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Uncertainty quantification (UQ) is a well-established category of methods to estimate the effect of parameter variations on a quantity of interest based on a solid mathematical foundation. In the wind energy field most UQ studies focus on the sensitivity of turbine loads. This article presents a framework, wrapped around a modern Python UQ library, to analyze the impact of uncertain turbine properties on aeroelastic stability. The UQ methodology applies a polynomial chaos expansion surrogate model. A comparison is made between different wind turbine simulation tools on the engineering model level (alaska/Wind, Bladed, HAWC2/HAWCStab2, and Simpack). Two case studies are used to demonstrate the effectiveness of the method to analyze the sensitivity of the aeroelastic damping of an unstable turbine mode to variations of structural blade cross-section parameters. The code-to-code comparison shows good agreement between the simulation tools for the reference model, but also significant differences in the sensitivities.

Background and Purpose: Conventionally, the quality of radiotherapy treatment plans is assessed through visual inspection of dose distributions and dose-volume histograms. This study developed a framework to evaluate plan quality using dose, complexity, and robustness metrics. Additionally, a method for predicting plan robustness metrics using dose and complexity metrics was introduced for cases where plan robustness evaluation is unavailable or impractical., Materials and Methods: The framework and prediction models were developed and validated using 103-bronchial Volumetric Modulated Arc Therapy (VMAT)-plans. The application of the framework was demonstrated using 25-VMAT-plans. To identify significant metrics for plan evaluation, 122-metrics were analysed and narrowed down using multivariate Spearman correlation. Metric limits were set with Statistical process control (SPC). Robustness metrics were predicted using multivariable or single linear regression models based on dose-and complexity-metrics., Results: Twenty-five-metrics were selected based on the amount and strength of correlations. R 95 (dose coverage) and HI 95/5 (homogeneity index) stood out among the dose-metrics, while the complexity-metrics showed similar correlations. Average scenarios dose at 95 % Clinical Target Volume D95 mean (CTV) and Errorbar-based Volume-Histograms (EVH) were notable for robustness metrics. Approximately 99 % of evaluated metrics fell within established SPC limits. The prediction model for D95 mean (CTV) showed good performance (adjusted R 2  = 0.88, mean squared error (MSE) = 3.84 × 10 -6 ), while the model for EVH demonstrated moderate reliability (adjusted R 2  = 0.52, MSE = 0.2). No statistically significant differences were found between the predicted (using dose-and complexity-metrics) and calculated robustness metrics (EVH ( p-value  = 0.9) and D95 mean (CTV) ( p-value  = 1))., Conclusions: The developed framework enables early detection of sub-optimal, complex and non-robust treatment plans. The predictive model can be used when robustness evaluations are impractical., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Author(s).)

Most trees form symbioses with ectomycorrhizal fungi (EMF) which influence access to growth-limiting soil resources. Mesocosm experiments repeatedly show that EMF species differentially affect plant development, yet whether these effects ripple up to influence the growth of entire forests remains unknown. Here we tested the effects of EMF composition and functional genes relative to variation in well-known drivers of tree growth by combining paired molecular EMF surveys with high-resolution forest inventory data across 15 European countries. We show that EMF composition was linked to a three-fold difference in tree growth rate even when controlling for the primary abiotic drivers of tree growth. Fast tree growth was associated with EMF communities harboring high inorganic but low organic nitrogen acquisition gene proportions and EMF which form contact versus medium-distance fringe exploration types. These findings suggest that EMF composition is a strong bio-indicator of underlying drivers of tree growth and/or that variation of forest EMF communities causes differences in tree growth. While it may be too early to assign causality or directionality, our study is one of the first to link fine-scale variation within a key component of the forest microbiome to ecosystem functioning at a continental scale., (© 2021. The Author(s).)

