a six degree-of-freedom couch

Purpose

To validate surface imaging (SI)‐reported offsets using a six degree‐of‐freedom couch and an anthropomorphic phantom for commissioning and routine quality assurance of an SI system used for stereotactic radiosurgery (SRS).

Methods

An anthropomorphic phantom with a radiopaque ball bearing (BB) placed either anterior, midline, or posterior, was tracked with SI with a typical SRS region of interest. Couch motion in all six degrees of freedom was programmed and delivered on a linac. SI system logs were synchronized with linac trajectory logs. Ten random couch positions were selected at couch 0°, 45°, 90°, 270°, 315° with megavolt (MV) images taken to account for couch walkout. The SI residual error (ε), the difference between SI reported offset and MV or trajectory log position, was calculated. Residual errors were measured with and without one SI pod blocked.

Results

The median [range] of magnitude of translational ε was 0.13 [0.07, 0.21], 0.16 [0.11, 0.26], 0.61 [0.50, 0.68], 0.49 [0.42, 0.55], 0.55 [0.38, 0.72] mm for couch rotations of 0°, 45°, 90°, 270°, 315°, respectively, for the midline BB and no pod blocked. The range of all translational ε from all couch angles (with and without pod block) at different BB positions is [0.05, 0.96] mm. The absolute range of difference when changing BB position when no pod is blocked in median translational ε is [0.01, 0.40] mm with the maximum at BB posterior. The absolute range of difference when not changing BB positions with and without pod block in median translational ε is [0.01, 0.37] mm with the maximum at BB posterior and couch 315°.

Conclusion

SI system and linac trajectory log analysis can be used to assess SI system performance with automated couch motion to validate SI accuracy.

Accuracy evaluation of surface registration algorithm using normal distribution transform in stereotactic body radiotherapy/radiosurgery: A phantom study

PURPOSE

To evaluate a feasibility of normal distribution transform (NDT) algorithm compared with the iterative closest point (ICP) method as a useful surface registration in stereotactic body radiotherapy (SBRT)/stereotactic radiosurgery (SRS).

METHODS

Point cloud images using the 3D triangulation technology were obtained from a depth camera-based optical imaging (OSI) system equipped in a radiosurgery room. Two surface registration algorithms, NDT and ICP, were used to measure and compare the discrepancy values between the reference and the current surfaces during the positioning of the patient. The performance evaluation was investigated by calculating the registration error and root-mean-square (RMS) values for the surface model, reposition, and target accuracy, which were analyzed statistically using a paired t-test.

RESULTS

For surface model accuracy, the average of the registration error and RMS values were measured as 3.56 ± 2.20 mm and 6.98 ± 1.89 mm for ICP method, and 1.76 ± 1.32 mm and 3.58 ± 1.30 mm for NDT method (p < 0.05). For reposition accuracy, the average registration error and RMS values were calculated as 1.41 ± 0.98 mm and 2.53 ± 1.64 mm using ICP method, and 0.92 ± 0.61 mm and 1.75 ± 0.80 mm using NDT method (p = 0.005). The overall target accuracy using the NDT method reduced the average of the reposition error and overall RMS value by 0.71 and 1.32 mm, respectively, compared to the ICP method (p = 0.03).

CONCLUSIONS

We found that the surface registration algorithm based on NDT method provides more reliable accuracy in the values of surface model, reposition, and target accuracies than the classic ICP method. The NDT method in OSI systems offers reasonable accuracy in SBRT/SRS.

Geometrical analysis for motion monitoring of rigid bodies with optical surface scanning in radiation oncology

BACKGROUND AND PURPOSE

Surface guided radiotherapy can be used to improve patient setup and for accurate intra-fraction motion monitoring in correspondence to the isocenter. For a clinical relevant motion analysis the actual displacement of the entire clinical target volume (CTV) is necessary. Therefore, the aim of this study was to develop a novel assessment method for intra-fraction motion for rigid body structures based on motion data and a geometrical analysis.

MATERIALS AND METHODS

A threshold value on the volume coverage (VC(t)) of the CTV by the planning target volume (PTV) was proposed as online motion monitoring method. Moreover, offline analysis was performed by using heat maps and by calculating VCx, the volume coverage for at least x% of treatment time. The method was applied retrospectively to patient treatment data for whole brain radiation treatment without a thermoplastic mask.

