Bone Registration Research Articles

Quantification of Esophageal Tumor Motion and Investigation of Different Image-Guided Correction Strategies

PurposeTo accurately quantify esophageal tumor position variability and to optimize image guided correction strategies. Material and MethodsEsophageal cancer patients receiving chemoradiotherapy (41.4-50.4 Gy in 23-28 fractions combined with carboplatin plus paclitaxel) were included in a prospective cohort study (NCT02139488). Gold fiducial markers were inserted into the esophageal tumors during diagnostic endoscopic ultrasound. Four-dimensional (4D) planning computed tomography (CT) and daily 4D cone beam (CB) CT scans were acquired. Each CBCT was registered to the planning CT using different regions of interest (bone; 3D), and carina, diaphragm, clinical target volume (CTV), and fiducial markers (4D) for alignment and using the fiducial markers as the true tumor position. Subsequently, a planning target volume (PTV) margin accounting for residual uncertainties, including the average respiratory motion, was calculated for each of these registrations. ResultsFifty-six patients with tumors located in the proximal (n = 1), mid (n = 7), or distal esophagus (n = 25) or at the gastroesophageal junction (n = 23) were included. The average peak-to-peak respiratory tumor motion was 0.20, 0.92, and 0.34 cm on the planning CT in left–right (LR), cranial–caudal (CC), and anterior–posterior (AP) directions, respectively. The required PTV margin with average motion amplitude, depending on the correction strategy used for image guidance, ranged from 0.8 cm to 1.0 cm, 1.1 cm to 1.6 cm, and 0.7 cm to 0.9 cm in LR, CC, and AP direction, respectively. A registration based on the CTV resulted in the smallest PTV margins (0.8, 1.1, and 0.7 cm in LR, CC, and AP direction, respectively). For bone registration the calculated PTV margins were 1.0, 1.3, and 0.7 cm in LR, CC, and AP directions, respectively. The registration based on the diaphragm increased PTV margins. ConclusionsSubstantial and anisotropic position variability of esophageal tumors was observed during radiation therapy, and nonuniform margins should be considered. Cranial-caudal PTV margins need to be larger than those commonly used. Target positioning during image-guided radiotherapy could be improved with a CTV registration-based correction strategy.

Scapholunate kinematics after flexible anchor repair

The scapholunate joint is one of the keystones of the wrist kinematics, and its study is difficult due to the carpal bones size and the richness of surrounding ligaments. We propose a new method of quantitative assessment of scapholunate kinematics through bone motion tracking in order to investigate scapholunate ligament lesion as well as repair techniques. On 6 intact wrists, steel beads were inserted into the bones of interest to track their motions. Experimental set up allowed wrist flexion extension and radio-ulnar deviation motions. Low-dose bi-planar radiographs were performed each 10° of movement for different configurations: 1) intact wrist, 2) scapholunate ligament division, 3) repair by soft anchors at the posterior then 4) anterior part. Beads’ 3D coordinates were computed at each position from biplanar X-Rays, allowing accurate registration of each wrist bone. The Monte Carlo sensitivity study showed accuracy between 0.2° and 1.6 ° for the scaphoid and the lunate in motions studied. The maximum flexion-extension range of motion of the scaphoid significantly decreased after anterior repair from 73° in injured wrist to 62.7°.The proposed protocol appears robust, and the tracking allowed to quantify the anchor's influence on the wrist kinematics.

A New CT Based Method for Post-operative Motion Analysis of Pelvic Fractures

Conventional X-ray is commonly used for pelvic fracture follow-ups, but has a precision of only ± 5 mm. Implantation of tantalum beads together with RSA has shown high precision but not applicable in clinical practice. CT scan has been shown a suitable substitute for RSA to follow the metal markers. We aimed to assess whether implantation of metal markers could be avoided using CT scan and merging of bone surface anatomy. A human cadaveric pelvis marked with 0.8 mm tantalum beads was fixed over the symphysis and the right SI-joint. Left hemi-pelvis was subsequently distracted using plastic spacers. Sequential CT exams was conducted and data were analyzed using Sectra® (Sectra AB), CTMA package. Examinations were repeated after 2 weeks. Bone registration showed better precision than registration based on tantalum beads. However, only the difference in angular changes was statistically significant (p = 0.008). The confidence interval of the repeatability was ± 0.5 mm for translation and ± 0.5° for rotation. This new non-invasive technique showed good precision and repeatability and might be a future option in clinical practice for post-operative follow-ups of patients with pelvic fractures.

