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| 2. |
- Lindblom, Emely, et al.
(författare)
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Accounting for Two Forms of Hypoxia for Predicting Tumour Control Probability in Radiotherapy : An In Silico Study
- 2018
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Ingår i: Advances in Experimental Medicine and Biology. - Cham : Springer International Publishing. - 0065-2598 .- 2214-8019. ; 1042, s. 183-187
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Tidskriftsartikel (refereegranskat)abstract
- The progress in functional imaging and dose delivery has opened the possibility of targeting tumour hypoxia with radiotherapy. Advanced approaches apply quantitative information on tumour oxygenation retrieved from imaging in dose prescription. These do not, however, take into account the potential difference in radiosensitivity of chronically and acutely hypoxic cells. It was the aim of this study to evaluate the implications of assuming the same or different sensitivities for the hypoxic cells. An in silico 3D-model of a hypoxic tumour with heterogeneous oxygenation was used to model the probabilities of tumour control with different radiotherapy regimens. The results show that by taking into account the potential lower radioresistance of chronically hypoxic cells deprived of oxygen and nutrients, the total dose required to achieve a certain level of control is substantially reduced for a given fractionation scheme in comparison to the case when chronically and acutely hypoxic cells are assumed to have similar features. The results also suggest that the presence of chronic hypoxia could explain the success of radiotherapy for some hypoxic tumours. Given the implications for clinical dose escalation trials, further exploration of the influence of the different forms of hypoxia on treatment outcome is therefore warranted.
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| 3. |
- Antonovic, Laura, 1982-, et al.
(författare)
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Relative clinical effectiveness of carbon ion radiotherapy: theoretical modelling for H&N tumours
- 2015
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Ingår i: Journal of radiation research. - : Oxford University Press (OUP). - 0449-3060 .- 1349-9157. ; 56:4, s. 639-645
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Tidskriftsartikel (refereegranskat)abstract
- Comparison of the efficiency of photon and carbon ion radiotherapy (RT) administered with the same number of fractions might be of limited clinical interest, since a wide range of fractionation patterns are used clinically today. Due to advanced photon treatment techniques, hypofractionation is becoming increasingly accepted for prostate and lung tumours, whereas patients with head and neck tumours still benefit from hyperfractionated treatments. In general, the number of fractions is considerably lower in carbon ion RT. A clinically relevant comparison would be between fractionation schedules that are optimal within each treatment modality category. In this in silico study, the relative clinical effectiveness (RCE) of carbon ions was investigated for human salivary gland tumours, assuming various radiation sensitivities related to their oxygenation. The results indicate that, for hypoxic tumours in the absence of reoxygenation, the RCE (defined as the ratio of D50 for photons to carbon ions) ranges from 3.5 to 5.7, corresponding to carbon ion treatments given in 36 and 3 fractions, respectively, and 30 fractions for photons. Assuming that interfraction local oxygenation changes take place, results for RCE are lower than that for an oxic tumour if only a few fractions of carbon ions are used. If the carbon ion treatment is given in more than 12 fractions, the RCE is larger for the hypoxic than for the well-oxygenated tumour. In conclusion, this study showed that in silico modelling enables the study of a wide range of factors in the clinical considerations and could be an important step towards individualisation of RT treatments.
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| 4. |
- Astaraki, Mehdi, PhD Student, 1984-, et al.
(författare)
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Early survival prediction in non-small cell lung cancer from PET/CT images using an intra-tumor partitioning method
- 2019
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Ingår i: Physica medica (Testo stampato). - : Elsevier BV. - 1120-1797 .- 1724-191X. ; 60, s. 58-65
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Tidskriftsartikel (refereegranskat)abstract
- PurposeTo explore prognostic and predictive values of a novel quantitative feature set describing intra-tumor heterogeneity in patients with lung cancer treated with concurrent and sequential chemoradiotherapy.MethodsLongitudinal PET-CT images of 30 patients with non-small cell lung cancer were analysed. To describe tumor cell heterogeneity, the tumors were partitioned into one to ten concentric regions depending on their sizes, and, for each region, the change in average intensity between the two scans was calculated for PET and CT images separately to form the proposed feature set. To validate the prognostic value of the proposed method, radiomics analysis was performed and a combination of the proposed novel feature set and the classic radiomic features was evaluated. A feature selection algorithm was utilized to identify the optimal features, and a linear support vector machine was trained for the task of overall survival prediction in terms of area under the receiver operating characteristic curve (AUROC).ResultsThe proposed novel feature set was found to be prognostic and even outperformed the radiomics approach with a significant difference (AUROCSALoP = 0.90 vs. AUROCradiomic = 0.71) when feature selection was not employed, whereas with feature selection, a combination of the novel feature set and radiomics led to the highest prognostic values.ConclusionA novel feature set designed for capturing intra-tumor heterogeneity was introduced. Judging by their prognostic power, the proposed features have a promising potential for early survival prediction.
