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You searched for +publisher:"Delft University of Technology" +contributor:("Schaart, Dennis"). Showing records 1 – 3 of 3 total matches.

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Delft University of Technology

1. van Aert, Emy (author). Gel dosimetry for a MR-linac: magnetic field and time dependency.

Degree: 2020, Delft University of Technology

The goal of this research was to perform a 3D end-to-end test on a MR-linac to check the whole workflow using a clinical treatment plan. Dosimetric gel was used to obtain 3D spatial information, with the phantom in the same position for irradiation and scanning. In order to achieve this, fundamental elements of gel dosimetry needed to be investigated. In the MR-linac, irradiation is delivered in the presence of a permanent magnetic field. Therefore, the dosimetric response within a 1.5 T magnetic field should be validated. It is also important to investigate the time-dependence of the gel. It is preferable to read-out the gels within approximately one hour, so that the phantom does not have to be moved. Ideally, scanning and irradiation would be done at the same time, to see the dynamical dose delivery. The VIPAR gel was used for this research. The experiments demonstrated that R2 values for doses irradiated with magnetic field were the same as R2 values for the same dose irradiated without magnetic field. R2 values are still proportional to the dose. It was also shown that it is possible to scan the phantom within 20 minutes after irradiation. Sensitivity is at its highest after approximately 8 hours and stays stable afterwards, so scanning after 8 hours will improve the read-out accuracy. It was also possible to make a fit for the R2 versus time plots, which makes it possible to correct for change over time. The fit can be divided in two linear parts if time is plotted on a logarithmic scale, one fit for the time points before 7 hours, one for the time points after 7 hours. The partial doses acquired by the gel during radiation delivery were estimated. The equivalent R2 values then agreed with the extrapolated fit to within 4%. This is a good indication that dynamic gel (4D) dosimetry may be achievable. A protocol for a relative end-to-end test was also developed. From the preliminary results, it appeared that a relative end-to-end test can be performed with the read-out of gel within 1 hour. A new MR sequence needs to be developed. For this end-to-end test, the sequence needs to scan a larger volume with a higher resolution, therefore, the scan time will increase and real-time dosimetry will not be possible. Changing the MR sequence might also change the optimal irradiation-scanning interval and the R2 versus time curve. To perform absolute dosimetry, an extra calibration would be required. Advisors/Committee Members: Denkova, Antonia (mentor), Wolthaus, Jochem (mentor), Woodings, Simon (mentor), Schaart, Dennis (graduation committee), Djanashvili, Kristina (graduation committee), Delft University of Technology (degree granting institution).

Subjects/Keywords: gel dosimetry; MR-linac; magnetic field

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

van Aert, E. (. (2020). Gel dosimetry for a MR-linac: magnetic field and time dependency. (Masters Thesis). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:4408f7c6-d16f-4cab-90c0-60dbf03d8a27

Chicago Manual of Style (16th Edition):

van Aert, Emy (author). “Gel dosimetry for a MR-linac: magnetic field and time dependency.” 2020. Masters Thesis, Delft University of Technology. Accessed May 09, 2021. http://resolver.tudelft.nl/uuid:4408f7c6-d16f-4cab-90c0-60dbf03d8a27.

MLA Handbook (7th Edition):

van Aert, Emy (author). “Gel dosimetry for a MR-linac: magnetic field and time dependency.” 2020. Web. 09 May 2021.

Vancouver:

van Aert E(. Gel dosimetry for a MR-linac: magnetic field and time dependency. [Internet] [Masters thesis]. Delft University of Technology; 2020. [cited 2021 May 09]. Available from: http://resolver.tudelft.nl/uuid:4408f7c6-d16f-4cab-90c0-60dbf03d8a27.

Council of Science Editors:

van Aert E(. Gel dosimetry for a MR-linac: magnetic field and time dependency. [Masters Thesis]. Delft University of Technology; 2020. Available from: http://resolver.tudelft.nl/uuid:4408f7c6-d16f-4cab-90c0-60dbf03d8a27


Delft University of Technology

2. den Boer, Erik (author). Irregular breathing in proton therapy: The effect of irregular breathing on the interplay effect in pencil beam scanning proton therapy.

