@article{BratengeierHolubyev2016, author = {Bratengeier, Klaus and Holubyev, Kostyantyn}, title = {Anisotropy of dose contributions-an instrument to upgrade real time IMRT and VMAT adaptation?}, series = {Medical Physics}, volume = {43}, journal = {Medical Physics}, number = {11}, doi = {10.1118/1.4963806}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-186833}, pages = {5826-5834}, year = {2016}, abstract = {Purpose: To suggest a definition of dose deposition anisotropy for the purpose of ad hoc adaptation of intensity modulated arc therapy (IMRT) and volumetric arc therapy (VMAT), particularly in the vicinity of important organs at risk (OAR), also for large deformations. Methods: Beam's-eye-view (BEV) based fluence warping is a standard adaptation method with disadvantages for strongly varying OAR shapes. 2-Step-adaptation overcomes these difficulties by a deeper analysis of the 3D properties of adaptation processes, but requires separate arcs for every OAR to spare, which makes it impractical for cases with multiple OARs. The authors aim to extend the 2-Step method to arbitrary intensity modulated plan by analyzing the anisotropy of dose contributions. Anisotropy was defined as a second term of Fourier transformation of gantry angle dependent dose contributions. For a cylindrical planning target volume (PTV) surrounding an OAR of varying diameter, the anisotropy and the dose-normalized anisotropy were analyzed for several scenarios of optimized fluence distributions. 2-Step adaptation to decreasing and increasing OAR diameter was performed, and compared to a usual fluence based adaptation method. For two clinical cases, prostate and neck, the VMAT was generated and the behavior of anisotropy was qualitatively explored for deformed organs at risk. \# Results: Dose contribution anisotropy in the PTV peaks around nearby OARs. The thickness of the "anisotropy wall" around OAR increases for increasing OAR radius, as also does the width of 2-Step dose saturating fluence peak adjacent to the OAR K. Bratengeier et al., "A comparison between 2-Step IMRT and conventional IMRT planning," Radiother. Oncol. 84, 298-306 (2007)]. Different optimized beam fluence profiles resulted in comparable radial dependence of normalized anisotropy. As predicted, even for patient cases, anisotropy was inflated even more than increasing diameters of OAR. Conclusions: For cylindrically symmetric cases, the dose distribution anisotropy defined in the present work implicitly contains adaptation-relevant information about 3D relationships between PTV and OAR and degree of OAR sparing. For more complex realistic cases, it shows the predicted behavior qualitatively. The authors claim to have found a first component for advancing a 2-Step adaptation to a universal adaptation algorithm based on the BEV projection of the dose anisotropy. Further planning studies to explore the potential of anisotropy for adaptation algorithms using phantoms and clinical cases of differing complexity will follow.}, language = {en} } @article{BratengeierHolubyev2015, author = {Bratengeier, Klaus and Holubyev, Kostyantyn}, title = {Characteristics of non-coplanar IMRT in the presence of target-embedded organs at risk}, series = {Radiation Oncology}, volume = {10}, journal = {Radiation Oncology}, number = {207}, doi = {10.1186/s13014-015-0494-5}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-125292}, year = {2015}, abstract = {Background The aim is to analyze characteristics and to study the potentials of non-coplanar intensity modulated radiation therapy (IMRT) techniques. The planning study applies to generalized organ at risk (OAR) - planning target volume (PTV) geometries. Methods The authors focus on OARs embedded in the PTV. The OAR shapes are spherically symmetric (A), cylindrical (B), and bended (C). Several IMRT techniques are used for the planning study: a) non-coplanar quasi-isotropic; b) two sets of equidistant coplanar beams, half of beams incident in a plane perpendicular to the principal plane; c) coplanar equidistant (reference); d) coplanar plus one orthogonal beam. The number of beam directions varies from 9 to 16. The orientation of the beam sets is systematically changed; dose distributions resulting from optimal fluence are explored. A selection of plans is optimized with direct machine parameter optimization (DMPO) allowing 120 and 64 segments. The overall plan quality, PTV coverage, and OAR sparing are evaluated. Results For all fluence based techniques in cases A and C, plan quality increased considerably if more irradiation directions were used. For the cylindrically symmetric case B, however, only a weak beam number dependence was observed for the best beam set