Impact of different leaf velocities and dose rates on the number of monitor units and the dose-volume-histograms using intensity modulated radiotherapy with sliding-window technique

<p>Abstract</p> <p>Background</p> <p>Intensity modulated radiotherapy (IMRT) using sliding window technique utilises a leaf sequencing algorithm, which takes some control system limitations like dose rates (DR) and velocity of the leafs (LV) into account. The effect of altering these limitations on the number of monitor units and radiation dose to the organs at risk (OAR) were analysed.</p> <p>Methods</p> <p>IMRT plans for different LVs from 1.0 cm/sec to 10.0 cm/sec and different DRs from 100 MU/min to 600 MU/min for two patients with prostate cancer and two patients with squamous cell cancer of the scalp (SCCscalp) were calculated using the same "optimal fluence map". For each field the number of monitor units, the dose volume histograms and the differences in the "actual fluence maps" of the fields were analysed.</p> <p>Results</p> <p>With increase of the DR and decrease of the LV the number of monitor units increased and consequentially the radiation dose given to the OAR. In particular the serial OARs of patients with SCCscalp, which are located outside the end position of the leafs and inside the open field, received an additional dose of a higher DR and lower LV is used.</p> <p>Conclusion</p> <p>For best protection of organs at risk, a low DR and high LV should be applied. But the consequence of a low DR is both a long treatment time and also that a LV of higher than 3.0 cm/sec is mechanically not applicable. Our recommendation for an optimisation of the discussed parameters is a leaf velocity of 2.5 cm/sec and a dose rate of 300–400 MU/min (prostate cancer) and 100–200 MU/min (SCCscalp) for best protection of organs at risk, short treatment time and number of monitor units.</p

Single fraction radiosurgery using Rapid Arc for treatment of intracranial targets

<p>Abstract</p> <p>Background</p> <p>Stereotactic-Radio-Surgery (SRS) using Conformal-Arc-Therapy (CAT) is a well established irradiation technique for treatment of intracranial targets. Although small safety margins are required because of very high accuracy of patient positioning and exact online localisation, there are still disadvantages like long treatment time, high number of monitor units (MU) and covering of noncircular targets. This planning study analysed whether Rapid Arc (RA) with stereotactic localisation for single-fraction SRS can solve these problems.</p> <p>Methods</p> <p>Ten consecutive patients were treated with Linac-based SRS. Eight patients had one or more brain metastases. The other patients presented a symptomatic vestibularis schwannoma and an atypic meningeoma. For all patients, two plans (CAT/RA) were calculated and analysed.</p> <p>Results</p> <p>Conformity was higher for RA with additional larger low-dose areas. Furthermore, RA reduced the number of MU and the treatment time for all patients. Dose to organs at risk were equal or slightly higher using RA in comparison to CAT.</p> <p>Conclusions</p> <p>RA provides a new alternative for single-fraction SRS irradiation combining advantages of short treatment time with lower number of MU and better conformity in addition to accuracy of stereotactic localisation in selected cases with uncomplicated clinical realization.</p

Guidelines for delineation of lymphatic clinical target volumes for high conformal radiotherapy: head and neck region

The success of radiotherapy depends on the accurate delineation of the clinical target volume. The delineation of the lymph node regions has most impact, especially for tumors in the head and neck region. The purpose of this article was the development an atlas for the delineation of the clinical target volume for patients, who should receive radiotherapy for a tumor of the head and neck region. Literature was reviewed for localisations of the adjacent lymph node regions and their lymph drain in dependence of the tumor entity. On this basis the lymph node regions were contoured on transversal CT slices. The probability for involvement was reviewed and a recommendation for the delineation of the CTV was generated

Dosimetrische und planungstechnische Untersuchungen der TomoTherapy (Accuray)

Die TomoTherapy bietet eine einzigartige Möglichkeit der intensitäts- modulierten Strahlentherapie. Ein schlitzartiger hochenergetischer, ionisierender Photonenstrahl wird durch einen binären Multi-Lamellen- Kollimator geformt und eine Vielzahl solcher Projektionen aus verschiedenen Einstrahlwinkeln auf ein Zielgebiet kumuliert. Durch diese Technik wird eine homogene Dosisverteilung im Zielgebiet, zumeist Tumorgewebe, mit steilen Gradienten zum Normalgewebe erreicht. Die Vorzüge der einzigartigen Bestrahlungstechnik der TomoTherapy wurden kombiniert, um eine neue Methode der robusten Ganzkörperbestrahlung zu entwickeln und in die klinische Routine zu implementieren. Von nationalen und internationalen Dosimetrieprotokollen vorgeschriebene Referenzbedingungen für die Absolutdosimetrie sind mit dem Bestrahlungsgerät TomoTherapyHD unter mehreren Aspekten nicht zu erreichen. Mittels Monte Carlo Simulationen werden Fragestellungen beantwortet, die Unsicherheiten der Absolutdosimetrie reduzieren. Die Unsicherheiten der Dosimetrie kleiner Felder werden in vielen Publikationen untersucht. In dieser Arbeit wird erstmalig eine fluenzgewichtete Subfeldgröße eines helikalen TomoTherapy Planes definiert. Dieser Parameter bietet die Möglichkeit einer Beschreibung der Komplexität eines Bestrahlungsplanes und ist eine Größe, um Genauigkeiten von Messsystemen für die Patientenqualitätssicherungen in der klinischen Dosimetrie zu verifizieren. In der vorliegenden kumulativen Dissertation werden Hintergründe zu den beschriebenen Sachverhalten beschrieben und die entsprechenden Ergebnisse vorgestellt. Mit dieser Arbeit wird ein Beitrag geleistet, die Qualitätssicherung der Strahlentherapie weiter zu verbessern und Ungenauigkeiten in der klinischen Dosimetrie zu minimieren

