Image-guided Alignment Research Articles

Image-Guided Measurement of Radiation Force Induced by Focused Ultrasound Beams.

The radiation force balance (RFB) is a widely used method for measuring acoustic power output of ultrasonic transducers. The reflecting cone target is attractive due to its simplicity and long-term stability, at a reasonable cost. However, accurate measurements using this method depend on the alignment between the ultrasound beam and cone axes, especially for highly focused beams utilized in therapeutic applications. With the advent of dual-mode ultrasound arrays (DMUAs) for imaging and therapy, image-guided measurements of acoustic output using the RFB method can be used to improve measurement accuracy. In this article, we describe an image-guided RFB measurement of focused DMUA beams using a widely used commercial instrument. DMUA imaging is used to optimize the alignment between the acoustic beam and reflecting cone axes. In addition to image-guided alignment, DMUA echo data is used to track the displacement of the cone, which provides an auxiliary measurement of acoustic power. Experimental results using a DMUA prototype with [Formula: see text] shows that 1-2 mm of misalignment can result in 5%-14% error in the measured acoustic power. In addition to the use of B-mode image guidance for improving measurement accuracy, we present preliminary results demonstrating the benefit of displacement tracking using real-time DMUA imaging during the application of (sub)therapeutic focused beams. Displacement tracking provides a direct measurement of the radiation force with high sensitivity and follows the expected dependence on changes in amplitude and duty cycle (DC) of the focused ultrasound (FUS) beam. This could lead to simpler, more reliable methods for measuring acoustic power based on the radiation force principle. Combined with appropriate computational modeling, the direct measurement of acoustic radiation force could lead to reliable dosimetry in situ in emerging applications such as transcranial FUS (tFUS) therapies.

Efficacy of the Image-Guided Alignment System for a Four-Haptic Hydrophobic Monofocal Toric Intraocular Lens.

To compare the difference in performance between the image-guided alignment system and the manual-marking method in the four-haptic hydrophobic monofocal toric intraocular lens (IOL). Medical records of patients who underwent cataract surgery with a four-haptic hydrophobic monofocal toric IOL implantation between May 2020 and April 2021 and with 3-month visit data available were investigated. Toric IOL misalignment, residual astigmatism, and mean prediction errors between the two groups were compared. This study included 49 eyes of 44 patients (women: 68%; mean age: 67.2±7.0 [range: 47-82] years). Twenty-nine eyes of 26 patients were treated with toric IOL implantation using the image-guided system and 20 eyes of 18 patients were treated using the manual-marking method. No statistical differences were observed regarding the baseline characteristics of the two groups. Three months after the surgery, the misalignment of the toric IOL was significantly lower in the image-guided group (2.18°±0.65°, range: 1.26°-3.95°) than in the manual; marking group (4.72°±0.74°, range: 3.44°-6.21°; P <0.001). In comparison to the manual-marking method, the image-guided system reduced the misalignment of a four-haptic hydrophobic monofocal toric IOL.

Impact of breath-hold level on positional error aligned by stent/Lipiodol in Hepatobiliary radiotherapy with breath-hold respiratory control

BackgroundRespiratory motion management with breath hold for patients with hepatobiliary cancers remain a challenge in the precise positioning for radiotherapy. We compared different image-guided alignment markers for estimating positional errors, and investigated the factors associated with positional errors under breath-hold control.MethodsSpirometric motion management system (SDX) for breath holds was used in 44 patients with hepatobiliary tumor. Among them, 28 patients had a stent or embolized materials (lipiodol) as alignment markers. Cone-beam computed tomography (CBCT) and kV-orthogonal images were compared for accuracy between different alignment references. Breath-hold level (BHL) was practiced, and BHL variation (ΔBHL) was defined as the standard deviation in differences between actual BHLs and baseline BHL. Mean BHL, ΔBHL, and body-related factors were analyzed for the association with positional errors.ResultsUsing the reference CBCT, the correlations of positional errors were significantly higher in those with stent/lipiodol than when the vertebral bone was used for alignment in three dimensions. Patients with mean BHL > 1.4 L were significantly taller (167.6 cm vs. 161.6 cm, p = 0.03) and heavier (67.1 kg vs. 57.4 kg, p = 0.02), and had different positional error in the craniocaudal direction (− 0.26 cm [caudally] vs. + 0.09 cm [cranially], p = 0.01) than those with mean BHL < 1.4 L. Positional errors were similar for patients with ΔBHL< 0.03 L and > 0.03 L.ConclusionUnder rigorous breath-hold respiratory control, BHL correlated with body weight and height. With more accurate alignment reference by stent/lipiodol, actual BHL but not breath-hold variation was associated with craniocaudal positional errors.

