Search

In phase I of the survey a planning intercomparison of patient-related QA was performed at 12 institutions. The participating clinics created phantom based IMRT and VMAT plans which were measured utilizing the ArcCheck diode array. Mobius3D (M3D) was used in phase II. It acts as a secondary dose verification tool for patient-specific QA based on average linac beam data collected by Mobius Medical Systems. All Quasimodo linac plans will be analyzed for the continuation of the intercomparison. We aim to determine if Mobius3D is suited for use with diverse treatment techniques, if beam model customization is needed. Initially we computed first Mobius3D results by transferring all plans from phase I to our Mobius3D server. Because of some larger PTV mean dose differences we checked if output factor customization would be beneficial. We performed measurements and output factor correction to account for discrepancies in reference conditions. Compared to Mobius3D's preconfigured average beam data values, these corrected output factors differed by ±1.5% for field sizes between 7x7cm2 and 30x30cm2 and to −3.9% for 3x3cm2. Our method of correcting the output factors turns out good congruence to M3D's reference values for these medium field sizes.

The biplanar diode arrays Delta4PT and Delta4+ has been used in our hospital since the introduction of the TomoTherapy in 2013 to ensure a good agreement between the calculated and the measured dose distributions in patient-related QA with helical TomoTherapy. The aim of this presentation is to evaluate the quality of the measurement procedure with the Delta4 phantoms Delta4PT and (since January 2016) Delta4+. This includes the influence of a cross calibration with a treatment plan with low modulation.

Abstract 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). Planning of static gantry IMRT was performed with KonRad, Pinnacle and Panther DAO based on step&shoot IMRT delivery and Eclipse for sliding window IMRT. The prescribed doses for the high dose PTVs were 65.1Gy or 60.9Gy and for the low dose PTVs 55.8Gy or 52.5Gy dependend on resection status. Plan evaluation was based on target coverage, conformity and homogeneity, DVHs of OARs and the volume of normal tissue receiving more than 5Gy (V5Gy). Additionally, the cumulative monitor units (MUs) and treatment times of the different technologies were compared. All evaluation parameters were averaged over all 10 patients for each technique and planning modality. Results Depending on IMRT technique and TPS, the mean CI values of all patients ranged from 1.17 to 2.82; and mean HI values varied from 0.05 to 0.10. The mean values of the median doses of the spared parotid were 26.5Gy for RapidArc and 23Gy for VMAT, 14.1Gy for Tomo. For fixed gantry techniques 21Gy was achieved for step&shoot+KonRad, 17.0Gy for step&shoot+Panther DAO, 23.3Gy for step&shoot+Pinnacle and 18.6Gy for sliding window. V5Gy values were lowest for the sliding window IMRT technique (3499 ccm) and largest for RapidArc (5480 ccm). The lowest mean MU value of 408 was achieved by Panther DAO, compared to 1140 for sliding window IMRT. Conclusions All IMRT delivery technologies with their associated TPS provide plans with satisfying target coverage while at the same time respecting the defined OAR criteria. Sliding window IMRT, RapidArc and Tomo techniques resulted in better target dose homogeneity compared to VMAT and step&shoot IMRT. Rotational IMRT based on C-arm linacs and Tomotherapy seem to be advantageous with respect to OAR sparing and treatment delivery efficiency, at the cost of higher dose delivered to normal tissues. The overall treatment plan quality using Tomo seems to be better than the other TPS technology combinations.

