Planning Benchmark Study for Stereotactic Body Radiation Therapy of Liver Metastases: Results of the DEGRO/DGMP Working Group on Stereotactic Radiation Therapy and Radiosurgery.

Purpose: Our purpose was to investigate whether liver stereotactic body radiation therapy treatment planning can be harmonized across different treatment planning systems, delivery techniques, and institutions by using a specific prescription method and to minimize the knowledge gap concerning intersystem and interuser differences. We provide best practice guidelines for all used techniques.

Methods And Materials: A multiparametric specification of target dose (gross target volume [GTV], GTV, GTV, planning target volume [PTV]) with a prescription dose of GTV = 3 × 20 Gy and organ-at-risk (OAR) limits were distributed with computed tomography and structure sets from 3 patients with liver metastases.

A multi-institutional initiative on patient-related quality assurance: Independent computational dose verification of fluence-modulated treatment techniques.

Purpose: This multi-institutional study investigates whether computational verification of fluence-modulated treatment plans using independent software with its own Strahlerkopfmodel is an appropriate method for patient-related quality assurance (PRQA) in the context of various combinations of linear accelerators (linacs), treatment techniques and treatment planning systems (TPS).

Materials And Methods: The PRQA-software's (Mobius3D) recalculations of 9 institutions' treatment plans were analyzed for a horseshoe-shaped planning target volume (PTV) inside a phantom. The recomputed dose distributions were compared to a) the dose distributions as calculated by all TPS's and b) the measured dose distributions, which were acquired using the same independent measuring system for all institutions.

Fluence-weighted average subfield size in helical TomoTherapy.

Introduction: Helical TomoTherapy allows a highly conformal dose distribution to complex target geometries with a good protection of organs at risk. However, the small field sizes associated with this method are a possible source of dosimetrical uncertainties. The IAEA has published detector-specific field output correction factors for static fields of the TomoTherapy in the TRS483.

Experimental and Monte Carlo-based determination of the beam quality specifier for TomoTherapyHD treatment units.

Reference dosimetry by means of clinical linear accelerators in high-energy photon fields requires the determination of the beam quality specifier TPR, which characterizes the relative particle flux density of the photon beam. The measurement of TPR has to be performed in homogenous photon beams of size 10×10cm with a focus-detector distance of 100cm. These requirements cannot be fulfilled by TomoTherapy treatment units from Accuray.

Patient-related quality assurance with different combinations of treatment planning systems, techniques, and machines : A multi-institutional survey.

Purpose: This project compares the different patient-related quality assurance systems for intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) techniques currently used in the central Germany area with an independent measuring system.

Materials And Methods: The participating institutions generated 21 treatment plans with different combinations of treatment planning systems (TPS) and linear accelerators (LINAC) for the QUASIMODO (Quality ASsurance of Intensity MODulated radiation Oncology) patient model. The plans were exposed to the ArcCHECK measuring system (Sun Nuclear Corporation, Melbourne, FL, USA).

Advanced optimization methods for whole pelvic and local prostate external beam therapy.

Purpose: Radiation treatment planning inherently involves multiple conflicting planning goals, which makes it a suitable application for multicriteria optimization (MCO). This study investigates a MCO algorithm for VMAT planning (VMAT-MCO) for prostate cancer treatments including pelvic lymph nodes and uses standard inverse VMAT optimization (sVMAT) and Tomotherapy planning as benchmarks.

Methods: For each of ten prostate cancer patients, a two stage plan was generated, consisting of a stage 1 plan delivering 22Gy to the prostate, and a stage 2 plan delivering 50.

Intensity-modulated Total Body Irradiation (TBI) with TomoDirect™.

Background: The new TomoDirect™ modality offers a non-rotational option with discrete beam angles. We have investigated this mode for TBI with the intention to test the feasibility and to establish it as a clinical routine method. Special foci were directed onto treatment planning, dosimetric accuracy and practical aspects.

Neural stem cell sparing by linac based intensity modulated stereotactic radiotherapy in intracranial tumors.

Background: Neurocognitive decline observed after radiotherapy (RT) for brain tumors in long time survivors is attributed to radiation exposure of the hippocampus and the subventricular zone (SVZ). The potential of sparing capabilities for both structures by optimized intensity modulated stereotactic radiotherapy (IMSRT) is investigated.