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| 5. |
- Bolsi, Alessandra, et al.
(författare)
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Practice patterns of image guided particle therapy in Europe : A 2016 survey of the European Particle Therapy Network (EPTN)
- 2018
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Ingår i: Radiotherapy and Oncology. - : Elsevier BV. - 0167-8140 .- 1879-0887. ; 128:1, s. 4-8
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Tidskriftsartikel (refereegranskat)abstract
- Background and purpose: Image guidance is critical in achieving accurate and precise radiation delivery in particle therapy, even more than in photon therapy. However, equipment, quality assurance procedures and clinical workflows for image-guided particle therapy (IGPT) may vary substantially between centres due to a lack of standardization. A survey was conducted to evaluate the current practice of IGPT in European particle therapy centres.Material and methods: In 2016, a questionnaire was distributed among 19 particle therapy centres in 12 European countries. The questionnaire consisted of 30 open and 37 closed questions related to image guidance in the general clinical workflow, for moving targets, current research activities and future perspectives of IGPT.Results: All centres completed the questionnaire. The IGPT methods used by the 10 treating centres varied substantially. The 9 non-treating centres were in the process to introduce IGPT. Most centres have developed their own IGPT strategies, being tightly connected to their specific technical implementation and dose delivery methods.Conclusions: Insight into the current clinical practice of IGPT in European particle therapy centres was obtained. A variety in IGPT practices and procedures was confirmed, which underlines the need for harmonisation of practice parameters and consensus guidelines.
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| 6. |
- Dasu, Alexandru, et al.
(författare)
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Impact of increasing irradiation time on the treatment of prostate cancers
- 2015
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Ingår i: World Congress on Medical Physics and Biomedical Engineering, June 7-12, 2015, Toronto, Canada. - Cham : Springer. - 9783319193861 - 9783319193878 ; 51, s. 490-493
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Konferensbidrag (refereegranskat)abstract
- This study aimed to investigate the expected impact of intrafraction repair during increasing irradiation times for the treatment of prostate cancers. Lengthy sessions are indeed expected for some advanced irradiation techniques capable to deliver the large fractional doses required by the increased fractionation sensitivity of the prostates. For this purpose, clinically-derived parameters characterizing repair rates and dose response curves for prostate tumors have been used to calculate the expected loss of effectiveness when increasing the irradiation time. The results have shown that treatment sessions lasting more than about 20 to 40 minutes could reduce the probability of biochemical control of prostate tumors by more than 20 to 30 percentage points. These results are in agreement with some observed clinical results and therefore they suggest that treatment durations in prostate radiation therapy should be carefully recorded in order to explicitly account for intrafraction repair, especially when irradiation techniques make use of multiple beams and imaging sessions. Failure to do so might overestimate the expected effectiveness of the treatment and could lead to disappointing clinical results precisely from the demanding treatment modalities expected to increase the therapeutic gain in prostate radiotherapy.
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| 7. |
- Dasu, Alexandru, et al.
(författare)
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Models for the risk of secondary cancers from radiation therapy
- 2017
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Ingår i: Physica medica (Testo stampato). - London : Elsevier BV. - 1120-1797 .- 1724-191X. ; 42, s. 232-238
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Tidskriftsartikel (refereegranskat)abstract
- The interest in the induction of secondary tumours following radiotherapy has greatly increased as developments in detecting and treating the primary tumours have improved the life expectancy of cancer patients. However, most of the knowledge on the current levels of risk comes from patients treated many decades ago. As developments of irradiation techniques take place at a much faster pace than the progression of the carcinogenesis process, the earlier results could not be easily extrapolated to modern treatments. Indeed, the patterns of irradiation from historically-used orthovoltage radiotherapy and from contemporary techniques like conformal radiotherapy with megavoltage radiation, intensity modulated radiation therapy with photons or with particles are quite different. Furthermore, the increased interest in individualised treatment options raises the question of evaluating and ranking the different treatment plan options from the point of view of the risk for cancer induction, in parallel with the quantification of other long-term effects. It is therefore inevitable that models for risk assessment will have to be used to complement the knowledge from epidemiological studies and to make predictions for newer forms of treatment for which clinical evidence is not yet available. This work reviews the mathematical models that could be used to predict the risk of secondary cancers from radiotherapy-relevant dose levels, as well as the approaches and factors that have to be taken into account when including these models in the clinical evaluation process. These include the effects of heterogeneous irradiation, secondary particles production, imaging techniques, interpatient variability and other confounding factors.
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| 8. |
- Dasu, Alexandru, et al.
(författare)
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Will intrafraction repair have negative consequences on extreme hypofractionation in prostate radiation therapy?