Effect of helical tomotherapy megavoltage CT under different acquisition pitch and registration conditions on the accuracy of radiotherapy for nasopharyngeal carcinoma

Objective To evaluate the effect of helical tomotherapy (HT) megavoltage CT (MVCT) under different acquisition pitch and registration conditions upon the accuracy of radiotherapy for used nasopharyngeal carcinoma, aiming to provide reference for image-guided radiotherapy (IGRT) for nasopharyngeal carcinoma. Methods MVCT scans were performed on an anthropomorphic head& neck phantom which was simulated the positioning errors in the x, y and z direction. The obtained images were registered with the planning CT images. Acquisition pitch was set as the coarse, normal and fine modes. Registration conditions were set as bone registration, bone and soft tissue registration and full-image registration. Registration accuracy was determined by comparing the measured value with the preset value. The accuracy of radiotherapy under different acquisition pitch and registration conditions was statistically compared. Results The 3D errors of bone, bone and soft tissue and full-image registration under different acquisition pitch (coarse, normal and fine) were (1.51±0.47, 1.54±0.35, 1.81±0.53) mm and (1.41±0.37, 1.53±0.36, 1.56±0.39) mm and (1.51±0.27, 1.57±0.32, 1.73±0.33) mm, respectively. The bone registration yielded the highest accuracy (P 0.05). The fine mode of acquisition pitch possessed the highest stability, whereas required the longest time. Conclusion The acquisition pitch and registration conditions should be selected during HT MVCT based on the clinical requirement of each patient with nasopharyngeal carcinoma. Key words: Nasopharyngeal neoplasms/helical tomotherapy; Acquisition pitch; Registration condition; Accuracy

Analysis of setup errors during radiotherapy for breast cancer patients immobilized with neck and breast thermoplastic mask

Objective To analyze the setup errors by cone-beam computed tomography (CBCT) for breast cancer patients who were immobilized with neck and breast thermoplastic mask and received intensity modulated radiation therapy (IMRT), and to calculate the external margins from the clinical target volume (CTV) to the planning target volume (PTV) (MPTV) of tumors. Methods Twenty-five breast cancer patients who were immobilized with neck and breast thermoplastic mask and received IMRT in the Oncology Department of Tongji Hospital Affiliated to Tongji Medical College of Huazhong University of Science and Technology from November 2016 to June 2017 were enrolled. The position of the patients were verified by CBCT before treatment. The linear and rotation errors of the X, Y and Z axes were analyzed by online bone registration. The systematic errors (Σ) and random errors (σ) of the patients were also calculated, and then the margins from CTV to PTV margins were calculated based on MPTV=2.5Σ+0.7σ. 25 patients' height, weight, body mass index (BMI) and the maximum diameters of CTV in the lateral, longitudinal and vertical directions were recorded, and the relation between the setup errors and the above mentioned was analyzed by using Spearman method. Results A total of 174 CBCT scans for 25 breast cancer patients were completed. The group Σ were 1.40 mm, 1.50 mm and 1.20 mm, and rotation errors were 0.9°, 0.7° and 0.8° at the X, Y and Z axes, respectively. The group σwere 2.20 mm, 3.00 mm and 1.40 mm, and rotation errors were 0.7°, 0.6° and 0.7° at the X, Y and Z axes, respectively. MPTV was recommended as 4.90 mm, 6.00 mm and 3.90 mm at the X, Y and Z axes, respectively. There was no correlation between the height, weight, BMI of the patients and the setup errors (all P > 0.05). However, there was a significant correlation between the maximum lateral, longitudinal diameters of the CTV and the setup errors (rs=0.406, P=0.044; rs=0.512, P=0.009). Conclusions The neck and breast thermoplastic mask can improve the diagnostic accuracy of radiotherapy in breast cancer patients. The data of setup errors verified by CBCT can provide meaningful references for the setting of MPTV. Key words: Breast neoplasms; Radiotherapy planning, computer-assisted; Cone beam computed tomography; Setup error

Improved Surface-Based Registration of CT and Intraoperative 3D Ultrasound of Bones.

The intraoperative registration of preoperative CT volumes is a key process of most computer-assisted orthopedic surgery (CAOS) systems. In this work, is reported a new method for automatic registration of long bones, based on the segmentation of the bone cortical in intraoperative 3D ultrasound images. A bone classifier was developed based on features, obtained from the principal component analysis of the Hessian matrix, of every voxel in an intraoperative ultrasound volume. 3D freehand ultrasound was used for the acquisition of the intraoperative ultrasound volumes. Corresponding bone surface segmentations in ultrasound and preoperative CT imaging were used for the intraoperative registration. Validation on a phantom of the tibia produced encouraging results, with a maximum mean segmentation error of 0.34⁡mm (SD=0.26⁡mm) and a registration accuracy error of 0.64⁡mm (SD=0.49⁡mm).

