Lorentz angle calibration for the barrel pixel detector

A method to measure the Lorentz angle in the barrel pixel detector of CMS is presented. This measurement from CMS data will be necessary during operation since the electric field in the sensors will change with increasing irradiation. The approach described in this note uses well measured muon tracks to determine the drift of the electrons in the pixel sensors. From an analysis of simulated data an accuracy of 2% on tau_L can be achieved from just 1000 muon tracks. This corresponds to a systematic shift in the hit reconstruction of less than 1.5 \mu m which will decrease with increasing integrated luminosity

Prospective assessment of stress and health concerns of radiation oncology staff during the COVID-19 pandemic

Introduction and background The COVID-19 pandemic has required rapid and repetitive adjustment of radiotherapy practice, hospital-level and department-level organization and hygiene measures. To prospectively monitor and manage stress levels and health concerns, employees of a radiation oncology department were invited to participate in weekly online surveys during the first year of the pandemic. Materials and methods Starting March 31st, 2020, cross-sectional online surveys were distributed to all employees of the Department of Radiation Oncology, University Hospital Zurich. The survey included questions about the profession, the work setting, the global stress level as well as the health concerns during the past work week. Stress levels and health concerns were assessed on a 10-point scale. SurveyMonkey® was used to conduct the survey. Distribution was performed via email. Participation was anonymous and voluntary. Results Between March 2020 and February 2021, 50 weekly surveys were distributed to 127 employees on average and resulted in 1,877 individual responses. The average response rate was 30%. The mean global stress level varied significantly by profession, ranging from 2.7 (±2.5) points for administrative staff to 6.9 (±2.3) points for radiation therapy technicians (p < 0.001). The mean global stress level was highest with 4.8 (±2.9) points for in-hospital work with direct patient contact. Health concerns were highest regarding family and friends with 4.0 (±3.1) points on average. Changes of the stress level varied in correlation with infection waves. Conclusion Weekly online surveys for prospective assessment of stress levels and health concerns were successfully conducted during the first year of the COVID-19 pandemic, indicating their feasibility and value to monitor profession and workplace specific stress patterns and to allowed for tailored interventions. The physical and mental health of frontline healthcare workers in radiation oncology should remain a top priority for departmental leadership beyond the COVID-19 pandemic

MR-guided beam gating: Residual motion, gating efficiency and dose reconstruction for stereotactic treatments of the liver and lung

PURPOSE This study aims to investigate the efficiency and the geometric as well as the dosimetric benefit of magnetic-resonance guided beam gating for stereotactic treatments in moving organs. METHOD Patients treated with MR-guided (MRIdian system) SBRT for lung (n = 10) and liver (n = 10) targets were analyzed. Breath-hold gating was performed based on lesion tracking in sagittal cine MRI images. The target offset from the geometric center of the gating window with and without gating was evaluated. A dose reconstruction workflow based on convolution of these 2D position-probability maps and the daily 3D dose distribution was used to estimate the daily delivered dose including motion. The dose to the clinical target volume (CTV) and to a 2-cm ring structure around the planning target volume were evaluated. RESULTS The applied gating protocol resulted in a mean (±standard deviation) gating efficiency of 55%±16%. Over all patients, the mean target offset (2D-root-mean-square error) was 8.3 ± 4.3 mm, which reduced to 2.4 ± 0.6 mm during gating. The dose reconstruction showed a mean deviation in CTV coverage (D95) from the static plans of -1.7%±1.8% with gating and -12.0%±8.4% if no gating would have been used. The mean dose (Dmean) in the ring structure, with respect to the static plans, showed mean deviations of -0.1%±0.3% with gating and -1.6%±1.8% without gating. CONCLUSION The MRIdian system enables gating based on the inner anatomy and the implemented dose reconstruction workflow demonstrated geometric robust delivery of the planned radiation doses

Leukoencephalopathy after prophylactic whole-brain irradiation with or without hippocampal sparing: a longitudinal magnetic resonance imaging analysis

