Purpose:To evaluate the feasibility of a workflow free of a simulation appointment using three-dimensional-printed heads and custom immobilization devices.Materials and Methods:Simulation computed tomography scans of 11 patients who received radiotherapy for brain tumors were used to create three-dimensional printable models of the patients’ heads and neck rests. The models were three-dimensional-printed using fused deposition modeling and reassembled. Then, thermoplastic immobilization masks were molded onto them. These setups were then computed tomography-scanned and compared against the volumes from the original patient computed tomography-scans. Following translational +/− rotational coregistrations of the volumes from three-dimensional-printed models and the patients, the similarities and accuracies of the setups were evaluated using Dice similarity coefficients, Hausdorff distances, differences in centroid positions, and angular deviations. Potential dosimetric differences secondary to inaccuracies in the rotational positioning of patients were calculated.Results:Mean angular deviation of the 3D-printout from the original volume for the Pitch, Yaw, and Roll were 1.1° (standard deviation = 0.77°), 0.59° (standard deviation = 0.41°), and 0.79° (standard deviation = 0.86°), respectively. Following translational + rotational shifts, the mean Dice similarity coefficients of the three-dimensional-printed and original volumes was 0.985 (standard deviation = 0.002) while the mean Hausdorff distance was 0.9 mm (standard error of the mean: 0.1 mm). The mean centroid vector displacement was 0.5 mm (standard deviation: 0.3 mm). Compared to plans that were coregistered using translational + rotational shifts, the D95 of the brain from three-dimensional-printed heads adjusted for TR shifts only differed by −0.1% (standard deviation = 0.2%).Conclusions:Patient head volumes and positions at simulation computed tomography scans can be accurately reproduced using three-dimensional-printed models, which can be used to mold radiotherapy immobilization masks onto. This strategy, if applied on diagnostic computed tomography scans, may allow symptomatic and frail patients to avoid a computed tomography-simulation and mask molding session in preparation for palliative whole brain radiotherapy.

In 2010, all young patients treated for intrathoracic Hodgkin lymphoma (HL) at one of 10 radiotherapy centers in the province of Quebec received 3D conformal photon therapy. These patients may now be at risk for late effects of their treatment, notably secondary malignancies and cardiac toxicity. We hypothesized that more complex radiotherapy, including intensity‐modulated proton therapy (IMPT) and possibly IMRT (in the form of helical tomotherapy (HT)), could benefit these patients. With institutional review board approval at 10 institutions, all treatment plans for patients under the age of 30 treated for HL during a six‐month consecutive period of 2010 were retrieved. Twenty‐six patients were identified, and after excluding patients with extrathoracic radiation or treatment of recurrence, 20 patients were replanned for HT and IMPT. Neutron dose for IMPT plans was estimated from published measurements. The relative seriality model was used to predict excess risk of cardiac mortality. A modified linear quadratic model was used to predict the excess absolute risk for induction of lung cancer and, in female patients, breast cancer. Model parameters were derived from published data. Predicted risk for cardiac mortality was similar among the three treatment techniques (absolute excess risk of cardiac mortality was not reduced for HT or IMPT (p>0.05,p>0.05) as compared to 3D CRT). Predicted risks were increased for HT and reduced for IMPT for secondary lung cancer (p<0.001,p<0.001) and breast cancers (p<0.001,p<0.001) as compared to 3D CRT.PACS numbers: 87.55.dh, 87.55.dk

Purpose: Electron radiotherapy (RT) offers a number of advantages over photons. The high surface dose, combined with a rapid dose fall‐off beyond the target volume presents a net increase in tumor control probability and decreases the normal tissue complication for superficial tumors. The current techniques involving electron RT are more seldom used than photon therapy due to the complexity of the electron transport involved and greater error in planning accuracy. Electron treatments are normally delivered clinically without previously calculated dose distributions. Our current research aims to use Monte Carlo (MC) methods to model clinical electron beams in order to accurately calculate electron beam dose distributions in patients. In addition to this, electron output factors can be quickly calculated, reducing the need for a clinical measurement. Methods: The present work is incorporated into a research MC calculation system: McGill Monte Carlo Treatment Planning (MMCTP) system. MMCTP streamlines the calculation of output factors for various electron beam energies and applicator sizes. Measurements of PDDs, profiles and output factors in addition to 2D EBT‐2 GAFCHROMIC measurements in heterogeneous phantoms were obtained to commission the electron beam model. Results: Forty‐nine output factors were measured and calculated. The mean percentage difference between measured and calculated was 1.35% with a maximum of 3.27%. The mean error and calculation time of the calculations were found to be 1.64% and 2 hours respectively. A dose difference of 3% and distance‐to‐agreement of 3 mm were used to compare two dimensional dose maps using the gamma method, yielding a good outcome. Conclusions: The use of MC for electron TP will provide more accurate treatments and yield greater knowledge of the electron dose distribution within the patient. The calculation of output factors could invoke a clinical time saving of up to 1 hour per patient.

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