While cardiovascular disease has been associated with an increased risk of coronavirus disease 2019 (COVID-19), no studies have described its clinical course in patients with aortic stenosis who had undergone transcatheter aortic valve replacement (TAVR). Numerous observational studies have reported an association between the A blood group and an increased susceptibility to SARS-CoV-2 infection. Our objective was to investigate the frequency and clinical course of COVID-19 in a large sample of patients who had undergone TAVR and to determine the associations of the ABO blood group with disease occurrence and outcomes. Patients who had undergone TAVR between 2010 and 2019 were included in this study and followed-up through the recent COVID-19 outbreak. The occurrence and severity (hospitalization and/or death) of COVID-19 and their associations with the ABO blood group served as the main outcome measures. Of the 1125 patients who had undergone TAVR, 403 (36%) died before 1 January 2020, and 20 (1.8%) were lost to follow-up. The study sample therefore consisted of 702 patients. Of them, we identified 22 cases (3.1%) with COVID-19. Fourteen patients (63.6%) were hospitalized or died of disease. Multivariable analysis identified the A blood group (vs. others) as the only independent predictor of COVID-19 in patients who had undergone TAVR (odds ratio (OR) = 6.32; 95% confidence interval (CI) = 2.11-18.92; p = 0.001). The A blood group (vs. others; OR = 8.27; 95% CI = 1.83-37.43, p = 0.006) and a history of cancer (OR = 4.99; 95% CI = 1.64-15.27, p = 0.005) were significantly and independently associated with disease severity (hospitalization and/or death). We conclude that patients who have undergone TAVR frequently have a number of cardiovascular comorbidities that may work to increase the risk of COVID-19. The subgroup with the A blood group was especially prone to developing the disease and showed unfavorable outcomes.

Background: Radiosurgical treatment of brain metastases is well established in daily clinical routine. Utilization of flattening-filter-free beams (FFF) may allow for more rapid delivery of treatment doses and improve clinical comfort. Hence, we compared plan quality and efficiency of radiosurgery in FFF mode to FF techniques., Materials and Methods: Between November 2014 and June 2015, 21 consecutive patients with 25 brain metastases were treated with stereotactic radiosurgery (SRS) in FFF mode. Brain metastases received dose-fractionation schedules of 1 × 20 Gy or 1 × 18 Gy, delivered to the conformally enclosing 80 % isodose. Three patients with critically localized or large (>3 cm) brain metastases were treated with 6 × 5 Gy. Plan quality and efficiency were evaluated by analyzing conformity, dose gradients, dose to healthy brain tissue, treatment delivery time, and number of monitor units. FFF plans were compared to those using the FF method, and early clinical outcome and toxicity were assessed., Results: FFF mode resulted in significant reductions in beam-on time (p < 0.001) and mean brain dose (p = 0.001) relative to FF-mode comparison plans. Furthermore, significant improvements in dose gradients and sharper dose falloffs were found for SRS in FFF mode (-1.1 %, -29.6 %; p ≤ 0.003), but conformity was slightly superior in SRS in FF mode (-1.3 %; p = 0.001). With a median follow-up time of 5.1 months, 6‑month overall survival was 63.3 %. Local control was observed in 24 of 25 brain metastases (96 %)., Conclusion: SRS in FFF mode is time efficient and provides similar plan quality with the opportunity of slightly reduced dose exposure to healthy brain tissue when compared to SRS in FF mode. Clinical outcomes appear promising and show only modest treatment-related toxicity.