Degree: 2020, Delft University of Technology

Pencil beam scanning is becoming a more common treatment modality. However, its ability to deal with moving targets is known to be limited, as beam motion and target motion can reinforce each other, deteriorating the planned dose distribution in what is called the interplay effect. Literature concerning breathing motion usually investigates regular patterns. This work aims to investigate the magnitude of the interplay effect when considering irregular breathing signals. In silico calculations of dose distributions were made in the treatment planning system RayStation (version 7.99), using an XCAT phantom with 50 CT phases to model moving patient anatomy. An interplay calculator was included in RayStation, allowing calculation of disturbed doses based on a treatment plan and an irradiation time model for a proton therapy accelerator. The target investigated was a spherical liver tumour with 5cm diameter, irradiated with two beams delivering a prescription dose of 63 Gy. Plans without and with 5x layered repainting were created. Clinically realistic regular breathing patterns were generated to establish a baseline, after which irregularities were introduced. The basic form for all patterns was a sin4 signal, with regular signal amplitudes ranging from 6 to 18 mm, period ranging from 3 to 4 s and phase between 0 and 2π rad. Considered irregularities were baseline shifts up to 34 mm, changing amplitudes between 6 and 18 mm, changing periods between 1.6 and 5.2 s and combinations. Evaluation was done by looking at dose homogeneity HI5 and the fraction of the CTV volume that received a dose outside of the clinical limits of 95% and 107%, V107/95. For the regular patterns, both a systematic and a randomised analysis were carried out. For irregular patterns, only a systematic analysis was carried out. The mean HI5 was found to be 31% for regular patterns; the means of all irregular patterns stay below this, even though the size of the irregularities for some breathing patterns was very large. The mean V107/95 was found to be 0.7 for regular patterns. Irregularities did not cause further deterioration. Five times layered repainting causes a statistically significant decrease in magnitude of the interplay effect across all breathing patterns by 50-80%, but is approximately 50% less effective against baseline shift than against other types of breathing. Interplay effect size correlates strongly with amplitude, but this correlation can be obscured because period and phase introduce very large variance. The interplay effect in general is large for investigated target size, prescription dose, beam configuration and machine performance. It can cause up to 100% of the CTV to receive a clinically unacceptable dose and lead to large inhomogeneities. Irregular breathing was not found to be notably worse. Repainting is effective, even against irregular breathing, but baseline shifts can undermine its effectiveness. Separately considering breathing irregularities for tumours similar to that investigated here is deemed of low… Advisors/Committee Members: Perko, Zoltan (mentor), Goorden, Marlies (graduation committee), Schaart, Dennis (graduation committee), Delft University of Technology (degree granting institution).

Subjects/Keywords: Proton Therapy; Irregular breathing; Pencil beam scanning; Interplay effect

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

den Boer, E. (. (2020). Irregular breathing in proton therapy: The effect of irregular breathing on the interplay effect in pencil beam scanning proton therapy. (Masters Thesis). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:b3b46f7a-a997-4905-ab77-ad4c54617e9b

Chicago Manual of Style (16th Edition):

den Boer, Erik (author). “Irregular breathing in proton therapy: The effect of irregular breathing on the interplay effect in pencil beam scanning proton therapy.” 2020. Masters Thesis, Delft University of Technology. Accessed May 09, 2021. http://resolver.tudelft.nl/uuid:b3b46f7a-a997-4905-ab77-ad4c54617e9b.

MLA Handbook (7th Edition):

den Boer, Erik (author). “Irregular breathing in proton therapy: The effect of irregular breathing on the interplay effect in pencil beam scanning proton therapy.” 2020. Web. 09 May 2021.

Vancouver:

den Boer E(. Irregular breathing in proton therapy: The effect of irregular breathing on the interplay effect in pencil beam scanning proton therapy. [Internet] [Masters thesis]. Delft University of Technology; 2020. [cited 2021 May 09]. Available from: http://resolver.tudelft.nl/uuid:b3b46f7a-a997-4905-ab77-ad4c54617e9b.

