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Comparative study of the calculated risk of radiation-induced cancer after photon- and 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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2017 (English)In: Physica medica (Testo stampato), ISSN 1120-1797, E-ISSN 1724-191X, Vol. 42, p. 263-270Article in journal (Refereed) Published
Abstract [en]

Introduction

The potential of proton therapy to improve the sparing of the healthy tissue has been demonstrated in several studies. However, even small doses delivered to the organs at risk (OAR) may induce long-term detriments after radiotherapy. In this study, we investigated the possibility to reduce the risk of radiation-induced secondary cancers with intensity modulated proton therapy (IMPT), when used for radiosurgery of liver metastases.

Material and methods

Ten patients, previously treated for liver metastases with photon-beam based stereotactic body radiation therapy (SBRT) were retrospectively planned for radiosurgery with IMPT. A treatment plan comparison was then performed in terms of calculated risk of radiation-induced secondary cancer. The risks were estimated using two distinct models (Dasu et al., 2005; Schneider et al., 2005, 2009). The plans were compared pairwise with a two-sided Wilcoxon signed-rank test with a significance level of 0.05.

Results

Reduced risks for induction of fatal and other types of cancers were estimated for the IMPT plans (p < 0.05) with the Dasu et al. model. Using the Schneider et al. model, lower risks for carcinomainduction with IMPT were estimated for the skin, lungs, healthy part of the liver, esophagus and the remaining part of the body (p < 0.05). The risk of observing sarcomas in the bone was also reduced with IMPT (p < 0.05).

Conclusion

The findings of this study indicate that the risks of radiation-induced secondary cancers after radiosurgery of liver metastases may be reduced, if IMPT is used instead of photon-beam based SBRT.

Place, publisher, year, edition, pages
2017. Vol. 42, p. 263-270
Keywords [en]
Liver metastases, Secondary cancers, SBRT, IMPT
National Category
Other Physics Topics
Research subject
Medical Radiation Physics
Identifiers
URN: urn:nbn:se:su:diva-142731DOI: 10.1016/j.ejmp.2017.03.019ISI: 000416522000036OAI: oai:DiVA.org:su-142731DiVA, id: diva2:1092738
Available from: 2017-05-04 Created: 2017-05-04 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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