Claudia Fellner

Bladder and rectum dose defined from MRI based treatment planning for cervix cancer brachytherapy: comparison of dose–volume histograms for organ contours and organ wall, comparison with ICRU rectum and bladder reference point

PURPOSE To analyze the correlation between dose-volume histograms based on organ contour and organ wall delineation for bladder and rectum, and to compare the doses to these organs with the absorbed doses at the ICRU bladder and rectum reference points. MATERIAL AND METHODS Individual MRI based brachytherapy treatment planning was performed in 15 patients as part of a prospective comparative trial. The external contours and the organ walls were delineated for the bladder and rectum in order to compute the corresponding dose-volume histograms. The minimum dose in 2 cm(3), 5 cm(3) and 10 cm(3) volumes receiving the highest dose were referred to as [D2], [D5] and [D10] and compared with the absorbed dose at the ICRU rectum and bladder reference point. RESULTS The bladder (bext) and rectal (rext) doses derived from external contours and computed for volumes of 2 cm(3) [D2], provided a good estimate for the doses computed for the organ walls (bw and rw) only (mean ratio [D2](bext)/[D2](bw)=1.1+/-0.2 and [D2](rext)/[D2](rw)=1.2+/-0.1, respectively). This correspondence was no longer true when larger volumes were considered (5 and 10 cm(3)). The dose at the ICRU rectum reference point did overestimate the dose computed for 2 cm(3) of the rectum wall (mean ratio: 1.5+/-0.4). In contrast, the dose at the ICRU bladder reference point did-in the case of inappropriate topographic location of the balloon-underestimate the dose computed for 2 cm(3) of the bladder wall (overall mean ratio: 0.9+/-0.4). CONCLUSION For clinical applications, when volumes smaller than 5 cm(3) are considered, the dose-volume histograms computed from external organ contours for the bladder and rectum can be used instead of dose-volume histograms computed for the organ walls only. External organ contours are indeed easier to obtain. The dose at the ICRU rectum reference point provides a good estimate of the rectal dose computed for volumes smaller than 2 cm(3) [D2] only for a midline position of the rectum. The ICRU bladder reference point provides a good estimate of the dose computed for the bladder wall [D2] only in cases of appropriate balloon position.

The impact of sectional imaging on dose escalation in endocavitary HDR-brachytherapy of cervical cancer: results of a prospective comparative trial

PURPOSE The purpose of this comparative prospective study was to assess the effect of CT and MR based individualisation and adaptation on the dose distribution in the target volume and organs at risk compared to a radiography based procedure. MATERIAL AND METHODS In 15 patients MR scans, in 10 patients additional axial CT-scans with compatible tube-ring applicator in situ were performed and digitally transferred to the PLATO(R) planning system. Considering clinical examination and MR-scan before radiotherapy individual 3-D dose distribution was calculated and adapted based on (1) two orthogonal radiographs; (2) isodoses superimposed on the CT images; and (3) isodoses superimposed on the MR images. Adaptation was strictly limited by the dose level at 2 cm(3) bladder or rectum volume (D(2)) to allow comparison of CT and MR plans. All three individualised dose distributions were superimposed on the MR images and cumulative dose-volume histograms were calculated for comparison. RESULTS 3-D individualisation based on sectional imaging enabled higher dose to the target volume (isodose enclosing 95% of the CTV=CTV(95)) compared to individualised treatment plans based on orthogonal radiographs by a mean factor of 1.2 (1-1.7). The dose to bladder and/or rectum wall was at the same time not increased beyond the prescribed tolerance level (71% of the prescribed target dose). In a subgroup of 10 patients MRI based treatment plans were superior to CT based treatment plans allowing for a higher dose (138% vs. 124%). CONCLUSION Sectional imaging based treatment planning, in particular using MR, was superior to radiography allowing for a clinical meaningful dose escalation without increasing the dose to bladder and rectum beyond the tolerance level.