orientation, for which non-coplanar directions could be found where OAR- and PTV-projections did not overlap. IMRT plans using quasi-isotropical distributed non-coplanar beams showed stable results for all topologies A, B, C, as long as 16 beams were chosen; also the most unfavorable beam arrangement created results of similar quality as the optimally oriented coplanar configuration. For smaller number of beams or application in the trunk, a coplanar technique with additional orthogonal beam could be recommended. Techniques using 120 segments created by DMPO could qualitatively reproduce the fluence based results. However, for a reduced number of segments the beam number dependence declined or even reversed for the used planning system and the plan quality degraded substantially. Conclusions Topologies with targets encompassing sensitive OAR require sufficient number of beams of 15 or more. For the subgroup of topologies where beam incidences are possible which cover the whole PTV without direct OAR irradiation, the quality dependence on the number of beams is much less pronounced above 9 beams. However, these special non-coplanar beam directions have to be found. On the basis of this work the non-coplanar IMRT techniques can be chosen for further clinical planning studies.}, language = {en} } @article{BratengeierGaineyFlentje2011, author = {Bratengeier, Klaus and Gainey, Mark B. and Flentje, Michael}, title = {Fast IMRT by increasing the beam number and reducing the number of segments}, series = {Radiation Oncology}, volume = {6}, journal = {Radiation Oncology}, number = {170}, doi = {10.1186/1748-717X-6-170}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-137994}, year = {2011}, abstract = {Purpose The purpose of this work is to develop fast deliverable step and shoot IMRT technique. A reduction in the number of segments should theoretically be possible, whilst simultaneously maintaining plan quality, provided that the reduction is accompanied by an increased number of gantry angles. A benefit of this method is that the segment shaping could be performed during gantry motion, thereby reducing the delivery time. The aim was to find classes of such solutions whose plan quality can compete with conventional IMRT. Materials/Methods A planning study was performed. Step and shoot IMRT plans were created using direct machine parameter optimization (DMPO) as a reference. DMPO plans were compared to an IMRT variant having only one segment per angle ("2-Step Fast"). 2-Step Fast is based on a geometrical analysis of the topology of the planning target volume (PTV) and the organs at risk (OAR). A prostate/rectum case, spine metastasis/spinal cord, breast/lung and an artificial PTV/OAR combination of the ESTRO-Quasimodo phantom were used for the study. The composite objective value (COV), a quality score, and plan delivery time were compared. The delivery time for the DMPO reference plan and the 2-Step Fast IMRT technique was measured and calculated for two different linacs, a twelve year old Siemens Primus™ ("old" linac) and two Elekta Synergy™ "S" linacs ("new" linacs). Results 2-Step Fast had comparable or better quality than the reference DMPO plan. The number of segments was smaller than for the reference plan, the number of gantry angles was between 23 and 34. For the modern linac the delivery time was always smaller than that for the reference plan. The calculated (measured) values showed a mean delivery time reduction of 21\% (21\%) for the new linac, and of 7\% (3\%) for the old linac compared to the respective DMPO reference plans. For the old linac, the data handling time per beam was the limiting factor for the treatment time reduction. Conclusions 2-Step Fast plans are suited to reduce the delivery time, especially if the data handling time per beam is short. The plan quality can be retained or even increased for fewer segments provided more gantry angles are used.}, language = {en} } @article{HolubyevBratengeierGaineyetal.2013, author = {Holubyev, Konstyantyn and Bratengeier, Klaus and Gainey, Mark and Polat, B{\"u}lent and Flentje, Michael}, title = {Towards automated on-line adaptation of 2-Step IMRT plans: QUASIMODO phantom and prostate cancer cases}, series = {Radiation Oncology}, journal = {Radiation Oncology}, doi = {10.1186/1748-717X-8-263}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-96818}, year = {2013}, abstract = {Background The standard clinical protocol of image-guided IMRT for prostate carcinoma introduces isocenter relocation to restore the conformity of the multi-leaf collimator (MLC) segments to the target as seen in the cone-beam CT on the day of treatment. The large interfractional deformations of the clinical target volume (CTV) still require introduction of safety margins which leads to undesirably high rectum toxicity. Here we present further results from the 2-Step IMRT method which generates adaptable prostate IMRT plans using Beam Eye View (BEV) and 3D information. Methods Intermediate/high-risk prostate carcinoma cases are treated using Simultaneous Integrated Boost at the Universit{\"a}tsklinkum W{\"u}rzburg (UKW). Based on the planning CT a CTV is defined as the prostate and the base of seminal vesicles. The CTV is expanded by 10 mm resulting in the PTV; the posterior margin is limited to 7 mm. The Boost is obtained by expanding the CTV by 5 mm, overlap with rectum is not allowed. Prescription doses to PTV and Boost are 60.1 and 74 Gy respectively given in 33 fractions. We analyse the geometry of the structures of interest (SOIs): PTV, Boost, and rectum, and generate 2-Step IMRT plans to deliver three fluence steps: conformal to the target SOIs (S0), sparing the rectum (S1), and narrow segments compensating the underdosage in the target SOIs due to the rectum sparing (S2). The width of S2 segments is calculated for every MLC leaf pair based on the target and rectum geometry in the corresponding CT layer to have best target coverage. The resulting segments are then fed into the DMPO optimizer of the Pinnacle treatment planning system for weight optimization and fine-tuning of the form, prior to final dose calculation using the collapsed cone algorithm. We adapt 2-Step IMRT plans to changed geometry whilst simultaneously preserving the number of initially planned Monitor Units (MU). The adaptation adds three further steps to the previous isocenter relocation: 1) 2-Step generation for the geometry of the day using the relocated isocenter, MU transfer from the planning geometry; 2) Adaptation of the widths of S2 segments to the geometry of the day; 3) Imitation of DMPO fine-tuning for the geometry of the day. Results and conclusion We have performed automated 2-Step IMRT adaptation for ten prostate adaptation cases. The adapted plans show statistically significant improvement of the target coverage and of the rectum sparing compared to those plans in which only the isocenter is relocated. The 2-Step IMRT method may become a core of the automated adaptive radiation therapy system at our department.}, language = {en} } @article{KraftWeickBreueretal.2022, author = {Kraft, Johannes and Weick, Stefan and Breuer, Kathrin and Lutyj, Paul and Bratengeier, Klaus and Exner, Florian and Richter, Anne and Tamihardja, J{\"o}rg and Lisowski, Dominik and Polat, B{\"u}lent and Flentje, Michael}, title = {Treatment plan comparison for irradiation of multiple brain metastases with hippocampal avoidance whole brain radiotherapy and simultaneous integrated boost using the Varian Halcyon and the Elekta Synergy platforms}, series = {Radiation Oncology}, volume = {17}, journal = {Radiation Oncology}, doi = {10.1186/s13014-022-02156-6}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-301221}, year = {2022}, abstract = {No abstract available.}, language = {en} } @article{TamihardjaSchortmannLawrenzetal.2021, author = {Tamihardja, J{\"o}rg and Schortmann, Max and Lawrenz, Ingulf and Weick, Stefan and Bratengeier, Klaus and Flentje, Michael and Guckenberger, Matthias and Polat, B{\"u}lent}, title = {Moderately hypofractionated radiotherapy for localized prostate cancer: updated long-term outcome and toxicity analysis}, series = {Strahlentherapie und Onkologie}, volume = {197}, journal = {Strahlentherapie und Onkologie}, issn = {0179-7158}, doi = {10.1007/s00066-020-01678-w}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-232509}, pages = {124-132}, year = {2021}, abstract = {Purpose Evaluation of long-term outcome and toxicity of moderately hypofractionated radiotherapy using intensity-modulated radiotherapy (IMRT) with simultaneous integrated boost treatment planning and cone beam CT-based image guidance for localized prostate cancer. Methods Between 2005 and 2015, 346 consecutive patients with localized prostate cancer received primary radiotherapy using cone beam CT-based image-guided intensity-modulated radiotherapy (IG-IMRT) and volumetric modulated arc therapy (IG-VMAT) with a simultaneous integrated boost (SIB). Total doses of 73.9 Gy (n = 44) and 76.2 Gy (n = 302) to the high-dose PTV were delivered in 32 and 33 fractions, respectively. The low-dose PTV received a dose (D95) of 60.06 Gy in single doses of 1.82 Gy. The pelvic lymph nodes were treated in 91 high-risk patients to 45.5 Gy (D95). Results Median follow-up was 61.8 months. The 5‑year biochemical relapse-free survival (bRFS) was 85.4\% for all patients and 93.3, 87.4, and 79.4\% for low-, intermediate-, and high-risk