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Purpose: We investigated the impact on computed tomography (CT) image quality and photon, electron, and proton head-and-neck (H&N) radiotherapy (RT) dose calculations of three CT metal artifact reduction (MAR) approaches: A CT-based algorithm (oMAR Philips Healthcare), manual water override, and our recently presented, Magnetic Resonance (MR)-based kerMAR algorithm. We considered the following three hypotheses: I: Manual water override improves MAR over the CT- and MR-based alternatives; II: The automatic algorithms (oMAR and kerMAR) improve MAR over the uncorrected CT; III: kerMAR improves MAR over oMAR. Methods: We included a veal shank phantom with/without six metal inserts and nine H&N RT patients with dental implants. We quantified the MAR capabilities by the reduction of outliers in the CT value distribution in regions of interest, and the change in particle range and photon depth at maximum dose. Results: Water override provided apparent image improvements in the soft tissue region but insignificantly or negatively influenced the dose calculations. We however found significant improvements in image quality and particle range impact, compared to the uncorrected CT, when using oMAR and kerMAR. kerMAR in turn provided superior improvements in terms of high intensity streak suppression compared to oMAR, again with associated impacts on the particle range estimates. Conclusion: We found no benefits of the water override compared to the rest, and tentatively reject hypothesis I. We however found improvements in the automatic algorithms, and thus support for hypothesis II, and found the MR-based kerMAR to improve upon oMAR, supporting hypothesis III.

Purpose: In radiotherapy (RT) based on magnetic resonance imaging (MRI) as the only modality, the information on electron density must be derived from the MRI scan by creating a so-called pseudo computed tomography (pCT). This is a nontrivial task, since the voxel-intensities in an MRI scan are not uniquely related to electron density. To solve the task, voxel-based or atlas-based models have typically been used. The voxel-based models require a specialized dual ultrashort echo time MRI sequence for bone visualization and the atlas-based models require deformable registrations of conventional MRI scans. In this study, we investigate the potential of a patch-based method for creating a pCT based on conventional T 1-weighted MRI scans without using deformable registrations. We compare this method against two state-of-the-art methods within the voxel-based and atlas-based categories. Methods: The data consisted of CT and MRI scans of five cranial RT patients. To compare the performance of the different methods, a nested cross validation was done to find optimal model parameters for all the methods. Voxel-wise and geometric evaluations of the pCTs were done. Furthermore, a radiologic evaluation based on water equivalent path lengths was carried out, comparing the upper hemisphere of the head in the pCT and the real CT. Finally, the dosimetric accuracy was tested and compared for a photon treatment plan. Results: The pCTs produced with the patch-based method had the best voxel-wise, geometric, and radiologic agreement with the real CT, closely followed by the atlas-based method. In terms of the dosimetric accuracy, the patch-based method had average deviations of less than 0.5% in measures related to target coverage. Conclusions: We showed that a patch-based method could generate an accurate pCT based on conventional T 1-weighted MRI sequences and without deformable registrations. In our evaluations, the method performed better than existing voxel-based and atlas-based methods and showed a promising potential for RT of the brain based only on MRI.

Purpose Dynamic treatment planning algorithms use a dosimetric leaf separation (DLS) parameter to model the multi-leaf collimator (MLC) characteristics. Here, we quantify the dosimetric impact of an incorrect DLS parameter and investigate whether common pretreatment quality assurance (QA) methods can detect this effect. Methods 16 treatment plans with intensity modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT) technique for multiple treatment sites were calculated with a correct and incorrect setting of the DLS, corresponding to a MLC gap difference of 0.5 mm. Pretreatment verification QA was performed with a bi-planar diode array phantom and the electronic portal imaging device (EPID). Measurements were compared to the correct and incorrect planned doses using gamma evaluation with both global (G) and local (L) normalization. Correlation, specificity and sensitivity between the dose volume histogram (DVH) points for the planning target volume (PTV) and the gamma passing rates were calculated. Results The change in PTV and organs at risk DVH parameters were 0.4–4.1%. Good correlation (>0.83) between the PTV mean dose deviation and measured gamma passing rates was observed. Optimal gamma settings with 3%L/3 mm (per beam and composite plan) and 3%G/2 mm (composite plan) for the diode array phantom and 2%G/2 mm (composite plan) for the EPID system were found. Global normalization and per beam ROC analysis of the diode array phantom showed an area under the curve Conclusions A DLS error can worsen pretreatment QA using gamma analysis with reasonable credibility for the composite plan. A low detectability was demonstrated for a 3%G/3 mm per beam gamma setting.

