| 1. |
- Adjeiwaah, Mary, 1980-, et al.
(author)
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Sensitivity analysis of different quality assurance methods for magnetic resonance imaging in radiotherapy
- 2020
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In: Physics and Imaging in Radiation Oncology. - : Elsevier. - 2405-6316. ; 13, s. 21-27
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Journal article (peer-reviewed)abstract
- Background and purpose: There are currently no standard quality assurance (QA) methods for magnetic resonance imaging (MRI) in radiotherapy (RT). This work was aimed at evaluating the ability of two QA protocols to detect common events that affect quality of MR images under RT settings.Materials and methods: The American College of Radiology (ACR) MRI QA phantom was repeatedly scanned using a flexible coil and action limits for key image quality parameters were derived. Using an exploratory survey, issues that reduce MR image quality were identified. The most commonly occurring events were introduced as provocations to produce MR images with degraded quality. From these images, detection sensitivities of the ACR MRI QA protocol and a commercial geometric accuracy phantom were determined.Results: Machine-specific action limits for key image quality parameters set at mean±3σ" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 16.2px; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">mean±3σ were comparable with the ACR acceptable values. For the geometric accuracy phantom, provocations from uncorrected gradient nonlinearity effects and a piece of metal in the bore of the scanner resulted in worst distortions of 22.2 mm and 3.4 mm, respectively. The ACR phantom was sensitive to uncorrected signal variations, electric interference and a piece of metal in the bore of the scanner but could not adequately detect individual coil element failures.Conclusions: The ACR MRI QA phantom combined with the large field-of-view commercial geometric accuracy phantom were generally sensitive in identifying some common MR image quality issues. The two protocols when combined may provide a tool to monitor the performance of MRI systems in the radiotherapy environment.
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| 2. |
- Andersson, Jonas, 1975-, et al.
(author)
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Artificial intelligence and the medical physics profession-A Swedish perspective
- 2021
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In: Physica Medica-European Journal of Medical Physics. - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 88, s. 218-225
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Journal article (peer-reviewed)abstract
- Background: There is a continuous and dynamic discussion on artificial intelligence (AI) in present-day society. AI is expected to impact on healthcare processes and could contribute to a more sustainable use of resources allocated to healthcare in the future. The aim for this work was to establish a foundation for a Swedish perspective on the potential effect of AI on the medical physics profession. Materials and methods: We designed a survey to gauge viewpoints regarding AI in the Swedish medical physics community. Based on the survey results and present-day situation in Sweden, a SWOT analysis was performed on the implications of AI for the medical physics profession. Results: Out of 411 survey recipients, 163 responded (40%). The Swedish medical physicists with a professional license believed (90%) that AI would change the practice of medical physics but did not foresee (81%) that AI would pose a risk to their practice and career. The respondents were largely positive to the inclusion of AI in educational programmes. According to self-assessment, the respondents' knowledge of and workplace preparedness for AI was generally low. Conclusions: From the survey and SWOT analysis we conclude that AI will change the medical physics profession and that there are opportunities for the profession associated with the adoption of AI in healthcare. To overcome the weakness of limited AI knowledge, potentially threatening the role of medical physicists, and build upon the strong position in Swedish healthcare, medical physics education and training should include learning objectives on AI.
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| 3. |
- Björeland, Ulrika, et al.