disease, respectively. The 5‑year prostate cancer-specific survival (PSS) was 94.8\% for all patients and 98.7, 98.9, 89.3\% for low-, intermediate-, and high-risk disease, respectively. The 5‑year and 10-year overall survival rates were 83.8 and 66.3\% and the 5‑year and 10-year freedom from distant metastasis rates were 92.2 and 88.0\%, respectively. Cumulative 5‑year late GU toxicity and late GI toxicity grade ≥2 was observed in 26.3 and 12.1\% of the patients, respectively. Cumulative 5‑year late grade 3 GU/GI toxicity occurred in 4.0/1.2\%. Conclusion Moderately hypofractionated radiotherapy using SIB treatment planning and cone beam CT image guidance resulted in high biochemical control and survival with low rates of late toxicity.}, language = {en} } @article{RichterWegenerBreueretal.2021, author = {Richter, Anne and Wegener, Sonja and Breuer, Kathrin and Razinskas, Gary and Weick, Stefan and Exner, Florian and Bratengeier, Klaus and Flentje, Michael and Sauer, Otto and Polat, B{\"u}lent}, title = {Comparison of sliding window and field-in-field techniques for tangential whole breast irradiation using the Halcyon and Synergy Agility systems}, series = {Radiation Oncology}, volume = {16}, journal = {Radiation Oncology}, doi = {10.1186/s13014-021-01942-y}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-265704}, year = {2021}, abstract = {Background To implement a tangential treatment technique for whole breast irradiation using the Varian Halcyon and to compare it with Elekta Synergy Agility plans. Methods For 20 patients two comparable treatment plans with respect to dose coverage and normal tissue sparing were generated. Tangential field-in-field treatment plans (Pinnacle/Synergy) were replanned using the sliding window technique (Eclipse/Halcyon). Plan specific QA was performed using the portal Dosimetry and the ArcCHECK phantom. Imaging and treatment dose were evaluated for treatment delivery on both systems using a modified CIRS Phantom. Results The mean number of monitor units for a fraction dose of 2.67 Gy was 515 MUs and 260 MUs for Halcyon and Synergy Agility plans, respectively. The homogeneity index and dose coverage were similar for both treatment units. The plan specific QA showed good agreement between measured and calculated plans. All Halcyon plans passed portal dosimetry QA (3\%/2 mm) with 100\% points passing and ArcCheck QA (3\%/2 mm) with 99.5\%. Measurement of the cumulated treatment and imaging dose with the CIRS phantom resulted in lower dose to the contralateral breast for the Halcyon plans. Conclusions For the Varian Halcyon a plan quality similar to the Elekta Synergy device was achieved. For the Halcyon plans the dose contribution from the treatment fields to the contralateral breast was even lower due to less interleaf transmission of the Halcyon MLC and a lower contribution of scattered dose from the collimator system.}, language = {en} } @article{BratengeierHerzogWegeneretal.2017, author = {Bratengeier, Klaus and Herzog, Barbara and Wegener, Sonja and Holubyev, Kostyantyn}, title = {Finer leaf resolution and steeper beam edges using a virtual isocentre in concurrence to PTV-shaped collimators in standard distance - a planning study}, series = {Radiation Oncology}, volume = {12}, journal = {Radiation Oncology}, number = {88}, doi = {10.1186/s13014-017-0826-8}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-157543}, year = {2017}, abstract = {Purpose: Investigation of a reduced source to target distance to improve organ at risk sparing during stereotactic irradiation (STX). Methods: The authors present a planning study with perfectly target-volume adapted collimator compared with multi-leaf collimator (MLC) at reduced source to virtual isocentre distance (SVID) in contrast to normal source to isocentre distance (SID) for stereotactic applications. The role of MLC leaf width and 20-80\% penumbra was examined concerning the healthy tissue sparing. Several prescription schemes and target diameters are considered. Results: Paddick's gradient index (GI) as well as comparison of the mean doses to spherical shells at several distances to the target is evaluated. Both emphasize the same results: the healthy tissue sparing in the high dose area around the planning target volume (PTV) is improved at reduced SVID ≤ 70 cm. The effect can be attributed more to steeper penumbra than to finer leaf resolution. Comparing circular collimators at different SVID just as MLC-shaped collimators, always the GI was reduced. Even MLC-shaped collimator at SVID 70 cm had better healthy tissue sparing than an optimal shaped circular collimator at SID 100 cm. Regarding penumbra changes due to varying SVID, the results of the planning study are underlined by film dosimetry measurements with Agility™ MLC. Conclusion: Penumbra requires more attention in comparing studies, especially studies using different planning systems. Reduced SVID probably allows usage of conventional MLC for STX-like irradiations.