The Effect of Including Bone in Dixon-Based Attenuation Correction for 18F-Fluciclovine PET/MRI of Prostate Cancer.

The objective of this study was to evaluate the effect of including bone in Dixon-based attenuation correction for 18F-fluciclovine PET/MRI of primary and recurrent prostate cancer. Methods:18F-fluciclovine PET data from 2 PET/MRI studies-one for staging of high-risk prostate cancer (28 patients) and one for diagnosis of recurrent prostate cancer (81 patients)-were reconstructed with a 4-compartment (reference) and 5-compartment attenuation map. In the latter, continuous linear attenuation coefficients for bone were included by coregistration with an atlas. The SUVmax and mean 50% isocontour SUV (SUViso) of primary, locally recurrent, and metastatic lesions were compared between the 2 reconstruction methods using linear mixed-effects models. In addition, mean SUVs were obtained from bone marrow in the third lumbar vertebra (L3) to investigate the effect of including bone attenuation on lesion-to-bone marrow SUV ratios (SUVRmax and SUVRiso; recurrence study only). The 5-compartment attenuation maps were visually compared with the in-phase Dixon MR images for evaluation of bone registration errors near the lesions. P values of less than 0.05 were considered significant. Results: Sixty-two lesions from 39 patients were evaluated. Bone registration errors were found near 19 (31%) of these lesions. In the remaining 8 primary prostate tumors, 7 locally recurrent lesions, and 28 lymph node metastases without bone registration errors, use of the 5-compartment attenuation map was associated with small but significant increases in SUVmax (2.5%; 95% confidence interval [CI], 2.0%-3.0%; P < 0.001) and SUViso (2.5%; 95% CI, 1.9%-3.0%; P < 0.001), but not SUVRmax (0.2%; 95% CI, -0.5%-0.9%; P = 0.604) and SUVRiso (0.2%; 95% CI -0.6%-1.0%; P = 0.581), in comparison to the 4-compartment attenuation map. Conclusion: The investigated method for atlas-based inclusion of bone in 18F-fluciclovine PET/MRI attenuation correction has only a small effect on the SUVs of soft-tissue prostate cancer lesions, and no effect on their lesion-to-bone marrow SUVRs when using signal from L3 as a reference. The attenuation maps should always be checked for registration artifacts for lesions in or close to the bones.

Technical Note: Feasibility of MRI-based estimation of water-equivalent path length to detect changes in proton range during treatment courses.

To evaluate the feasibility of using on-treatment magnetic resonance imaging (MRI) to detect proton range changes during treatment courses. MRI-based virtual computed tomography (vCT) was generated to calculate water-equivalent path length (WEPL) at the distal surface of a clinical target volume. T2-weighted MR images with and without fat suppression were processed by thresholding and fuzzy c-mean clustering to assign a bulk HU (Hounsfield Unit) to each segment of fat, water, and air. Bony tissues in vCT were transferred from planning CT via a region-based registration. We validated this method using images from three patients (aged 9, 12, and 17 yr old) with pelvic sarcomas who underwent proton therapy. MRI-based WEPL was evaluated against those of repeat CT (rCT) and cone beam CT (CBCT). The vCT agreed well with the rCT, wherein the use of bulk HU and imperfect bone registration contributed to discrepancies. The 99th percentile error of the MRI-based WEPL was up to 3.3 mm for posterior fields when we compensated the effect of mobile air. The gamma index (2-mm WEPL/2-mm pixel distance) was greater than 99% for those fields. We observed larger errors for anterior fields, which were due to bowel gas movement, mismatched respiratory motion, and differences in patient posture between the vCT and rCT. Applied to multiple on-treatment MRI of a patient, the estimated WEPL demonstrated an underrange trend, which was consistent with the CBCT results and the increased patient body circumference. The MRI-based vCT produced highly accurate WEPL estimates, demonstrating the potential of using on-treatment MRI for detecting changes in proton ranges.

Cone-Beam CT-based position verification for oesophageal cancer: Evaluation of registration methods and anatomical changes during radiotherapy.