An end-to-end assessment of range uncertainty in proton therapy using animal tissues

Accurate assessment of range uncertainty is critical in proton therapy. However, there is a lack of data and consensus on how to evaluate the appropriate amount of uncertainty. The purpose of this study is to quantify the range uncertainty in various treatment conditions in proton therapy, using transmission measurements through various animal tissues.Animal tissues, including a pig head, beef steak, and lamb leg, were used in this study. For each tissue, an end-to-end test closely imitating patient treatments was performed. This included CT scan simulation, treatment planning, image-guided alignment, and beam delivery. Radio-chromic films were placed at various depths in the distal dose falloff region to measure depth dose. Comparisons between measured and calculated doses were used to evaluate range differences.The dose difference at the distal falloff between measurement and calculation depends on tissue type and treatment conditions. The estimated range difference was up to 5, 6 and 4 mm for the pig head, beef steak, and lamb leg irradiation, respectively.Our study shows that the TPS was able to calculate proton range within about 1.5% plus 1.5 mm. Accurate assessment of range uncertainty in treatment planning would allow better optimization of proton beam treatment, thus fully achieving proton beams’ superior dose advantage over conventional photon-based radiation therapy.

Acute and Late Toxicity of Prostate Radiation Therapy Utilizing Fiducial Versus Cone Beam Computed Tomography Daily Alignment

Purpose/Objective(s)To compare the rates of acute and late gastrointestinal (GI) and genitourinary (GU) toxicity associated with daily alignment to implanted fiducials via kV radiographs versus alignment to the prostate via cone-beam computed tomography (CBCT).Materials/MethodsTwo hundred twelve patients with clinically localized prostate cancer treated with hypofractionated prostate radiation therapy (RT) between 2005 and 2011 were included in this analysis. All patients received 70 Gy to the prostate in 28 fractions and 103 patients received simultaneous 50.4 Gy to the pelvic lymph nodes. Daily image-guided alignment was performed either to implanted fiducial markers with kV radiographs or to the prostate or prostate-rectum interface via CBCT. Acute and late GI and GU toxicity were retrospectively scored by the CTCAE 4.0 scale and statistical analysis was performed using IBM SPSS version 22 software.ResultsScientific Abstract 2589; TableProstate-only (n = 109)Fiducials (n = 23)CBCT (n = 86)PAcute GI217.214Acute GU1141.990Late GI32.020Late GU26.650Lymph Nodes treated (n = 103)Fiducials (n = 19)CBCT (n = 84)PAcute GI731.996Acute GU1341.122Late GI113.383Late GU17.842 Open table in a new tab ConclusionsThe acute GU and GI toxicities are similar in patients receiving fiducial-based or CBCT alignment. For patients receiving prostate-only RT, the rate of late GI toxicity was increased for patients with implanted fiducials. Late GU toxicity was not increased for patients receiving fiducial-based alignment despite the inability to evaluate daily bladder filling in this group. Purpose/Objective(s)To compare the rates of acute and late gastrointestinal (GI) and genitourinary (GU) toxicity associated with daily alignment to implanted fiducials via kV radiographs versus alignment to the prostate via cone-beam computed tomography (CBCT). To compare the rates of acute and late gastrointestinal (GI) and genitourinary (GU) toxicity associated with daily alignment to implanted fiducials via kV radiographs versus alignment to the prostate via cone-beam computed tomography (CBCT). Materials/MethodsTwo hundred twelve patients with clinically localized prostate cancer treated with hypofractionated prostate radiation therapy (RT) between 2005 and 2011 were included in this analysis. All patients received 70 Gy to the prostate in 28 fractions and 103 patients received simultaneous 50.4 Gy to the pelvic lymph nodes. Daily image-guided alignment was performed either to implanted fiducial markers with kV radiographs or to the prostate or prostate-rectum interface via CBCT. Acute and late GI and GU toxicity were retrospectively scored by the CTCAE 4.0 scale and statistical analysis was performed using IBM SPSS version 22 software. Two hundred twelve patients with clinically localized prostate cancer treated with hypofractionated prostate radiation therapy (RT) between 2005 and 2011 were included in this analysis. All patients received 70 Gy to the prostate in 28 fractions and 103 patients received simultaneous 50.4 Gy to the pelvic lymph nodes. Daily image-guided alignment was performed either to implanted fiducial markers with kV radiographs or to the prostate or prostate-rectum interface via CBCT. Acute and late GI and GU toxicity were retrospectively scored by the CTCAE 4.0 scale and statistical analysis was performed using IBM SPSS version 22 software. ResultsScientific Abstract 2589; TableProstate-only (n = 109)Fiducials (n = 23)CBCT (n = 86)PAcute GI217.214Acute GU1141.990Late GI32.020Late GU26.650Lymph Nodes treated (n = 103)Fiducials (n = 19)CBCT (n = 84)PAcute GI731.996Acute GU1341.122Late GI113.383Late GU17.842 Open table in a new tab ConclusionsThe acute GU and GI toxicities are similar in patients receiving fiducial-based or CBCT alignment. For patients receiving prostate-only RT, the rate of late GI toxicity was increased for patients with implanted fiducials. Late GU toxicity was not increased for patients receiving fiducial-based alignment despite the inability to evaluate daily bladder filling in this group. The acute GU and GI toxicities are similar in patients receiving fiducial-based or CBCT alignment. For patients receiving prostate-only RT, the rate of late GI toxicity was increased for patients with implanted fiducials. Late GU toxicity was not increased for patients receiving fiducial-based alignment despite the inability to evaluate daily bladder filling in this group.

