Ulla Ramm

Three-dimensional BANG gel dosimetry in conformal carbon ion radiotherapy.

In this study we applied BANG polymer-gel dosimetry using magnetic resonance imaging (MRI) to densely ionizing radiation such as carbon ion beams. BANG polymer gels were irradiated with a quadratic field of monoenergetic 12C ions at different beam energies in the range of 135 MeV u(-1) to 410 MeV u(-1). They were irradiated at the radiotherapy facility of the GSI, Darmstadt, Germany. Our object was to examine the saturation effect for densely ionizing radiation that occurs at high values of linear energy transfer (LET). The examination yielded the first effectiveness values that will be discussed in the following sections. A solid sphere and a hollow sphere were both irradiated with a horizontal pencil beam from the raster scanning facility at energies of 268 MeV u(-1) (solid sphere) and 304 MeV u(-1) (hollow sphere) respectively. MR dosimetry measurements were compared with data from a planning system. As far as quality is concerned, there is good agreement between the measured dose distributions of both samples and the dose maps from the planning software. The measured MR signals cannot be converted into absolute dose, since the relative efficiency is still unknown for mixed radiation fields of primary carbon ions and it is known only to a limited extent for nuclear fragments with different energies from highly energetic photon radiation. Model calculations are in progress in order to facilitate conversions of measured MR signals into dose.

Influence of CT contrast agents on dose calculations in a 3D treatment planning system

In treatment planning for conformal radiotherapy, it is possible to attain high accuracy in contouring the outline of the target volume and organs at risk by giving contrast agents (CAs) during the CT scan. In order to calculate the dose from the CT scans, Hounsfield units (HUs) are converted into the parameters of a standard set of tissues with given atomic composition and density. Due to the high atomic number of contrast media, high HU values are obtained during CT scanning. The Helax treatment planning system, for instance, erroneously takes them for high density tissue. This misinterpretation results in high absorption of high-energy photon beams and thus affects the dose calculation significantly. A typical bolus diameter of 3 cm and HU values of 1,400 cause an overdose of up to 7.4% and 5.4% for 6 MV and 25 MV photon beams, respectively. However, since the CA concentration and its expansion are rather low the effect on dose calculation in treatment planning is negligible.