RESULTS

In 132 out of 142 fractions in total the proportion of the CTV that was inside the PTV for at least 99% of the time (VC99) was more than 95%, for a CTV-to-PTV margin of 5 mm. The source-voxel heat map showed which part of the CTV had a reduced coverage and the target heat map showed the movement of the CTV.

CONCLUSION

Instead of using an action threshold on the movements of the isocenter, a threshold on the VC(t) of the CTV by the PTV was proposed. The heat maps and resulting values of VCx can be used to adapt the VC(t) threshold or the CTV-to-PTV margin for subsequent fractions.

Faster and more accurate patient positioning with surface guided radiotherapy for ultra-hypofractionated prostate cancer patients

INTRODUCTION

The aim of this study was to evaluate if surface guided radiotherapy (SGRT) can decrease patient positioning time for localized prostate cancer patients compared to the conventional 3-point localization setup method. The patient setup accuracy was also compared between the two setup methods.

MATERIALS AND METHODS

A total of 40 localized prostate cancer patients were enrolled in this study, where 20 patients were positioned with surface imaging (SI) and 20 patients were positioned with 3-point localization. The setup time was obtained from the system log files of the linear accelerator and compared between the two methods. The patient setup was verified with daily orthogonal kV images which were matched based on the implanted gold fiducial markers. Resulting setup deviations between planned and online positions were compared between SI and 3-point localization.

RESULTS

Median setup time was 2:50 min and 3:28 min for SI and 3-point localization, respectively (p < 0.001). The median vector offset was 4.7 mm (range: 0-10.4 mm) for SI and 5.2 mm for 3-point localization (range: 0.41-17.3 mm) (p = 0.01). Median setup deviation in the individual translations for SI and 3-point localization respectively was: 1.1 mm and 1.9 mm in lateral direction (p = 0.02), 1.8 and 1.6 mm in the longitudinal direction (p = 0.41) and 2.2 mm and 2.6 mm in the vertical direction (p = 0.04).

CONCLUSIONS

Using SGRT for positioning of prostate cancer patients provided a faster and more accurate patient positioning compared to the conventional 3-point localization setup.

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  

Correlation between 3D scanner image and MRI for tracking volume changes in head and neck cancer patients

Introduction

We investigated the correlation between optical surface imaging using a three‐dimensional (3D) scanner and magnetic resonance imaging (MRI) for suggesting feasibility in the clinical process of tracking volume changes in head and neck patients during radiation treatment.

Methods

Ten patients were divided into two groups depending on the location of their tumor (i.e., right or left side). With weekly imaging data, the change in volume based on MRI was evaluated during the treatment course. Four volumes of interest (VOIs) were calculated on the 3D surface image of the facial and cervical areas using an optical 3D scanner, and the correlation between volumetric parameters were analyzed.

Results

The target volume changed significantly overall for both groups. The changes parotid volume reduced by up to 3.8% and 28.0% for groups A (right side) and B (left side), respectively. In Group A, VOI 1 on the facial area and VOI 3 on the cervical area decreased gradually during the treatment course by up to 3.3% and 10.7%, respectively. In Group B, only VOI 4 decreased gradually during the treatment course and reduced by up to 9.2%. In group A, the change in target volume correlated strongly with right‐side parotid, VOI 1, and VOI 3, respectively. The parotid also showed strong correlations with VOIs (P < 0.01). The weight loss was strongly correlated with either PTV or parotid without statistical significance (P > 0.05). In group B (left side), the change in target volume correlated strongly with each volumetric parameter, including weight loss. For individual patient, PTV showed more correlation with VOIs on the cervical area than VOIs on the facial area.

Conclusions

An optical 3D scanner can be applied to track changes in volume without radiation exposure during treatment and the optical surface image correlated with MRI.

Surface guided imaging during stereotactic radiosurgery with automated delivery

PURPOSE

To report on the use of surface guided imaging during frameless intracranial stereotactic radiotherapy with automated delivery via HyperArc^TM (Varian Medical Systems, Palo Alto, CA).