PURPOSE Neurocognitive changes are well described after prophylactic or therapeutic whole-brain radiotherapy (WBRT) and have been reported as early as 3 months after radiotherapy (RT). Therefore, WBRT with protection of the hippocampal region (hippocampal avoidance, HA) has been proposed to preserve neurocognition. Our aim was to compare the risk of leukoencephalopathy after prophylactic cranial irradiation (PCI) with or without HA. METHODS Patients with small-cell lung cancer who received either lateral-opposed field PCI (non-HA-PCI; n = 9) or hippocampus avoidance PCI (HA-PCI; n = 9) with available magnetic resonance imaging (MRI) follow-up were identified and age matched. Pre-therapeutic and follow-up MRI after RT was analysed for leukoencephalopathy based on the Fazekas score. Bilateral cortical and subcortical brain structures were segmented and analysed for alterations in dosimetric parameters and volumes. RESULTS There was no significant difference of Fazekas scores between groups at baseline. Fazekas score differed in post-treatment with a median of 1 in the HA-PCI group and 2 in the non-HA-PCI group (p = 0.007). Significant increase of Fazekas score over time after RT was observed for HA-PCI patients (p = 0.001) but not for non-HA-PCI patients. Dmax (highest radiation dose) and brain volume receiving doses >25Gy were higher in HA-PCI patients. There were no significant volumetric differences for segmented brain structures between groups. CONCLUSION Radiological changes are more prominent after HA-PCI than after non-HA-PCI. Although no standardised neurocognitive testing was performed, the significantly increased Fazekas scores after HA-PCI are expected to interfere with neurocognitive function. Prospective long-term neurocognitive studies are warranted before HA-PCI is implemented in routine clinical practice

MR-guided adaptive stereotactic body radiotherapy (SBRT) of primary tumor for pain control in metastatic pancreatic ductal adenocarcinoma (mPDAC): an open randomized, multicentric, parallel group clinical trial (MASPAC)

BACKGROUND Pain symptoms in the upper abdomen and back are prevalent in 80% of patients with metastatic pancreatic ductal adenocarcinoma (mPDAC), where the current standard treatment is a systemic therapy consisting of at least doublet-chemotherapy for fit patients. Palliative low-dose radiotherapy is a well-established local treatment option but there is some evidence for a better and longer pain response after a dose-intensified radiotherapy of the primary pancreatic cancer (pPCa). Stereotactic body radiation therapy (SBRT) can deliver high radiation doses in few fractions, therefore reducing chemotherapy-free intervals. However, prospective data on pain control after SBRT of pPCa is very limited. Therefore, we aim to investigate the impact of SBRT on pain control in patients with mPDAC in a prospective trial. METHODS This is a prospective, double-arm, randomized controlled, international multicenter study testing the added benefit of MR-guided adaptive SBRT of the pPca embedded between standard of care-chemotherapy (SoC-CT) cycles for pain control and prevention of pain in patients with mPDAC. 92 patients with histologically proven mPDAC and at least stable disease after initial 8 weeks of SoC-CT will be eligible for the trial and 1:1 randomized in 3 centers in Germany and Switzerland to either experimental arm A, receiving MR-guided SBRT of the pPCa with 5 × 6.6 Gy at 80% isodose with continuation of SoC-CT thereafter, or control arm B, continuing SoC-CT without SBRT. Daily MR-guided plan adaptation intents to achieve good target coverage, while simultaneously minimizing dose to organs at risk. Patients will be followed up for minimum 6 and maximum of 18 months. The primary endpoint of the study is the "mean cumulative pain index" rated every 4 weeks until death or end of study using numeric rating scale. DISCUSSION An adequate long-term control of pain symptoms in patients with mPDAC is an unmet clinical need. Despite improvements in systemic treatment, local complications due to pPCa remain a clinical challenge. We hypothesize that patients with mPDAC will benefit from a local treatment of the pPCa by MR-guided SBRT in terms of a durable pain control with a simultaneously favorable safe toxicity profile translating into an improvement of quality-of-life. TRIAL REGISTRATION German Registry for Clinical Trials (DRKS): DRKS00025801. Meanwhile the study is also registered at ClinicalTrials.gov with the Identifier: NCT05114213

