Navigating the medical physics education and training landscape.

Purpose: The education and training landscape has been profoundly reshaped by the ABR 2012/2014 initiative and the MedPhys Match. This work quantifies these changes and summarizes available reports, surveys, and statistics on education and training.

Methods: We evaluate data from CAMPEP-accredited program websites, annual CAMPEP graduate and residency program reports, and surveys on the MedPhys Match and Professional Doctorate degree (DMP).

A serial 4DCT study to quantify range variations in charged particle radiotherapy of thoracic cancers.

Weekly serial 4DCT scans were acquired under free breathing conditions to assess water-equivalent path length (WEL) variations due to both intrafractional and interfractional changes in tissue thickness and density and to calculate proton dose distributions resulting from anatomical variations observed in serial 4DCT. A template of region of interests (ROIs) was defined on the anterior-posterior (AP) beam's eye view, and WEL measurements were made over these ROIs to quantify chest wall thickness variations. Interfractional proton dose distributions were calculated to assess changes in the expected dose distributions caused by range variations.

SU-E-E-02: The Use of Social Media in a Medical Physics Classroom.

Purpose: The purpose of this presentation is to provide an example of how Facebook has been used in a medical physics classroom.

Methods: Facebook was used in an introductory course in radiation interactions taken by graduate students in a CAMPEP-accredited medical physics program. Facebook served two major functions in the class, as a means for communicating announcements to students, and as a forum for discussion of unclear points in the course.

Quantifying the interfractional displacement of the gastroesophageal junction during radiation therapy for esophageal cancer.

Purpose: Accounting for interfractional changes in tumor location improves the accuracy of radiation treatment delivery. The purpose of this study was to quantify the interfractional displacement of the gastroesophageal junction (GEJ) based on standard treatment setup in patients with esophageal cancer undergoing radiation therapy.

Methods And Materials: Free-breathing four-dimensional computed tomography (4D-CT) datasets were acquired weekly from 22 patients during treatment for esophageal adenocarcinoma.

Dosimetric effects of jaw tracking in step-and-shoot intensity-modulated radiation therapy.

The purpose of this work was to determine the dosimetric benefit to normal tissues by tracking the multi-leaf collimator (MLC) apertures with the photon jaws in step-and-shoot intensity-modulated radiation therapy (IMRT) on the Varian 2100 platform. Radiation treatment plans for ten thoracic, three pediatric, and three head and neck cancer patients were converted to plans with the jaws tracking each segment's MLC apertures, and compared to the original plans in a commercial radiation treatment planning system (TPS). The change in normal tissue dose was evaluated in the new plan by using the parameters V5, V10, and V20 (volumes receiving 5, 10 and 20 Gy, respectively) in the cumulative dose-volume histogram for the following structures: total lung minus gross target volume, heart, esophagus, spinal cord, liver, parotids, and brainstem.

Thoracic target volume delineation using various maximum-intensity projection computed tomography image sets for radiotherapy treatment planning.

Purpose: Four-dimensional computed tomography (4D-CT) is commonly used to account for respiratory motion of target volumes in radiotherapy to the thorax. From the 4D-CT acquisition, a maximum-intensity projection (MIP) image set can be created and used to help define the tumor motion envelope or the internal gross tumor volume (iGTV). The purpose of this study was to quantify the differences in automatically contoured target volumes for usage in the delivery of stereotactic body radiation therapy using MIP data sets generated from one of the four methods: (1) 4D-CT phase-binned (PB) based on retrospective phase calculations, (2) 4D-CT phase-corrected phase-binned (PC-PB) based on motion extrema, (3) 4D-CT amplitude-binned (AB), and (4) cine CT built from all available images.

Interfractional reproducibility of lung tumor location using various methods of respiratory motion mitigation.

Purpose: To determine interfractional reproducibility of the location of lung tumors using respiratory motion mitigation.

Methods And Materials: Free-breathing four-dimensional computed tomography (CT) data sets and CT data sets during breath hold were acquired weekly for 17 patients undergoing treatment for non-small-cell lung cancer. Distances between the center of the gross tumor volume (GTV) and a reproducible bony reference point under conditions of breath hold on end inspiration (EI) and end expiration (EE) and during free breathing on the 0% phase (corresponding to EI) and 50% phase (corresponding to EE) were analyzed for interfractional reproducibility.

Evaluation of tumor position and PTV margins using image guidance and respiratory gating.

Purpose: To evaluate the margins currently used to generate the planning target volume for lung tumors and to determine whether image-guided patient setup or respiratory gating is more effective in reducing uncertainties in tumor position.

Methods And Materials: Lung tumors in 7 patients were contoured on serial four-dimensional computed tomography (4DCT) data sets (4-8 4DCTs/patient; 50 total) obtained throughout the course of treatment. Simulations were performed to determine the tumor position when the patient was aligned using skin marks, image-guided setup based on vertebral bodies, fiducials implanted near the tumor, and the actual tumor volume under various scenarios of respiratory gating.

