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Comparison of gastric-cancer radiotherapy performed with volumetric modulated arc therapy or single-field uniform-dose proton therapy
Stockholm University, Faculty of Science, Department of Physics. Universidade Eduardo Mondlane, Mozambique.ORCID iD: 0000-0002-9904-7217
Stockholm University, Faculty of Science, Department of Physics.
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2017 (English)In: Acta Oncologica, ISSN 0284-186X, E-ISSN 1651-226X, Vol. 56, no 6, p. 832-838Article in journal (Refereed) Published
Abstract [en]

Background: Proton-beam therapy of large abdominal cancers has been questioned due to the large variations in tissue density in the abdomen. The aim of this study was to evaluate the importance of these variations for the dose distributions produced in adjuvant radiotherapy of gastric cancer (GC), implemented with photon-based volumetric modulated arc therapy (VMAT) or with proton-beam single-field uniform-dose (SFUD) method. Material and methods: Eight GC patients were included in this study. For each patient, a VMAT- and an SFUD-plan were created. The prescription dose was 45 Gy (IsoE) given in 25 fractions. The plans were prepared on the original CT studies and the doses were thereafter recalculated on two modified CT studies (one with extra water filling and the other with expanded abdominal air-cavity volumes). Results: Compared to the original VMAT plans, the SFUD plans resulted in reduced median values for the V18 of the left kidney (26%), the liver mean dose (14.8 Gy (IsoE)) and the maximum dose given to the spinal cord (26.6 Gy (IsoE)). However, the PTV coverage decreased when the SFUD plans were recalculated on CT sets with extra air- (86%) and water-filling (87%). The added water filling only led to minor dosimetric changes for the OARs, but the extra air caused significant increases of the median values of V18 for the right and left kidneys (10% and 12%, respectively) and of V10 for the liver (12%). The density changes influenced the dose distributions in the VMAT plans to a minor extent. Conclusions: SFUD was found to be superior to VMAT for the plans prepared on the original CT sets. However, SFUD was inferior to VMAT for the modified CT sets.

Place, publisher, year, edition, pages
2017. Vol. 56, no 6, p. 832-838
Keywords [en]
Gastric cancer, radiotherapy, scanned-proton beams, density variations, dosimetric comparison
National Category
Physical Sciences Cancer and Oncology
Research subject
Medical Radiation Physics
Identifiers
URN: urn:nbn:se:su:diva-140567DOI: 10.1080/0284186X.2017.1297536ISI: 000400796200013OAI: oai:DiVA.org:su-140567DiVA, id: diva2:1080738
Funder
Sida - Swedish International Development Cooperation AgencyAvailable from: 2017-03-10 Created: 2017-03-10 Last updated: 2018-07-31Bibliographically approved
In thesis
1. Radiation therapy of upper gastrointestinal cancers with scanned proton beams: A treatment planning study
Open this publication in new window or tab >>Radiation therapy of upper gastrointestinal cancers with scanned proton beams: A treatment planning study
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Proton beam therapy (PBT), using scanned beams, is an emerging modality used for the treatment of cancer. The clinical advantages of PBT, compared to commonly used photon beam therapy, have been demonstrated in different studies. However, the techniques used for planning and delivering treatments with photon beams have gradually been improved over the years. With the introduction of PBT in the clinic, guidelines to select patients to photon- or proton-beam therapy are indispensable.

A simple approach used for selecting patients for PBT is based on the patient age. The paediatric patient group is considered to be the most radiosensitive and, therefore, in larger need of RT techniques that provide improved sparing of the organs at risk (OARs). With the increasing number of cancer clinics with access to PBT, combined with the constant clinical need of reducing the frequency of acute and late toxicities, there has been an increased use of PBT also for adult patients. At present, there is only limited clinical follow-up data available regarding the outcome of PBT for different tumour sites, in particular for extra-cranial tumours. The use of photon beams for such cancer treatments is, on the other hand, well-established. Therefore, the expected benefit of using proton beams in cancer therapy can be translated from the results obtained in the clinical experience attained from photon-beam treatments. The evaluation of the different uncertainties influencing the radiotherapy (RT) of different tumour sites carried out with photon- or proton-beams, will also create an improved understanding of the feasibility of treating cancer with scanned proton beams instead of with photon beams. 

The comparison of two distinct RT modalities is normally performed by studying the calculated dose distributions superimposed on the patient CT images and by evaluating the dosimetric values obtained from the dose volume histograms (DVHs). The dosimetric evaluation can be complemented with treatment outcome predictions in terms of local disease control and normal tissue toxicity. In this regard, radiobiological models can be an indispensable tool for the prediction of the outcome of cancer treatments performed with different types of ionising radiation. These estimates can in turn be used in the decision process for selecting patients for treatments with a specific RT modality.

This thesis consists of five articles. In these studies, treatment plans for RT with scanned proton-beams have been prepared and compared with clinical plans used for photon-beam based RT. For this purpose, dosimetric and biological-model based evaluations of these plans were performed. These studies were carried out for two distinct upper gastrointestinal (GI) cancers, namely, gastric cancer (GC) and liver metastases. RT treatments with both conventional fractionation schemes (implemented in the planning for the GC treatments) and hypofractionated regimens (implemented in the planning for the liver metastases cases) were considered. For the GC cases, the impact of changes in tissue density, resulting from a variable gas content (which can be observed inter-fractionally), was investigated. Proton therapy was found to provide the possibility to reduce the doses given to normal tissues surrounding the target volumes, compared to photon RT. This dose reduction with PBT resulted in reduced risks for both treatment-induced normal tissue toxicities and secondary malignancies. The impact of the introduced density changes on the dose distributions were found to be more pronounced for the PBT plans, if plan robustness approaches were disregarded. The findings presented in this thesis can be of clinical importance in the selection process between different RT modalities.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2018. p. 141
Keywords
Treatment planning, gastric cancer, liver metastases, photon beam therapy, proton beam therapy, dosimetric comparison, normal tissue complication probability, risk of radiation-induced secondary cancer, patient selection
National Category
Physical Sciences
Research subject
Medical Radiation Physics
Identifiers
urn:nbn:se:su:diva-158411 (URN)978-91-7797-378-2 (ISBN)978-91-7797-379-9 (ISBN)
Public defence
2018-09-14, Radiumhemmets föreläsningssal, P1:01, Karolinska Universitetssjukhuset, Solna, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Sida - Swedish International Development Cooperation Agency
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Submitted.

Available from: 2018-08-22 Created: 2018-07-31 Last updated: 2018-09-26Bibliographically approved

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