Stefan Wachter

The influence of a rectal balloon tube as internal immobilization device on variations of volumes and dose-volume histograms during treatment course of conformal radiotherapy for prostate cancer

PURPOSE A prospective comparative study of a subset of 10 consecutive patients was performed, to describe the effects of an air-inflated rectal balloon tube that has been used for prostate immobilization in 360 patients since 1994. In particular, influences on prostate motion, rectum filling variations, and dose-volume histograms (DVHs) of the rectum during a course of conformal radiotherapy were investigated. METHODS AND MATERIALS Computed tomographic (CT) examinations without and with rectal balloon (filled with 40 mL air) were performed at the start (t(0)), middle (t(mi)), and end of treatment (t(e)), resulting in 6 CT scans for each patient. Prostate displacement was measured from a lateral beams-eye-view. DVHs of rectum as a solid organ, and anterior, posterior, and whole rectum wall were calculated at t(0), t(mi), and t(e), and variations during treatment were analyzed for both examinations, with and without balloon. RESULTS By use of the balloon, rectum filling variations (p = 0.04) and maximum anterior-posterior displacements of the prostate (p = 0.008) were reduced significantly, leading to a reduction in DVH variations during treatment. Maximum displacements of posterior prostate border (>5 mm) were found in 8/10 patients without a rectum balloon and in only 2/10 patients with the balloon. The balloon led to a significant reduction in partial posterior rectal wall volumes included in the high-dose regions, without significant changes at the anterior rectum wall in cases of irradiation of the prostate only. However, when entirely irradiating the whole seminal vesicles, this advantage was lost. CONCLUSIONS The rectal balloon catheter represents a simple technique to immobilize the prostate and to determine the position of the anterior rectal wall at daily treatment. This allows a reduction of margins, because of reduced prostate movement during treatment course.

Rectal sequelae after conformal radiotherapy of prostate cancer: dose-volume histograms as predictive factors.

PURPOSE To identify clinically relevant parameters predictive of late rectal bleeding derived from cumulative dose-volume histograms (DVHs) of the rectum after conformal radiotherapy of prostate cancer. MATERIALS AND METHODS One hundred and nine patients treated with 3D conformal radiotherapy between 1/1994 and 1/1996 for localized prostate cancer (clinical stage T1-T3) were available for analysis. All patients received a total dose of 66 Gy/2 Gy per fraction (specified at the International Commission on Radiation Units and Measurements ICRU reference point). DVHs of the contoured rectum were analyzed by defining the absolute (aV) and relative (rV) rectum volume that received more than 30% (V30), 50% (V50), 70% (V70), 80% (V80), 90% (V90) and 100% (V100) of the prescribed dose. Additionally, a new aspect of DVH analysis was investigated by calculation of the area under the DVH-curve between several dose levels (area under the curve (AUC)-DVH). DVH-variables were correlated with radiation side effects evaluated in 3-6 months intervals and graded according to the EORTC/RTOG score. The median follow-up was 30 months (12-60 months). RESULTS Univariate and multivariate stepwise Cox-Regression analysis including age, PTV, rectum size, rV100, rV90, rV80, rV70, rV50 rV30 and aV30 to aV100 were calculated. Late rectal bleeding (EORTC/RTOG grade 2) was significantly correlated with the percentage of rectum volume receiving > or = 90% of the prescribed dose (rV90) (P = 0.007) and inversely correlated in a significant way with the size of contoured rectum (P = 0.006) in multivariate analysis. In our series, a proportion of the rectum volume > or = 57% were included in the 90%-isodose (rV90 > or = 57%) in one half of the patients, with an actuarial incidence of 31% of late rectal bleeding at 3 years. In the other half of the patients, when rV90 < 57%, the 3-year actuarial incidence was 11% (P < 0.03). CONCLUSION Our data demonstrate a dose-volume relationship at the reference dose of 60 Gy ( approximately 90% of the prescribed dose) with respect to late rectal toxicity. The rV90 seems to be the most useful and easily obtained parameter when comparing treatment plans to evaluate the risk of rectal morbidity.

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.