Abstract 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 concomittant cis-platin based chemotherapy, 20 3D-c-IMRT alone. Initially the dose distribution was calculated with Helax ® and photon fluence was modulated using metallic compensators made of tin-granulate (n = 22). Later the dose distribution was calculated with KonRad ® and fluence was modified by MCP 96 alloy compensators (n = 17). Gross tumor/tumor bed (PTV 1) was irradiated up to 60–70 Gy, [5 fractions/week, single fraction dose: 2.0–2.2 (simultaneously integrated boost)], adjuvantly irradiated bilateral cervical lymph nodes (PTV 2) with 48–54 Gy [single dose: 1.5–1.8]). Toxicity was scored according the RTOG scale and patient-reported xerostomia questionnaire (XQ). Results Mean of the median doses at the parotid glands to be spared was 25.9 (16.3–46.8) Gy, for tin graulate 26 Gy, for MCP alloy 24.2 Gy. Tin-granulate compensators resulted in a median parotid dose above 26 Gy in 10/22, MCP 96 alloy in 0/17 patients. Following acute toxicities were seen (°0–2/3): xerostomia: 87%/13%, dysphagia: 84%/16%, mucositis: 89%/11%, dermatitis: 100%/0%. No grade 4 reaction was encountered. During therapy the XQ forms showed °0–2/3): 88%/12%. 6 months postRT chronic xerostomia °0–2/3 was observed in 85%/15% of patients, none with °4 xerostomia. Conclusion 3D-c-IMRT using metallic compensators along with inverse calculation algorithm achieves sufficient parotid gland sparing in virtually all advanced head and neck cancers. Since the concept of lower single (and total) doses in the adjuvantly treated volumes reduces acute morbidity 3D-c-IMRT nicely meets demands of concurrent chemotherapy protocols.

Copyright of Strahlentherapie und Onkologie is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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. For narrow fields, the natural diamond detector and the diodes PTW-60012 and SCX_WH-PFD measured output factors close to those of the EBT-Gafchromic film. The output facto rfor large fields was overestimated by the unshielded diode PTW 60012 and the PinPoint-chamber PTW-31006 because of their over-response to scattered photons. The relative depth dose distributions for wide beams at large depths agree well for the diamond, the ionisation chambers and the shielded Diode SCX_ WH-PFD and PTW-60008, while the measured dose was overestimated by an unshielded diode PTW-60012. Considering the influence due to the sensitive materials and the construction of the detectors the manufacturers of dosimeters have specified the application ranges for the various types of detectors.

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. Immobilization was provided by a two layer thermoplastic mask system (BrainLab). 18 of these patients received an additional custom made fixation either of the upper jaw (OKF) or of the mandibula (UKF). The positioning accuracy was assessed by measurements of the shifting of anatomical landmarks in relation to the rigid mask system on biplanar simulator films using a digital imaging system. Before each measurement a fine adjustment of the simulator to an optical ring system was performed. The reference radiographs were done just before CT-planning. During a 2-7 weeks lasting course of radiotherapy displacement measurements in relation to the reference images for all three dimensions (z, y and x) were done once a week. In 29 patients 844 measurements were analyzed., Results: An additional jaw fixation improves the reproducibility of patient positioning significantly in all three spatial dimensions. The standard deviation in lateral direction (x) was 0.6 mm with jaw fixation vs. 0.7 mm without jaw fixation (p < 0.001); in longitudinal direction (z) (measured in 0 degree radiographs) 0.5 mm vs. 1.3 mm (p < 0.001); in longitudinal direction (measured in 90 degrees radiographs) 0.5 mm vs. 1.5 mm (p < 0.001); in vertical direction (y) 0.6 mm vs. 0.9 mm (p = 0.001). No significant differences in standard deviations were found comparing OKF (n = 14) with UKF (n = 4)., Conclusion: A significant improvement in reposition accuracy using an additional, individually formed jaw fixation can be acquired. The variability of positioning can be reduced especially in the z-direction. A further reduction of the safety margin around the target volume--especially in benign tumors--is possible by improved fixation technique.

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. In order to minimise the fitting errors, we employed a linear combination of n equations with 2n-1 parameters. The fitting errors are now considerably smaller. The measurement of the transmission function requires that the energy-dependent detector response is taken into account. We analysed the underlying physical context and developed a function that corrects for the energy-dependent detector response. The factors of this function were experimentally determined or calculated from tabulated values.