(author)
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Hyaluronic acid spacer in prostate cancer radiotherapy : dosimetric effects, spacer stability and long-term toxicity and PRO in a phase II study
- 2023
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In: Radiation Oncology. - : BioMed Central (BMC). - 1748-717X. ; 18:1
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Journal article (peer-reviewed)abstract
- BACKGROUND: Perirectal spacers may be beneficial to reduce rectal side effects from radiotherapy (RT). Here, we present the impact of a hyaluronic acid (HA) perirectal spacer on rectal dose as well as spacer stability, long-term gastrointestinal (GI) and genitourinary (GU) toxicity and patient-reported outcome (PRO).METHODS: In this phase II study 81 patients with low- and intermediate-risk prostate cancer received transrectal injections with HA before external beam RT (78 Gy in 39 fractions). The HA spacer was evaluated with MRI four times; before (MR0) and after HA-injection (MR1), at the middle (MR2) and at the end (MR3) of RT. GI and GU toxicity was assessed by physician for up to five years according to the RTOG scale. PROs were collected using the Swedish National Prostate Cancer Registry and Prostate cancer symptom scale questionnaires.RESULTS: There was a significant reduction in rectal V70% (54.6 Gy) and V90% (70.2 Gy) between MR0 and MR1, as well as between MR0 to MR2 and MR3. From MR1 to MR2/MR3, HA thickness decreased with 28%/32% and CTV-rectum space with 19%/17% in the middle level. The cumulative late grade ≥ 2 GI toxicity at 5 years was 5% and the proportion of PRO moderate or severe overall bowel problems at 5 years follow-up was 12%. Cumulative late grade ≥ 2 GU toxicity at 5 years was 12% and moderate or severe overall urinary problems at 5 years were 10%.CONCLUSION: We show that the HA spacer reduced rectal dose and long-term toxicity.
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| 4. |
- Björeland, Ulrika, et al.
(author)
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Impact of neoadjuvant androgen deprivation therapy on magnetic resonance imaging features in prostate cancer before radiotherapy
- 2021
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In: Physics and Imaging in Radiation Oncology. - : Elsevier. - 2405-6316. ; 17, s. 117-123
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Journal article (peer-reviewed)abstract
- Background and purpose: In locally advanced prostate cancer (PC), androgen deprivation therapy (ADT) in combination with whole prostate radiotherapy (RT) is the standard treatment. ADT affects the prostate as well as the tumour on multiparametric magnetic resonance imaging (MRI) with decreased PC conspicuity and impaired localisation of the prostate lesion. Image texture analysis has been suggested to be of aid in separating tumour from normal tissue. The aim of the study was to investigate the impact of ADT on baseline defined MRI features in prostate cancer with the goal to investigate if it might be of use in radiotherapy planning.Materials and methods: Fifty PC patients were included. Multiparametric MRI was performed before, and three months after ADT. At baseline, a tumour volume was delineated on apparent diffusion coefficient (ADC) maps with suspected tumour content and a reference volume in normal prostatic tissue. These volumes were transferred to MRIs after ADT and were analysed with first-order -and invariant Haralick -features.Results: At baseline, the median value and several of the invariant Haralick features of ADC, showed a significant difference between tumour and reference volumes. After ADT, only ADC median value could significantly differentiate the two volumes.Conclusions: Invariant Haralick -features could not distinguish between baseline MRI defined PC and normal tissue after ADT. First-order median value remained significantly different in tumour and reference volumes after ADT, but the difference was less pronounced than before ADT.