WE-F-16A-04: Micro-Irradiator Treatment Verification with High-Resolution 3D-Printed Rodent-Morphic Dosimeters

Purpose: Pre-clinical micro-radiation therapy studies often utilize very small beams (∼0.5-5mm), and require accurate dose delivery in order to effectively investigate treatment efficacy. Here we present a novel high-resolution absolute 3D dosimetry procedure, capable of ∼100-micron isotopic dosimetry in anatomically accurate rodent-morphic phantoms Methods: Anatomically accurate rat-shaped 3D dosimeters were made using 3D printing techniques from outer body contours and spinal contours outlined on CT. The dosimeters were made from a radiochromic plastic material PRESAGE, and incorporated high-Z PRESASGE inserts mimicking the spine. A simulated 180-degree spinal arc treatment was delivered through a 2 step process: (i) cone-beam-CT image-guided positioning was performed to precisely position the rat-dosimeter for treatment on the XRad225 small animal irradiator, then (ii) treatment was delivered with a simulated spine-treatment with a 180-degree arc with 20mm x 10mm cone at 225 kVp. Dose distribution was determined from the optical density change using a high-resolution in-house optical-CT system. Absolute dosimetry was enabled through calibration against a novel nano-particle scintillation detector positioned in a channel in the center of the distribution. Results: Sufficient contrast between regular PRESAGE (tissue equivalent) and high-Z PRESAGE (spinal insert) was observed to enable highly accurate image-guided alignment and targeting. The PRESAGE was found to have linear optical density (OD) change sensitivity with respect to dose (R2 = 0.9993). Absolute dose for 360-second irradiation at isocenter was found to be 9.21Gy when measured with OD change, and 9.4Gy with nano-particle detector- an agreement within 2%. The 3D dose distribution was measured at 500-micron resolution Conclusion: This work demonstrates for the first time, the feasibility of accurate absolute 3D dose measurement in anatomically accurate rat phantoms containing variable density PRESAGE material (tissue equivalent and bone equivalent). This method enables precise treatment verification of micro-radiation therapies, and enhances the robustness of tumor radio-response studies. This work was supported by NIH R01CA100835.

Estimation of optimal pivot point for remote center of motion alignment in surgery.

The determination of an optimal pivot point ([Formula: see text]) is important for instrument manipulation in minimally invasive surgery. Such knowledge is of particular importance for robotic-assisted surgery where robots need to rotate precisely around a specific point in space in order to minimize trauma to the body wall while maintaining position control. Remote center of motion (RCM) mechanisms are commonly used, where the RCM point is manually and visually aligned. If not positioned appropriately, this misalignment might lead to intolerably high forces on the body wall with increased risk of postoperative complications or instrument damage. An automated method to align the RCM with the [Formula: see text] was developed and tested. Computer vision and a lightweight calibration procedure are used to estimate the optimal pivot point. One or two pre-calibrated cameras viewing the surgical scene are employed. The surgeon is asked to make short pivoting movements, applying as little torque as possible, with an instrument of choice passing through the insertion point while camera images are being recorded. The physical properties of an instrument rotating around a pivot point are exploited in a random sample consensus scheme to robustly estimate the ideal position of the RCM in the image planes. Triangulation is used to estimate the RCM position in 3D. Experiments were performed on a specially designed mockup to test the method. The position of the pivot point is estimated with an average error less than 1.85 mm using two webcams placed from approximately 30 cm to 1 m away from the scene. The entire procedure was completed in a few seconds. In automated method to estimate the ideal position of the RCM was shown to be reliable. The method can be implemented within a visual servoing approach to automatically place the RCM point, or the results can be displayed on a screen to provide guidance to the surgeon. Further work includes the development of an image-guided alignment method and validation with in vivo experiments.