Study of the B-S-meson with the first LHC data

After more than twenty years of development, collisions at the Large Hadron Collider at CERN are expected to take place at the end of 2009. The aim of the CMS detector is to measure the particles emerging from these interactions. The innermost detector of this high energy experiment is a silicon pixel detector starting only 4 cm apart from the interaction point. Its main goal is to measure tracks and vertices with high precision. Charged particles passing the silicon pixel detector produce charge carriers that drift in a high electric field (Vbias ≈ 100 − 600 V). Due to the magnetic field of 3.8 T present in the inner part of the CMS detector, charge carriers experience an angular deflection due to the Lorentz force. This leads to a shift in the measured hit coordinate (Lorentz drift). The first part of this thesis presents a measurement of the Lorentz drift based on cosmic data taken in autumn 2008. The drift is approximately 66 µm for the barrel detector and 20 µm for the forward detectors. Furthermore, a method to measure the Lorentz drift from collision data is developed. This is necessary because tracks from collision data cover a different range of incident angles on the detector surface than cosmic rays: In general, in the plane transverse to the beam axis cosmic rays traverse the silicon sensors at larger angles than particles originating from the collision point. This method will allow to monitor the Lorentz drift as the bias voltage is increased to compensate for irradiation damages. In the second part of this thesis, a physics analysis to measure various properties of the Bs-meson system is developed. The pixel detector allows a precise measurement of the Bs decay vertices which are displaced from the proton-proton interaction point. Thus it is the key detector component for this analysis. A decay time-dependent angular analysis is performed on selected Bs → J/ψ(→ µ+ µ− )φ(→ K + K −) events. With an integrated luminosity of 1.3 fb−1, the width difference ∆Γs between the CP eigenstates BsL and BsH could be extracted with an uncertainty of 0.028 ps−1, yielding a better measurement than the one currently available from Tevatron (CDF measures ∆Γs = 0.02 ± 0.05(stat.) ± 0.01(sys.) ps−1 [1] and D0 ∆Γs = 0.085+0.072 (stat.) ± −0.078 0.06(sys.) ps−1 [2]). On the other hand, the CP-violating phase in this decay is expected to be very small in the Standard Model (φs ≈ −0.03). However, the angular analysis proposed here would be sensitive to non-Standard Model contributions, which are expected to be rather large. Nach über 20 Jahren Entwicklungsarbeit werden Ende 2009 die ersten Proton-ProtonKollisionen am LHC in Genf erwartet. Der CMS Detektor wird die bei diesen Kollisionen erzeugten Elementarteilchen registrieren. Die innerste Komponente dieses Grossexperimentes wird von einem Silizium-Pixeldetektor gebildet, dessen Messbereich nur 4 cm vom Wechselwirkungspunkt entfernt beginnt. Hauptaufgabe dieses Pixeldetektors ist die präzise Vermessung von Teilchenspuren und deren Zerfallsvertices. Beim Durchgang geladener Teilchen durch den Silizium-Pixeldetektor werden freie Ladungsträger erzeugt, welche sich in einem starken äusseren elektrischen Feld bewegen (Vbias ≈ 100 − 600 V). Da im zentrum des CMS-Detektors ein magnetisches Feld von 3.8 T herrscht, unterliegen die Ladungsträger einer zusätzlichen Ablenkung infolge der Lorentzkraft. Dies führt zu einer Verschiebung in der gemessenen Hit-koodinate (Lorentz-Verschiebung). Im ersten Teil dieser Arbeit wird eine Messung der Lorentz-Verschiebung vorgestellt, die auf einer Messung kosmischer Teilchen im Herbst 2008 beruht. Die Verschiebung beträgt durchschnittlich 66 µm für den Barrel-Pixeldetektor und 20 µm für den Vorwärts-Pixeldetektor. Weiterhin wird eine Methode entwickelt, die die Bestimmung der Lorentz-Verschiebung aus Kollisionsdaten gestattet. Die Entwicklung einer solchen Methode war notwendig, da Spuren, welche von Wechselwirkungspunkt kommen einen anderen Bereich im Einfallswinkel abdecken als kosmische Spuren. In der Ebene senkrecht zur Strahlröhre passieren kosmische Teilchen den Pixeldetektor im allgemeinen mit einem grösseren Winkel als Teilchen, welche vom Wechselwirkungspunkt kommen. Mit Hilfe der vorgestellten Methode lässt sich die Änderung der Lorentz-Verschiebung messen, die über die Laufzeit des Experiments infolge zunehmender Strahlenschäden und einer dadurch notwendingen Erhöhung der Bias-Spannung im Pixeldetektor erwartet wird. Im zweiten Teil dieser Arbeit wird eine Methode zur Messung verschiedener Eigenschaften des Bs-Meson-Systems entwickelt. Der Pixeldetektor ist die für diese Analyse wichtigste Detektorkomponente, da er die präzise Messung der Entfernung der Bs Zerfallsvertices vom Proton-Proton-Wechselwirkungspunkt erlaubt. Eine Zerfallszeitabhängige Winkelanalyse wird auf Bs → J/ψ(→ µ+ µ− )φ(→ K + K − ) Ereignisse angewendet, die geeignete Selektionskriterien erfüllen. Die Analyse einer integrierten Luminosität von 1.3 fb−1 gestattet die Bestimmung der Zerfallsbreiten-Differenz ∆Γs zwischen den CP-Eigenzuständen BsL und BsH mit einer Unsicherheit von 0.028 ps−1 , was eine Verbesserung der bisher verfügbaren Messungen vom Tevatron darstellt (Messungen bei CDF ergaben ∆Γs = 0.02 ± 0.05(stat.) ± 0.01(sys.) ps−1 [1] und bei D0 ∆Γs = 0.085+0.072 (stat.) ± 0.06(sys.) ps−1 [2]). Das Standardmodel sagt für die −0.078 CP-verletzende Phase bei diesem Zerfall einen sehr kleinen Wert voraus (φs ≈ −0.03). Die hier vorgeschlagene Winkelanalyse ist sensitiv gegenüber Beiträgen von Prozessen jenseits des Standardmodells, welche einen vergleichsweise grossen Wert ergeben