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| 5. |
- Björeland, Ulrika, 1974-
(author)
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MRI in prostate cancer : implications for target volume
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Prostate cancer (PCa) is the most common cancer among men, with 10 000 new cases per year in Sweden [1]. To diagnose PCa, magnetic resonance imaging (MRI) is used to identify and classify the disease. The patient’s treatment strategy depends on PCa classification and clinical data, which are weighted together into a risk group classification from 1–5. For patients with higher risk classes (>3), radiotherapy together with hormone therapy is a common treatment option [2].In radiotherapy (RT), individual treatment plans are created based on the patient’s anatomy. These plans are based on computed tomography (CT), often supplemented with MRI images. MRI and CT complement each other, as MRI has better soft tissue contrast and CT has better bone contrast. Based on the images, the volumes to be treated (target) and the volumes to be avoided (risk organs) are defined. Prostate RT is complex, and there are uncertainties regarding the patient's internal movements and how the patient is positioned before each treatment. To account for these uncertainties, the radiation field is expanded (extended margins to target) to ensure that the treatment volume receives its radiotherapy. RT is most often given in fractions. Fractionation, dose, and treatment volume depend on the patient’s risk category. The treatment area can be, for example, only prostate, prostate with extra radiation dose (boost) to an intraprostatic tumour, or prostate with lymph node (LN) irradiation. LN irradiation is most often given for preventive purposes for PCa with a risk classification >4, which means no cancer has been identified, but any microscopic spread to the LNs is being treated profylactically.In RT, target identification is essential both in the treatment planning images (CT/MRI) and at treatment. Studies have shown that PCa often re-occurs in or near the volume of the dominant (often largest) intraprostatic tumour [3, 4], and this volume is relevant for boosting. For patients treated with hormone therapy before radiotherapy, tumour identification is complicated. Hormones change the tumour characteristics, affecting the image contrast and making the tumour difficult to identify. To study this, we investigated whether texture analysis could identify the tumour volume after hormone therapy (paper II). However, even with texture analysis, the tumour was difficult to identify. A follow-up study examined whether the image information in MRI images taken before hormone therapy could indicate how the treatment fell out (paper IV). However, no correlation was seen between image features and the progression of PCa.Identifying the target and correctly positioning the patient for each treatment fraction is the most important procedure in radiotherapy. The prostate is a mobile organ; therefore, intraprostatic fiducial markers are inserted before treatment planning to reduce positioning uncertainties. Each radiotherapy session begins with an X-ray image where the markers are visible, and the radiation can be delivered based on the markers' position. The markers are also used as guidance for large target volumes, such as for prostate with LN irradiation. With better knowledge of the prostate and LN movements, the margins can potentially be reduced, followed by reduced radiation dose to healthy tissue and therefore reduced side effects for patients. Movements in the radiotherapy volume were the focus of paper I. Using MRI images, the movements of the prostate and LNs were measured during the course of radiotherapy, and we found that LN movement is independent of the movement of the prostate and that the movement varies in the target volume.In addition to the recurrence of PCa in the tumour area, there is an increased risk of recurrence in the prostate periphery close to the rectum. Since the rectum and prostate are in contact for some patients, RT must be adapted to make rectum side effects tolerable. One way to increase the distance between the prostate and the rectum is to inject a gel between the two organs. The distance makes it easier to achieve a better dose distribution to the PCa. This idea resulted in paper III, where patients were given a gel between the prostate and rectum. MRI was used to check the stability of the gel during the course of RT and was evaluated together with long-term follow-up of the patient’s well-being and acceptance of the gel. We found that the radiation dose to the rectum was lower with a spacer, although the spacer was not completely stable during treatment.
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| 6. |
- Combs, Stephanie E., et al.
(author)
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ESTRO ACROP guideline for target volume delineation of skull base tumors
- 2021
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In: Radiotherapy and Oncology. - : Elsevier. - 0167-8140 .- 1879-0887. ; 156, s. 80-94
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Journal article (peer-reviewed)abstract
- Background and purpose: For skull base tumors, target definition is the key to safe high-dose treatments because surrounding normal tissues are very sensitive to radiation. In the present work we established a joint ESTRO ACROP guideline for the target volume definition of skull base tumors.Material and methods: A comprehensive literature search was conducted in PubMed using various combinations of the following medical subjects headings (MeSH) and free-text words: “radiation therapy” or “stereotactic radiosurgery” or “proton therapy” or “particle beam therapy” and “skull base neoplasms” “pituitary neoplasms”, “meningioma”, “craniopharyngioma”, “chordoma”, “chondrosarcoma”, “acoustic neuroma/vestibular schwannoma”, “organs at risk”, “gross tumor volume”, “clinical tumor volume”, “planning tumor volume”, “target volume”, “target delineation”, “dose constraints”. The ACROP committee identified sixteen European experts in close interaction with the ESTRO clinical committee who analyzed and discussed the body of evidence concerning target delineation.Results: All experts agree that magnetic resonance (MR) images with high three-dimensional spatial accuracy and tissue-contrast definition, both T2-weighted and volumetric T1-weighted sequences, are required to improve target delineation. In detail, several key issues were identified and discussed: i) radiation techniques and immobilization, ii) imaging techniques and target delineation, and iii) technical aspects of radiation treatments including planning techniques and dose-fractionation schedules. Specific target delineation issues with regard to different skull base tumors, including pituitary adenomas, meningiomas, craniopharyngiomas, acoustic neuromas, chordomas and chondrosarcomas are presented.Conclusions: This ESTRO ACROP guideline achieved detailed recommendations on target volume definition for skull base tumors, as well as comprehensive advice about imaging modalities and radiation techniques.