Background: Stereotactic body radiotherapy (SBRT) using flattening filter free (FFF)-techniques has been increasingly applied during the last years. However, clinical studies investigating this emerging technique are still rare. Hence, we analyzed toxicity and clinical outcome of pulmonary SBRT with FFF-techniques and performed dosimetric comparison to conventional techniques using flattening filters (FF)., Materials and Methods: Between 05/2014 and 06/2015, 56 consecutive patients with 61 pulmonary lesions were treated with SBRT in FFF-mode. Central lesions received 8 × 7.5 Gy delivered to the conformally enclosing 80 %-isodose, while peripheral lesions were treated with 3 × 15 Gy, prescribed to the 65 %-isodose. Early and late toxicity (after 6 months) as well as initial clinical outcomes were evaluated. Furthermore, [deleted] plan quality and efficiency were evaluated by analyzing conformity, beam- on and total treatment delivery times in comparison to plans with FF-dose application., Results: Median follow-up time was 9.3 months (range 1.5-18.0 months). Early toxicity was low with only 5 patients (8.9 %) reporting CTCAE 2° or higher side-effects. Only one patient (1.8 %) was diagnosed with radiation-induced pneumonitis CTCAE 3°, while 2 (3.6 %) patients suffered from pneumonitis CTCAE 2°. After 6 months, no toxicity greater than CTCAE 2° was reported. 1-year local progression-free survival, distant progression-free survival and overall survival were 92.8 %, 78.0 %, and 94.4 %, respectively. While plan quality was similar for FFF- and FF-plans in respect to conformity (p = 0.275), median beam-on time as well as total treatment time were significantly reduced for SBRT in FFF-mode compared to FF-mode (p ≤ 0.001, p ≤ 0.001)., Conclusions: Patient treatment with SBRT using FFF-techniques is safe and provides promising clinical results with only modest toxicity at significantly increased dose delivery speed.

Purpose: To evaluate long-term clinical outcome and determine prognostic factors for local-control, hearing preservation and cranial nerve toxicity in 449 patients treated for 451 vestibular schwannomas (VS) with radiosurgery (n=169; 38%) or fractionated stereotactic radiotherapy (FSRT; n=291; 62%)., Methods and Materials: 245 patients were male (55%), and 204 were female (45%). Median age was 60 years (range 17-88 years). Median tumor diameter was 15mm. For FSRT, a median dose of 57.6Gy in median single doses of 1.8Gy was applied. For SRS, median dose was 13Gy. The median follow-up time was 67 months., Results: Local control was 97% at 36 months, 95% at 60 months, and 94% at 120 months with no difference between FSRT and SRS (p=0.39). "Useful hearing" was present 46%. After RT, "useful hearing" was preserved in 85% of the patients. Loss of useful hearing was observed in the FSRT group in 14%, and in the SRS group in 16% of the patients. For patients treated with SRS ⩽13Gy, useful hearing deterioration was 13%. For trigeminal and facial nerve toxicity, there was no difference between FSRT and SRS., Conclusion: Supported by this large multicentric series, both SRS and FSRT can be recommended for the treatment of VS. SRS application is limited by tumor size, and is associated with a steep dose-response-curve. When chosen diligently based on tumor volume, pre-treatment characteristics and volume-dependent dose-prescription in SRS (⩽13Gy), both treatments may be considered equally effective., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

The purpose of this study was to test the accuracy of a commercially available deformable image registration tool in a clinical situation. In addition, to demonstrate a method to evaluate the resulting transformation of such a tool to a reference defined by multiple experts. For 16 patients (seven head and neck, four thoracic, five abdominal), 30-50 anatomical landmarks were defined on recognizable spots of a planning CT and a corresponding fraction CT. A commercially available deformable image registration tool, Velocity AI, was used to align all fraction CTs with the respective planning CTs. The registration accuracy was quantified by means of the target registration error in respect to expert-defined landmarks, considering the interobserver variation of five observers. The interobserver uncertainty of the landmark definition in our data sets is found to be 1.2 ± 1.1 mm. In general the deformable image registration tool decreases the extent of observable misalignments from 4-8 mm to 1-4 mm for nearly 50% of the landmarks (to 77% in sum). Only small differences are observed in the alignment quality of scans with different tumor location. Smallest residual deviations were achieved in scans of the head and neck region (79%, ≤ 4 mm) and the thoracic cases (79%, ≤ 4 mm), followed by the abdominal cases (59%, ≤ 4 mm). No difference is observed in the alignment quality of different tissue types (bony vs. soft tissue). The investigated commercially available deformable image registration tool is capable of reducing a mean target registration error to a level that is clinically acceptable for the evaluation of retreatment plans and replanning in case of gross tumor change during treatment. Yet, since the alignment quality needs to be improved further, the individual result of the deformable image registration tool has still to be judged by the physician prior to application.