Carbon Fiber/Polyether Ether Ketone (CF/PEEK) Implants Allow for More Effective Radiation in Long Bones

Background: Metallic implants show dose-modulating effects in radiotherapy and complicate its computed tomography (CT)-based planning. Dose deviations might not only affect the surrounding tissues due to backscattering and inadvertent dose increase but might also compromise the therapeutic effect to the target lesion due to beam attenuation. Later on, follow-up imaging is often obscured by metallic artefacts. Purposes: This study investigates the dosimetric impact of titanium and radiolucent carbon fiber/polyether ether ketone (CF/PEEK) implants during adjuvant radiation therapy in long bones. (1) Does the use of CF/PEEK implants allow for a more homogenous application of radiation? (2) Is the dose delivery to the target volume more efficient when using CF/PEEK implants? (3) Do CF/PEEK implants facilitate CT-based radiation therapy planning? Materials and methods: After CT-based planning, bone models of six ovine femora were irradiated within a water phantom in two immersion depths to simulate different soft-tissue envelopes. Plates and intramedullary nails of both titanium and CF/PEEK were investigated. Radiation dosage and distribution patterns were mapped using dosimetry films. Results: First, the planned implant-related beam attenuation was lower for the CF/PEEK plate (1% vs. 5%) and the CF/PEEK nail (2% vs. 9%) than for corresponding titanium implants. Secondly, the effective decrease of radiation dosage behind the implants was noticeably smaller when using CF/PEEK implants. The radiation dose was not significantly affected by the amount of surrounding soft tissues. A significant imaging artefact reduction was seen in all CF/PEEK models. Conclusion: CF/PEEK implants lead to a more reliable and more effective delivery of radiation dose to an osseous target volume. With regard to radiation therapy, the use of CF/PEEK implants appears to be particularly beneficial for intramedullary nails

Long-term cancer survivors treated with multiple courses of repeat radiation therapy