To evaluate different registration methods, setup margins and number of corrections for CBCT-based position verification for oesophageal cancer and to evaluate anatomical changes during the course of radiotherapy treatment. From 50 patients, 440 CBCT-scans were registered automatically using a soft tissue or bone registration algorithm and compared to the clinical match. Moreover, relevant anatomical changes were monitored. A sub-analysis was performed to evaluate if tumour location influenced setup variations. Margin calculation was performed and the number of setup corrections was estimated. Results were compared to a patient group previously treated with MV-EPID based position verification. CBCT-based setup variations were smaller than EPID-based setup variations, resulting in smaller setup margins of 5.9mm (RL), 7.5mm (CC) and 4.7mm (AP) versus 6.0mm, 7.8mm and 5.5mm, respectively. A reduction in average number of setup corrections per patient was found from 0.75 to 0.36. From all automatically registered CBCT-scans, a clipbox around PTV and vertebras combined with soft tissue registration resulted in the smallest setup margins of 5.9mm (RL), 7.7mm (CC), 4.8mm (AP) and smallest average number of corrections of 0.38. For distally located tumours, a setup margin of 7.7mm (CC) was required compared to 5.6mm for proximal tumours. Reduction of GTV volume, heart volume and change in diaphragm position were observed in 16, 10 and 15 patients, respectively. CBCT-based set-up variations are smaller than EPID-based variations and vary according to tumour location. When using kV-CBCT a large variety of anatomical changes is revealed, which cannot be observed with MV-EPID.

Feasibility of dynamic adaptive passive scattering proton therapy with computed tomography image guidance in the lung.

Hypo-fractionated proton beam therapy (PBT) is an approach that has been increasingly explored over the past decade. It requires high geometric accuracy for targeting of the PBT beams. However, image-guided PBT is currently commonly performed with kV X-ray images of bony anatomy. A dynamic adaptive passive scattering PBT system using computed tomography-based three-dimensional image guidance was developed, and its effectiveness was then evaluated retrospectively in patients with nonsmall cell lung cancer (NSCLC). The dynamic adaptive PBT system consisted of computed tomography-based image registration and proton dose calculation using a simplified Monte Carlo algorithm, with a range adaptation system that could adjust the range shifter thickness to alter the dose distribution. Three patients were retrospectively analyzed. All plans, which each had a total dose of 60 Gy (relative biological effectiveness; RBE), were generated using two fields (Gantry angles: 270 degree and 180 degree) in a passive scattering method. Three dose distributions were generated for each patient according to the following different registrations: bone registration, tumor registration, and tumor registration with range adaptation. The following dosimetric parameters were compared with the original plan: target dose coverage at D95% for the clinical target volume (CTV), homogeneity of D5% to D95% for the CTV, and dose distributions in normal tissue (Dmax of Spinal cord and V20 Gy of lung). For the bone registration method, the average D95% and D5% to D95% for the CTV showed average differences from the original plan of -3.7 ± 4.1 Gy (mean ± 1SD; RBE) and 3.6 ± 3.9 Gy (RBE) respectively. The tumor registration method achieved better coverage than the bone registration method, although the dosimetric parameters for coverage and homogeneity still showed average differences in -2.0 ± 2.3 Gy (RBE) and 1.9 ± 2.2 Gy (RBE) respectively. The range adaptive plan showed comparable coverage and homogeneity [D95%: -1.0 ± 1.3 Gy (RBE) and D5% to D95%: 0.9 ± 1.0 Gy (RBE) on average] to the original plan, as well as demonstrating similar normal tissue sparing. The approach could be completed in less than 10 min, including CT acquisition, image registration, dose recalculation with range optimization, and the operator's visual verification. The tumor dose coverage in patients with NSCLC may deteriorate as a result of respiratory or body movement if daily proton range adaptation is not performed. Our approach may provide higher geometric accuracy for localization of the tumor, and the dynamic range adaptation enables us to achieve the planned dose distribution for hypo-fractionated PBT in the lung.