VerstÄrkung der radiotherapeutischen wirkung auf HeLa-Zellen durch gemcitabine

HintergrundDas difluorierte Deoxycytidinderivat Gemcitabine (dFdC) ist ein neues Nukleosidanalogon, das in vivo und in vitro bei soliden Tumoren zytotoxisch wirkt. In Untersuchungen mit Pankreas- und Kolonkarzinomzellinien wurde ein radiosensibilisierender Effekt von dFdC beschrieben. Ziel unserer Untersuchung war die überprüfung dieses Effekts an Plattenepithelkarzinomzellen der Zervix (HeLa-Zellen, ATCC CCL-2).Material und MethodenUnter standardisierten Bedingungen wurden HeLa-Zellen in Monolayer-Kulturen mit dFdC in unterschiedlicher Konzentration (0,003, 0,01 und 0,03 umol/1) und Expositionszeit (vier bis 24 Stunden) inkubiert. Die nachfolgende Bestrahlung erfolgte mit 2 bis 6 Gy unmittelbar bzw. zwölf Stunden nach durchgeführter Gemcitabine-Exposition. Das Zellüberleben wurde im Koloniebildungstest evaluiert. Die Zeilüberlebenskurven wurden nach Korrektur der chemotherapeutischen ZytotoxizitÄt unter Anwendung des linearquadratischen Modells erstellt, um die mittlere Inaktivierungsdosis (MID) berechnen zu können. Eine RadiotherapieverstÄrkung war definiert als VerhÄltnis MIDRT(=Kontrolle)/MIDRT+dFdc > 1.ErgebnisseNach vier-bzw. achtstündiger Gemcitabine-Exposition und unmittelbar nachfolgender Bestrahlung errechnet sich bei einer dFdC-Dosis von 0,01 und 0,03 Μmol/l eine VerstÄrkung der radiotherapeutischen Wirkung um den Faktor 1,07 und 1,14 bzw. 1,04 und 1,22. Bei einer 16-bzw. 24stündigen dFdC-Exposition zeigt sich eine weitere Steigerung des Bestrahlungseffekts bereits für dFdC-Konzentrationen von > - 0,003 bis 0,03 umol/1 (Faktor 1,08 bis 2,0 bzw. 1,08 bis 2,48). Wird erst zwölf Stunden nach einer 24stündigen dFdC-Exposition (0,01 bzw. 0,03 umol/1) bestrahlt, betrÄgt der VerstÄrkungsfaktor 1,18 bzw. 1,7.Schlu\folgerungenDie In-vitro-Untersuchungen an HeLa-Zellen weisen dFdC als potenten Radiosensitizer aus. Die Wirkung der auf die Gemcitabine-Exposition nachfolgenden Radiotherapie wird durch die nicht bzw. kaum zytotoxischen dFdC-Konzentrationen dosis- und zeitabhÄngig verstÄrkt.AbstractBackgroundGemcitabine (21).21-difluorodeoxycytidine; dFdC) is a new nucleoside analog with promising activity in different solid tumors in vivo and in vitro. As published up to now, combined with irradiation dFdC demonstrates a radio-sensitizing effect on pancreas and colon carcinoma cell lines. We investigated the influence of dFdC on the radiosensitization of human squamous carcinoma cells of the cervix (HeLa-cells, ATCC CCL-2).Material and MethodsUnder standardized conditions monolayer cultures of HeLa-cells were incubated in medium with dFdC for different times (4 to 24 hours) and exposed to different concentrations (0.003, 0.01 and 0.03 umol/1). Irradiation (2 to 6 Gy, electron beam) followed immediately or 12 hours after dFdC-exposure. Cell survival was determined by colony forming assay. Using the linear-quadratic model cell survival curves were fit after correction for drug-induced cytotoxicity and the mean inactivation dose (MID) was calculated. Radiation enhancement was defined as the ratio MIDRT(=Control)/MIDRT+dFdC > 1.ResultsExposed to gemcitabine for 4 and 8 hours and followed by immediate irradiation the radiation enhancement ratio (Table 1) is 1.07 to 1.14 and 1.04 to 1.22, respectively, if dFdC concentration is > 0.01 to 0.03 umol/1. Further increase of the irradiation effect is demonstrated in cells exposed to > 0.003 to 0.03 imol/l dFdC for 16 and 24 hours (radiation enhancement ratio 1.08 to 2.0 and 1.08 to 2.48, respectively) (Figure 3). If irradiation is applied 12 hours after 24-hour-exposure (0.01 and 0.03 umol/1) the enhancement ratio was 1.18 and 1.7, respectively (Figure 4).ConclusionsIn cell cultures the assays combining irradiation with dFdC demonstrate that dFdC is a potent radiation sensitizer of HeLa-cells. The effect of irradiation on cells pre-treated with non- and hardly cytotoxic concentrations of dFdC is increased in dependence of dose and time of exposure.

Out-of-field dose studies with an anthropomorphic phantom: Comparison of X-rays and particle therapy treatments

BACKGROUND AND PURPOSE Characterization of the out-of-field dose profile following irradiation of the target with a 3D treatment plan delivered with modern techniques. METHODS An anthropomorphic RANDO phantom was irradiated with a treatment plan designed for a simulated 5 × 2 × 5 cm(3) tumor volume located in the center of the head. The experiment was repeated with all most common radiation treatment types (photons, protons and carbon ions) and delivery techniques (Intensity Modulated Radiation Therapy, passive modulation and spot scanning). The measurements were performed with active diamond detector and passive thermoluminescence (TLD) detectors to investigate the out-of-field dose both inside and outside the phantom. RESULTS The highest out-of-field dose values both on the surface and inside the phantom were measured during the treatment with 25 MV photons. In the proximity of the Planned Target Volume (PTV), the lowest lateral dose profile was observed for passively modulated protons mainly because of the presence of the collimator in combination with the chosen volume shape. In the far out-of-field region (above 100mm from the PTV), passively modulated ions were characterized by a less pronounced dose fall-off in comparison with scanned beams. Overall, the treatment with scanned carbon ions delivered the lowest dose outside the target volume. CONCLUSIONS For the selected PTV, the use of the collimator in proton therapy drastically reduced the dose deposited by ions or photons nearby the tumor. Scanning modulation represents the optimal technique for achieving the highest dose reduction far-out-of-field.

