Validation of biomechanical deformable image registration in the abdomen, thorax, and pelvis in a commercial radiotherapy treatment planning system.

Purpose: The accuracy of deformable image registration tools can vary widely between imaging modalities and specific implementations of the same algorithms. A biomechanical model-based algorithm initially developed in-house at an academic institution was translated into a commercial radiotherapy treatment planning system and validated for multiple imaging modalities and anatomic sites.

Methods: Biomechanical deformable registration (Morfeus) is a geometry-driven algorithm based on the finite element method.

Utility and validation of biomechanical deformable image registration in low-contrast images.

Purpose: The application of a biomechanical deformable image registration algorithm has been demonstrated to overcome the potential limitations in the use of intensity-based algorithms on low-contrast images that lack prominent features. Because validation of deformable registration is particularly challenging on such images, the dose distribution predicted via a biomechanical algorithm was evaluated using the measured dose from a deformable dosimeter.

Methods And Materials: A biomechanical model-based image registration algorithm registered computed tomographic (CT) images of an elastic radiochromic dosimeter between its undeformed and deformed positions.

Dose escalated liver stereotactic body radiation therapy at the mean respiratory position.

Purpose: The dosimetric impact of dose probability based planning target volume (PTV) margins for liver cancer patients receiving stereotactic body radiation therapy (SBRT) was compared with standard PTV based on the internal target volume (ITV). Plan robustness was evaluated by accumulating the treatment dose to ensure delivery of the intended plan.

Methods And Materials: Twenty patients planned on exhale CT for 27 to 50 Gy in 6 fractions using an ITV-based PTV and treated free-breathing were retrospectively evaluated.

Simplified strategies to determine the mean respiratory position for liver radiation therapy planning.

Purpose: Establishing the time-weighted mean respiratory position in the liver is challenging due to poor tumor contrast on 4-dimensional (4D) imaging. The purpose of this study is to validate simplified strategies in determining the mean position of liver tumors for radiation therapy planning, and quantify the potential for planning target volume (PTV) reduction.

Methods And Materials: Full, 10-phase 4D computed tomography (CT) data sets from 10 liver radiation therapy patients were analyzed to compare 2 techniques.

Individualized 3D reconstruction of normal tissue dose for patients with long-term follow-up: a step toward understanding dose risk for late toxicity.

Purpose: Understanding the relationship between normal tissue dose and delayed radiation toxicity is an important component of developing more effective radiation therapy. Late outcome data are generally available only for patients who have undergone 2-dimensional (2D) treatment plans. The purpose of this study was to evaluate the accuracy of 3D normal tissue dosimetry derived from reconstructed 2D treatment plans in Hodgkin's lymphoma (HL) patients.

A novel technique to enable experimental validation of deformable dose accumulation.

Purpose: To propose a novel technique to experimentally validate deformable dose algorithms by measuring 3D dose distributions under the condition of deformation using deformable gel dosimeters produced by a novel gel fabrication method.

Method: Five gel dosimeters, two rigid control gels and three deformable gels, were manufactured and treated with the same conformal plan that prescribed 400 cGy to the isocenter. The control gels were treated statically; the deformable gels were treated while being compressed by an actuation device to simulate breathing motion (amplitude of compression  = 1, 1.

Navigator channel adaptation to reconstruct three dimensional heart volumes from two dimensional radiotherapy planning data.

Background: Biologically-based models that utilize 3D radiation dosimetry data to estimate the risk of late cardiac effects could have significant utility for planning radiotherapy in young patients. A major challenge arises from having only 2D treatment planning data for patients with long-term follow-up. In this study, we evaluate the accuracy of an advanced deformable image registration (DIR) and navigator channels (NC) adaptation technique to reconstruct 3D heart volumes from 2D radiotherapy planning images for Hodgkin's Lymphoma (HL) patients.

Accumulated dose in liver stereotactic body radiotherapy: positioning, breathing, and deformation effects.

Purpose: To investigate the accumulated dose deviations to tumors and normal tissues in liver stereotactic body radiotherapy (SBRT) and investigate their geometric causes.

Methods And Materials: Thirty previously treated liver cancer patients were retrospectively evaluated. Stereotactic body radiotherapy was planned on the static exhale CT for 27-60 Gy in 6 fractions, and patients were treated in free-breathing with daily cone-beam CT guidance.

Rectal motion in patients receiving preoperative radiotherapy for carcinoma of the rectum.