Adaptive kinematics of the proximal carpal row

Objective To analyze the in vivo three-dimensional kinematics of the proximal carpal row by magnetic resonance imaging (MRI) and to delineate the characteristics of the adaptive kinematics of the proximal carpal row in different movement patterns. Methods We studied the in vivo three-dimensional kinematics of the proximal carpal row with a markerless bone registration technique. Magnetic resonance images of 12 healthy volunteers' wrist were acquired during motion patterns of dart throwing motion (DTM), extension-flexion motion (EFM), and radioulnar deviation (RUD). A total of 15 different wrist positions were performed and recorded from each volunteer. Image data were entered into the software designated for carpal kinematics measurement. The respective motions of the scaphoid and triquetrum relative to the lunate in cross-sectional, sagittal and coronal planes were analyzed. Results In DTM, rotation of the scaphoid relative to the lunate was 0 ° in the cross-sectional plane, 23° in the sagittal plane, and 0° in the coronal plane. In cross-sectional and coronal planes, the range of rotation was not statistically significant (t=-0.039, P=0.970; t=0.163, P=0.873), whereas rotation in the sagittal plane was significant (t=-4.521, P=0.001). In EFM, rotation of the scaphoid relative to the lunate was 2 ° in the cross-sectional plane, 48° in the sagittal plane and 15 °in the coronal plane. In the cross-sectional plane, the movement was not significant (t=0.312, P=0.761), whereas rotation in the sagittal and coronal planes showed statistically significant differences (t=-9.206, P=0.000; t=5.697, P=0.000). In RUD, rotation of the scaphoid relative to the lunate was 7° in the cross-sectional plane, 15° in the sagittal plane and 6° in the coronal plane. Data in the cross-sectional and coronal planes were not significant (t=-1.402, P=0.188; t=-1.410, P=0.186), whereas rotation in the sagittal plane showed statistically significant difference (t=3.180, P=0.009). In DTM, rotation of the triquetrum relative to the lunate was 8° in the cross-sectional plane, 8° in the sagittal plane and 8 ° in the coronal plane. Data in the cross-sectional plane were not significant (t= 2.128, P=0.057), whereas rotation in the sagittal and coronal planes showed statistically significant difference (t=-4.439, P=0.001; t=-3.078, P=0.011). In EFM, rotation of the triquetrum relative to the lunate was 2 ° in the cross-sectional plane, 15° in the sagittal plane and 3 ° in the coronal plane. Data in cross-sectional and coronal planes were not significant (t=0.487, P=0.636; t=-1.455, P=0.174), whereas rotation in the sagittal plane showed significant difference (t=-3.547, P=0.005). In RUD, rotation of the triquetrum relative to the lunate was 4 ° in cross-sectional plane, 4° in the sagittal plane and 7° in the coronal plane. Data in the cross-sectional and sagittal planes were not significant (t=1.006, P=0.336; t=1.015, P=0.332), whereas rotation in the coronal plane showed significant differences (t=-2.236, P=0.047). Conclusion In different movement patterns, the proximal carpal row adapts accordingly. The adaptive motion in the sagittal plane is the most significant, yet the intercarpal motion of proximal carpal row in the cross-sectional and coronal planes are synchronous. Adaptive range of motion between the scaphoid and lunate is much more than that between the lunate and triquetrum. Adaptive range of motion in the EFM is greater than that in the DTM and RUD. The adaptive motion of the proximal carpal row maintains the overall harmonious motion of the wrist. Key words: Carpal bones; Magnetic resonance imaging; Imaging,three-dimensional; Kinematics

Target localization of 3D versus 4D cone beam computed tomography in lipiodol-guided stereotactic radiotherapy of hepatocellular carcinomas.

BackgroundAim of this study was to comparatively evaluate the accuracy of respiration–correlated (4D) and uncorrelated (3D) cone beam computed tomography (CBCT) in localizing lipiodolized hepatocellular carcinomas during stereotactic body radiotherapy (SBRT).Methods4D–CBCT scans of eighteen HCCs were acquired during free–breathing SBRT following trans–arterial chemo–embolization (TACE) with lipiodol. Approximately 1320 x–ray projections per 4D–CBCT were collected and phase–sorted into ten bins. A 4D registration workflow was followed to register the reconstructed time–weighted average CBCT with the planning mid–ventilation (MidV) CT by an initial bone registration of the vertebrae and then tissue registration of the lipiodol. For comparison, projections of each 4D–CBCT were combined to synthesize 3D–CBCT without phase–sorting. Using the lipiodolized tumor, uncertainties of the treatment setup estimated from the absolute and relative lipiodol position to bone were analyzed separately for 4D– and 3D–CBCT.ResultsQualitatively, 3D–CBCT showed better lipiodol contrast than 4D–CBCT primarily because of a tenfold increase of projections used for reconstruction. Motion artifact was observed to subside in 4D–CBCT compared to 3D–CBCT. Group mean, systematic and random errors estimated from 4D– and 3D–CBCT agreed to within 1 mm in the cranio–caudal (CC) and 0.5 mm in the anterior–posterior (AP) and left–right (LR) directions. Systematic and random errors are largest in the CC direction, amounting to 4.7 mm and 3.7 mm from 3D–CBCT and 5.6 mm and 3.8 mm from 4D–CBCT, respectively. Safety margin calculated from 3D–CBCT and 4D–CBCT differed by 2.1, 0.1 and 0.0 mm in the CC, AP, and LR directions.Conclusions3D–CBCT is an adequate alternative to 4D–CBCT when lipoid is used for localizing HCC during free–breathing SBRT. Similar margins are anticipated with 3D– and 4D–CBCT.

