Prediction of Tumor Control in Y Radioembolization by Logit Models with PET/CT-Based Dose Metrics.

The aim of this work was to develop models for tumor control probability (TCP) in radioembolization with Y PET/CT-derived radiobiologic dose metrics. Patients with primary liver cancer or liver metastases who underwent radioembolization with glass microspheres were imaged with Y PET/CT for voxel-level dosimetry to determine lesion absorbed dose (AD) metrics, biological effective dose (BED) metrics, equivalent uniform dose, and equivalent uniform BED for 28 treatments (89 lesions). The lesion dose-shrinkage correlation was assessed on the basis of RECIST and, when available, modified RECIST (mRECIST) at first follow-up.

Impact of Y PET gradient-based tumor segmentation on voxel-level dosimetry in liver radioembolization.

Background: The purpose was to validate Y PET gradient-based tumor segmentation in phantoms and to evaluate the impact of the segmentation method on reported tumor absorbed dose (AD) and biological effective dose (BED) in Y microsphere radioembolization (RE) patients. A semi-automated gradient-based method was applied to phantoms and patient tumors on the Y PET with the initial bounding volume for gradient detection determined from a registered diagnostic CT or MR; this PET-based segmentation (PS) was compared with radiologist-defined morphologic segmentation (MS) on CT or MRI. AD and BED volume histogram metrics (D90, D70, mean) were calculated using both segmentations and concordance/correlations were investigated.

Beyond Dose: Using Pretherapy Biomarkers to Improve Dose Prediction of Outcomes for Radioimmunotherapy of Non-Hodgkin Lymphoma.

Introduction: Non-Hodgkin Lymphoma patients respond differently to therapy according to inherent biological variations. Pretherapy biomarkers may improve dose-response prediction.

Materials And Methods: Hybrid single-photon emission computed tomography (SPECT)/computed tomography (CT) three-dimensional imaging at multiple time points plus follow-up positron emission tomography (PET)/CT or CT at 2 and 6 months post therapy were used to fit tumor response to combined biological effect and cell clearance models from which three biological effect response parameters (radiosensitivity, cold effect sensitivity, and proliferation potential) were determined per patient.

Using a 2D detector array for meaningful and efficient linear accelerator beam property validations.

Following linear accelerator commissioning, the qualified medical physicist is responsible for monitoring the machine's ongoing performance, detecting and investigating any changes in beam properties, and assessing the impact of unscheduled repairs. In support of these responsibilities, the authors developed a method of using a 2D ionization chamber array to efficiently test and validate important linear accelerator photon beam properties. A team of three physicists identified critical properties of the accelerator and developed constancy tests that were sensitive to each of the properties.

Tumor-Absorbed Dose Predicts Progression-Free Survival Following (131)I-Tositumomab Radioimmunotherapy.

Unlabelled: The study aimed at identifying patient-specific dosimetric and nondosimetric factors predicting outcome of non-Hodgkin lymphoma patients after (131)I-tositumomab radioimmunotherapy for potential use in treatment planning.

Methods: Tumor-absorbed dose measures were estimated for 130 tumors in 39 relapsed or refractory non-Hodgkin lymphoma patients by coupling SPECT/CT imaging with the Dose Planning Method (DPM) Monte Carlo code. Equivalent biologic effect was calculated to assess the biologic effects of nonuniform absorbed dose including the effects of the unlabeled antibody.

Biological-effect modeling of radioimmunotherapy for non-hodgkins lymphoma: determination of model parameters.

Unlabelled: Treatment with Tositumomab and 131I tositumomab anti-CD20 radioimmunotherapy (Bexxar) yields a nonradioactive antibody antitumor response (the so-called cold effect) and a radiation response. Numerical parameter determination by least-squares (LS) fitting was implemented for more accurate parameter estimates in equivalent biological-effect calculations.

Methods: One hundred thirty-two tumors in 37 patients were followed using five or six SPECT/CT studies per patient, three each (typical) post-tracer (0.