Definitive radiotherapy based on HDR brachytherapy with iridium 192 in uterine cervix carcinoma: report on the Vienna University Hospital findings (1993–1997) compared to the preceding period in the context of ICRU 38 recommendations

UNLABELLED According to the reports described in the literature, fractionated HDR brachytherapy seems to represent one option for the primary treatment of cervical carcinoma. In order to render such treatment transparent and comparable for those interested in the field, we have attempted to report our recent experience obtained in Vienna from 1993-1997 using the terminology proposed by the ICRU report 38, focusing in particular on dose and volume reporting and a linear-quadratic model. Based on these parameters, a comparison with the preceding period in Vienna (LDR/HDR) has been made, with an attempt to correlate different methods and parameters with outcome. MATERIAL AND METHODS One hundred and eighty-nine patients (mean age 67 years) were treated with curative intent (stage Ia: 2, Ib: 11, IIa: 11, IIb: 79, IIIa: 19, IIIb: 59, IVa: 5, IVb: 3 patients) using a combination of intracervical high-dose rate (HDR) brachytherapy (ring-tandem applicator) and a box technique for external-beam therapy (EBT: 48.6-50 Gy, linac 25 MV). Small tumors were treated with 5-6 fractions of 7 Gy at point A and 50 Gy EBT (25 Gy in the brachytherapy reference volume) which is isoeffective to 76-86 Gy at point A. Large tumors received 3-4 fractions of 7 Gy after 50 Gy EBT with open fields, which is isoeffective to 82-92 Gy at point A. TRAK varied from mean 1.4 cGy (3 fractions) to 2.8 cGy (6 fractions) at one meter. 3-D treatment planning for brachytherapy was based on conventional X-rays and in 181/189 patients on computed tomography (CT) with the applicator in place. Computer-calculated volumes of the brachytherapy reference isodose (7 Gy/fraction) ranged from 46-155 ccm (mean 87 ccm); the respective mean hwt-volume (height x width x thickness) was 180 ccm. The 60 Gy HWT volumes (25 Gy from EBT) for the irradiation of small tumors ranged from 240 to 407 ccm (mean 337 ccm) and for larger tumors (50 Gy for EBT) from 452 to 785 ccm (mean 607 ccm). The mean dose for brachytherapy was 16.2 Gy (6.2-37.8 Gy) at the ICRU rectum reference point and 14.4 Gy (4.6-35.7 Gy) at the ICRU bladder point. Taking into account the dose for EBT, the mean isoeffective dose at the ICRU rectum reference point was 69.9 Gy (28.4-98.7 Gy). Overall treatment time was six weeks for small tumors and eight weeks for large tumors. RESULTS After a mean follow-up of 34 months, actuarial pelvic control and disease-specific survival rates at three years were 77.6/68.6% for all patients, 100/77.1% for stage Ib, 100/100% stage IIa, 87.0/78.0% stage IIb, 52.7/52.1% stage IIIa, 69.1/58.6% stage IIIb and 60/53.3% stage IVa. According to the LENT/SOMA score which had been prospectively introduced, the actuarial late complication rate for grades 3 and 4 was 2.9% for the bladder, 4.0% for the bowel, 6.1% for the rectum and 30.6% for the vagina (shortening and obliteration); in total for all grades 23.6, 18.4, 24.2, and 67.6%, respectively. CONCLUSION In our experience, HDR brachytherapy combined with EBT is an efficient method if sufficient radiation doses and volumes are applied, both with regard to tumor control and adverse side effects. In future, the therapeutic window will be increased by systematic integration of magnetic resonance imaging (MRI) into treatment planning, thus allowing for a highly individualized approach with further adaptation of radiation dose and volume both to the target and to the individual topography of organs at risk.

High-dose-rate (HDR) brachytherapy with or without external beam radiotherapy in the treatment of primary vaginal carcinoma: Long-term results and side effects