This planning study was performed to compare stereotactic linac based radiosurgery of Arteriovenous Malformations (AVM) with current Helical Tomotherapy (HT) and future HT techniques. For 10 patients with AVM, dose distributions and treatment times of "regular" HT delivery (Reg 2.5/1/0.6 cm field width), Running-Start-Stop Treatment (RSS 5/2.5 cm), Axial Mode (Axial 5 cm) and Dynamic Jaw/Dynamic Couch delivery with a maximum field width of 5 cm (DJDC 5) were analysed and compared to linac-based stereotactic radiosurgery. Axial produced the fastest treatment (Axial 4:47 min vs. Linac 32:42 min) at the cost of large brain exposure (V10% 289 ml). Except for Reg 0.6, all other HT techniques achieved significantly shorter treatment times than linac-based treatment (e.g. Reg 1, 19:42 min, DJDC 6:30 min). However, high-dose brain exposure (V60%) was higher in all HT plans (e.g. Reg 0.6, 10 ml, Linac 9 ml), and only Reg 0.6 showed better low-dose exposure (V10% of 167 ml vs. 199 ml, not significant). Neither current nor future HT modes in their current version outperformed linac-based stereotactic radiosurgery. However, AVM with special geometry might still benefit from HT.

Purpose: To evaluate long-term results and patients' self-reported outcome of high-precision photon radiotherapy for the treatment of patients with vestibular schwannoma (VS)., Methods and Materials: We treated 246 patients with 248 VS with fractionated stereotactic radiotherapy (FSRT) or stereotactic radiosurgery (SRS). For FSRT, a median total dose of 57.6 Gy was prescribed in median single doses of 1.8 Gy, for SRS, a median dose of 13 Gy/80% isodose was applied. Of all patients, 51 patients died during follow-up. To evaluate long-term toxicity and QOL, we sent out a questionnaire to all living patients; of these, 81 patients (42%) sent back the questionnaire., Results: Median local control was 84 months, actuarial local control rates for both groups (SRS and FSRT) were 98% after 2, 95% after 5, and 93% after 10 years; there was no statistical difference between FSRT and SRS. Hearing deterioration was significantly higher in the SRS group than the FSRT group. However, when comparing FSRT to SRS with doses ≤ 13 Gy, hearing preservation is comparable. In patients with useful hearing, hearing preservation was 89.7% at 1 year, 84.7% at 3 years, 76.5% at 5 years, and 68.6% at 10 years. After 10 years of follow-up, hearing deterioration can be observed in both subgroups. In the FSRT group, facial nerve toxicity rate was 1.6%. Trigeminal nerve toxicity was observed in 2.1% after FSRT. Overall QOL was unchanged in 47% of the patients after RT, and 31% reported an improvement in QOL during follow-up., Conclusion: Patients' self-reported outcome confirms good results with respect to tumor control and QOL after FSRT or SRS in patients with VS. SRS can be associated with higher side effect following a dose-dependency. In long-term follow-up, hearing deterioration is most likely attributed to normal aging, but not treatment-related., (Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.)

Purpose. To compare the impact of prognostic factors of patients treated with definitive radio(chemo)therapy versus patients treated with surgery and postoperative radiotherapy for squamous cell carcinoma of the oro- and hypopharynx. Patients and Methods. 162 patients treated with definitive radiotherapy and 126 patients treated with postoperative radiotherapy were retrospectively analysed. The impact of the prognostic factors gender, age, total tumor volume (TTV), pre-radiotherapy hemoglobin level (Hb-level), tumor site, T- and N-classification, radiotherapy interruptions >5 days, radiotherapy versus simultaneous radiochemotherapy, R-status and time interval between surgery and radiotherapy were investigated. Results. The median follow-up time for the censored patients treated with definitive radio(chemo)therapy was 28.5 months and for postoperative radiotherapy 36.5 months. On univariate analysis, the TTV, Hb-level, and simultaneous radiochemotherapy had a significant impact on the survival of patients treated with definitive radio(chemo)therapy. For patients treated with postoperative radiotherapy, only the TTV showed a statistical trend for the survival (P = 0.13). On multivariate analysis, the TTV and simultaneous radiochemotherapy maintained their statistical significance for patients treated with definitive raditherapy, and the TTV, the statistical trend for patients treated with postoperative radiotherapy (P = 0.19). Conclusions. The TTV was the predominant prognostic factor for both, patients treated with definitive or postoperative radiotherapy.