Audit tool for external beam radiation therapy departments.

Purpose: Development of a self-contained audit tool for external beam radiation therapy to assess compliance with the major recommendations from professional organizations and generally accepted standards of practice. Intensity modulated radiation therapy, stereotactic body radiation therapy, stereotactic radiosurgery, and volumetric modulated arc therapy were included in this review.

Methods And Materials: A physics quality working group developed a department vision, distinguished and summarized key references, and condensed important elements of good documentation practices.

Bio-effect model applied to 131I radioimmunotherapy of refractory non-Hodgkin's lymphoma.

Purpose: Improved data collection methods have improved absorbed dose estimation by tracking activity distributions and tumor extent at multiple time points, allowing individualized absorbed dose estimation. Treatment with tositumomab and (131)I-tositumomab anti-CD20 radioimmunotherapy (BEXXAR) yields a cold antibody antitumor response (cold protein effect) and a radiation response. Biologically effective contributions, including the cold protein effect, are included in an equivalent biological effect model that was fit to patient data.

Analysis of variation in calibration curves for Kodak XV radiographic film using model-based parameters.

Film calibration is time-consuming work when dose accuracy is essential while working in a range of photon scatter environments. This study uses the single-target single-hit model of film response to fit the calibration curves as a function of calibration method, processor condition, field size and depth. Kodak XV film was irradiated perpendicular to the beam axis in a solid water phantom.

131I-tositumomab radioimmunotherapy: initial tumor dose-response results using 3-dimensional dosimetry including radiobiologic modeling.

Unlabelled: For optimal treatment planning in radionuclide therapy, robust tumor dose-response correlations must be established. Here, fully 3-dimensional (3D) dosimetry was performed coupling SPECT/CT at multiple time points with Monte Carlo-based voxel-by-voxel dosimetry to examine such correlations.

Methods: Twenty patients undergoing (131)I-tositumomab for the treatment of refractory B-cell lymphoma volunteered for the study.

Dose discrepancies in the buildup region and their impact on dose calculations for IMRT fields.

Purpose: Dose accuracy in the buildup region for radiotherapy treatment planning suffers from challenges in both measurement and calculation. This study investigates the dosimetry in the buildup region at normal and oblique incidences for open and IMRT fields and assesses the quality of the treatment planning calculations.

Methods: This study was divided into three parts.

Methodology to incorporate biologically effective dose and equivalent uniform dose in patient-specific 3-dimensional dosimetry for non-Hodgkin lymphoma patients targeted with 131I-tositumomab therapy.

Unlabelled: A 3-dimensional (3D) imaging-based patient-specific dosimetry methodology incorporating antitumor biologic effects using biologically effective dose (BED) and equivalent uniform dose (EUD) was developed in this study. The methodology was applied to the dosimetry analysis of 6 non-Hodgkin lymphoma patients with a total of 10 tumors.

Methods: Six registered SPECT/CT scans were obtained for each patient treated with (131)I-labeled antibody.

Radiographic film dosimetry for IMRT fields in the nearsurface buildup region.

Radiographic film dosimetry provides fast, convenient 2-D dose distributions, but is challenged by the dependence of film response on scatter conditions (i.e., energy dependence).

Assessment of skin dose for breast chest wall radiotherapy as a function of bolus material.

Skin dose assessment for chest wall radiotherapy is important to ensure sufficient dose to the surface target volume without excessive skin reaction. This study quantified changes to the surface doses as a function of bolus material for conventional and intensity modulated radiation therapy (IMRT) tangential fields. Three types of bolus materials (2 mm solid, 2 mm fine mesh and 3.

Accuracy of rapid radiographic film calibration for intensity-modulated radiation therapy verification.

A single calibration film method was evaluated for use with intensity-modulated radiation therapy film quality assurance measurements. The single-film method has the potential advantages of exposure simplicity, less media consumption, and improved processor quality control. Potential disadvantages include cross contamination of film exposure, implementation effort to document delivered dose, and added complication of film response analysis.