Auto-masked 2D/3D image registration and its validation with clinical cone-beam computed tomography

Image-guided alignment procedures in radiotherapy aim at minimizing discrepancies between the planned and the real patient setup. For that purpose, we developed a 2D/3D approach which rigidly registers a computed tomography (CT) with two x-rays by maximizing the agreement in pixel intensity between the x-rays and the corresponding reconstructed radiographs from the CT. Moreover, the algorithm selects regions of interest (masks) in the x-rays based on 3D segmentations from the pre-planning stage. For validation, orthogonal x-ray pairs from different viewing directions of 80 pelvic cone-beam CT (CBCT) raw data sets were used. The 2D/3D results were compared to corresponding standard 3D/3D CBCT-to-CT alignments. Outcome over 8400 2D/3D experiments showed that parametric errors in root mean square were <0.18° (rotations) and <0.73 mm (translations), respectively, using rank correlation as intensity metric. This corresponds to a mean target registration error, related to the voxels of the lesser pelvis, of <2 mm in 94.1% of the cases. From the results we conclude that 2D/3D registration based on sequentially acquired orthogonal x-rays of the pelvis is a viable alternative to CBCT-based approaches if rigid alignment on bony anatomy is sufficient, no volumetric intra-interventional data set is required and the expected error range fits the individual treatment prescription.

Evaluation of Image-Guided Positioning for Frameless Intracranial Radiosurgery

The standard for target alignment and immobilization in intracranial radiosurgery is frame-based alignment and rigid immobilization using a stereotactic head ring. Recent improvements in image-guidance systems have introduced the possibility of image-guided radiosurgery with nonrigid immobilization. We present data on the alignment accuracy and patient stability of a frameless image-guided system. Isocenter alignment errors were measured for in vitro studies in an anthropomorphic phantom for both frame-based stereotactic and frameless image-guided alignment. Subsequently, in vivo studies assessed differences between frame-based and image-guided alignment in patients who underwent frame-based intracranial radiosurgery. Finally, intratreatment target stability was determined by image-guided alignment performed before and after image-guided mask immobilized radiosurgery. In vitro hidden target localization errors were comparable for the framed (0.7 +/- 0.5 mm) and image-guided (0.6 +/- 0.2 mm) techniques. The in vivo differences in alignment were 0.9 +/- 0.5 mm (anteroposterior), -0.2 +/- 0.4 mm (superoinferior), and 0.3 +/- 0.5 mm (lateral). For in vivo stability tests, the mean distance differed between the pre- and post-treatment positions with mask-immobilized radiosurgery by 0.5 +/- 0.3 mm. Frame-based and image-guided alignment accuracy in vitro was comparable for the system tested. In vivo tests showed a consistent trend in the difference of alignment in the anteroposterior direction, possibly due to torque to the ring and mounting system with frame-based localization. The mask system as used appeared adequate for patient immobilization.

Proton Treatment Room Concepts for Precision and Efficiency

Proton radiation therapy involves accurate delivery of proton beams to targets inside the body without direct visual control of the internal anatomy. Targeting of the tumor and avoidance of critical structures within the patient have to be both accurate and precise to achieve the desired therapeutic results. Good understanding of proton radiation delivery and patient alignment concepts in the treatment room is essential to achieve this goal. This overview article presents treatment room concepts that will ensure precise proton beam delivery and, at the same time, guarantee an efficient patient throughput. Concepts discussed include effective patient immobilization, image-guided alignment verification, appropriate training of radiotherapists, and the physician's integrative role in understanding the complex spatial relationships between tumor, organs at risk, treatment beam configuration, and application of proton radiation dose. It will be demonstrated that in addition to the technical armamentarium, now commonplace in modern radiation oncology departments, the interaction between radiation oncologist, medical physicist and radiotherapist is important for efficient operation of a proton treatment facility.

Image-Guided Alignment Verification with Submillimeter Precision for Functional Proton Radiosurgery

Image-Guided Alignment Verification with Submillimeter Precision for Functional Proton Radiosurgery