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Dosimetric Comparison of Plans for Photon- or Proton-Beam Based Radiosurgery of Liver Metastases
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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2016 (English)In: International Journal of Particle Therapy, ISSN 2331-5180, Vol. 3, no 2, p. 277-284Article in journal (Refereed) Published
Abstract [en]

Purpose: Radiosurgery treatment of liver metastases with photon beams has been an established method for more than a decade. One method commonly used is the stereotactic body radiation therapy (SBRT) technique. The aim of this study was to investigate the potential sparing of the organs at risk (OARs) that the use of intensity-modulated proton therapy (IMPT), instead of SBRT, could enable.

Patients and Methods: A comparative treatment-planning study of photon-beam and proton-beam based liver-cancer radiosurgery was performed. Ten patients diagnosed with liver metastasis and previously treated with SBRT at the Karolinska University Hospital were included in the study. New IMPT plans were prepared for all patients, while the original plans were set as reference plans. The IMPT planning was performed with the objective of achieving the same target dose coverage as with the SBRT plans. Pairwise dosimetric comparisons of the treatment plans were then performed for the OARs. A 2-sided Wilcoxon signed-rank test with significance level of 5% was carried out.

Results: Improved sparing of the OARs was made possible with the IMPT plans. There was a significant decrease of the mean doses delivered to the following risk organs: the nontargeted part of the liver (P = .002), the esophagus (P = .002), the right kidney (P = .008), the spinal cord (P = .004), and the lungs (P = .002). The volume of the liver receiving less than 15 Gy was significantly increased with the IMPT plans (P = .004).

Conclusion: The IMPT-based radiosurgery plans provided similar target coverage and significant dose reductions for the OARs compared with the photon-beam based SBRT plans. Further studies including detailed information about varying tissue heterogeneities in the beam path, due to organ motion, are required to evaluate more accurately whether IMPT is preferable for the radiosurgical treatment of liver metastases.

Place, publisher, year, edition, pages
2016. Vol. 3, no 2, p. 277-284
Keywords [en]
liver metastases, treatment planning, stereotactic body radiation therapy, intensity-modulated proton therapy
National Category
Physical Sciences Cancer and Oncology Surgery
Research subject
Medical Radiation Physics
Identifiers
URN: urn:nbn:se:su:diva-139738DOI: 10.14338/IJPT-16-00010.1OAI: oai:DiVA.org:su-139738DiVA, id: diva2:1073573
Funder
Sida - Swedish International Development Cooperation AgencyAvailable from: 2017-02-11 Created: 2017-02-11 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: 2018-09-04Bibliographically approved

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