Radiotherapy immobilization mask molding through the use of 3D-printed head models

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 degrees (standard deviation = 0.77 degrees ), 0.59 degrees (standard deviation = 0.41 degrees ), and 0.79 degrees (standard deviation = 0.86 degrees ), 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

Monte Carlo based electron treatment planning and cutout output factor calculations

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. Electron treatments are normally delivered clinically without previously calculated dose distributions due to the complexity of the electron transport involved and greater error in planning accuracy. This research uses Monte Carlo (MC) methods to model clinical electron beams in order to accurately calculate electron beam dose distributions in patients as well as calculate cutout output factors, reducing the need for a clinical measurement. The present work is incorporated into a research MC calculation system: McGill Monte Carlo Treatment Planning (MMCTP) system. Measurements of PDDs, profiles and output factors in addition to 2D GAFCHROMIC EBT2 film measurements in heterogeneous phantoms were obtained to commission the electron beam model. 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.La radiotherapie d'électrons offre plusieurs avantages en comparaison avec les photons. La dose de surface élevée, en combinaison avec une dose descendante plus rapide au-delà du volume prévu présente un taux plus élevé de la probabilité de contrôle tumoral et diminue les complications dans les tissus normaux en évitant les tumeurs superficiel. Les traitements d'électrons sont habituellement utilisés cliniquement sans calculations de doses prévu, due à leurs complexités du transport d'électron qui sont impliqués et plusieurs erreurs de precision en planification. Cette recherche utilise les methodes de Monte Carlo (MC) pour démontrer cliniquement les faisceaux d'électrons pour précisément calculer la dose d'électron distribuée au patients mais aussi pour pouvoir calculer les facteurs de dendements de cutout, et ceci réduit le besoin d'une mesure clinique. Ce projet a été élaboré dans un environnement de calculation par MC: McGill Monte Carlo Treatment Planning (MMCTP) System. Mesure de pourcentage de dose en profondeur, profiles et les facteurs de rendements de cutout ainsi que de doses mesurés avec des films GAFCHROMIC EBT2 dans les phantoms hétérogène ont été obtenu pour déléguer la modèle de faisceau d'électron. L'utilisation de MC pour l'électrode TP sera apporter des traitements plus précis et en consequence produire plus de connaissance de la dose d'electrons plus approprié pour le patient. Ces attributions pourront sauver jusqu'à une heure par patient en terme de temps passé en clinique