In Vivo Dosimetry with Semiconducting Diodes for Dose Verification in Total-Body Irradiation

Background and Purpose:For total-body irradiation (TBI) using the translation method, dose distribution cannot be computed with computer-assisted three-dimensional planning systems. Therefore, dose distribution has to be primarily estimated based on CT scans (beam-zone method) which is followed by in vivo measurements to ascertain a homogeneous dose delivery. The aim of this study was to clinically establish semiconductor probes as a simple and fast method to obtain an online verification of the dose at relevant points.Patients and Methods:In 110 consecutively irradiated TBI patients (12.6 Gy, 2 × 1.8 Gy/day), six semiconductor probes were attached to the body surface at dose-relevant points (eye/head, neck, lung, navel). The mid-body point of the abdomen was defined as dose reference point. The speed of translation was optimized to definitively reach the prescribed dose in this point. Based on the entrance and exit doses, the mid-body doses at the other points were computed. The dose homogeneity in the entire target volume was determined comparing all measured data with the dose at the reference point.Results:After calibration of the semiconductor probes under treatment conditions the dose in selected points and the dose homogeneity in the target volume could be quantitatively specified. In the TBI patients, conformity of calculated and measured doses in the given points was achieved with small deviations of adequate accuracy. The data of 80% of the patients are within an uncertainty of ± 5%.Conclusion:During TBI using the translation method, dose distribution and dose homogeneity can be easily controlled in selected points by means of semiconductor probes. Semiconductor probes are recommended for further use in the physical evaluation of TBI.Hintergrund und Ziel:Die Dosisverteilung bei Ganzkörperbestrahlung (TBI) mit Translationstechnik lässt sich in der klinischen Routine bisher nicht mit computergestützten dreidimensionalen Planungssystemen berechnen. Die notwendige Kontrolle der auf der Basis von CT-Daten mit Hilfe von Abschätzverfahren manuell berechneten Dosisverteilung (Feldzonenverfahren) lässt sich nur mittels In-vivo-Messungen durchführen, um eine homogene Dosisverteilung abzusichern. Ziel dieser Studie war es, Halbleitersonden als eine einfache und schnelle Methode zu etablieren, um eine Onlineverifikation an relevanten Punkten zu ermöglichen.Patienten und Methodik:Bei 110 konsekutiv bestrahlten TBI-Patienten (12,6 Gy, 2 × 1,8 Gy/Tag) wurden sechs Halbleitersonden an dosisrelevanten Punkten der Körperoberfläche (Auge/Kopf, Hals, Lunge, Bauchnabel) befestigt. Der Punkt in der Abdomenmitte wurde als Dosisreferenzpunkt definiert. Die Translationsgeschwindigkeit wurde derart optimiert, dass an diesem Punkt die vorgeschriebene Herddosis erreicht wurde. Basierend auf der Eintritts- und Austrittsdosis an den jeweils anderen Punkten wurde die Dosis in der dortigen Körpermitte berechnet. Die Dosishomogenität im gesamten Zielvolumen wurde durch den Vergleich der einzelnen Messwerte mit der Dosis am Referenzpunkt ermittelt.Ergebnisse:Nach Kalibrierung der Halbleitersonden unter Bestrahlungsbedingungen konnten die Dosis in ausgewählten Punkten und die Dosishomogenität im Zielvolumen quantitativ angegeben werden. Dosismessungen während der TBI zeigten eine Übereinstimmung der erwarteten und der gemessenen Dosis mit Abweichungen in den untersuchten Punkten mit hinreichender Genauigkeit. Die Daten zeigen für 80% der Patienten eine Unsicherheit von weniger als ± 5%.Schlussfolgerung:Mit Halbleitersonden können in der klinischen Routine mit geringem Aufwand die Dosis während der Translations-TBI in ausgewählten Punkten gemessen und die Dosishomogenität im Zielvolumen überprüft werden. Daher bieten sich Halbleitersonden für die physikalische Überprüfung der TBI an.

