| 61. |
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| 62. |
- Mondlane, Gracinda, 1987-
(författare)
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Comparative study of Radiation Therapy of Targets in the Upper Abdomen with Photon- or Scanned Proton-beams
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recently, there has been an increase in the number of proton beam therapy (PBT) centers operating worldwide. For certain cases, proton beams have been shown to provide dosimetric and radiobiological advantages when used for cancer treatment, compared to the regular photon-beam based treatments. Under ideal circumstances, the dose given to the tissues surrounding a target can be reduced with PBT. The risk for side effects following treatment is then expected to decrease. Until present, mainly stationary targets, e.g. targets in the brain, have been treated with PBT. There is currently a growing interest to treat also target volumes in other parts of the body with PBT. However, there are sources of uncertainties, which must be more carefully considered when PBT is used, especially for PBT carried out with scanned proton beams. PBT is more sensitive to anatomical changes, e.g. organ motion or a variable gas content in the intestines, which requires that special precautions are taken prior to treating new tumour sites. In photon beam radiotherapy (RT) of moving targets, the main consequence of organ motion is the loss of sharpness of the dose gradients (dose smearing). When scanned proton beams are used, dose deformation caused by the fluctuations in the proton beam range, due to varying tissue heterogeneities (e.g., the ribs moving in and out of the beam path) and the so-called interplay effect, can be expected to impact the dose distributions in addition to the dose smearing. The dosimetric uncertainties, if not accounted for, may cause the planned and accurately calculated dose distribution to be distorted, compromising the main goal of RT of achieving the maximal local disease control while accepting certain risks for normal tissue complications.Currently there is a lack of clinical follow-up data regarding the outcome of PBT for different tumour sites, in particular for extra-cranial tumour sites in moving organs. On the other hand, the use of photon beams for this kind of cancer treatment is well-stablished. A treatment planning comparison between RT carried out with photons and with protons may provide guidelines for when PBT could be more suitable. New clinical applications of particle beams in cancer therapy can also be transferred from photon-beam treatments, for which there is a vast clinical experience. The evaluation of the different uncertainties influencing RT of different tumour sites carried out with photon- and with proton-beams, will hopefully create an understanding for the feasibility of treating cancers with scanned proton beams instead of photon beams. The comparison of two distinct RT modalities is normally performed by studying the dosimetric values obtained from the dose volume histograms (DVH). However, in dosimetric evaluations, the outcome of the treatments in terms of local disease control and healthy tissue toxicity are not estimated. 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. In this thesis, different factors that should be taken into consideration in PBT, for treatments influenced by organ motion and density heterogeneities, were studied and their importance quantified.This thesis consists of three published articles (Articles I, II and III). In these reports, the dosimetric and biological evaluations of photon-beam and scanned proton-beam RT were performed and the results obtained were compared. The studies were made for two tumour sites influenced by organ motion and density changes, gastric cancer (GC) and liver metastases. For the GC cases, the impact of changes in tissue density, resulting from variable gas content (which can be observed inter-fractionally), was also studied. In this thesis, both conventional fractionations (implemented in the planning for GC treatments) and hypofractionated regimens (implemented in the planning for the liver metastases cases) were considered. In this work, it was found that proton therapy provided the possibility to reduce the irradiations of the normal tissue located near the target volumes, compared to photon beam RT. However, the effects of density changes were found to be more pronounced in the plans for PBT. Furthermore, with proton beams, the reduction of the integral dose given to the OARs resulted in reduced risks of treatment-induced secondary malignancies.
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| 63. |
- Mondlane, Gracinda, 1987-
(författare)
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Radiation therapy of upper gastrointestinal cancers with scanned proton beams : A treatment planning study
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 64. |
- Munck af Rosenschöld, Per, et al.