Intraperitoneal radioimmunotherapy with a humanized anti-TAG-72 (CC49) antibody with a deleted CH2 region.

The application of intraperitoneal (i.p.) radioimmunotherapy to treat i.

Functional anatomy of the prostate: implications for treatment planning.

Purpose: To summarize the functional anatomy relevant to prostate cancer treatment planning.

Methods And Materials: Coronal, axial, and sagittal T2 magnetic resonance imaging (MRI) and MRI angiography were fused by mutual information and registered with computed tomography (CT) scan data sets to improve definition of zonal anatomy of the prostate and critical adjacent structures.

Results: The three major prostate zones (inner, outer, and anterior fibromuscular) are visible by T2 MRI imaging.

Use and uncertainties of mutual information for computed tomography/ magnetic resonance (CT/MR) registration post permanent implant of the prostate.

Post-implant dosimetric analysis for permanent implant of the prostate benefits from the use of a computed tomography (CT) dataset for optimal identification of the radioactive source (seed) positions and a magnetic resonance (MR) dataset for optimal description of the target and normal tissue volumes. The CT/MR registration process should be fast and sufficiently accurate to yield a reliable dosimetric analysis. Since critical normal tissues typically reside in dose gradient regions, small shifts in the dose distribution could impact the prediction of complication or complication severity.

Surface buildup dose dependence on photon field delivery technique for IMRT.

The more complex delivery techniques required for implementation of intensity-modulated radiotherapy (IMRT) based on inverse planning optimization have changed the relationship between dose at depth and dose at buildup regions near the surface. Surface buildup dose is dependent on electron contamination primarily from the unblocked view of the flattening filter and secondarily from air and collimation systems. To evaluate the impact of beam segmentation on buildup dose, measurements were performed with 10 x 10 cm2 fields, which were delivered with 3 static 3.

Randomized trial of high- and low-source strength (125)I prostate seed implants.

Purpose: A range of (125)I isotope activities is used in permanent prostate implants. In this study, we compared the implant quality and cost in patients randomized to high-source or low-source strength permanent implants.

Methods And Materials: Forty patients were randomized to receive high (0.

Vessel-sparing prostate radiotherapy: dose limitation to critical erectile vascular structures (internal pudendal artery and corpus cavernosum) defined by MRI.

Purpose: Most evidence suggests that impotence after prostate radiation therapy has a vascular etiology. The corpus cavernosum (CC) and the internal pudendal artery (IPA) are the critical vascular structures related to erectile function. This study suggests that it is feasible to markedly decrease radiation dose to the CC and the IPA and directly determine the impact of dose limitation on potency.

The use of mutual information in registration of CT and MRI datasets post permanent implant.

Purpose: To determine the feasibility of registration of MRI and CT datasets post permanent prostate implant by the use of mutual information.

Methods And Materials: Five patients who underwent permanent (125)I implant for prostate carcinoma were studied. Two weeks postimplant an axial CT, T2-weighted-axial, sagittal and coronal MRI, and T1-fat-saturation MRI scans were obtained.

Three-dimensional dose model for the comparison of 177Lu-HuCC49DeltaCH2 and 177Lu-HuCC49 radioimunotherapy in mice bearing intraperitoneal xenografts.

Uptake and dose distributions in peritoneal LS174T colon tumor xenografts were compared for a humanized construct of the CC49 (HuCC49) high-affinity anti-TAG-72 monoclonal antibody and a construct with the CH2 region deleted (HuCC49DeltaCH2), both labeled with (177)Lu using a PA-DOTA bifunctional chelating agent and injected in the peritoneum. Tumors were resected and serially sectioned at 1 h, 4 h, 24 h, and 48 h postinjection. Between 5 and 24 (average 16) sections were retained per tumor for autoradiography.