Simple Proposal for Dosimetry with an Elekta iViewGTTM Electronic Portal Imaging Device (EPID) Using Commercial Software Modules

Background:An electronic portal imaging device (EPID) is used to control for patient setup and positioning during fractionated radiotherapy. Due to the rising complexity and conformity of irradiation techniques, the demand for an accurate verification of the dose delivered to the patient has also increased. The purpose of this study was to investigate a simple guidance for dosimetry with an Elekta iViewGTTM EPID using commercial software modules.Material and Methods:EPID measurements were performed using an Elekta iViewGTTM EPID on a linear accelerator with 6 MV x-ray beam. The EPID signal was studied for reproducibility, as well as characteristics as a function of dose, dose rate, and field size. A series of experiments, comparing the response of the flat panel imager and ionization chamber measurements of dose, determine the parameters for the calibration model. EPID measurements were also compared with calculations of the treatment planning system.Results:We found a stable response of the EPID signal over a period of 14 months. It showed nonlinearity depending on dose up to 6.8%. There were low oscillations up to 1.2% depending on dose rate. For all fields, the calibrated flat panel profiles match the measured and calculated dose profiles with maximum deviation of 2–3% for the in-field region. In the high gradient areas, higher differences up to 6% were found.Conclusions:The gamma evaluation indicates good correlation between predicted and acquired EPID images. The EPID-based pretreatment IMRT verification method will help to improve the quality assurance procedure.ZusammenfassungHintergrund:Ein Electronic Portal Imaging Device (EPID) wird zur Kontrolle der Positionierung und Lagerung des Patienten während der fraktionierten Strahlentherapie genutzt. Infolge der zunehmenden Komplexität und Konformität der Bestrahlungstechniken wächst auch die Forderung einer genauen Verifikation der am Patienten applizierten Dosis. Das Ziel dieser Untersuchungen war die Ausarbeitung einer einfachen Anleitung für die Dosimetrie mit einem Elekta iViewGTTM EPID mit kommerziellen Softwaremodulen.Material und Methode:Die Messungen wurden an einem Elektronenlinearbeschleuniger mit 6-MV-Photonenenergie der Firma Elekta, ausgestattet mit einem iViewGTTM EPID, durchgeführt. Die Reproduzierbarkeit sowie die Eigenschaften des EPID-Signals in Abhängigkeit von der applizierten Dosis, der Dosisleistung und der Feldgröße wurden untersucht. Eine Reihe von Experimenten, zum Vergleich des Ansprechvermögens des EPIDs und Dosismessungen mit einer Ionisationskammer, bestimmen die Parameter für das Modell zur Kalibrierung. Außerdem wurden die Messungen mit dem EPID mit Berechnungen des Bestrahlungsplanungssystems verglichen.Ergebnisse:Das EPID zeigt ein stabiles Ansprechvermögen über einen Zeitraum von 14 Monaten. Es wurde eine Nicht-Linearität in Abhängigkeit von der applizierten Dosis von bis zu 6,8% festgestellt. Geringe Abweichungen von maximal 1,2% ergaben sich in Abhängigkeit von der Dosisleistung. Für alle Felder stimmen die Ergebnisse für das kalibrierte EPID im Vergleich mit dem Bestrahlungsplanungssystem mit Abweichungen von maximal 2–3% innerhalb des Feldes überein. In Regionen mit hohen Dosisgradienten ergaben sich größere Abweichungen von bis zu 6%.Schlussfolgerung:Die Auswertung mit dem γ-Index ergibt eine gute Übereinstimmung der Ergebnisse, gemessen mit dem EPID im Vergleich zum Bestrahlungsplanungssystem. Die Verifikation der IMRT-Dosisverteilung mit dem EPID wird die Qualitätssicherung verbessern.