(författare)
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Current status of dosimetry at the boron neutron capture therapy facility at Studsvik, Sweden
- 2002
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Ingår i: Research and Development in Neutron Capture Therapy. - 9788832329094 ; , s. 437-441
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Konferensbidrag (refereegranskat)abstract
- The beam was successfully characterized in air and in phantom using various radiation dosimeter:,. The determination of the thermal neutron and photon components of the mixed beam in phantom can be determined with acceptable uncertainties, while the uncertainty of the high-energy neutron component is considerable but of limited clinical significance. The beam intensity is sufficiently high for reasonably short treatment times. A novel approach to in-vivo dosimetry and quality assurance of treatment time in terms of monitor units was introduced in order to comply with national regulations regarding radiation therapy.
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| 65. |
- Munck af Rosenschöld, Per, et al.
(författare)
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Prompt gamma tomography during BNCT – a feasibility study
- 2006
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 1
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Tidskriftsartikel (refereegranskat)abstract
- The success of clinical boron neutron capture therapy (BNCT) lies in the ability to manage the radiobiological effect on the tumour and healthy tissue, and thus, accurate dosimetry measurements is pertinent for each individual patient. In the present work we investigate the possibility of performing online prompt gamma tomography (PGT) during BNCT. A prototype detector system was constructed, which is in principle a pin-hole collimator with a HPGe crystal to be mounted on a C-bow device, with shielding of lithium-plastic and lead. The detector system was used to measure on a phantom placed in an epithermal neutron beam and on a 137Cs-source. The possibility of tomographic reconstruction using the detector system was tested on a phantom filled with a 131I-solution with a smaller sphere inserted containing a higher specific activity (ratio 10:1). The detector system was possible to operate up to about 6 × 108 cm-2 s-1 thermal neutron fluence at the peak in the phantom, at which time it was saturated. A 478 keV boron-peak was visible in the measured spectra but the signal-to-noise-ratio was rather low. No post-irradiation damage or neutron activation was detectable. A tomographic reconstruction of the phantom filled with 131I-solutions was performed using an algorithm developed in house and based on the MLEM method. The image quality is fairly good and the results provide a clear indication that the detector system can be used to obtain data that enables tomographic reconstruction. A spatial resolution of the detector system of about 2 cm was obtained from both the measurement on the 137Cs-source and the 131I-phantom. In conclusion, the presented feasibility study on a prototype PGT system is encouraging further studies specifically directed at improving the signal-to-noise-ratio in measurements in epithermal neutron beams.
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| 66. |
- Munck af Rosenschöld, Per, et al.
(författare)
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Quality assurance of patient dosimetry in boron neutron capture therapy
- 2004
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Ingår i: Acta Oncologica. - : Informa UK Limited. - 1651-226X .- 0284-186X. ; 43:4, s. 404-411
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Tidskriftsartikel (refereegranskat)abstract
- The verification of the correctness of planned and executed treatments is imperative for safety in radiotherapy. The purpose of the present work is to describe and evaluate the quality assurance (QA) procedures for patient dosimetry implemented at the boron neutron capture therapy (BNCT) facility at Studsvik, Sweden. The dosimetric complexity of the mixed neutron-photon field during BNCT suggests a careful verification of routine procedures, specifically the treatment planning calculations. In the present study, two methods for QA of patient dosimetry are presented. The first is executed prior to radiotherapy and involves an independent check of the planned absorbed dose to be delivered to a point in the patient for each treatment field. The second QA procedure involves in vivo dosimetry measurements using posttreatment activation analysis. Absorbed dose conversion factors taking the difference in material composition and geometry of the patient and the PMMA phantom used for reference dosimetry were determined using the Monte Carlo method. The agreement of the QA procedure prior to radiotherapy reveals an acceptably small deviation for 60 treatment fields of ±4.2% (1 SD), while the in vivo dosimetry method presented may benefit from improvements, as the deviations observed were quite substantial (±12%, 1 SD), and were unlikely to be due to actual errors in the clinical dosimetry.