Council of Science Editors:

den Boer E(. Irregular breathing in proton therapy: The effect of irregular breathing on the interplay effect in pencil beam scanning proton therapy. [Masters Thesis]. Delft University of Technology; 2020. Available from: http://resolver.tudelft.nl/uuid:b3b46f7a-a997-4905-ab77-ad4c54617e9b


Delft University of Technology

3. Moret, Thijs (author). Feasibility of 3D-printed phantoms for quantifying Bragg peak degeneration due to tissue heterogeneity in lung proton therapy.

Degree: 2019, Delft University of Technology

In the field of radiation oncology, proton therapy is a relatively new technique. It shows a great advantage over conventional radiation therapy in the depth-dose relation, which results in the possibility to deliver dose far more concentrated at a specific depth. This in turn has the potential to spare the healthy tissue surrounding a tumour from receiving a very high dose. However, this depth-dose relation has the downside that it is very sensitive to small uncertainties in geometry and tissue composition, which are present in heterogeneous tissues such as lung tissue. Because of this sensitivity, it is essential that the dose delivery can be verified properly for these heterogeneous tissues, which requires highly accurate quality assurance. To improve this quality assurance, highly anthropomorphic phantoms could offer a solution. The currently commercially available phantoms however lack the high level of detail necessary, as these are produced using casting techniques. Thus a new production technique should be considered to create phantoms of greater heterogeneity and at a higher level of detail. A possible solution to this problem is to apply additive manufacturing, since this manufacturing technique can supposedly address both these issues. An important issue with the application of additive manufacturing is the lack of knowledge on the accuracy of 3D-printers. Next to the unknown accuracy, there are other challenges concerning additive manufacturing, such as the layered creation of objects and the material that is to be printed over an air cavity and the support structures this is associated with. The goal of this research is to explore the possibility to apply additive manufacturing in the creation of a phantom with a high level of detail and heterogeneity and the effect of the heterogeneous object on the quality of the Bragg peak. More specifically, simulations are performed on porous materials to quantify the degeneration of the Bragg peak. Also, a literature study on additive manufacturing will be performed, combined with the use of commercially available tabletop 3D-printers. Together, the capacity of the printer to create a high level of heterogeneity and the simulations performed on these heterogeneous structures, should give an indication on the feasibility to create a 3D-printed phantom for lung proton therapy. Advisors/Committee Members: Schaart, Dennis (mentor), Delft University of Technology (degree granting institution).

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Moret, T. (. (2019). Feasibility of 3D-printed phantoms for quantifying Bragg peak degeneration due to tissue heterogeneity in lung proton therapy. (Masters Thesis). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:4e5f6904-9c56-4b08-8168-8a12f29f8654

Chicago Manual of Style (16th Edition):

Moret, Thijs (author). “Feasibility of 3D-printed phantoms for quantifying Bragg peak degeneration due to tissue heterogeneity in lung proton therapy.” 2019. Masters Thesis, Delft University of Technology. Accessed May 09, 2021. http://resolver.tudelft.nl/uuid:4e5f6904-9c56-4b08-8168-8a12f29f8654.

MLA Handbook (7th Edition):

Moret, Thijs (author). “Feasibility of 3D-printed phantoms for quantifying Bragg peak degeneration due to tissue heterogeneity in lung proton therapy.” 2019. Web. 09 May 2021.

Vancouver:

Moret T(. Feasibility of 3D-printed phantoms for quantifying Bragg peak degeneration due to tissue heterogeneity in lung proton therapy. [Internet] [Masters thesis]. Delft University of Technology; 2019. [cited 2021 May 09]. Available from: http://resolver.tudelft.nl/uuid:4e5f6904-9c56-4b08-8168-8a12f29f8654.

Council of Science Editors:

Moret T(. Feasibility of 3D-printed phantoms for quantifying Bragg peak degeneration due to tissue heterogeneity in lung proton therapy. [Masters Thesis]. Delft University of Technology; 2019. Available from: http://resolver.tudelft.nl/uuid:4e5f6904-9c56-4b08-8168-8a12f29f8654

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