In vivo dose increase in the presence of dental alloys during 60Co-gamma-ray therapy of the oral cavity

During irradiation of the mouth cavity, dental metallic materials emit secondary electrons and thus increase the applied radiation dose in their vicinity. Therefore, local destruction of the mucous membrane contacting metallic dental crowns and fillings may be observed. Available data on this dose increase are based on measurements with beam arrangements perpendicular to the metallic surface. Since the dose modification depends on the beam direction in relation to specimen surface, a reliable prediction of dose modification in the close vicinity of dental caps on fillings under complex beam arrangements, as applied in the irradiation of head and neck region from the published data is not possible. Therefore, we measured dose increase in the immediate surrounding of metallic dental material using thermoluminescence dosimetry on the phantom and during routinely applied 60Co gamma ray therapy. Phantom measurements were carried out using several oblique irradiation angles and rotational therapy. In vivo measurements were carried out at alloy specimens containing gold, palladium, and amalgam in six patients and at permanently fixed golden teeth in five patients. In vivo, the following relative dose increase values according to a simultaneously measured reference value were obtained at the surface of different dental materials: 61% for fixed golden caps. 68% for the specimen containing gold, 33% for the specimen of palladium and 61% for the specimen of amalgam. The measured dose increases due to metallic dental material during routinely applied external 60Co beam irradiation are lower compared with those of perpendicular beam arrangements. Although, the extent of dose modification is less than expected, we still advocate protection of the oral mucosa to prevent painful lesion spots.

INCREASE OF SURFACE DOSE USING WOUND DRESSINGS DURING PERCUTANEOUS RADIOTHERAPY WITH PHOTONS AND ELECTRONS

Different wound dressings are used for the supportive treatment of patients with radiation-induced skin lesions. Depending on beam quality and energy, an increase of the dose administered to the skin and thus an aggravated skin reaction is to be expected during percutaneous irradiation. The increase of the skin dose during irradiation with photons (Co60, 6 MV, 42 MV) and electrons (7 MeV, 20 MeV, 42 MeV) was determined using thermoluminescence dosimetry. The use of wound dressings during electron irradiation and during soft irradiation therapy does not significantly increase the dose administered to the skin and does not therefore cause any problems. During irradiation with high energy photons only extremely thin dressings should be used; if there is an aggravated skin reaction, the dressing should be taken off before irradiation commences.

High resolution ion chamber array delivery quality assurance for robotic radiosurgery: Commissioning and validation.

PURPOSE High precision radiosurgery demands comprehensive delivery-quality-assurance techniques. The use of a liquid-filled ion-chamber-array for robotic-radiosurgery delivery-quality-assurance was investigated and validated using several test scenarios and routine patient plans. METHODS AND MATERIAL Preliminary evaluation consisted of beam profile validation and analysis of source-detector-distance and beam-incidence-angle response dependence. The delivery-quality-assurance analysis is performed in four steps: (1) Array-to-plan registration, (2) Evaluation with standard Gamma-Index criteria (local-dose-difference⩽2%, distance-to-agreement⩽2mm, pass-rate⩾90%), (3) Dose profile alignment and dose distribution shift until maximum pass-rate is found, and (4) Final evaluation with 1mm distance-to-agreement criterion. Test scenarios consisted of intended phantom misalignments, dose miscalibrations, and undelivered Monitor Units. Preliminary method validation was performed on 55 clinical plans in five institutions. RESULTS The 1000SRS profile measurements showed sufficient agreement compared with a microDiamond detector for all collimator sizes. The relative response changes can be up to 2.2% per 10cm source-detector-distance change, but remains within 1% for the clinically relevant source-detector-distance range. Planned and measured dose under different beam-incidence-angles showed deviations below 1% for angles between 0° and 80°. Small-intended errors were detected by 1mm distance-to-agreement criterion while 2mm criteria failed to reveal some of these deviations. All analyzed delivery-quality-assurance clinical patient plans were within our tight tolerance criteria. CONCLUSION We demonstrated that a high-resolution liquid-filled ion-chamber-array can be suitable for robotic radiosurgery delivery-quality-assurance and that small errors can be detected with tight distance-to-agreement criterion. Further improvement may come from beam specific correction for incidence angle and source-detector-distance response.