Methods: Brain tumors were irradiated by stereotactic 3D conformal RT or IMSRT using m3 collimator optimized for PTV and for sparing of the conventional OARs (lens, retina, optic nerve, chiasm, cochlea, brain stem and the medulla oblongata).

Investigations of peripheral dose for helical tomotherapy.

Purpose: Whenever treating a patient with percutaneous radiotherapy, a certain amount of dose is inevitably delivered to healthy tissue. This is mainly due to beam's entry and exit in the region of the target volume. In regions distant from the target volume, dose is delivered by leakage from the MLC and head scatter from the accelerator head and phantom scatter from the target volume (peripheral dose).

Does IMRT increase the peripheral radiation dose? A comparison of treatment plans 2000 and 2010.

It has been reported in several papers and textbooks that IMRT treatments increase the peripheral dose in comparison with non-IMRT fields. But in clinical practice not only open fields have been used in the pre-IMRT era, but also fields with physical wedges or composed fields. The aim of this work is to test the hypothesis of increased peripheral dose when IMRT is used compared to standard conformal radiotherapy.

Rotational IMRT techniques compared to fixed gantry IMRT and tomotherapy: multi-institutional planning study for head-and-neck cases.

Background: Recent developments enable to deliver rotational IMRT with standard C-arm gantry based linear accelerators. This upcoming treatment technique was benchmarked in a multi-center treatment planning study against static gantry IMRT and rotational IMRT based on a ring gantry for a complex parotid gland sparing head-and-neck technique.

Methods: Treatment plans were created for 10 patients with head-and-neck tumours (oropharynx, hypopharynx, larynx) using the following treatment planning systems (TPS) for rotational IMRT: Monaco (ELEKTA VMAT solution), Eclipse (Varian RapidArc solution) and HiArt for the helical tomotherapy (Tomotherapy).

Flattening filter free beams in SBRT and IMRT: dosimetric assessment of peripheral doses.

Purpose: Recently, there has been a growing interest in operating medical linear accelerators without a flattening filter. Due to reduced scatter, leaf transmission and radiation head leakage a reduction of out-of-field dose is expected for flattening filter free beams. The aim of the present study was to determine the impact of unflattened beams on peripheral dose for advanced treatment techniques with a large number of MUs.

Experimental study on photon-beam peripheral doses, their components and some possibilities for their reduction.

The component analysis of the peripheral doses produced at typical accelerators such as the Siemens Primus 6/15 is regarded as an approach enabling technical strategies towards the reduction of second malignancies associated with photon beam radiotherapy. Suitable phantom and detector arrangements have been applied to show that the unavoidable peripheral dose contribution due to photon scattering from the directly irradiated part of the body or phantom does not constitute the entirety of the peripheral doses. Rather, there are peripheral dose contributions due to beam head leakage and to extrafocal radiation which can be regarded as partly avoidable.

The influence of different IMRT techniques on the peripheral dose: a comparison between sMLM-IMRT and helical tomotherapy.

Purpose: To investigate how segmented multileaf modulation-(sMLM-)based intensity-modulated radiotherapy (IMRT) and dynamic helical tomotherapy (ToTh) affect the peripheral dose (PD) outside the treated region.

Material And Methods: A cuboid Perspex phantom was scanned in a computed tomograph. Different artificial cases were contoured consisting of OARs surrounded by cylindrically shaped planning target volumes (PTVs) with different dimensions.

Dosimetry of a linear accelerator under respiratory gating.

In the present study, the impact of respiratory gating on the beam characteristics of a linear accelerator is investigated. The main focus is put on the influence of the duty cycle. Measurements were performed on a linear accelerator type Oncor (Siemens) with photon energies 6 MV and 15 MV, equipped with the Anzai gating system AZ-733V.

Experimental determination of peripheral photon dose components for different IMRT techniques and linear accelerators.

Purpose: To quantify the relative peripheral photon doses (PD) to healthy tissues outside the treated region for different IMRT technologies and linac head designs.

Material And Methods: Measurements were performed on an Elekta linac for various energies (6 MV, 10 MV, 25 MV) at different depths at a distance of 29 cm off-axis (vertical measurements) and different distances from the field edge at constant depth of 10 cm (horizontal measurements). These measurements were compared with results obtained on a Siemens linac at 6 MV and 15 MV.

