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Background: Hybrid devices of MR-scanners and linear accelerators (MR-Linacs) represent a new and promising extension of radiotherapeutic options for prostate cancer. The potential advantage of magnetic resonance imaging (MRI) over computed tomography (CT) for soft tissue contrast is well-known and leads to more consistent and smaller target volumes and improved normal tissue sparing., Objectives: This article presents an overview of clinical experience, indications, advantages and challenges of utilizing a 1.5 T MR-Linac in the setting of radiotherapy of prostate cancer., Results: All current indications for radiotherapy of prostate cancer can be treated with an MR-Linac. The advantages include daily MR-based imaging in treatment position and daily adaption of the treatment plan on current anatomy (adaptive radiotherapy). Additionally, functional MRI sequences might be exploited to enhance treatment individualization and response assessment. Ultimately treatment on an MR-Linac might further increase the therapeutic window. The limitations of using MR-Linac include treatment complexity and the duration of each session., Conclusions: MR-Linacs expand the spectrum of radiotherapeutic options for prostate cancer. Increased precision can be reached with daily MRI-based target volume definition and plan adaption. Clinical studies are necessary to identify patient groups who would benefit most from radiotherapy on a MR-Linac., (© 2021. The Author(s).)

Meningiomas are slow growing tumours, usually becoming symptomatic with visual loss or diplopia, or they are found incidentally. Not all meningiomas need to be treated. Treatment consists of neuro-surgical removal or radiotherapy if surgery is not possible. Whether a meningioma of the anterior visual pathways needs to be treated is mainly determined by the ophthalmological state. This must also include assessment of the prognosis by evaluation of the clinical findings and OCT scanning. This contribution is intended as an overview of all relevant factors with meningiomas of the anterior visual pathways. It is mainly based on the authors' own experiences., Competing Interests: Die Autoren geben an, dass kein Interessenkonflikt besteht., (Georg Thieme Verlag KG Stuttgart · New York.)

Purpose: Measurement of the radiation dose of different radiotherapy techniques with a phantom at the position of the uterus of a pregnant patient with and without a special radiation shielding., Material and Methods: A special radiation shielding for the radiation therapy of a pregnant patient was constructed in the shape of a tunnel over the abdomen from 1 cm thick lead to reduce scatter radiation to the uterus and the fetus therein. The reduction of the scatter radiation to the lower abdomen was measured for three typical cases (cerebrum with lateral opposed fields, 6-MV photons; tangential fields for mamma irradiation, 6 MV; and anteroposterior-posteroanterior [AP-PA] opposed fields of 15 MV for treatment of the mediastinum) at an anthropomorphic Alderson phantom with thermoluminescence dosimeters in different depths and with an ionization chamber positioned in an RW3 solid water phantom. In the case of lateral opposed fields, a movable lead wall was additionally positioned next to the accelerator's head to reduce the scatter radiation from this source., Results: Depending on the geometry of the radiation fields and on the photon energy, a reduction of the dose to the lower abdomen averaged over the depths of 6, 9, and 12 cm from 16% (15 MV, mediastinum case) to 51% (6 MV, cerebrum with additional lead wall) was achieved. The absolute scattered dose with shielding in place for a 2-Gy fraction dose results to 3.85 mGy and 0.27 mGy, respectively., Conclusion: National and international recommendations on the radiation dose to a fetus of a pregnant patient state limits of 200 mSv (DGMP report no. 7) and 100 mGy (ICRP 84), below which an abortion should not be considered and above which an indication for termination of the pregnancy could be given, respectively. The dose to the fetus can be kept below these limits with the shielding described in this work. Therefore, a radiation therapy of a pregnant patient is possible when these special precautions to reduce the scatter radiation to the fetus are met.

Clinical applications of high-energy electron beams, for example for the irradiation of internal mammary lymph nodes, can lead to oblique incidence of the beams. It is well known that oblique incidence of electron beams can alter the depth dose distribution as well as the specific dose per monitor unit. The dose per monitor unit is the absorbed dose in a point of interest of a beam, which is reached with a specific dose monitor value (DIN 6814-8). Dose distribution and dose per monitor unit at oblique incidence were measured with a small-volume thimble chamber in a water phantom, and compared to both normal incidence and calculations of the Helax TMS 6.1 treatment planning system. At 4 MeV and 60 degrees, the maximum measured dose per monitor unit at oblique incidence was decreased up to 11%, whereas at 18 MeV and 60 degrees this was increased up to 15% compared to normal incidence. Comparisons of measured and calculated dose distributions showed that the predicted dose at shallow depths is usually higher than the measured one, whereas it is smaller at depths beyond the depth of maximum dose. On the basis of the results of these comparisons, normalization depths and correction factors for the dose monitor value were suggested to correct the calculations of the dose per monitor unit.

Background: Conformal radiotherapy techniques as used in prostate treatment allow to spare normal tissue by conforming the radiation fields to the shape of the planning target volume (PTV). To be able to fully utilize the advantages of these techniques correct patient positioning is an important prerequisite. This study employing an electronic portal imaging device (EPID) investigated the positioning uncertainties that occur in the pelvic region for different patient positioning devices., Patients and Methods: 15 patients with prostate cancer were irradiated with or without rectal balloon/pelvic mask at a linear accelerator with multileaf collimator (MLC). For each patient multiple portal images were taken from different directions and compared to the digitally reconstructed radiographs (DRRs) of the treatment planning system and to simulation films (Table 1, Figure 1)., Results: In spite of different positioning devices, all patients showed comparable total positioning uncertainties of 4.0 mm (lateral), 4.5 mm (cranio-caudal) and 1.7 mm (dorso-ventral). The lateral positioning error was reduced for the pelvic mask patients while the cranio-caudal error increased (Table 2, Figure 2). A systematic and a random component sum up to the total positioning error, and a good estimate of the magnitudes of the two is possible from six to eight portal images (Figure 3)., Conclusions: With a small number of portal images it is possible to find out the systematic and random positioning error of a patient. Knowledge of the random error can be used to resize the treatment margin which is clinically relevant since this error differs greatly for different patients (Figure 4). Image analysis with EPID is convenient, yet has some problems. For example, one only gets indirect information on the movement of the ventral rectum wall (Figure 5). The successful operation of positioning devices, although, needs further improvement--especially if one focuses on IMRT.