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Development of an interlaced-crossfiring geometry for proton grid therapy
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.ORCID iD: 0000-0002-4160-1078
Stockholm University, Faculty of Science, Department of Physics.
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Number of Authors: 62017 (English)In: Acta Oncologica, ISSN 0284-186X, E-ISSN 1651-226X, Vol. 56, no 11, p. 1437-1443Article in journal (Refereed) Published
Abstract [en]

Background: Grid therapy has in the past normally been performed with single field photon-beamgrids. In this work, we evaluated a method to deliver grid therapy based on interlacing and crossfiringgrids of mm-wide proton beamlets over a target volume, by Monte Carlo simulations.

Material and methods: Dose profiles for single mm-wide proton beamlets (1, 2 and 3 mm FWHM) inwater were simulated with the Monte Carlo code TOPAS. Thereafter, grids of proton beamlets weredirected toward a cubic target volume, located at the center of a water tank. The aim was to deliver anearly homogeneous dose to the target, while creating high dose heterogeneity in the normal tissue,i.e., high gradients between valley and peak doses in the grids, down to the close vicinity of thetarget.

Results: The relative increase of the beam width with depth was largest for the smallest beams(þ6.9mm for 1 mm wide and 150MeV proton beamlets). Satisfying dose coverage of the cubic targetvolume (r< ±5%) was obtained with the interlaced-crossfiring setup, while keeping the grid pattern ofthe dose distribution down to the target (valley-to-peak dose ratio<0.5 less than 1 cm before the tar-get). Center-to-center distances around 7–8 mm between the beams were found to give the best com-promise between target dose homogeneity and low peak doses outside of the target.

Conclusions: A nearly homogeneous dose distribution can be obtained in a target volume by crossfir-ing grids of mm-wide proton-beamlets, while maintaining the grid pattern of the dose distribution atlarge depths in the normal tissue, close to the target volume. We expect that the use of this methodwill increase the tumor control probability and improve the normal tissue sparing in grid therapy.

Place, publisher, year, edition, pages
2017. Vol. 56, no 11, p. 1437-1443
National Category
Other Physics Topics
Research subject
Medical Radiation Physics
Identifiers
URN: urn:nbn:se:su:diva-148188DOI: 10.1080/0284186X.2017.1350287ISI: 000423464400014OAI: oai:DiVA.org:su-148188DiVA, id: diva2:1150062
Conference
15th Acta Oncologica Symposium - Biology-Guided Adaptive Radiotherapy (BiGART), Aarhus, Denmark, June 13-16, 2017
Available from: 2017-10-17 Created: 2017-10-17 Last updated: 2018-09-24Bibliographically approved
In thesis
1. Interlaced proton grid therapy: development of an innovative radiation treatment technique
Open this publication in new window or tab >>Interlaced proton grid therapy: development of an innovative radiation treatment technique
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Spatially fractionated radiotherapy, also known as grid therapy (GRID), has been used for more than a century to try to treat several kinds of lesions. Yet, the grid technique remains a relatively unknown and uncommon treatment modality nowadays. Spatially fractionated beams, instead of conventional homogeneous fields, have been used to exploit the experimental finding that normal tissue can tolerate higher doses when smaller tissue volumes are irradiated. This increase in tolerance with reducing beam size is known as the dose-volume effect. Despite the fact that targets were given inhomogeneous dose distribution, sometimes with some volumes receiving close to no dose, good results in the form of shrinking of bulky tumors have been observed in palliative treatments. The biological processes responsible for this effect are still under discussion, with several possible causes. However, numerous experiments on mice, rats and pigs have confirmed the existence of such effect, which in turn motivates the present development of grid therapy.While mainly photons have been used in grid therapy, proton and ion grid therapies are also emerging as potential alternatives. In this work, an innovative form of grid therapy was proposed. Grids of proton beamlets were interlaced over a target volume with the intention of achieving two main objectives: (1) to keep the grid pattern (made of adjacent high and low doses) from the skin up to the vicinity of the target while (2) delivering nearly homogeneous dose to the target volume. This interlaced proton grid therapy was explored with the use of different beam sizes, from conventional sizes deliverable at modern proton facilities, down to millimeter sized beams. Other considerations that would prevent its clinical use, such as the variable relative biological effectiveness of protons or the use of cone beam computed tomography, were also evaluated. The overall aim was to assess if, and how, such treatment modality could be applied clinically, from a physics and dosimetry point of view. While it presented several theoretical advantages, its potential issues of concern and limitations were also evaluated.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2018. p. 65
Keywords
proton therapy, grid therapy, spatially fractionated therapy, interlacing
National Category
Cancer and Oncology
Research subject
Medical Radiation Physics
Identifiers
urn:nbn:se:su:diva-160427 (URN)978-91-7797-442-0 (ISBN)978-91-7797-443-7 (ISBN)
Public defence
2018-11-09, CCK Lecture Hall, Building R8, Karolinska University Hospital, Solna, Stockholm, 09:00 (English)
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Available from: 2018-10-17 Created: 2018-09-24 Last updated: 2018-10-16Bibliographically approved

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