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Advisor(s)
Abstract(s)
Purpose: To assess out-of-field doses in radiotherapy treatments of pediatric patients, using Monte Carlo methods to implement a new model of the linear accelerator validated against measurements and developing a voxelized anthropomorphic pediatric phantom. Methods: CT images of a physical anthropomorphic pediatric phantom were acquired and dosimetric planning using a TPS was obtained. The CT images were used to perform the voxelization of the physical phantom using the ImageJ software and later implemented in MCNP. In order to validate the Monte Carlo model, dose measurements of the 6 MV beam and Linac with 120 MLC were made in a clinical setting, using ionization chambers and a water phantom. afterward, TLD measurements in the physical anthropomorphic phantom were performed in order to assess the out-of-field doses in the eyes, thyroid, c-spine, heart, and lungs. Results: The Monte Carlo model was validated for in-field and out-of-field doses with average relative differences below 3%. The average relative differences between TLD measurements and Monte Carlo is 14,3% whilst the average relative difference between TLD and TPS is 55,8%. Moreover, organs up to 22.5 cm from PTV center show TLD and MCNP6 relative differences and TLD and TPS relative differences up to 21.2% and 92.0%, respectively. Conclusions: Our study provides a novel model that could be used in clinical research, namely in dose evaluation outside the treatment fields. This is particularly relevant, especially in pediatric patients, for studying new radiotherapy treatment techniques, since it can be used to estimate the development of secondary tumors.
Description
Keywords
Radiotherapy Monte Carlo method Out-of-field doses Clinical measurement Anthropomorphic paediatric phantom
Citation
Sá AC, Barateiro A, Bednarz B, Borges C, Pereira J, Baptista M, et al. Assessment of out-of-field doses in radiotherapy treatments of paediatric patients using Monte Carlo methods and measurements. Phys Med. 2020;71:53-64.
Publisher
Elsevier