METHODS

All patients received intracranial radiotherapy with HyperArc^TM and were monitored for intrafraction motion by the AlignRT® (VisionRT, London, UK) surface imaging (SI) system. Immobilization was with the Encompass^TM (Qfix, Avondale, PA) aquaplast mask device. AlignRT® log files were correlated with trajectory log files to correlate treatment parameters with SI reported offsets. SI reported offsets were correlated with gantry angle and analyzed for performance issues at non-zero couch angles and during camera-pod blockage during gantry motion. Demographics in the treatment management system were used to identify race and determine if differences in SI reported offsets are due to skin tone settings.

RESULTS

A total of 981 fractions were monitored over 14 months and 819 were analyzed. The median AlignRT® reported motion from beginning to the end of treatment was 0.24 mm. The median offset before beam on at non-zero couch angles was 0.55 mm. During gantry motion when camera pods are blocked, the median magnitude was below 1 mm. Median magnitude of offsets at non-zero couch angles was not found to be significantly different for patients stratified by race.

CONCLUSIONS

Surface image guidance is a viable alternative to scheduled mid-treatment imaging for monitoring intrafraction motion during stereotactic radiosurgery with automated delivery.

Recent advanced in Surface Guided Radiation Therapy

The growing acceptance and recognition of Surface Guided Radiation Therapy (SGRT) as a promising imaging technique has supported its recent spread in a large number of radiation oncology facilities. Although this technology is not new, many aspects of it have only recently been exploited. This review focuses on the latest SGRT developments, both in the field of general clinical applications and special techniques.SGRT has a wide range of applications, including patient positioning with real-time feedback, patient monitoring throughout the treatment fraction, and motion management (as beam-gating in free-breathing or deep-inspiration breath-hold). Special radiotherapy modalities such as accelerated partial breast irradiation, particle radiotherapy, and pediatrics are the most recent SGRT developments.The fact that SGRT is nowadays used at various body sites has resulted in the need to adapt SGRT workflows to each body site. Current SGRT applications range from traditional breast irradiation, to thoracic, abdominal, or pelvic tumor sites, and include intracranial localizations.Following the latest SGRT applications and their specifications/requirements, a stricter quality assurance program needs to be ensured. Recent publications highlight the need to adapt quality assurance to the radiotherapy equipment type, SGRT technology, anatomic treatment sites, and clinical workflows, which results in a complex and extensive set of tests.Moreover, this review gives an outlook on the leading research trends. In particular, the potential to use deformable surfaces as motion surrogates, to use SGRT to detect anatomical variations along the treatment course, and to help in the establishment of personalized patient treatment (optimized margins and motion management strategies) are increasingly important research topics. SGRT is also emerging in the field of patient safety and integrates measures to reduce common radiotherapeutic risk events (e.g. facial and treatment accessories recognition).This review covers the latest clinical practices of SGRT and provides an outlook on potential applications of this imaging technique. It is intended to provide guidance for new users during the implementation, while triggering experienced users to further explore SGRT applications.

Optical Surface Scanning for Patient Positioning in Radiation Therapy: A Prospective Analysis of 1902 Fractions

Purpose/Objective:

Reproducible patient positioning remains one of the major challenges in modern radiation therapy. Recently, optical surface scanners have been introduced into clinical practice in addition to well-established positioning systems, such as room laser and skin marks. The aim of this prospective study was to evaluate setup errors of the optical surface scanner Catalyst HD (C-RAD AB) in different anatomic regions.

Material/Methods:

Between October 2016 and June 2017 a total of 1902 treatment sessions in 110 patients were evaluated. The workflow of this study included conventional setup procedures using laser-based positioning with skin marks and an additional registration of the 3-dimensional (3D) deviations detected by the Catalyst system. The deviations of the surface-based method were then compared to the corrections of cone beam computed tomography alignment which was considered as gold standard. A practical Catalyst setup error was calculated between the translational deviations of the surface scanner and the laser positioning. Two one-sided t tests for equivalence were used for statistical analysis.