Lack of correlation between external fiducial positions and internal tumor positions during breath-hold CT.

Purpose: For thoracic tumors, if four-dimensional computed tomography (4DCT) is unavailable, the internal margin can be estimated by use of breath-hold (BH) CT scans acquired at end inspiration (EI) and end expiration (EE). By use of external surrogates for tumor position, BH accuracy is estimated by minimizing the difference between respiratory extrema BH and mean equivalent-phase free breathing (FB) positions. We tested the assumption that an external surrogate for BH accuracy correlates with internal tumor positional accuracy during BH CT.

Impact of gastric filling on radiation dose delivered to gastroesophageal junction tumors.

Purpose: This study examined the impact of gastric filling variation on target coverage of gastroesophageal junction (GEJ) tumors in three-dimensional conformal radiation therapy (3DCRT), intensity-modulated radiation therapy (IMRT), or IMRT with simultaneous integrated boost (IMRT-SIB) plans.

Materials And Methods: Eight patients previously receiving radiation therapy for esophageal cancer had computed tomography (CT) datasets acquired with full stomach (FS) and empty stomach (ES). We generated treatment plans for 3DCRT, IMRT, or IMRT-SIB for each patient on the ES-CT and on the FS-CT datasets.

Comparing the accuracy of four-dimensional photon dose calculations with three-dimensional calculations using moving and deforming phantoms.

Purpose: Four-dimensional (4D) dose calculation algorithms, which explicitly incorporate respiratory motion in the calculation of doses, have the potential to improve the accuracy of dose calculations in thoracic treatment planning; however, they generally require greater computing power and resources than currently used for three-dimensional (3D) dose calculations. The purpose of this work was to quantify the increase in accuracy of 4D dose calculations versus 3D dose calculations.

Methods: The accuracy of each dose calculation algorithm was assessed using measurements made with two phantoms.

Verification of four-dimensional photon dose calculations.

Recent work in the area of thoracic treatment planning has been focused on trying to explicitly incorporate patient-specific organ motion in the calculation of dose. Four-dimensional (4D) dose calculation algorithms have been developed and incorporated in a research version of a commercial treatment planning system (Pinnacle3, Philips Medical Systems, Milpitas, CA). Before these 4D dose calculations can be used clinically, it is necessary to verify their accuracy with measurements.

Respiratory gating with EPID-based verification: the MDACC experience.

We have investigated the feasibility and accuracy of using a combination of internal and external fiducials for respiratory-gated image-guided radiotherapy of liver tumors after screening for suitable patients using a mock treatment. Five patients were enrolled in the study. Radio-opaque fiducials implanted adjacent to the liver tumor were used for daily online positioning using either electronic portal or kV images.

Potential dosimetric benefits of four-dimensional radiation treatment planning.

Purpose: To determine the extent of dosimetric differences between conventional three-dimensional (3D) dose calculations and four-dimensional (4D) dose calculations based on deformation of organ models.

Methods And Materials: Four-dimensional dose calculations were retrospectively performed on computed tomography data sets for 15 patients with Stage III non-small-cell lung cancer, using a model-based deformable registration algorithm on a research version of a commercial radiation treatment planning system. Target volume coverage and doses to critical structures calculated using the 4D methodology were compared with those calculated using conventional 3D methodology.

Determination of patient-specific internal gross tumor volumes for lung cancer using four-dimensional computed tomography.

Background: To determine the optimal approach to delineating patient-specific internal gross target volumes (IGTV) from four-dimensional (4-D) computed tomography (CT) image data sets used in the planning of radiation treatment for lung cancers.

Methods: We analyzed 4D-CT image data sets of 27 consecutive patients with non-small-cell lung cancer (stage I: 17, stage III: 10). The IGTV, defined to be the envelope of respiratory motion of the gross tumor volume in each 4D-CT data set was delineated manually using four techniques: (1) combining the gross tumor volume (GTV) contours from ten respiratory phases (IGTVAllPhases); (2) combining the GTV contours from two extreme respiratory phases (0% and 50%) (IGTV2Phases); (3) defining the GTV contour using the maximum intensity projection (MIP) (IGTVMIP); and (4) defining the GTV contour using the MIP with modification based on visual verification of contours in individual respiratory phase (IGTVMIP-Modified).

Influence of source parameters on large-field electron beam profiles calculated using Monte Carlo methods.

The purpose of this paper was to study the source model for a Monte Carlo simulation of electron beams from a medical linear accelerator. In a prior study, a non-divergent Gaussian source with a full-width at half-maximum (FWHM) of 0.15 cm was successful in predicting relative dose distributions for electron beams with applicators.