Purpose: To investigate the influence of local density increase by i.v. contrast agent on dose calculation in linac-based radiosurgery (RS) of cerebral arteriovenous malformations (AVMs)., Material and Methods: RS was performed after three-dimensional (3-D) treatment planning using a total number of nine to 14 beams. Mean target volume was 5.3 cm(3) (range, 0.1-41.2 cm(3)). Mean maximum diameter was 23.2 mm (range, 8-51 mm). Dose deviation was estimated and calculated from the enhanced and unenhanced datasets of 30 patients. Dose calculation was performed using the same RS treatment plan on both datasets. Both plans were standardized to 1 Gy at isocenter with the same dose weight for all beams., Results: Mean difference of Hounsfield units (DeltaHU) between enhanced and unenhanced CT was 152 HU (range, 50-350 HU). The estimated dose deviation was

Purpose: To evaluate the predictive value of radiotherapeutically relevant tumor hypoxia by contrast-enhanced color duplex sonography (CDS). The objectification was based on pO(2) histography., Material and Methods: 25 patients with metastatic neck lymph node from a primary squamous carcinoma of the head and neck were examined. To visualize as many vessels as possible, a contrast enhancer (Levovist), Schering Corp., Germany) was administered. Horizontal and longitudinal sonographic scans with a thickness of 5 mm were performed on the metastatic neck lymph node. Color pixel density (CPD) was defined as the ratio of colored to gray pixels in a region of interest. It represents the extent of vascularization in the investigated slice. To assess the biological and clinical relevance of oxygenation measurement, the relative frequency of pO(2) readings < or = 2.5, 5.0, and 10.0 mmHg, as well as mean and median pO(2), were documented., Results: In order to investigate the degree of linear association, the Pearson correlation coefficient was calculated. Moderate (/r/ > 0.5) to high (/r/ > 0.7) correlation was found between the CPD and the parameters of hypoxic fraction (pO(2) readings with values < or = 5.0 and 10.0 mmHg, as well as mean and median). There was only a slight correlation between CPD and the fraction of pO(2) values < or = 2.5 mmHg (r = -0.479)., Conclusion: CPD represents the mean degree of vascularization. As a noninvasive measurement, this method seems feasible for evaluating the state of global oxygenation in superficial tumors. Nevertheless, this method is limited through its deficiency in describing the vascular heterogeneity of tumors.

Objective: Description of a new noninvasive method for the evaluation of tissue oxygenation in head and neck cancer., Study Design and Setting: Prospective nonrandomized controlled study in an academic medical center on 20 patients with neck metastases of head and neck cancer. Metastases were investigated using color duplex sonography and pO2 histography. The vascularization in sonography was quantitatively evaluated by color pixel density and compared to the pO2 values of the same nodes., Results: The correlation between vascularization and flow velocity was 0.71. For the mean/median pO2 -values and for the pO2 readings <10.0 mmHg correlations were r = 0.65 / 0.76 and 0.71., Conclusion: This sonographic method allows a safe and reliable evaluation of oxygenation in metastases of head and neck cancer., Significance: The new approach is an alternative to pO2 histography and may play a future role in the planning of radiotherapy in the neck.

