Dosimetric uncertainties as a result of temporal resolution in 4D dose calculations for PBS proton therapy.

Dosimetric uncertainties as a result of temporal resolution in 4D dose calculations for PBS proton therapy. Phys Med Biol. 2019 Apr 29;: Authors: Zhang Y, Huth I, Weber DC, Lomax AJ Abstract This work investigates the dosimetric impact on 4D dose distribution estimation for pencil beam scanned (PBS) proton therapy as function of the temporal resolution used for the time resolved dose calculation. For three liver patients (CTV volume: 403/122/264cc), 10-phase 4DCT-MRI datasets with ~15mm tumour motion were simulated for seven different motion periods (2-8s). 4D dose distributions were calculated and compared by considering both coarser and finer temporal resolutions (200-800ms and 20ms). Single scanned 4D plans for seven fraction doses (0.7/2/4/6/8/10/12Gy) were investigated, whose dose delivery timelines were simulated by assuming two types of PBS scanning modes: (1) layer-wise raster scanning with varying dose rate per layer and (2) fixed dose rate, discrete scanning. For both delivery scenarios, dosimetric assessments were performed by comparing corresponding dose distributions derived from the two 4D dose calculation (4DDC) results. Differences were quantified as the difference in D5-D95 of the CTV and by comparing total volume of the CTV receiving point-to-point absolute dose difference more than 5%. Our results show that varying temporal resolution in 4DDC has a direct influence on the final accumulated dose distribution. For all scenarios, patients...
Source: Physics in Medicine and Biology - Category: Physics Authors: Tags: Phys Med Biol Source Type: research

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Abstract The step-and-shoot method of pencil beam scanning delivers the dose on a three-dimensional grid in the target volume, with one dimension defined by the proton energy. While the dose per pencil beam may vary substantially within an iso-energy layer, the beam current typically remains constant. In this static operation mode, the inherent latency of the beam switch-off mechanism results in a lower limit for the deliverable spot dose, which may prevent the application of some of the low-weighted spots prescribed by the treatment planning system. To overcome this limitation, we introduced dynamic beam current ...
Source: Physics in Medicine and Biology - Category: Physics Authors: Tags: Phys Med Biol Source Type: research
Abstract Positron emission tomography (PET) has been extensively studied and clinically investigated for dose verification in proton therapy. However, the production distributions of positron emitters are not proportional to the dose distribution. Thus, direct dose evaluation is limited when using the conventional PET-based approach. We propose a method for estimating the dose distribution from the positron emitter distributions using the maximum likelihood (ML) expectation maximization (EM) algorithm combined with filtering. In experiments to verify the effectiveness of the proposed method, mono-energetic and spr...
Source: Physics in Medicine and Biology - Category: Physics Authors: Tags: Phys Med Biol Source Type: research
Our institution utilizes both biologic and standard dose models in spot scanning proton treatment planning. This analysis examines the rates of post-treatment radiologic change as detected on post-treatment MRI scans, and toxicities for pediatric brain tumor patients treated during the first year of our institution ’s experience. Our novel biologic dose model was found to demonstrate greater volumetric overlap with the post-treatment radiologic changes, than the standard dose model.
Source: International Journal of Radiation Oncology * Biology * Physics - Category: Radiology Authors: Source Type: research
CONCLUSION: We have carried out an extensive measurement of H*(10) under different conditions. The shielding thickness of our PT facility is adequate to limit the dose to occupational worker and general public within the permissible stipulated limit. The data reported here can bridge the knowledge gap in ambient dose around PT facility and can also be used as a reference for any new and existing proton facility for inter comparison and validation. ADVANCES IN KNOWLEDGE: First extensive investigation of neutron and photon H*(10) around PT facility and can bridge the knowledge gap on ambient dose. PMID: 31287739 [P...
Source: The British Journal of Radiology - Category: Radiology Authors: Tags: Br J Radiol Source Type: research
o T, Khan R Abstract Radiochromic films have been widely studied for clinical dosimetry in conventional external beam radiation therapy. With an increase in practice of proton therapy, such films are being conveniently used; however, their spectroscopic characterization for this modality is lacking. This work investigated the response of the EBT3 radiochromic films irradiated in a Mevion S250™ clinical proton beam. Dose, dose rate, inter-batch, sensitivity, and linear energy transfer (LET) dependencies of the films were studied. Pieces of the radiochromic films from different batches were irradiated using a ...
Source: Physics in Medicine and Biology - Category: Physics Authors: Tags: Phys Med Biol Source Type: research
We describe the iterative process we have applied to design the magnets and the beam transport, for which we have used different codes. <i>COSY Infinity</i> and <i>OPAL</i> have been used to design the beam transport optics and to track the particles in the magnetic fields, which are produced by the magnets designed in <i>Opera</i>. With beam optics calculations we have derived an optimal achromatic beam transport with the large momentum acceptance of the proton pencil beam and we show the agreement with particle tracking calculations in th...
Source: Physics in Medicine and Biology - Category: Physics Authors: Tags: Phys Med Biol Source Type: research
Conclusions: Image analysis revealed a slight advantage of 2D Unets compared to 3D Unets. Similar dose calculation performance was reached for the 2D and 3D network. PMID: 31271093 [PubMed - as supplied by publisher]
Source: Acta Oncologica - Category: Cancer & Oncology Authors: Tags: Acta Oncol Source Type: research
Würl M Abstract Background: Precision small animal radiotherapy research is a young emerging field aiming to provide new experimental insights into tumor and normal tissue models in different microenvironments, to unravel complex mechanisms of radiation damage in target and non-target tissues and assess efficacy of novel therapeutic strategies. For photon therapy, modern small animal radiotherapy research platforms have been developed over the last years and are meanwhile commercially available. Conversely, for proton therapy, which holds potential for an even superior outcome than photon therapy, no commerci...
Source: Acta Oncologica - Category: Cancer & Oncology Authors: Tags: Acta Oncol Source Type: research
Conclusion: The automated prior-plan adaptation method can successfully adapt for the large day-to-day variations observed in cervical cancer patients. PMID: 31271076 [PubMed - as supplied by publisher]
Source: Acta Oncologica - Category: Cancer & Oncology Authors: Tags: Acta Oncol Source Type: research
Conclusion: FLASH dose rates were not achieved for conventional planning and clinical spot-scanning machines. As such, increased spot-wise beam intensities, spot-reduced planning, hypofractionation and arc-shoot-through plans were required to achieve FLASH compatible dose rates. PMID: 31241377 [PubMed - as supplied by publisher]
Source: Acta Oncologica - Category: Cancer & Oncology Authors: Tags: Acta Oncol Source Type: research
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