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| 7. |
- Fetty, Lukas, et al.
(author)
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Investigating conditional GAN performance with different generator architectures, an ensemble model, and different MR scanners for MR-sCT conversion
- 2020
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In: Physics in Medicine and Biology. - : Institute of Physics Publishing (IOPP). - 0031-9155 .- 1361-6560. ; 65:10
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Journal article (peer-reviewed)abstract
- Recent developments in magnetic resonance (MR) to synthetic computed tomography (sCT) conversion have shown that treatment planning is possible without an initial planning CT. Promising conversion results have been demonstrated recently using conditional generative adversarial networks (cGANs). However, the performance is generally only tested on images from one MR scanner, which neglects the potential of neural networks to find general high-level abstract features. In this study, we explored the generalizability of the generator models, trained on a single field strength scanner, to data acquired with higher field strengths. T2-weighted 0.35T MRIs and CTs from 51 patients treated for prostate (40) and cervical cancer (11) were included. 25 of them were used to train four different generators (SE-ResNet, DenseNet, U-Net, and Embedded Net). Further, an ensemble model was created from the four network outputs. The models were validated on 16 patients from a 0.35T MR scanner. Further, the trained models were tested on the Gold Atlas dataset, containing T2-weighted MR scans of different field strengths; 1.5T(7) and 3T(12), and 10 patients from the 0.35T scanner. The sCTs were dosimetrically compared using clinical VMAT plans for all test patients. For the same scanner (0.35T), the results from the different models were comparable on the test set, with only minor differences in the mean absolute error (MAE) (35-51HU body). Similar results were obtained for conversions of 3T GE Signa and the 3T GE Discovery images (40-62HU MAE) for three of the models. However, larger differences were observed for the 1.5T images (48-65HU MAE). The overall best model was found to be the ensemble model. All dose differences were below 1%. This study shows that it is possible to generalize models trained on images of one scanner to other scanners and different field strengths. The best metric results were achieved by the combination of all networks.
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| 8. |
- Fetty, Lukas, et al.
(author)
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Latent space manipulation for high-resolution medical image synthesis via the StyleGAN
- 2020
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In: Zeitschrift für Medizinische Physik. - : Elsevier. - 0939-3889 .- 1876-4436. ; 30:4, s. 305-314
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Journal article (peer-reviewed)abstract
- Introduction: This paper explores the potential of the StyleGAN model as an high-resolution image generator for synthetic medical images. The possibility to generate sample patient images of different modalities can be helpful for training deep learning algorithms as e.g. a data augmentation technique.Methods: The StyleGAN model was trained on Computed Tomography (CT) and T2- weighted Magnetic Resonance (MR) images from 100 patients with pelvic malignancies. The resulting model was investigated with regards to three features: Image Modality, Sex, and Longitudinal Slice Position. Further, the style transfer feature of the StyleGAN was used to move images between the modalities. The root-mean-squard error (RMSE) and the Mean Absolute Error (MAE) were used to quantify errors for MR and CT, respectively.Results: We demonstrate how these features can be transformed by manipulating the latent style vectors, and attempt to quantify how the errors change as we move through the latent style space. The best results were achieved by using the style transfer feature of the StyleGAN (58.7 HU MAE for MR to CT and 0.339 RMSE for CT to MR). Slices below and above an initial central slice can be predicted with an error below 75 HU MAE and 0.3 RMSE within 4 cm for CT and MR, respectively.Discussion: The StyleGAN is a promising model to use for generating synthetic medical images for MR and CT modalities as well as for 3D volumes.