INTRODUCTION AND BACKGROUND Through recent advances in cancer care, the number of long-term survivors has continuously increased. As a result, repetitive use of local radiotherapy for curative or palliative indications might have increased as well. This analysis aims to describe patterns of care and outcome of patients treated with multiple courses of repeat radiotherapy. MATERIALS AND METHODS All patients treated with radiotherapy between 2011 and 2019 at our department of Radiation Oncology were included into this analysis. A course of radiotherapy was defined as all treatment sessions to one anatomical site under one medical indication. Demographics, cancer and treatment characteristics and overall survival of patients having undergone multiple radiotherapy courses (minimum n = 5) were evaluated. RESULTS The proportion of cancer patients treated with a minimum five courses of radiotherapy increased continuously from 0.9% in 2011 to 6.5% in 2019. In the 112 patients treated with a minimum of five radiotherapy courses, the primary tumor was lung in 41.9% (n = 47), malignant melanoma in 8.9% (n = 10) and breast in 8.0% (n = 9) of cases. A median interval of 3 years (maximum 8 years) elapsed between the first and the last radiotherapy course. The maximum number of courses in a single patient were n = 10. Treatment intent was curative or palliative in 46.4% and 53.6% for the first radiotherapy, respectively. The proportion of curative intent decreased to 11.6% at the 5th, and the last radiotherapy course was following a palliative intent in all patients. Five-year overall survival measured from the 1st radiotherapy course was 32.7%. Median overall survival was 3.3, 2.4, 1.3, and 0.6 years when measured from the 1st, the 1st palliative, the 5th and last course of radiotherapy, respectively. DISCUSSION AND CONCLUSION A continuously increasing number of patients is treated with multiple courses of radiotherapy throughout their long-term cancer survivorship

Management of multiple brain metastases: a patterns of care survey within the German Society for Radiation Oncology

PURPOSE The treatment of brain metastases (BM) has changed considerably in recent years and in particular, the management of multiple BM is currently undergoing a paradigm shift and treatment may differ from current guidelines. This survey was designed to analyze the patterns of care in the management of multiple BM. METHODS An online survey consisting of 36 questions was distributed to the members of the German Society for Radiation Oncology (DEGRO). RESULTS In total, 193 physicians out of 111 institutions within the German Society for Radiation oncology responded to the survey. Prognostic scores for decision making were not used regularly. Whole brain radiotherapy approaches (WBRT) are the preferred treatment option for patients with multiple BM, although stereotactic radiotherapy treatments are chosen by one third depending on prognostic scores and overall number of BM. Routine hippocampal avoidance (HA) in WBRT is only used by a minority. In multiple BM of driver-mutated non-small cell lung cancer origin up to 30% favor sole TKI therapy as upfront treatment and would defer upfront radiotherapy. CONCLUSION In multiple BM WBRT without hippocampal avoidance is still the preferred treatment modality of choice regardless of GPA and mutational status, while SRT is only used in patients with good prognosis. Evidence for both, SRS and hippocampal avoidance radiotherapy, is growing albeit the debate over the appropriate treatment in multiple BM is yet not fully clarified. Further prospective assessment of BM management-ideally as randomized trials-is required to align evolving concepts with the proper evidence and to update current guidelines

Characterization of spatial integrity with active and passive implants in a low-field magnetic resonance linear accelerator scanner

BACKGROUND AND PURPOSE Standard imaging protocols can guarantee the spatial integrity of magnetic resonance (MR) images utilized in radiotherapy. However, the presence of metallic implants can significantly compromise this integrity. Our proposed method aims at characterizing the geometric distortions induced by both passive and active implants commonly encountered in planning images obtained from a low-field 0.35 T MR-linear accelerator (LINAC). MATERIALS AND METHODS We designed a spatial integrity phantom defining 1276 control points and covering a field of view of 20x20x20 cm3. This phantom was scanned in a water tank with and without different implants used in hip and shoulder arthroplasty procedures as well as with active cardiac stimulators. The images were acquired with the clinical planning sequence (balanced steady-state free-precession, resolution 1.5x1.5x1.5 mm3). Spatial integrity was assessed by the Euclidian distance between the control point detected on the image and their theoretical locations. A first plane free of artefact (FPFA) was defined to evaluate the spatial integrity beyond the larger banding artefact. RESULTS In the region extending up to 20 mm from the largest banding artefacts, the tested passive and active implants could cause distortions up to 2 mm and 3 mm, respectively. Beyond this region the spatial integrity was recovered and the image could be considered as unaffected by the implants. CONCLUSIONS We characterized the impact of common implants on a low field MR-LINAC planning sequence. These measurements could support the creation of extra margin while contouring organs at risk and target volumes in the vicinity of implants