Silicon Diodes as an Alternative to Diamond Detectors for Depth Dose Curves and Profile Measurements of Photon and Electron Radiation

Background:Depth dose curves and lateral dose profiles should correspond to relative dose to water in any measured point, what can be more or less satisfied with different detectors. Diamond as detector material has similar dosimetric properties like water. Silicon diodes and ionization chambers are also commonly used to acquire dose profiles.Material and Methods:The authors compared dose profiles measured in an MP3 water phantom with a diamond detector 60003, unshielded and shielded silicon diodes 60008 and 60012 and a 0.125-cm3 thimble chamber 233642 (PTW, Freiburg, Germany) for 6- and 25-MV photons. Electron beams of 6, 12 and 18 MeV were investigated with the diamond detector, the unshielded diode and a Markus chamber 23343.Results:The unshielded diode revealed relative dose differences at the water surface below +10% for 6-MV and +4% for 25-MV photons compared to the diamond data. These values decreased to less than 1% within the first millimeters of water depth. The shielded diode was only required to obtain correct data of the fall-off zones for photon beams larger than 10 × 10 cm2 because of important contributions of low-energy scattered photons. For electron radiation the largest relative dose difference of –2% was observed with the unshielded silicon diode for 6 MeV within the build-up zone. Spatial resolutions were always best with the small voluminous silicon diodes.Conclusion:Relative dose profiles obtained with the two silicon diodes have the same degree of accuracy as with the diamond detector.Hintergrund:Tiefendosiskurven und Dosisquerprofile sollten in allen Messpunkten der relativen Wasserenergiedosis entsprechen, was mit verschiedenen Messsonden mehr oder weniger gut erreicht wird. Diamantsonden verhalten sich dosimetrisch fast wasseräquivalent. P-Typ-Siliciumdioden und Ionisationskammern werden ebenfalls häufig zur Messung von Dosisprofilen genutzt.Material und Methodik:In einem MP3-Wasserphantom wurden gemessene Tiefendosiskurven und Dosisquerprofile einer Diamantsonde 60003, je einer ungekapselten und einer gekapselten Si-Diode 60012 und 60008 und einer 0,125-cm3-Schlauchkammer 233642 (alle von PTW, Freiburg) für 6- und 25-MV-Photonenstrahlung verglichen. Elektronenfelder (6, 12 und 18 MeV) wurden mit der Diamantsonde, der ungekapselten Diode und einer Markus-Kammer 23343 untersucht.Ergebnisse:Bei Photonenstrahlung konnte für die ungekapselte Diode an der Wasseroberfläche eine Abweichung der relativen Tiefendosis im Vergleich zur Diamantsonde kleiner +10% bei 6 MV und kleiner +4% bei 25 MV festgestellt werden. Diese Abweichungen sanken bereits in einigen Millimetern Wassertiefe auf unter 1% ab. Die gekapselte Diode war ausschließlich für die korrekte Messung der abfallenden Bereiche von Tiefendosiskurven bei Feldern über 10 × 10 cm2 erforderlich, da die hier hohen Beiträge der niederenergetischen Streustrahlungsphotonen von Silicium überproportional stark absorbiert und registriert werden. Die maximal gemessene Abweichung der relativen Tiefendosis mit der ungekapselten Diode bei Elektronenstrahlung betrug –2% innerhalb der Aufbauzone bei 6 MeV. Bei allen untersuchten Strahlenarten übertraf das räumliche Auflösungsvermögen der kleinvolumigen Dioden das der Diamantsonde.Schlussfolgerung:Mit den beiden Dioden gemessene relative Dosisprofile sind vergleichbar genau wie die mit der Diamantsonde gemessenen.