Evaluation and development of an image-guided radiotherapy protocol for prostate and nodes

AbstractPurposeTo evaluate and develop an image-guided radiotherapy (IGRT) protocol for the effective treatment of prostate and pelvic lymph nodes.Methods and materialsThis study comprised of nine patients receiving radiotherapy for node negative prostate cancer, who had a pair of planar kV images taken for 37 treatment fractions. The positioning accuracy for both implanted fiducial markers and pelvic bony anatomy (surrogate for pelvic node position) was calculated using random and systematic errors. Appropriate margins were also determined. All patients followed a strict bladder and bowel protocol before computed tomography planning and treatment.ResultsIn total, 292 sets of images were used for fiducial marker and pelvic bone registration. A discrepancy of &gt;5 mm between the fiducial markers and the anatomical pelvic bone was seen in 4% of treatment sessions. The maximum displacement observed between the fiducial match and the bone match was 7, 10 and 4 mm in the A/P (anterior/posterior), S/I (superior/inferior) and R/L (right/left) directions, respectively.ConclusionThe margins used in combination with an online IGRT strategy ensure both the fiducial match and the bone match correlate within 5 mm thus allows good coverage of both prostate and nodal target volumes. It is essential that this is combined with a strict bladder and rectal preparation protocol to ensure accuracy and reproducibility.

SU‐F‐J‐57: Effectiveness of Daily CT‐Based Three‐Dimensional Image Guided and Adaptive Proton Therapy

Purpose:Daily CT‐based three‐dimensional image‐guided and adaptive (CTIGRT‐ART) proton therapy system was designed and developed. We also evaluated the effectiveness of the CTIGRT‐ART.Methods:Retrospective analysis was performed in three lung cancer patients: Proton treatment planning was performed using CT image datasets acquired by Toshiba Aquilion ONE. Planning target volume and surrounding organs were contoured by a well‐trained radiation oncologist. Dose distribution was optimized using 180‐deg. and 270‐deg. two fields in passive scattering proton therapy. Well commissioned Simplified Monte Carlo algorithm was used as dose calculation engine. Daily consecutive CT image datasets was acquired by an in‐room CT (Toshiba Aquilion LB). In our in‐house program, two image registrations for bone and tumor were performed to shift the isocenter using treatment CT image dataset. Subsequently, dose recalculation was performed after the shift of the isocenter. When the dose distribution after the tumor registration exhibits change of dosimetric parameter of CTV D90% compared to the initial plan, an additional process of was performed that the range shifter thickness was optimized. Dose distribution with CTV D90% for the bone registration, the tumor registration only and adaptive plan with the tumor registration was compared to the initial plan.Results:In the bone registration, tumor dose coverage was decreased by 16% on average (Maximum: 56%). The tumor registration shows better coverage than the bone registration, however the coverage was also decreased by 9% (Maximum: 22%) The adaptive plan shows similar dose coverage of the tumor (Average: 2%, Maximum: 7%).Conclusion:There is a high possibility that only image registration for bone and tumor may reduce tumor coverage. Thus, our proposed methodology of image guidance and adaptive planning using the range adaptation after tumor registration would be effective for proton therapy.This research is partially supported by Japan Agency for Medical Research and Development (AMED).