Purpose: To assess the movement of rectum, mesorectum, and rectal primary during a course of preoperative chemoradiotherapy.

Methods And Materials: Seventeen patients with Stage II or III rectal cancer had a planning CT scan with rectal contrast before commencement of preoperative chemoradiation. The scan was repeated during Weeks 1, 3, and 5 of chemoradiation.

Interfraction liver shape variability and impact on GTV position during liver stereotactic radiotherapy using abdominal compression.

Purpose: For patients receiving liver stereotactic body radiotherapy (SBRT), abdominal compression can reduce organ motion, and daily image guidance can reduce setup error. The reproducibility of liver shape under compression may impact treatment delivery accuracy. The purpose of this study was to measure the interfractional variability in liver shape under compression, after best-fit rigid liver-to-liver registration from kilovoltage (kV) cone beam computed tomography (CBCT) scans to planning computed tomography (CT) scans and its impact on gross tumor volume (GTV) position.

Evaluating the extent of cell death in 3D high frequency ultrasound by registration with whole-mount tumor histopathology.

Purpose: High frequency ultrasound imaging, 10-30 MHz, has the capability to assess tumor response to radiotherapy in mouse tumors as early as 24 h after treatment administration. The advantage of this technique is that the image contrast is generated by changes in the physical properties of dying cells. Therefore, a subject can be imaged before and multiple times during the treatment without the requirement of injecting specialized contrast agents.

Effect of breathing motion on radiotherapy dose accumulation in the abdomen using deformable registration.

Purpose: To investigate the effect of breathing motion and dose accumulation on the planned radiotherapy dose to liver tumors and normal tissues using deformable image registration.

Methods And Materials: Twenty-one free-breathing stereotactic liver cancer radiotherapy patients, planned on static exhale computed tomography (CT) for 27-60 Gy in six fractions, were included. A biomechanical model-based deformable image registration algorithm retrospectively deformed each exhale CT to inhale CT.

Reconstruction of 3D lung models from 2D planning data sets for Hodgkin's lymphoma patients using combined deformable image registration and navigator channels.

Purpose: Late complications (cardiac toxicities, secondary lung, and breast cancer) remain a significant concern in the radiation treatment of Hodgkin's lymphoma (HL). To address this issue, predictive dose-risk models could potentially be used to estimate radiotherapy-related late toxicities. This study investigates the use of deformable image registration (DIR) and navigator channels (NCs) to reconstruct 3D lung models from 2D radiographic planning images, in order to retrospectively calculate the treatment dose exposure to HL patients treated with 2D planning, which are now experiencing late effects.

Adapting population liver motion models for individualized online image-guided therapy.

Respiratory motion varies on a daily basis in abdominal cancer patients, affecting the ability to successfully deliver local therapy and requiring increased treatment margins to account for this variation. Deformable registration techniques can accurately describe respiratory motion, however, online application can be limited by long computational times and user intervention. A technique has been developed to quickly quantify patient breathing motion from respiratory-sorted volumetric images by calculating 1D shifts in image intensities between spatially corresponding regions of interest (navigator channels) on patient's images.

Accuracy and sensitivity of finite element model-based deformable registration of the prostate.

Purpose: Evaluate the accuracy and the sensitivity to contour variation and model size of a finite element model-based deformable registration algorithm for the prostate.

Methods And Materials: Two magnetic resonance images (MRIs) were obtained for 21 prostate patients with three implanted markers. A single observer contoured the prostate and markers and performed blinded recontouring of the first MRI.

Improving image-guided target localization through deformable registration.

Purpose: To quantify the improvements in online target localization using kV cone beam CT (CBCT) with deformable registration.

Methods And Material: Twelve patients treated under a 6 fraction liver cancer radiation therapy protocol were imaged in breath hold using kV CBCT at each treatment fraction. The images were imported into the treatment planning software and rigidly registered by fitting the liver, identified on the daily kV CBCT image, into the liver contours, previously drawn on the planning CT.

Development of multiorgan finite element-based prostate deformation model enabling registration of endorectal coil magnetic resonance imaging for radiotherapy planning.

Purpose: Endorectal coil (ERC) magnetic resonance imaging (MRI) provides superior visualization of the prostate compared with computed tomography at the expense of deformation. This study aimed to develop a multiorgan finite element deformable method, Morfeus, to accurately co-register these images for radiotherapy planning.

Methods: Patients with prostate cancer underwent fiducial marker implantation and computed tomography simulation for radiotherapy planning.