Results:

Data analysis revealed total deviations of 0.09 mm ± 2.03 mm for the lateral axis, 0.07 mm ± 3.21 mm for the longitudinal axis, and 0.44 mm ± 3.08 mm vertical axis for the Catalyst system, compared to −0.06 ± 3.54 mm lateral, 0.53 ± 3.47 mm longitudinal, and 0.19 ± 3.49 mm vertical for the laser positioning compared to cone beam computed tomography. The lowest positional deviations were found in the cranial region, and larger deviations occurred in the thoracic and abdominal sites. A statistical comparison using 2 one-sided t tests showed a general concordance of the 2 methods (P ≤ 0.036), excluding the vertical direction of the abdominal region (P = 0.198).

Conclusion:

The optical surface scanner Catalyst HD is a reliable and feasible patient positioning system without any additional radiation exposure. From the head to the thoracic and abdominal region, a decrease in accuracy was observed within a comparable range for Catalyst and laser-assisted positioning.

Optical Surface Management System for Patient Positioning in Interfractional Breast Cancer Radiotherapy

Background

The Optical Surface Management System (OSMS) is a simple, fast, reproducible, and accurate solution for patient set-up and can minimize random day-to-day set-up errors. However, studies in breast cancer patients are rare.

Objective

To analyze 200 patient set-ups in 20 patients with breast cancer by comparing the OSMS with the conventional cone-beam computed tomography (CBCT).

Method

Displacements from concurrent OSMS and CBCT registrations were compared in a total of 200 setups of 20 patients to analyze the interfractional displacement and positioning displacement in three dimensions (lateral, longitudinal, and vertical directions).

Results

The interfractional displacement on the lateral, longitudinal, and vertical directions for OSMS versus CBCT was 0.049 ± 0.254 versus 0.041 ± 0.244 centimeters (cm); 0.018 ± 0.261 versus 0.040 ± 0.242 cm; 0.062 ± 0.254 versus 0.065 ± 0.240 cm, respectively, without any significant difference (all P > 0.05). The duration for CBCT scan was about 60 seconds (s), while that for image processing, matching, and couch displacement was at least 5 minutes (min). The average scanning time with OSMS was less than 20 s, and the total duration for positioning was less than 1 min.

Conclusion

OSMS is an efficient tool to improve the accuracy and increase the speed for verifying the patient positioning in radiotherapy for breast cancer.

Evaluation of daily patient positioning for radiotherapy with a commercial 3D surface-imaging system (Catalyst™)

Background

To report our initial clinical experience with the novel surface imaging system Catalyst™ (C-RAD AB, Sweden) in connection with an Elekta Synergy linear accelerator for daily patient positioning in patients undergoing radiation therapy.

Methods

We retrospectively analyzed the patient positioning of 154 fractions in 25 patients applied to thoracic, abdominal, and pelvic body regions. Patients were routinely positioned based on skin marks, shifted to the calculated isocenter position and treated after correction via cone beam CT which served as gold standard. Prior to CBCT an additional surface scan by the Catalyst™ system was performed and compared to a reference surface image cropped from the planning CT to obtain shift vectors for an optimal surface match. These shift vectors were subtracted from the vectors obtained by CBCT correction to assess the theoretical setup error that would have occurred if the patients had been positioned using solely the Catalyst™ system. The mean theoretical set up-error and its standard deviation were calculated for all measured fractions and the results were compared to patient positioning based on skin marks only.

Results

Integration of the surface scan into the clinical workflow did not result in a significant time delay. Regarding the entire group, the mean setup error by using skin marks only was 0.0 ± 2.1 mm in lateral, −0.4 ± 2.4 mm in longitudinal, and 1.1 ± 2.6 mm vertical direction. The mean theoretical setup error that would have occurred using solely the Catalyst™ was −0.1 ± 2.1 mm laterally, −1.8 ± 5.4 mm longitudinally, and 1.4 ± 3.2 mm vertically. No significant difference was found in any direction. For thoracic targets the mean setup error based on the Catalyst™ was 0.6 ± 2.6 mm laterally, −5.0 ± 7.9 mm longitudinally, and 0.5 ± 3.2 mm vertically. For abdominal targets, the mean setup error was 0.3 ± 2.2 mm laterally, 2.6 ± 1.8 mm longitudinally, and 2.1 ± 5.5 mm vertically. For pelvic targets, the setup error was −0.9 ± 1.5 mm laterally, −1.7 ± 2.8 mm longitudinally, and 1.6 ± 2.2 mm vertically. A significant difference between Catalyst™ and skin mark based positioning was only observed in longitudinal direction of pelvic targets.