Background: Tumor oxygenation is an important aspect of radiosensitivity. The authors describe a new method for a non-invasive assessment of tumor oxygenation in head and neck cancer., Patients and Methods: A group of 20 patients with neck metastases of squamous cell cancer of the head and neck region was surveyed. At first a pO (2)-polarography was performed in the metastatic cervical nodes to investigate the tissue oxygenation. In a second step, the vascularisation of these nodes was visualised by color duplex sonography. In order to evaluate the extent of vascularisation in these nodes, the density of color pixels was quantified by a custom-made software program. The color pixel density and the pO (2) values were correlated and the statistic significance was calculated by Pearson's test., Results: The mean vascularisation as evaluated by the means of color duplex sonography was 7.78 % [95 % CI 6.04 - 9.51]. The interindividual pO (2) values in the stroma of metastatic lymph nodes ranged between 9.0 and 27.4 mmHg (16.6 [95 % CI 14.06 - 19.13]). The mean values of pO (2)-fractions < 2.5/< 5.0/10 mm Hg were 32.25 %, 44.25 % and 53.29 % respectively. The median value of the pO (2)-fraction was 10.49 % [95 % CI 7.13 - 13.85]. The vascularisation as evaluated by color pixel density showed a statistically significant correlation with the pO (2)-fractions < 5.0 and < 10 mmHg (p < 0.045 and < 0.0001) and with the mean (p < 0.002) and median values of tissue pO (2) values (p < 0.0001) in polarography., Conclusion: The results in a limited number of patients suggest, that the proposed sonographic method allows a reliable non-invasive evaluation of tissue oxygenation in cervical metastases of squamous cell head and neck cancers.

Aim: The aim of this study was the validation of the visual image quality of electronic portal imaging devices (EPID) and conventional verification films from the point of view of the end-viewers of portal films, the radiotherapists., Material and Methods: The verification image was represented in two different forms, viz. an electronic portal image employing Siemens Beamview Plus (on a computer monitor) and two different portal films using the conventional verification films CEA-TVS and DuPont CQL-7 (on a negatoscope). A total of 270 image sets (simulation film and portal image) were evaluated by each radiotherapist, evaluation extending to 90 sets of each type of verification film. Each set was evaluated by three specialists in radiotherapy examining subjective visual image quality whereby the following aspects served as evaluation criteria: contrast, artifacts, determination of actual radiation field edge position, anatomical structures and main structural feature for the determination of treatment field position. In addition, the anatomical structures employed for visual feature correlation between reference and portal films were classified according to their importance., Results: In general the electronic portal image was rated significantly "visible" or better. Only the evaluation of artifacts showed an appreciable disadvantage for electronic portal imaging caused by physical artifacts due to radiographic technique and data processing aspects peculiar to the Siemens Beamview Plus 1.1. and also caused by different image processing tools reducing physical artifacts and enhancing the visibility of anatomical structures and likewise of anatomical artifacts (e.g. intestinal gas). By calculating the Spearman correlation coefficient to detect a possible relationship between the different criteria of subjective visual image quality, the research demonstrated that artifacts when limited to a tolerable proportion had no significant impact on the other criteria., Conclusions: As data of EPIDS are digital, images can be postprocessed and enhanced in a wide variety of ways. Using this tool the electronic portal imaging device provides images that, in terms of visual image quality, are at least comparable to the two evaluated types of radiographic films and also have the added advantage that such images are stored and can be transferred electronically being presupposition for digital patient documentation.

Purpose: To identify prognostic clinical and treatment related factors for local control, distant metastasis-free survival, and survival by means of a multivariate analysis in patients with advanced squamous cell carcinoma of the head and neck after concomitant boost radiochemotherapy., Patients and Methods: From 1992 to 1995, 68 patients with squamous cell cancer of the head and neck (93% stage IV disease) were treated with a simultaneous radiochemotherapy with Carboplatin using a concomitant boost technique. The total tumor volume (TTV) was quantitatively determined based on computed tomography scans in 56 patients. A Cox proportional hazards regression analysis was performed for each of the above endpoints and statistical significance of the Cox models was verified using the likelihood ratio test and Bonferroni correction for multiple testing., Results: The survival and locoregional control rates at three years were 35 and 32%. The multivariate analysis revealed a significant association between the TTV and survival (P = 0.0008) and between the pretreatment serum hemoglobin concentration and locoregional control (P = 0.01) and survival (P = 0.05). The locoregional control was significantly associated with the N-stage (P = 0.007) and there was a good correlation between the N-stage and TTV in this study population., Conclusion: Our data corroborate the prognostic relevance of the tumor volume and hemoglobin concentration. In studies comparing the survival of patients with advanced cancer of the head and neck, the use of the TTV as a covariable may improve the statistical power.