PURPOSE To report toxicity, prognostic factors, and outcome of HDR brachytherapy in the primary management of vaginal carcinoma. METHODS AND MATERIALS A total of 86 patients receiving radiotherapy for primary vaginal carcinoma were analyzed. FIGO stages 0-IV were found in 6, 17, 38, 20, and 5 patients, respectively. Early stages of disease (Stages 0-II) were treated with intravaginal HDR brachytherapy alone (n = 26/86), whereas locally advanced diseases (Stages II-IV) received HDR brachytherapy combined with external beam therapy (n = 55/86). Teletherapy only was used in 5 of 86 cases, all of which were treated with palliative intent (i.e., advanced stage, poor general status). Recurrence-free intervals as well as overall- and disease-specific survival rates were determined for all patients. Frequencies of side effects and the influence of prognostic factors and treatment modalities on outcome were analyzed. RESULTS Five-year overall survival rates for Stages 0-IV diseases were 83%, 41%, 43%, 37%, and 0%, respectively. Corresponding 5-year disease-specific survival rates were 100%, 92%, 57%, 59%, and 0%. Regarding 5-year recurrence-free intervals, values of 100%, 77%, 50%, 23%, and 0% (Stages 0-IV) were found, respectively. Tumor stage was the most significant prognostic factor. Chronic side effects G 1-4 were observed in <or=2% (bladder, rectum) and 1%-6% (vagina). CONCLUSION In the treatment of primary vaginal carcinoma, HDR brachytherapy appeared to be well-tolerated and as effective as LDR brachytherapy techniques.

The benefit of Beam's eye view based 3D treatment planning for cervical cancer

PURPOSE The aim of this study was to evaluate the possibility of Beams eye view (BEV) based three dimensional (3D) treatment planning, to reduce portions of organs at risk included in the treated volume without increasing the risk of geographical miss in external beam therapy of cervical cancer. MATERIALS AND METHODS Three dimensional dose distribution of BEV based 3D treatment plans was compared to the 3D dose distribution derived from a four-field-box-technique using standard portals. A total of 20 patients with cervical cancer stage FIGO IIB and FIGO IIIB was included. Dose distribution in the target volumes and in the organs at risk of BEV based treatment planning, was compared to the dose distribution of the standard field technique using dose-volume-histograms. RESULTS In 4/20 patients (20%) a geographical miss at the cervix uteri was observed for the standard field technique. The BEV based treatment planning resulted in an adequate coverage of target volume and additionally in a reduction of portions of bladder and bowel volume included in the treated volume (-13.5, -10%). In contrast the BEV based technique resulted in an increase of portions of the rectum volume included in the treated volume compared to standard portals due to a shift of the rectum by the enlarged cervix uteri from its posterior to a lateral position. An overall 7% reduction of treated volume was observed, although the maximum width of lateral fields increased for the BEV technique. Moreover, we have found a remarkable impact of bladder fillings on the amount of bowel and bladder volume included in the treated volume. CONCLUSION BEV based 3D treatment planning for external beam therapy of cervical cancer offers a possibility to avoid geographical miss of part of the CTV with reduced portions of bladder and bowel volume included in the treated volume.

Vergleich der CT-gestützten 3D-planung mit der simulatorplanung bei der beckenbestrahlung des primÄren zervixkarzinoms