Endoscopic scoring of late rectal mucosal damage after conformal radiotherapy for prostatic carcinoma

PURPOSE To describe rectal mucosal damage in an endoscopic study after conformal radiotherapy of prostate cancer and to correlate this with clinical outcome. MATERIALS AND METHODS Flexible rectosigmoidoscopy was performed on 44 patients who voluntarily accepted the examination. The median follow-up was 29 months (20-41 months) after 3-D-planned conformal radiotherapy of prostate cancer (66 Gy at the ICRU Reference point, 2 Gy per fraction). To enable a systematic topographic description of endoscopic findings the rectum was divided into four sections. Additionally we differentiated between anterior, posterior, right and left lateral rectal wall. Due to the lack of an existing valid graduation system for radiation induced proctitis, we introduced a six-scaled rectoscopy score for describing and reporting endoscopic findings based on the standardization of the endoscopic terminology published by the ESGE (European Society for Gastrointestinal Endoscopy). Endoscopic findings were compared to the EORTC/RTOG morbidity score. In addition, since 3-D dose distribution of organs at risks was available, a correlation could be made between the location of the rectal lesions and the absorbed dose at that level. RESULTS In general, endoscopic findings increased from the proximal rectum to the anorectal transition, as well as from the posterior to the anterior rectum wall. Telangiectasia grade 1 and 2 were observed at the whole circumference, only telangiectasia grade 3 were limited to the high dose region at the anterior rectum wall. Similar results were found for congested mucosa (reddening and edematous mucosa). Correlation with symptoms, 7/9 patients who suffered from intermittent rectal bleeding (EORTC/RTOG grade 2) had multiple telangiectasia grade 2-3 and/or congested mucosa grade 3 and microulcerations. However, the same extent of mucosal damage (rectoscopy score 2-3) was found in seven out of 35 patients who have never developed a period of macroscopic rectal bleeding. CONCLUSION Rectoscopy offers the possibility of detecting signs of tissue dysfunction below the level of subjective symptoms. Systematic analytic examinations such as rectoscopy, in addition to clinical examinations, as already foreseen in the LENT-SOMA-score, will be necessary due to the fact that even telangiectatic lesions have been observed for asymptomatic patients. For the opportunity of sharing and comparing data collected from endoscopy after radiotherapy a graduation system as proposed based on a standardisation of the endoscopic terminology will be necessary.

11C-Acetate Positron Emission Tomography Imaging and Image Fusion With Computed Tomography and Magnetic Resonance Imaging in Patients With Recurrent Prostate Cancer

PURPOSE To assess the clinical value of computed tomography (CT) and magnetic resonance imaging (MRI) image fusion with 11C-acetate (AC) positron emission tomography (PET) imaging for detection and exact location of clinically occult recurrences. PATIENTS AND METHODS Fifty prostate cancer patients with elevated/increasing serum prostate-specific antigen levels after radical therapy underwent whole-body AC PET. Uptake was initially interpreted as normal, abnormal, or equivocal. In case of abnormal or equivocal uptake, additional conventional imaging techniques, such as CT, MRI, and bone scans, were performed. To precisely define the anatomic location of abnormal uptake and to improve characterization of equivocal lesions, a software-assisted image fusion (CT-PET, MRI-PET) was performed and evaluated as site-by-site analysis of 51 abnormal (n = 37) or equivocal (n = 14) sites of all 50 patients. In 17 patients, additional histopathologic evaluation was available. RESULTS In five (10%), 13 (26%), and 32 (64%) of the 50 patients, AC PET studies demonstrated AC uptake judged as normal, equivocal, and abnormal, respectively. Image fusion changed characterization of equivocal lesions as normal in five (10%) of 51 sites and abnormal in nine (18%) of 51 sites. It precisely defined the anatomic location of abnormal uptake in 37 (73%) of 51 sites. AC PET findings did influence patient management in 14 (28%) of 50 patients. CONCLUSION Retrospective fusion of AC PET and CT/MRI is feasible and seems to be essential for final diagnosis. This is particularly true in patients with AC uptake in the prostate region.

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.