Purpose: A system for digital integration of an open MR scanner (0.23 T, Figure 1) in therapy simulation and 3D radiation treatment planning is described., Method: MR images were acquired using the body coil and various positioning and immobilization aids. A gradient echo sequence (TR/TE 320 ms/24 ms) was used to create axial and coronal data sets. Image distortions were measured and corrected using phantom measurements (Figure 2) and specially developed software., Results: Maximal and mean distortions of the MR images could be reduced from 19 mm to 8.2 mm and from 2.7 mm to 0.7 mm, respectively (Figure 3 to 5, Table 1). Coronal MR images were recalculated in fan beam projection for use at the therapy simulator. Tumor and organ contours were transferred from the MR image to the digitally acquired and corrected simulator image using a landmark matching algorithm (Figure 6 and 7). For 3D treatment planning, image fusion of axial MR images with standard CT planning images was performed using a landmark matching algorithm, as well (Figure 8). Representative cases are shown to demonstrate potential applications of the system., Conclusion: The described system enables the integration of the imaging information from an open MR system in therapy simulation and 3D treatment planning. The low-field MR scanner is an attractive adjunct for the radio-oncologist because of the open design and the low costs.

Background and Purpose: Simulation of 3D-treatment plans for head and neck malignancy is difficult due to complex anatomy. Therefore, CT-simulation and stereotactic techniques are becoming more common in the treatment preparation, overcoming the need for simulation. However, if simulation is still performed, it is an important step in the treatment preparation/execution chain, since simulation errors, if not detected immediately, can compromise the success of treatment. A recently developed PC-based system for on-line image matching and comparison of digitally reconstructed radiographs (DRR) and distortion corrected simulator monitor images that enables instant correction of field placement errors during the simulation process was evaluated. The range of field placement errors with non-computer aided simulation is reported., Materials and Methods: For 14 patients either a primary 3D-treatment plan or a 3D-boost plan after initial treatment with opposing laterals for head and neck malignancy with a coplanar or non-coplanar two- or three-field technique was simulated. After determining the robustness of the matching process and the accuracy of field placement error detection with phantom measurements, DRRs were generated from the treatment planning CT-dataset of each patient and were interactively matched with on-line simulator images that had undergone correction for geometrical distortion, using a landmark algorithm. Translational field placement errors in all three planes as well as in-plane rotational errors were studied and were corrected immediately., Results: The interactive matching process is very robust with a tolerance of <2 mm when suitable anatomical landmarks are chosen. The accuracy for detection of translational errors in phantom measurements was <1 mm and for in-plane rotational errors the accuracy had a maximum of only 1.5 degrees. For patient simulation, the mean absolute distance of the planned versus simulated isocenter was 6.4 +/- 3.9 mm. The in-plane rotational error in both planes was <3 degrees with one exception. Three large field placement errors (two patients with 11.5 and 16.0 mm distances of the planned versus simulated isocenter, respectively and one patient with a 7 degree rotational error) were detected and, as with the smaller errors, were immediately corrected., Conclusion: On-line image matching of treatment planning CT-derived DRRs and distortion corrected treatment simulator images is a precise and reliable method to reduce field placement errors in the simulation of complex 3D-treatment plans for head and neck malignancy and thus enhances accuracy in the first step of the treatment preparation/execution chain. However, out-of-plane rotational errors could not be assessed and assumedly they are comparatively small since due to rigid fixation, detected in-plane errors were small.