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| 67. |
- Nilsson, Per, et al.
(författare)
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A template for writing radiotherapy protocols
- 2015
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Ingår i: Acta Oncologica. - 0284-186X .- 1651-226X. ; 54:2, s. 275-279
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Tidskriftsartikel (refereegranskat)abstract
- Background. Well-specified and unambiguous treatment protocols are essential both for current practice and for the future development of radiation therapy. In order to provide assistance for writing good protocols, irrespective of treatment intention and complexity, up-to-date guidelines are highly desirable. Methods. We have analysed the radiotherapy work-flow, including clinical and physical aspects, such as preparatory imaging, treatment planning, delivery and evaluation, with the aim to outline a consistent framework covering the entire radiotherapy process. Results. Based on the analysis, a recipe-style template for specifying the description of the radiotherapy process has been designed. The template is written in a general format, which allows for modified phrasing, and should be customised for the specific clinical situation and diagnosis, as well as facility resources. Conclusions. The template can be used as a tool to ensure a consistent and comprehensive description of the radiotherapy section of clinical guidelines, care programmes and clinical trial protocols.
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| 68. |
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| 69. |
- Nordström, Fredrik, et al.
(författare)
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Control chart analysis of data from a multicenter monitor unit verification study.
- 2012
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Ingår i: Radiotherapy and Oncology. - : Elsevier BV. - 1879-0887 .- 0167-8140. ; 102:3, s. 364-370
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND AND PURPOSE: This study aims to investigate the process of monitor unit verification using control charts. Control charts is a key tool within statistical process control (SPC), through which process characteristics can be visualized, usually chronologically with statistically determined limits. MATERIAL AND METHODS: Our group has developed a monitor unit verification software that has been adopted at several Swedish institutions for pre-treatment verification of radiotherapy treatments. Deviations between point dose calculations using the treatment planning systems and using the independent monitor unit verification software from 9219 treatment plans and five different institutions were included in this multicenter study. The process of monitor unit verification was divided into subprocesses. Each subprocess was analyzed using probability plots and control charts. RESULTS: Differences in control chart parameters for the investigated subprocesses were found between different treatment sites and different institutions, as well as between different treatment techniques. 19 of 37 subprocesses met the clinical specification (±5%), i.e. process capability index was equal to or above one. CONCLUSIONS: Control charts were found to be a useful tool for continuous analysis of data from the monitor unit verification software for patient specific quality control, as well as for comparisons between different institutions and treatment sites. The derived control chart limits were in agreement with AAPM TG114 guidelines on action levels.
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| 70. |
- Nordström, Fredrik, et al.
(författare)
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Ensuring the integrity of treatment parameters throughout the radiotherapy process.
- 2012
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Ingår i: Radiotherapy and Oncology. - : Elsevier BV. - 1879-0887 .- 0167-8140. ; 103:3, s. 299-304
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND AND PURPOSE: Ensuring data integrity in radiotherapy is of major importance and a complex task. The aim of this study was to compare three different combinations of treatment planning and record and verify systems with respect to data integrity. MATERIALS AND METHODS: A software for comparison of treatment parameters in DICOM-RT files was developed using the MATLAB R2010a (MathWorks Inc.) environment. One hundred treatment plans were analyzed for each system combination. In the first step of the analysis, all parameters were compared and a normal condition for each system combination was identified. The second step focused on the discovery of potential special cause deviations, e.g. by applying tolerance levels. RESULTS: In total, 15% and 0.37% of all comparisons failed to meet the defined integrity demands in step 1 and step 2 of the analysis, respectively. Differences in the data integrity level between the systems were observed, ranging on average from 3.1 to 11.9 discrepancies per beam for the different RV-TPS combinations. CONCLUSIONS: The proposed method can be used to increase the safety for individual patients by ensuring that the intended treatment is delivered. The system combination with the highest level of data integrity was found to be the one which shares a single database.
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