HintergrundBei der Standardsimulatorplanung der Beckenbestrahlung anhand knöcherner Referenzstrukturen beim primÄren Zervixkarzinom kann es in Unkenntnis der individuellen anatomischen Situation bei einigen Patientinnen zu einem topographischen Verfehlen des Tumors oder der potentiellen Tumorausbreitung kommen. Es stellt sich die Frage, ob für Patientinnen mit dieser Indikation der erhöhte zeitliche und personelle Aufwand für die routinemÄ\ige 3D-Bestrahlungsplanung im Vergleich zur Simulatorplanung gerechtfertigt ist.Patienten und MethodeIm Rahmen einer prospektiven Studie wurde bei 20 aufeinanderfolgenden Patientinnen mit primÄren Zervixkarzinomen der Stadien I bis III zunÄchst eine Simulatorplanung einer Vier-Felder-Box-Technik durchgeführt. Nach erfolgter Definition des Planungszielvolumens im 3D-Planungssystem wurden die Feldkonfigurationen der Simulatorplanung in den Rechner übertragen und der resultierende Bestrahlungsplan sowie ein individueller Bestrahlungsplan auf Basis des definierten Planungszielvolumens erstellt. Es erfolgte eine qualitative Auswertung der Simulatorplanung hinsichtlich möglichem “geographical miss” und Erfassung des Planungszielvolumens durch das behandelte Volumen (gemÄ\ ICRU). Berechnet wurden im Vergleich beider Planungstechniken die Volumina der offenen und der geformten Felder.ErgebnisseNach Simulatorplanung fand sich ein “geographical miss” und in weiteren zehn FÄllen eine nicht adÄquate Erfassung des Planungszielvolumens durch das behandelte Volumen. Bei einem Planungszielvolumen von im Mittel 1729 cm3 betrugen die bei der Simulatorplanung definierten Volumina im Mittel 3 120 cm3 für die offenen Felder im Mittel 2 702 cm3 für die geformten Felder. Die Volumenreduktion durch Ausblockung betrug im Mittel 13,4%. Bei der CT-gestützten 3D-Bestrahlungsplanung vergrö\erte sich das Volumen der offenen Felder im Mittel um 3,3% auf 3 224 ccm. Die resultierenden Volumina der geformten Felder betrugen im Mittel 2 458 cm3. Die Reduktion gegenüber den offenen Feldern betrug im Mittel 23,8%. Die Reduktion der behandelten Volumina betrug im Vergleich zur Simulatorplanung im Mittel 244 cm3 (9%). Der Quotient “behandeltes Volumen/Planungszielvolumen” verringerte sich von 1,59 auf 1,42.Schlu\folgerungIn unserer Erfahrung ist die Einführung der 3D-Bestrahlungsplanung bei der Beckenbestrahlung des Zervixkarzinoms zunÄchst als Ma\nahme zur QualitÄtssicherung zu empfehlen. Eine Reduktion des behandelten Volumens ist möglich; inwieweit dies bereits zu einer Verringerung der Komplikationsraten führen kann, ist derzeit nicht abschÄtzbar.AbstractBackgroundUsing standardized simulator planning guided by bony landmarks for pelvic irradiation of primary cervical carcinoma with some patients a geographical miss regarding tumor or potential tumorspread can happen because of insufficient knowledge of the individual anatomical situation. The question arises whether for patients with this indication the higher effort in terms of time and personnel for 3D treatment planning is justified.Patients and MethodIn a prospective study on 20 subsequent patients with primary cervical carcinoma in Stages I to III simulator planning of a 4-field box-technique was performed. After defining the planning target volume (PTV) in the 3D planning system the field configuration of the simulator planning was transmitted. The resulting plan was compared to a second one based on the defined PTV and evaluated regarding a possible geographical miss and encompassment of the PTV by the treated volume (ICRU). Volumes of open and shaped portals were calculated for both techniques.ResultsPlanning by simulation resulted in 1 geographical miss and in 10 more cases the encompassment of the PTV by the treated volume was inadequate. For a PTV of mean 1 729 cm3 the mean volume defined by simulation was 3 120 cm3 for the open portals and 2 702 cm3 for the shaped portals (Figure 1). The volume reduction by blocks was 13.4% (mean). With CT-based 3D treatment planning the volume of the open portals was 3.3% (mean) enlarged to 3 224 cm3 (Figure 2). The resulting mean volume of the shaped portals was 2 458 ccm. The reduction compared to the open portals was 23.8% (mean). The treated volumes were 244 cm3 or 9% (mean) smaller compared to simulator planning. The “treated volume/planning target volume ratio” was decreased from 1.59 to 1.42.ConclusionThe introduction of 3D treatment planning for pelvic irradiation of cervical carcinoma is to be recommended for reasons of quality assurance. Reduction of the treated volume is possible but further research has to be done to determine whether the rate of complications can be decreased as well.

Possible impact of iridium-192 source centering on restenosis rate after femoro-popliteal angioplasty and endovascular brachytherapy in Vienna-2 study