}, language = {en} } @article{RichterExnerBratengeieretal.2019, author = {Richter, Anne and Exner, Florian and Bratengeier, Klaus and Polat, B{\"u}lent and Flentje, Michael and Weick, Stefan}, title = {Impact of beam configuration on VMAT plan quality for Pinnacle\(^3\)Auto-Planning for head and neck cases}, series = {Radiation Oncology}, volume = {14}, journal = {Radiation Oncology}, doi = {10.1186/s13014-019-1211-6}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-200301}, pages = {12}, year = {2019}, abstract = {Background The purpose of this study was to compare automatically generated VMAT plans to find the superior beam configurations for Pinnacle3 Auto-Planning and share "best practices". Methods VMAT plans for 20 patients with head and neck cancer were generated using Pinnacle3 Auto-Planning Module (Pinnacle3 Version 9.10) with different beam setup parameters. VMAT plans for single (V1) or double arc (V2) and partial or full gantry rotation were optimized. Beam configurations with different collimator positions were defined. Target coverage and sparing of organs at risk were evaluated based on scoring of an evaluation parameter set. Furthermore, dosimetric evaluation was performed based on the composite objective value (COV) and a new cross comparison method was applied using the COVs. Results The evaluation showed a superior plan quality for double arcs compared to one single arc or two single arcs for all cases. Plan quality was superior if a full gantry rotation was allowed during optimization for unilateral target volumes. A double arc technique with collimator setting of 15° was superior to a double arc with collimator 60° and a two single arcs with collimator setting of 15° and 345°. Conclusion The evaluation showed that double and full arcs are superior to single and partial arcs in terms of organs at risk sparing even for unilateral target volumes. The collimator position was found as an additional setup parameter, which can further improve the target coverage and sparing of organs at risk.}, language = {en} } @article{BratengeierHolubyevWegener2019, author = {Bratengeier, Klaus and Holubyev, Kostyantyn and Wegener, Sonja}, title = {Steeper dose gradients resulting from reduced source to target distance—a planning system independent study}, series = {Journal of Applied Clinical Medical Physics}, volume = {20}, journal = {Journal of Applied Clinical Medical Physics}, number = {1}, doi = {10.1002/acm2.12490}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-177424}, pages = {89-100}, year = {2019}, abstract = {Purpose: To quantify the contribution of penumbra in the improvement of healthy tissue sparing at reduced source-to-axis distance (SAD) for simple spherical target and different prescription isodoses (PI). Method: A TPS-independent method was used to estimate three-dimensional (3D) dose distribution for stereotactic treatment of spherical targets of 0.5 cm radius based on single beam two-dimensional (2D) film dosimetry measurements. 1 cm target constitutes the worst case for the conformation with standard Multi-Leaf Collimator (MLC) with 0.5 cm leaf width. The measured 2D transverse dose cross-sections and the profiles in leaf and jaw directions were used to calculate radial dose distribution from isotropic beam arrangement, for both quadratic and circular beam openings, respectively. The results were compared for standard (100 cm) and reduced SAD 70 and 55 cm for different PI. Results: For practical reduction of SAD using quadratic openings, the improvement of healthy tissue sparing (HTS) at distances up to 3 times the PTV radius was at least 6\%-12\%; gradient indices (GI) were reduced by 3-39\% for PI between 40\% and 90\%. Except for PI of 80\% and 90\%, quadratic apertures at SAD 70 cm improved the HTS by up to 20\% compared to circular openings at 100 cm or were at least equivalent; GI were 3\%-33\% lower for reduced SAD in the PI range 40\%-70\%. For PI = 80\% and 90\% the results depend on the circular collimator model. Conclusion: Stereotactic treatments of spherical targets delivered at reduced SAD of 70 or 55 cm using MLC spare healthy tissue around the target at least as good as treatments at SAD 100 cm using circular collimators. The steeper beam penumbra at reduced SAD seems to be as important as perfect target conformity. The authors argue therefore that the beam penumbra width should be addressed in the stereotactic studies.}, language = {en} }