Conclusion

Optical surface scanning using Catalyst™ seems potentially useful for daily positioning at least to complement usual imaging modalities in most patients with acceptable accuracy, although a significant improvement compared to skin mark based positioning could not be derived from the evaluated data. However, this effect seemed to be rather caused by the unexpected high accuracy of skin mark based positioning than by inaccuracy using the Catalyst™. Further on, surface registration in longitudinal axis seemed less reliable especially in pelvic localization. Therefore further prospective evaluation based on strictly predefined protocols is needed to determine the optimal scanning approaches and parameters.

Surface imaging, portal imaging, and skin marker set-up vs. CBCT for radiotherapy of the thorax and pelvis

AIM

The aim of this study was to compare surface imaging, portal imaging, and skin marker set-up in radiotherapy of thoracic and pelvic regions, using cone beam computed tomography (CBCT) data as the gold standard.

PATIENTS AND METHODS

Twenty patients were included in this study. CBCT, surface acquisition (SA), and two orthogonal portal images (PI) were acquired during the first four treatment sessions. Patient set-up corrections, obtained by registering the planning CT with CBCT, were used as the gold standard. Registration results of the PI and SA were evaluated and compared with those obtained with CBCT. The advantage derived from using SA or PI verification systems over a skin marker set-up was also quantified.

RESULTS

A statistically significant difference between PI and SA (in favour of PI) was observed in seven patients undergoing treatment of the pelvic region and in two patients undergoing treatment of the thoracic region. The use of SA or PI, compared with a skin marker set-up, improved patient positioning in 50% and 57% of the thoracic fractions, respectively. For pelvic fractions, the use of PI was beneficial in 73% of the cases, while the use of SA was beneficial in only 45%. Patient positioning worsened with SA, particularly along longitudinal and vertical directions.

CONCLUSION

PI yielded more accurate registration results than SA for both pelvic and thoracic fractions. Compared with the skin marker set-up, PI performances were superior to SA for pelvic fractions while comparable results were obtained for thoracic fractions.

Technical evaluation of a laser-based optical surface scanning system for prospective and retrospective breathing adapted computed tomography

BACKGROUND

For breathing adapted radiotherapy, the same motion monitoring system can be used for imaging and triggering of the accelerator.

PURPOSE

To evaluate a new technique for prospective gated computed tomography (CT) and four-dimensional CT (4DCT) using a laser based surface scanning system (Sentinel(™), C-RAD, Uppsala, Sweden). The system was compared to the AZ-733V respiratory gating system (Anzai Medical, Tokyo, Japan) and the Real-Time Position Management System (RPM(™)) (Varian Medical Systems, Palo Alto, CA, USA).

MATERIAL AND METHODS

Temporal accuracy was evaluated using a moving phantom programmed to move a platform along trajectories following a sin(6)(ωt) function with amplitudes from 6 to 20 mm and periods from 2 to 5 s during 120 s while the motion was recorded. The recorded data was Fourier transformed and the peak area at the fundamental and harmonic frequencies compared to data generated using the same sinusoidal function. For verification of the 4DCT reconstruction process, the phantom was programmed to move along a sinusoidal trajectory. Ten phase series were reconstructed. The distance from the couch to the platform was measured in each image. By fitting the function sin(ωt-ϕ) to the values measured in the images corresponding to each slice, the phase of each image was verified.

RESULTS AND CONCLUSION

In the recorded data, the peak area at the fundamental frequency covered on average 104 ± 4%, 102 ± 4% and 91 ± 27% of the peak area in the generated data for the Sentinel(™), RPM(™) and AZ-733V systems, respectively. All systems managed to resolve both harmonic frequencies. The second experiment showed that all images were sorted into the correct series using breathing data recorded by each system. The systems generated very similar results, however, it is preferable to use the same system both for imaging and treatment.