PURPOSE Endovascular brachytherapy (EVBT) has been proven to significantly reduce restenosis after percutaneous transluminal angioplasty (PTA). The object of this analysis was to assess the possible correlation between iridium-192 source non-centering and angiographic-determined restenosis. MATERIALS AND METHODS A total of 113 patients with long-segment lesions of the superficial femoro-popliteal artery (SFA) were randomized to receive either PTA alone or PTA followed by EVBT in the Vienna-2 study. This analysis was performed on a subgroup of 34 out of 57 patients, who received PTA+EVBT. Angiographic restenosis was defined as lumen reduction of more than 50%. Angiograms taken immediately after PTA (34 patients) and at follow-up (25 patients) were analyzed. The distance between the vessel wall and the actual position of the source at the time of EVBT was measured (in mm) and correlated with the follow-up vessel lumen diameter. Measurements were performed at points at a distance of 10 mm from each other. The dose was determined at the luminal surface and at the reference depth of 2 mm into the vessel wall for different distances from the source. RESULTS Among the 622 measured points, 62 (10.0%) were within restenotic areas; 560 (90.0%) were in arterial segments without proven angiographic restenosis. As far as source centering is concerned, 7.9% of restenotic points were observed when the maximum distance to the arterial wall was <3 mm and 9.6% for 4 mm, respectively. The percentage of restenotic points increased up to 15.9% when the maximum distance to the arterial wall was 5 mm and reached 22.2% when it was >5 mm. CONCLUSIONS The proportion of restenotic points significantly increased with source non-centering. This observation was interpreted as being related to a decrease in dose at the target. When the maximum distance between the source and the vessel surface was >5 mm, the dose at the reference depth (2 mm into the vessel wall) decreased to values lower than 5 Gy.

Analyse unterschiedlicher Applikationsformen und CT-gestützter Planungsvarianten in der Behandlung primärer Endometriumkarzinome