WE-FG-202-05: Quantification of Bone Flare On [F-18] NaF PET/CT in Metastatic Prostate Cancer

Purpose: Bone flare has been observed on Tc-99m bone scans during early assessment in metastatic Castration-Resistant Prostate Cancer (mCRPC) patients receiving select androgen-signaling pathway (AR) targeted treatments, including CYP17-inhibitor Abiraterone. This study investigates the appearance and potential clinical impact of bone flare in mCRPC patients receiving CYP17-inhibitors using 18F-NaF PET/CT. Methods: Twenty-three mCRPC patients being treated with CYP17-inhibitors received NaF PET/CT scans at baseline, week 6, and week 12 of treatment. Individual lesions were identified using a SUV>15 threshold within skeletal regions and articulated bone registration was used to track lesions between scans. Standard SUV metrics were extracted globally for each patient (pSUV) and for each individual lesion (iSUV). Differences in metrics across time-points were compared using Wilcoxon signed-rank tests. Cox proportional hazard regression analyses were conducted between global metrics and progression-free survival (PFS). Results: Nineteen patients (83%) showed increasing NaF PET global metrics at week 6, with pSUVtotal reflecting consensus change across other global metrics with median increase +33% (range +2 to 205%). Of these patients, 14 showed subsequent decrease in pSUVtotal, with a median of −17% (range −76 to −1%), indicating flare phenomenon. Increasing pSUVmean at week 6 correlated with extended clinical PFS (HR = 0.58, p=0.02). New lesions did not account for the initial increase in global NaF metrics. Lesion-level analysis reveals 316 lesions in the 14 patients exhibiting global flare. On average, 75% (sd: 22%) of lesions follow global trends with iSUVtotal increasing at week 6 and 65% (sd: 17%) showing iSUVtotal decrease at week 12. Conclusion: Bone flare was detected on NaF PET/CT in the first 6 weeks of treatment for mCRPC patients receiving CYP17-inhibitors, subsiding by week 12. Characterization provided in this study suggests prolonged PFS in patients showing bone flare early in select AR-directed treatments. Prostate Cancer Foundation

In vivo three-dimensional elbow biomechanics during forearm rotation

It is unclear how elbow kinematics changes during forearm rotation. This study investigated in vivo 3-dimensional elbow kinematics during forearm rotation. We studied 12 normal elbows using in vivo 3-dimensional computed tomography data in maximum forearm supination, neutral, and maximum pronation with the elbows in extension. We measured the motion of the radius and ulna relative to the humerus using a markerless bone registration technique and the contact area of the radiocapitellar joint, proximal radioulnar joint, and ulnohumeral joint using a proximity mapping method. When the forearm rotated from the supinated position to the pronated position, the radius showed significant varus rotation, internal rotation, and extension relative to the humerus. The center of the radial head significantly translated anteriorly, proximally, and laterally. The ulna significantly rotated in valgus, and the deepest point on the sagittal ridge of the trochlear notch translated medially with forearm pronation. The contact area of the radiocapitellar joint was largest in pronation. The contact area of the proximal radioulnar joint was largest in supination. The contact area of the ulnohumeral joint showed no significant change during forearm rotation. In pronation, because of the proximal migration of the radial head, the radiocapitellar joint was most congruent compared with other positions. The proximal radioulnar joint was most congruent in supination. The ulnohumeral joint congruency was not affected by forearm rotation. This study provides useful information for understanding 3-dimensional elbow motion and joint osseous stability related to forearm rotation.

Tomographie conique quotidienne pour les traitements pelviens et prostatiques : étude interobservateurs

PurposeThis work evaluated the interobserver variability in cone beam computed tomography (CBCT) registration for prostate cancers treated with intensity-modulated radiotherapy. Material and methodsTwelve technologists realized 286 CBCT/CT registrations (bone registration followed by prostate to prostate registration). The registration results were compared to those obtained by two radiation oncologists (reference). Each technologist reported the shifts calculated by the software in all three axes. A statistical analysis allowed us to calculate the minimum threshold under which 95% of the observers found similar values. A variance analysis followed by the post hoc test were used to find differences in interobserver registration variability and determine whether any individual users performed registrations which differed significantly from those of the other users. ResultsThe registration differences compared to the reference in the three directions in terms of 95th percentile are: 2.1mm left–right, 3.5mm target–gun, 7.3mm anterior–posterior. In the posterior direction, 4% of the observers have found differences superior to 8mm, margin used in routine without the use of a daily CBCT. The variance test revealed a P-value <0.05 only for target–gun and for all observers there was no significant difference compared to the reference. ConclusionThis study confirmed the interest of a 3D tissue registration for prostate treatments. The registration study showed a good interobserver reproducibility. This showed the importance of a daily CBCT/CT registration in prostate treatment with the possibility of a planning target volume margin reduction in the three directions. An evaluation of a partial delegation of registration to technologists should be done by the radiation oncologists.