Experimental determination of peripheral doses for different IMRT techniques delivered by a Siemens linear accelerator.

Purpose: To quantify the relative peripheral doses (PD) to healthy tissues outside the treated region for different intensity-modulated radiotherapy (IMRT) technologies.

Material And Methods: On a linear accelerator (linac) Oncor Impression (Siemens OCS) with two photon energies (6 MV, 15 MV), point dose measurements were performed at different depths in a solid phantom at 29 cm off-axis distance inplane. PD associated with artificial fluence distributions were compared with open beam contributions, where intensity-modulated (IM) beams were generated by segmented multileaf-modulated (sMLM) IMRT, by tin+wax compensators (TWComp), and by lead-containing cerrobend compensators (CComp).

[Radiophysical characteristics of different detectors for use in dosimetry].

The present study investigated the radiophysical influences on the measurement of dosimetry basic data, attributable to field size, photon energy and detector type. A natural diamond detector, two ionisation chambers, different Si-diodes and a EBT-Gafchromic film were studied for this purpose. The characteristics of the detectors were investigated with regard to the measurement of output factors, lateral beam profiles and relative depth-dose curves for narrow and wide photon beams of 15 MV Significant differences in output factors were obtained with different detectors.

3D-conformal-intensity modulated radiotherapy with compensators for head and neck cancer: clinical results of normal tissue sparing.

Background: To investigate the potential of parotic gland sparing of intensity modulated radiotherapy (3D-c-IMRT) performed with metallic compensators for head and neck cancer in a clinical series by analysis of dose distributions and clinical measures.

Materials And Methods: 39 patients with squamous cell cancer of the head and neck irradiated using 3D-c-IMRT were evaluable for dose distribution within PTVs and at one parotid gland and 38 patients for toxicity analysis. 10 patients were treated primarily, 29 postoperatively, 19 received concomitant cis-platin based chemotherapy, 20 3D-c-IMRT alone.

IMRT with compensators for head-and-neck cancers treatment technique, dosimetric accuracy, and practical experiences.

Background And Purpose: With three-dimensional conformal intensity-modulated radiotherapy (3D-c-IMRT) a heterogeneous dose distribution can be achieved in both planning treatment volume and in adjacent normal tissues and organs to be spared. 3D-c-IMRT demands for modified photon fluence profiles which can be accomplished with different techniques. This report deals with the commissioning of metal compensators and the first experiences in clinical use.

Dosimetric quality assurance for intensity-modulated radiotherapy feasibility study for a filmless approach.

Purpose: Test and comparison of various 2-D real-time detectors for dosimetric quality assurance (QA) of intensity-modulated radiotherapy (IMRT) with the vision to replace radiographic films for 2-D dosimetry.

Material And Methods: All IMRT treatment plans were created with the Konrad software (Siemens OCS). The final dose calculation was also carried out in Konrad.

[Improved patient repositioning accuracy by integrating an additional jaw fixation into a high precision face mask system in stereotactic radiotherapy of the head].

Background: For high precision radiotherapy of the neurocranium a precise, reproducible positioning technique is the basic prerequisite. The aim of this study was to assess the influence of a modification of the commercially available stereotactical BrainLab-head mask system on accuracy in patient positioning during fractionated radiotherapy.

Material And Methods: 29 patients were treated with stereotactic radiotherapy of the head.

[Improvement of the accuracy of the Laplace transform method for the determination of radiotherapy spectra of clinical linear accelerators].

The present study focused on the reconstruction of the bremsstrahlung spectrum of a clinical linear accelerator from the measured transmission curve, with the aim of improving the accuracy of this method. The essence of the method was the analytic inverse Laplace transform of a parameter function fitted to the measured transmission curve. We tested known fitting functions, however they resulted in considerable fitting inaccuracy, leading to inaccuracies of the bremsstrahlung spectrum.

VERIDOS: a new tool for quality assurance for intensity modulated radiotherapy.

Background: The use of intensity modulated radiation fields needs an extended quality assurance concept. This consists of a linac related part and a case related part. Case related means the verification of an individual treatment plan, optimized on a CT data set of an individual patient and prepared for the treatment of this patient.