ZusammenfassungHintergrundIn der Primärbehandlung des Endometriumkarzinoms bei inoperablen Patientinnen stellt die intrakorporale Brachytherapie einen wesentlichen Bestandteil dar. Bei häufig unklarer Tumorausdehnung betrachtet man hierbei den gesamten Uterus als zu behandelndes Zielvolumen. Im Rahmen dieser Analyse werden unterschiedliche Applikations-und Planungsvarianten des intrakavitären Afterloadings hinsichtlich der Korrelation zwischen Ziel- und Behandlungsvolumen vergleichend gegenübergestellt.Patienten und MethodeBei zehn aufeinanderfolgenden Patientinnen mit primär bestrahlten Endometriumkarzinomen wurden die Ziel- und Behandlungsvolumina bei Verwendung eines standardisierten Ein-Kanal-Applikators sowie individueller Heyman-Applikatoren bestimmt. Die Berechnung der individuellen Zielvolumina (Uterusvolumina) erfolgte am 3D-Planungssystem anhand der computertomographischen (CT) Aufnahmen mit liegenden Applikatoren. Analog der gemessenen Länge des Cavum uteri (Sondenlänge) wurde das entsprechende standardisierte Bestrahlungsprogramm mit resultierendem Behandlungsvolumen ermittelt. In bezug auf die individuellen Heyman-Applikationen wurden zwei unterschiedliche — als standardisiert bzw. optimiert bezeichnete — Planungsvarianten durchgeführt, um die Verbesserungsmöglichkeiten einer detaillierteren Planungsform zu ermitteln.ErgebnisseDas mittlere Uterusvolumen belief sich auf 180 cm3 (Streubreite 57 bis 316 cm3). In 40% der Fälle lag eine asymmetrische Uteruskonfiguration mit koronaren bzw. sagittalen Seitendifferenzen von mehr als 1 cm vor. Bei Verwendung eines standardisierten Ein-Kanal-Applikators wurden durchschnittlich 47% (Streubreite 25 bis 89%) des Uterusvolumens erfaßt. Im Vergleich hierzu betrug der entsprechende Durchschnittswert bei individueller Heyman-Applikation insgesamt 70% (Streubreite 36 bis 110%). Differenziert man dieses Ergebnis je nach durchgeführter Planungsform, so ergaben sich durchschnittlich 66% (Streubreite 36 bis 110%) bei der standardisierten sowie durchschnittlich 73% (Streubreite 48 bis 95%) bei der optimierten Variante. In bezug auf die individuellen Heyman-Applikationen konnte mittels optimierter Planungsform eine verbesserte Zielvoluminaerfassung in fünf von zehn Fällen erreicht werden, was mit einem Anstieg des Behandlungsvolumens um durchschnittlich 20% einherging (Streubreite 11 bis 32%). In drei Fällen ergaben sich Veränderungen des Behandlungsvolumens von weniger als 5% (keine Verbesserungen). In zwei Fällen wurde das Volumen zur Schonung der Risikoorgane um 19% bzw. 40% reduziert.SchlußfolgerungenIn der brachytherapeutischen Behandlung des primären Endometriumkarzinoms konnten durch Verwendung individualisierter Applikations- und Planungstechniken verbesserte Zielvoluminaerfassungen erreicht werden. Eine vollständige Erfassung des Uterus, was der eigentlichen Zielsetzung entspricht, war jedoch nicht möglich. Im Rahmen einer optimierten, brachytherapeutischen Behandlung erschein die Berücksichtigung der individuellen Tumorausdehnung bzw. Uteruskonfiguration erforderlich. In diesem Zusammenhang ist die Verwendung von entsprechend unterschiedlichen Applikatoren sicherlich notwendig.AbstractBackgroundIntracorporal brachytherapy is regarded as the definitive component of treatment for inoperable patients with endometrial carcinoma. Until now the whole uterus has been claimed to represent the target volume independent of individual tumor spread. The purpose of this work is to analyse the correlation between target volume and treated volume using different application- and planning procedures.Patients and MethodsIn a consecutive series of 10 patients with primary irradiated endometrial carcinoma we analyzed the correlation between target volume and treated volume using either standard 1-channel applicators or individual Heyman-applicators. Application of the ovoids was followed by a planning CT scan for all patients. Based on this, target volume (uterus volume) was estimated on a 3D-planning system. According to the measurable length of the uterus cavity we determined the corresponding standard 1-channel applicator and calculated the respectively treated volume. Estimating the advantages of an optimized treatment planning strategy for individual Heyman- applications we compared the treated volumes, which result from a standardized and optimized treatment planning procedure.Resultsthe mean uterus volume was 180 cm3 (range 57 to 316 cm3). Asymmetric uterus configurations with longitudinal or sagittal side differences exceeding 1 cm were found in 40% of the cases. Using standard 1-channel applicators on average 47% (range 25 to 89%) of the uterus volume were enclosed by the treated volume compared to 70% for Heymanapplications. Differentiating these individual applications according to the variable treatment modality values of mean 66% (range 36 to 110%) for the standardized and 73% (range 48 to 95%) for the optimized treatment planning strategy were found. Moreover optimized planning modalities led to an improved coverage of the target volume in 5 out of 10 cases with an increase in volume of 20% on average (range 11 to 32%). In 3 cases changes of less than 5% were noticed (no improvement). In order to protect organs at risk treated volume had to be decreased in 2 cases for 19% and 40% respectively.ConclusionsIntracavitary brachytherapy of primary endometrial carcinoma was improved by individualized application-and planning procedures, which led to better adaptations of the treated volumes to the target volumes. Nevertheless a complete coverage — corresponding to the primary intent — was not possible. Individualized and optimized brachytherapy must be performed according to the individual tumor spread and uterus configuration. Therefore, different applicators are required.BACKGROUND Intracorporal brachytherapy is regarded as the definitive component of treatment for inoperable patients with endometrial carcinoma. Until now the whole uterus has been claimed to represent the target volume independent of individual tumor spread. The purpose of this work is to analyse the correlation between target volume and treated volume using different application- and planning procedures. PATIENTS AND METHODS In a consecutive series of 10 patients with primary irradiated endometrial carcinoma we analyzed the correlation between target volume and treated volume using either standard 1-channel applicators or individual Heyman-applicators. Application of the ovoids was followed by a planning CT scan for all patients. Based on this, target volume (uterus volume) was estimated on a 3D-planning system. According to the measurable length of the uterus cavity we determined the corresponding standard 1-channel applicator and calculated the respectively treated volume. Estimating the advantages of an optimized treatment planning strategy for individual Heyman-applications were compared the treated volumes, which result from a standardized and optimized treatment planning procedure. RESULTS The mean uterus volume was 180 cm3 (range 57 to 316 cm3). Asymmetric uterus configurations with longitudinal or sagittal side differences exceeding 1 cm were found in 40% of the cases. Using standard 1-channel applicators on average 47% (range 25 to 89%) of the uterus volume were enclosed by the treated volume compared to 70% for Heyman-applications. Differentiating these individual applications according to the variable treatment modality values of mean 66% (range 36 to 110%) for the standardized and 73% (range 48 to 95%) for the optimized treatment planning strategy were found. Moreover optimized planning modalities led to an improved coverage of the target volume in 5 out of 10 cases with an increase in volume of 20% on average (range 11 to 32%). In 3 cases changes of less than 5% were noticed (no improvement). In order to protect organs at risk treated volume had to be decreased in 2 cases for 19% and 40% respectively. CONCLUSIONS Intracavitary brachytherapy of primary endometrial carcinoma was improved by individualized application- and planning procedures, which led to better adaptations of the treated volumes to the target volumes. Nevertheless a complete coverage--corresponding to the primary intent--was not possible. Individualized and optimized brachy-therapy must be performed according to the individual tumor spread and uterus configuration. Therefore, different applicators are required.