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| 9. |
- Fransson, Samuel, et al.
(author)
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Intrafractional motion models based on principal components in Magnetic Resonance guided prostate radiotherapy
- 2021
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In: Physics and Imaging in Radiation Oncology. - : Elsevier. - 2405-6316. ; 20, s. 17-22
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Journal article (peer-reviewed)abstract
- Background and purpose: Devices that combine an MR-scanner with a Linac for radiotherapy, referred to as MR-Linac systems, introduce the possibility to acquire high resolution images prior and during treatment. Hence, there is a possibility to acquire individualised learning sets for motion models for each fraction and the construction of intrafractional motion models. We investigated the feasibility for a principal component analysis (PCA) based, intrafractional motion model of the male pelvic region.Materials and methods: 4D-scans of nine healthy male volunteers were utilized, FOV covering the entire pelvic region including prostate, bladder and rectum with manual segmentation of each organ at each time frame. Deformable image registration with an optical flow algorithm was performed for each subject with the first time frame as reference. PCA was performed on a subset of the resulting displacement vector fields to construct individualised motion models evaluated on the remaining fields.Results: The registration algorithm produced accurate registration result, in general DICE overlap >0.95 across all time frames. Cumulative variance of the eigen values from the PCA showed that 50% or more of the motion is explained in the first component for all subjects. However, the size and direction for the components differed between subjects. Adding more than two components did not improve the accuracy significantly and the model was able to explain motion down to about 1 mm.onclusions: An individualised intrafractional male pelvic motion model is feasible. Geometric accuracy was about 1 mm based on 1-2 principal components.
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| 10. |
- Grönlund, Eric, 1987-, et al.
(author)
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Robust treatment planning of dose painting for prostate cancer based on ADC-to-Gleason score mappings : what is the potential to increase the tumor control probability?
- 2021
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In: Acta Oncologica. - : Taylor & Francis. - 0284-186X .- 1651-226X. ; 60:2, s. 199-206
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Journal article (peer-reviewed)abstract
- Background and Purpose The aim of this study was to evaluate the potential to increase the tumor control probability (TCP) with ‘dose painting by numbers’ (DPBN) plans optimized in a treatment planning system (TPS) compared to uniform dose plans. The DPBN optimization was based on our earlier published formalism for prostate cancer that is driven by dose-responses of Gleason scores mapped from apparent diffusion coefficients (ADC).Material and MethodsFor 17 included patients, a set of DPBN plans were optimized in a TPS by maximizing the TCP for an equal average dose to the prostate volume (CTVT) as for a conventional uniform dose treatment. For the plan optimizations we applied different photon energies, different precisions for the ADC-to-Gleason mappings, and different CTVT positioning uncertainties. The TCP increasing potential was evaluated by the DPBN efficiency, defined as the ratio of TCP increases for DPBN plans by TCP increases for ideal DPBN prescriptions (optimized without considering radiation transport phenomena, uncertainties of the CTVT positioning, and uncertainties of the ADC-to-Gleason mapping).ResultsThe median DPBN efficiency for the most conservative planning scenario optimized with a low precision ADC-to-Gleason mapping, and a positioning uncertainty of 0.6 cm was 10%, meaning that more than half of the patients had a TCP gain of at least 10% of the TCP for an ideal DPBN prescription. By increasing the precision of the ADC-to-Gleason mapping, and decreasing the positioning uncertainty the median DPBN efficiency increased by up to 40%.ConclusionsTCP increases with DPBN plans optimized in a TPS were found more likely with a high precision mapping of image data into dose-responses and a high certainty of the tumor positioning. These findings motivate further development to ensure precise mappings of image data into dose-responses and to ensure a high spatial certainty of the tumor positioning when implementing DPBN clinically.
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