Background. Radiotherapy based on MRI only (MRI-only RT) shows a promising potential for the brain. Much research focuses on creating a pseudo computed tomography (pCT) from MRI for treatment planning while little attention is often paid to the treatment delivery. Here, we investigate if cone beam CT (CBCT) can be used for MRI-only image-guided radiotherapy (IGRT) and for verifying the correctness of the corresponding pCT.Material and methods. Six patients receiving palliative cranial RT were included in the study. Each patient had three-dimensional (3D) T1W MRI, a CBCT and a CT for reference. Further, a pCT was generated using a patch-based approach. MRI, pCT and CT were placed in the same frame of reference, matched to CBCT and the differences noted. Paired pCT-CT and pCT-CBCT data were created in bins of 10 HU and the absolute difference calculated. The data were converted to relative electron densities (RED) using the CT or a CBCT calibration curve. The latter was either based on a CBCT phantom (phan) or a paired CT-CBCT population (pop) of the five other patients.Results. Non-significant (NS) differences in the pooled CT-CBCT, MRI-CBCT and pCT-CBCT transformations were noted. The largest deviations from the CT-CBCT reference were < 1 mm and 1°. The average median absolute error (MeAE) in HU was 184 ± 34 and 299 ± 34 on average for pCT-CT and pCT-CBCT, respectively, and was significantly different (p < 0.01) in each patient. The average MeAE in RED was 0.108 ± 0.025, 0.104 ± 0.011 and 0.099 ± 0.017 for pCT-CT, pCT-CBCT phan (p < 0.01 on 2 patients) and pCT-CBCT pop (NS), respectively.Conclusions. CBCT can be used for patient setup with either MRI or pCT as reference. The correctness of pCT can be verified from CBCT using a population-based calibration curve in the treatment geometry.

A new system for in vivo dosimetry during radiotherapy has been introduced. Luminescence signals from a small crystal of carbon-doped aluminium oxide (Al 2 O 3 :C) are transmitted through an optical fibre cable to an instrument that contains optical filters, a photomultiplier tube and a green (532 nm) laser. The prime output is continuous wave optically stimulated luminescence (CW-OSL) used for the measurement of the integrated dose. We demonstrate a measurement protocol with high reproducibility and improved linearity, which is suitable for clinical dosimetry. A crystal-specific minimum pre-dose is necessary for signal stabilisation. Simple background subtraction only partially removes the residual signal present at long integration times. Instead, the measurement protocol separates the decay curve into three individual components and only the fast and medium components were used.

In this investigation of 2,091 eyes the occurrence of retinal detachment in the aphakic eye has been studied. Two groups are compared as to the incidence and type of cataract. Among 187 cases of aphakic retinal detachment in the second group, the relation between type of cataract, type of tear, cataract surgery and reattachment is recorded and the surgical procedure of the detachment discussed. The significant features and the course of the aphakic detachment are outlined and the predisposition to cataractous eye is emphasized.

To determine whether or not the electrophysiological status of the eye can give information as to the result of vitreous surgery, the visual evoked potential to flash stimulation was measured prior to vitreous surgery. Seventy-four eyes were submitted to surgery. Latencies of flash evoked potentials showed a distribution suggestive of a Gaussian curve with an abnormal extension. Dividing the material into 2 groups based on a latency longer or shorter than 100 millisec revealed a highly significant difference in visual improvement after surgery between patients with long latency and patients with short latency (P less than 0.001). With a latency longer than 100 millisec the patient has an almost equal chance of visual improvement or visual reduction by surgery. The frequency of operative complications was twice as high in patients with latency longer than 100 millisec compared to patients with a latency shorter than 100 millisec.

A method for dynamic angiography and quantitative measurement of fluorescence in ocular vessels in an in vitro experiment and in corneo-conjunctival angiography is described.

Based on a period of introduction with the vitrectomy technic the visual acuity results in 143 consecutive cases performed between 1976 and 1980 are related to the anamnestic information, the pre-, per- and post-operative findings. In this introductional period the patients referred had longstanding retinovitreal changes, and, because of lack of prognostic parameters, all patients were offered surgery regardless of the observed pathology. All vitrectomies were carried out with the Kloti macrostripper and diathermy unit, without any additional instrumentation. From the results of these early cases, we have changed our surgical method to a three-port entrance with a separate infusion canula, a separate fiberoptic illumination and an interchange between vitrector, automatic scissors, hook, stilleto, vacuo needle, forceps and intravitreous photocoagulation through a third port. Diabetics should be offered vitrectomy if vitreous haemorrhages last for more than 3 months. Vitrectomy is considered useless or contraindicated in diabetics with lack of light perception or light projection, neovascular glaucoma, extinguished visual evoked potential. Only an improvement in the peripheral vision can be expected in diabetics with macular detachment. In rhegmatogenous detachment cases with intravitreal traction, vitreous operations should be performed only where intraretinal or retroretinal changes do not prevent mobilization or unfolding of the retina. Traumatic vitreoretinal disorders should be operated upon early.