- 2015
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Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 88:1056, s. Article ID 20150588-
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The aim of the present study was to investigate the impact of increasing fraction delivery time on the outcome of hypofractionated radiation therapy for prostate cancer.Methods: Monoexponential and biexponential repair models have been used for patients with prostate cancer to study the loss of biochemical control at 5 years for several clinically relevant irradiation times. The theoretical predictions were compared with newly reported clinical results from 4607 patients undergoing conventionally fractionated and hypofractionated prostate radiation therapy.Results: Time-demanding irradiation techniques appear to lead to biochemical control rates that sometimes are about 10–20 percentage points below predictions that neglect intrafraction repair. This difference appears to be of the same order of magnitude as that predicted by moderately slow to slow repair taking place during the irradiation time. The impact is largest for the patient risk groups receiving doses corresponding to the steepest part of the dose–response curve. By contrast, for treatment techniques requiring irradiation times shorter than about 20 min, the impact of intrafraction repair appears to be much smaller and probably difficult to be observed in the light of other sources of uncertainty in clinical data.Conclusion: Neglecting intrafraction repair might overestimate the effectiveness of some treatment schedules and could also influence any subsequent estimations of fractionation sensitivity for prostate tumours.Advances in knowledge: The effect of intrafraction repair for prostate cancer should be taken into account for long irradiation sessions as might be expected from scanned beams and/or from multiple intrafraction imaging sessions to check the positioning of the patient.
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| 9. |
- dos Santos Matias, Lucílio, et al.
(författare)
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Dosimetric and radiobiological evaluation of hybrid inverse planning and optimization for cervical cancer brachytherapy
- 2015
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Ingår i: Anticancer Research. - 0250-7005 .- 1791-7530. ; 35:11, s. 6091-6096
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Tidskriftsartikel (refereegranskat)abstract
- Aim: To compare manual graphical optimization (GrO) with hybrid inverse planning optimization (HIPO) of cervical cancer brachytherapy treatment plans using physical and radiobiological tools. Patients and Methods: Ten patients suffering from cervical cancer, treated with pulsed brachytherapy using GrO plans, were included in the study. For each patient, four different HIPO class solutions with different dose objectives to the target and constraints to the organs at risk (OAR) produced four optimized plans, that were each compared to the corresponding GrO plan. Class solution in HIPO is a set of parameters consisting of dose constraints and penalty weights, which are used for optimization. The comparison was based on the following dosimetric parameters: conformity index (COIN), minimum dose received by 98% and 90% of the high-risk clinical target volume (represented by D98 and D90, respectively), and the minimum dose imparted to 2 cm3 (D2cm3) of the most exposed OAR i.e. bladder, sigmoid colon or rectum. The HIPO class solution which produced plans with overall better dosimetric parameters was selected and its plans were compared with manual GrO plans from a radiobiological viewpoint based on the calculated complication-free tumour control probability, P+. Results: The average COIN for the GrO and the selected HIPO plans were 0.22 and 0.30, respectively. The median COIN of the GrO and the HIPO plans were not statistically different (p>0.05, Wilcoxon test). The relative percentage difference of the averaged P+ values between the HIPO and GrO plans evaluated together with the external beam radiation therapy plans was 0.01%, 0.37% and 0.98% for the bladder, sigmoid colon and rectum, respectively. The lowest P+ value for all the plans was 98.44% for sigmoid colon. Conclusion: HIPO presented comparable results in relation to manual planning with respect to dosimetric and radiobiological parameters.
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| 10. |
- Fager, Marcus, et al.
(författare)
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Linear energy transfer painting with proton therapy : a means of reducing radiation doses with equivalent clinical effectiveness
- 2015
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Ingår i: International Journal of Radiation Oncology, Biology, Physics. - : Elsevier BV. - 0360-3016 .- 1879-355X. ; 91:5, s. 1057-1064
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The purpose of this study was to propose a proton treatment planning method that trades physical dose (D) for dose-averaged linear energy transfer (LETd) while keeping the radiobiologically weighted dose (DRBE) to the target the same.Methods and Materials: The target is painted with LETd by using 2, 4, and 7 fields aimed at the proximal segment of the target (split target planning [STP]). As the LETd within the target increases with increasing number of fields, D decreases to maintain the DRBE the same as the conventional treatment planning method by using beams treating the full target (full target planning [FTP]).Results: The LETd increased 61% for 2-field STP (2STP) compared to FTP, 72% for 4STP, and 82% for 7STP inside the target. This increase in LETd led to a decrease of D with 5.3 ± 0.6 Gy for 2STP, 4.4 ± 0.7 Gy for 4STP, and 5.3 ± 1.1 Gy for 7STP, keeping the DRBE at 90% of the volume (DRBE, 90) constant to FTP.Conclusions: LETd painting offers a method to reduce prescribed dose at no cost to the biological effectiveness of the treatment.
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