SU-E-J-88: The Study of Setup Error Measured by CBCT in Postoperative Radiotherapy for Cervical Carcinoma

Purpose: To compare two registration methods in the CBCT guided radiotherapy for cervical carcinoma, analyze the setup errors and registration methods, determine the margin required for clinical target volume(CTV) extending to planning target volume(PTV). Methods: Twenty patients with cervical carcinoma were enrolled. All patients were underwent CT simulation in the supine position. Transfering the CT images to the treatment planning system and defining the CTV, PTV and the organs at risk (OAR), then transmit them to the XVI workshop. CBCT scans were performed before radiotherapy and registered to planning CT images according to bone and gray value registration methods. Compared two methods and obtain left-right(X), superior-inferior(Y), anterior-posterior (Z) setup errors, the margin required for CTV to PTV were calculated. Results: Setup errors were unavoidable in postoperative cervical carcinoma irradiation. The setup errors measured by method of bone (systemic ± random) on X(1eft.right),Y(superior.inferior),Z(anterior.posterior) directions were(0.24±3.62),(0.77±5.05) and (0.13±3.89)mm, respectively, the setup errors measured by method of grey (systemic ± random) on X(1eft-right), Y(superior-inferior), Z(anterior-posterior) directions were(0.31±3.93), (0.85±5.16) and (0.21±4.12)mm, respectively.The spatial distributions of setup error was maximum in Y direction. The margins were 4 mm in X axis, 6 mm in Y axis, 4 mm in Z axis respectively.These two registration methodsmore » were similar and highly recommended. Conclusion: Both bone and grey registration methods could offer an accurate setup error. The influence of setup errors of a PTV margin would be suggested by 4mm, 4mm and 6mm on X, Y and Z directions for postoperative radiotherapy for cervical carcinoma.« less

SU‐E‐J‐25: End‐To‐End (E2E) Testing On TomoHDA System Using a Real Pig Head for Intracranial Radiosurgery

Purpose:To determine the MVCT imaging uncertainty on the TomoHDA system for intracranial radiosurgery treatments. To determine the end‐to‐end (E2E) overall accuracy of the TomoHDA system for intracranial radiosurgery.Methods:A pig head was obtained from the butcher, cut coronally through the brain, and preserved in formaldehyde. The base of the head was fixed to a positioning plate allowing precise movement, i.e. translation and rotation, in all 6 axes. A repeatability test was performed on the pig head to determine uncertainty in the image bone registration algorithm. Furthermore, the test studied images with MVCT slice thicknesses of 1 and 3 mm in unison with differing scan lengths. A sensitivity test was performed to determine the registration algorithm's ability to find the absolute position of known translations/rotations of the pig head. The algorithm's ability to determine absolute position was compared against that of manual operators, i.e. a radiation therapist and radiation oncologist. Finally, E2E tests for intracranial radiosurgery were performed by measuring the delivered dose distributions within the pig head using Gafchromic films.Results:The repeatability test uncertainty was lowest for the MVCTs of 1‐mm slice thickness, which measured less than 0.10 mm and 0.12 deg for all axes. For the sensitivity tests, the bone registration algorithm performed better than human eyes and a maximum difference of 0.3 mm and 0.4 deg was observed for the axes. E2E test results in absolute position difference measured 0.03 ± 0.21 mm in x‐axis and 0.28 ± 0.18 mm in y‐axis. A maximum difference of 0.32 and 0.66 mm was observed in × and y, respectively. The average peak dose difference between measured and calculated dose was 2.7 cGy or 0.4%.Conclusion:Our tests using a pig head phantom estimate the TomoHDA system to have a submillimeter overall accuracy for intracranial radiosurgery.

Automatic bone detection and soft tissue aware ultrasound-CT registration for computer-aided orthopedic surgery.

The transfer of preoperative CT data into the tracking system coordinates within an operating room is of high interest for computer-aided orthopedic surgery. In this work, we introduce a solution for intra-operative ultrasound-CT registration of bones. We have developed methods for fully automatic real-time bone detection in ultrasound images and global automatic registration to CT. The bone detection algorithm uses a novel bone-specific feature descriptor and was thoroughly evaluated on both in-vivo and ex-vivo data. A global optimization strategy aligns the bone surface, followed by a soft tissue aware intensity-based registration to provide higher local registration accuracy. We evaluated the system on femur, tibia and fibula anatomy in a cadaver study with human legs, where magnetically tracked bone markers were implanted to yield ground truth information. An overall median system error of 3.7 mm was achieved on 11 datasets. Global and fully automatic registration of bones aquired with ultrasound to CT is feasible, with bone detection and tracking operating in real time for immediate feedback to the surgeon.