Students’ learning behavior in digital education for radiation oncology

Purpose!#!Digitalization of medical education is an important trend in terms of reforming and modernizing the global education environment. It has been long requested by students and politicians. The goal of this study was to assess the student perception of a newly developed digital educational program in radiation oncology (RO) using an interactive e‑book combined with short learnings clips on a YouTube channel combined with periodic videoconferences and a forum for queries.!##!Methods!#!We performed five evaluations during and at the end of two terms with multiple-choice and free-text answers. We evaluated student perception of our new digital learning scenario in three semesters: one pre-clinical and two clinical semesters. In addition, we analyzed all comments from the kMED forum, the YouTube channel, or the e‑mail contacts. We analyzed the learning behavior of the students based on access to the videos and the number and quality of the reflective questions answered as well as the results of the final examinations.!##!Results!#!The students accepted the offer for asynchronous teaching and mainly learned on weekdays (74% of the videos), but also on weekends (23%) and less on public holidays (4%). The answer quality of the reflective questions was good with over 50% correct answers on the first attempt. Learning to be on one's own authority was very difficult for the students, even in the last clinical semesters of the medical study. Without direct intervention by the teacher, access to the learning material by the students was limited and delayed. Therefore, voluntary interim tests were performed during the first analysis term, which led to an increased number of student accesses to the videos and higher number of answers. Nevertheless, in the first analysis term, the average results in the final exam of the students who did not perform the interim test were below average at 59.1%, and the students who performed the test had better results at 69.5% but this was also not satisfactory. In the second analysis term, we taught with the same digital teaching model but with an additional scheme for learning over the term, 2‑week compulsory intermediate tests, and frequent videoconferences to answer any questions. In this term, we measured a success rate of 93% in the final exam. All annotations were very positive regarding the new educational project. The evaluations showed high acceptance of the new education program. The students stated they would prefer the new education course to be continued in future.!##!Conclusion!#!Digital teaching methods make not only the type and quality of teaching transparent, but also the learning behavior of the students. Our analysis has shown that, in addition to the quality of the teaching, the clear structure and specification of the learning content per learning week as well as regular monitoring of what has been learned are of decisive importance for the learning success of the students

Radiotherapy of malignant gliomas: Comparison of volumetric single arc technique (RapidArc), dynamic intensity-modulated technique and 3D conformal technique

Purpose: The analysis was designed to identify the optimal radiation technique for patients with malignant glioma Methods A volumetric-modulated radiation treatment technique (RapidArc), an IMRT technique anti a 3D conformal technique were calculated on Computed tomograms of 14 consecutive patients with malignant glioma. The treatment plans were compared with each other using dose-volume histograms Results The 3D conformal technique showed a good PTV coverage. if PTV was distant to organs at risk (OAR). If PTV was nearby OAR, the 3D technique revealed a poor PTV coverage in contrast to both intensity-modulated techniques The conventional IMRT technique showed a slightly better PTV coverage than RapidArc The advantages of RapidArc were a shorter treatment time, less monitor units and a small V(107%) Conclusions: If PTV is distant to OAR. the use of 3D conformal technique is sufficient. Otherwise an intensity-modulated technique should be used RapidArc was faster than conventional IMRT and should be preferred if PTV coverage is adequate (C) 2009 Elsevier Ireland Ltd All rights reserved Radiotherapy and Oncology 93 (2009) 593-59

Interfractional and intrafractional accuracy during radiotherapy of gynecologic carcinomas: a comprehensive evaluation using the ExacTrac system

Purpose: To evaluate positioning uncertainties with an infrared body marker-based positioning system (ExacTrac) compared with conventional laser positioning in patients treated for gynecologic carcinomas, and to investigate patient movement during therapy. Methods and Materials: Ten patients were positioned both with a conventional laser system and with the ExacTrac system. Positioning accuracy was evaluated using repeated electronic portal images. Average displacements and overall, systematic, and random errors were calculated and compared for the two positioning methods. Further, inter- and intrafractional patient movement including time trends in positioning displacements, respiratory amplitudes, and breathing frequencies were analyzed by online documentation of body marker movement with the ExacTrac system. Results: Average displacements ranged between -3.6 and 6.7 mm for the three coordinates. Mean systematic and random errors ranged from 1.6 to 3.7 mm and 2.2 to 3.7 mm, respectively, with no significant differences between conventional and ExacTrac positioning (p > 0.07). The main breathing direction was from dorsocaudal to anterocranial in 9 of 10 patients. The mean 3D breathing amplitude in the pelvis was 2.4 mm (0.49-6.96 mm). Significant interfractional and intrafractional time trends were observed concerning breathing amplitudes and positioning displacements. Conclusions: The observed displacements did not vary significantly between the two evaluated positioning systems. The analysis of registered body marker positions revealed a wide variation in respiratory frequencies, breathing amplitudes, and patient displacements with interfractional and intrafractional time trends. Systems that allow the measurement of each patient's motion characteristics are a necessary requirement for all efforts at individually tailored radiation therapy. (C) 2003 Elsevier Inc