Berechnungsgenauigkeit von Volumina zur Evaluierung von Dosis-Volumen-Histogrammen

ZusammenfassungHintergrundModerne dreidimensionale Bestrahlungsplanungssysteme auf der Basis von Schnittbildern ermöglichen die Berechnung von Organvolumina. Ziel dieser Arbeit ist die systematische Untersuchung der Berechnungsgenauigkeit von Volumina mit Hilfe eines Phantoms bei vier verschiedenen Planungssystemen.Material und MethodeEs wurde ein Phantom mit fünf Zylindern und sechs Kugeln verschiedener Durchmesser konstruiert. Nach Anfertigung einer CT-Studie wurden die Daten in die verschiedenen Planungssysteme eingelesen und die Strukturen konturiert. Danach wurden die Volumina der Zylinder und Kugeln von den Systemen berechnet und ein Vergleich mit den nach mathematischen Formeln berechneten „Sollwerten” durchgeführt. Dieser Vergleich erfolgte als Funktion verschiedener Parameter.ErgebnisseGenerell hatte die Wahl der Methoden der Konturierung großen Einfluß auf die Ergebnisse. Hingegen zeigten Parameter wie Anzahl an Berechnungspunkten oder Länge der Zylinder keine signifikanten Unterschiede. Zusammenfassend waren die gemittelten Abweichungen für Zylinder +7% für System A, −2% für B, −17% für C und 0% für D. Für die größeren Kugeln (Radien zwischen 5 und 2,5 cm) ergaben sich gemittelte Abweichungen von −5% für A, +3% für B, +1% für C und +5% für D. Für die kleineren Kugeln (Radien zwischen 1,75 und 1,25 cm) ergaben sich gemittelte Abweichungen von −14% für A, −2% für B, −10% für C und −4% für D.SchlußfolgerungBei allen Ergebnissen ist die starke Abhängigkeit des Volumens von geringfügigen Änderungen im Radius zu berücksichtigen. Die Abweichungen werden auch durch die Ungenauigkeiten der gesamten Erfassung der Daten, der CT-Studie, der Berechnungsalgorithmen, der Abgrenzbarkeit der Struktur und der Erfaßbarkeit der geometrischen Abmessungen verusacht. Es zeigte sich, daß die Verifikation der Parameter eines Planungssystemes wichtig ist.AbstractBackgroundModern 3-dimensional treatment planning systems on the basis of sectional imaging allow the calculation of volumes for organs of interest. The aim of this study is to investigate systematically the accuracy of calculations of volumes by the use of a phantom for 4 different treatment planning systems.Material and MethodThe tests were done with a phantom with 5 cylindrical structures and 6 spherical shaped structures. After performing a CT-scan and reading the data into the planning systems the structures were contoured and the volumes were calculated in order to compare these values with the values calculated by mathematical equations. This was systematically done as a function of different parameters.ResultsComparing different methods of contouring showed notable influence on the result. Parameters as number of calculation points or length of cylinders showed no significant differences. In summary, the mean deviations for cylinders were +7% for system A, −2% for B, −17% for C, and 0% for D. For larger spheres (radii between 5 and 2.5 cm) the mean deviations were −5% for A, +3% for B, +1% for C, and +5% for D. For smaller spheres (radii between 1.75 and 1.25 cm) the mean deviations were −14% for A, −2% for B, −10% for C, and −4% for D.ConclusionVerifying results of planning systems is important for the daily routine, but it has to be taken into account, that small changes of the radius of a cylinder or sphere cause substantial volume changes. The differences are also caused by inaccuracies of the whole procedure, e. g., the CT study, the shape and dimensions of the cylinders and the spheres and the CT information and the delineariation of the structures.