Die bedeutung eines rektumballons als interne immobilisation bei der konformalen strahlentherapie des prostatakarzinoms

BACKGROUND As known from the literature, prostate motion depends on different bladder and/or rectum fillings. The aim of this study was to analyze the influence of a rectum balloon catheter, used as an internal immobilization device, on prostate and rectum motion during the treatment course. Moreover we have analyzed if the balloon enables an increase of the distance between the prostate and the posterior rectum wall. PATIENTS AND METHODS Ten patients with localized prostate cancer (T1 to T3) underwent computed tomographic examinations with and without rectal balloon (filled with 40 ml air) at 3 times during treatment course (at the start, middle and end of treatment). Edges of prostate, rectum and bladder were measured in relation to bony reference structures and compared for both examination series (with and without balloon). RESULTS An increase of the distance between the prostate and the posterior rectal wall of 8 mm was observed at the base of the prostate when using the rectum balloon (Figures 1a,b and 2). Moreover prostate motion in the ventrodorsal direction > or = 4 mm (1 SD) was reduced from 6/10 patients (60%) to 1/10 patients (10%) using the rectal balloon (Table 3, Figure 3). In general, deviations in the latero-lateral and cranio-caudal directions were less (mean < or = 2 mm, 1 SD), no difference between both examination series (with and without balloon) was observed. CONCLUSION Rectal balloon catheter offers a possibility to reduce prostate motion and rectum filling variations during treatment course. In addition it enables an increase in the distance between prostate and posterior rectal wall, which could enable an improved protection of the posterior rectal wall.HintergrundDie Lageveränderung der Prostata, bedingt durch unterschiedliche Harnblasen- und Rektumfüllungen, wurde bereits in einigen Studien untersucht. Ziel dieser Studie war es, zu prüfen, ob durch die Anwendung eines Rektumballonkatheters als interne Immobilisation der Prostata eine Reduktion der Prostataeigenbeweglichkeit möglich ist. Darüber hinaus wurde untersucht, inwieweit durch den Rektumballon der Abstand zwischen Prostata und Rektumhinterwand vergrößert werden kann.Patienten und MethodeDrei konsekutive Planungscomputertomographien (Therapiebeginn, Therapiemitte, Therapieende) von zehn Patienten mit lokal begrenztem Prostatakarzinom (Tl bis T3) wurden jeweils mit und ohne Rektumballon (gefüllt mit 40 ml Luft) angefertigt. Die Lage von Prostata und Rektum im Therapieverlauf beider Untersuchungsserien (mit und ohne Rektumballon) wurde in Relation zu knöchernen Referenzstrukturen vermessen und miteinander verglichen.ErgebnisseDurch die Anwendung des Rektumballons konnte der Abstand zwischen Prostata und Rektumhinterwand an der Prostatabasis im Mittel um 8 mm vergrößert werden. Insgesamt konnte durch den Rektumballon die Prostatabewegung in ventrodorsaler Richtung deutlich reduziert werden. Die Anzahl jener Patienten, bei denen eine ventrodorsale Bewegung der zentralen Prostata im Therapieverlauf ≥ 4 mm (1 SD) beobachtet wurde, konnte durch die Anwendung des Rektumballons von 6/10 Patienten (60%) auf 1/10 Patienten (10%) reduziert werden. Die Lageveränderungen der Prostata in laterolateraler und kraniokaudaler Richtung waren deutlich geringer als jene in ventrodorsaler Richtung (im Mittel ≤ 2 mm, 1 SD) und wurden durch den Rektumballon nicht beeinflußt.SchlußfolgerungDie Anwendung des Rektumballons ermöglicht eine Reduktion der Prostataeigenbeweglichkeit in ventrodorsaler Richtung im Sinne einer internen Immobilisation. Zusätzlich wird eine Vergrößerung des Abstands zwischen Prostata und Rektumhinterwand erreicht, wodurch eine bessere Schonung der Rektumhinterwand möglich scheint.AbstractBackgroundAs known from the literature, prostate motion depends on different bladder and/or rectum fillings. The aim of this study was to analyze the influence of a rectum balloon catheter, used as an internal immobilization device, on prostate and rectum motion during the treatment course. Moreover we have analyzed if the balloon enables an increase of the distance between the prostate and the posterior rectum wall.Patients and MethodsTen patients with localized prostate cancer (Tl to T3) underwent computed tomographic examinations with and without rectal balloon (filled with 40 ml air) at 3 times during treatment course (at the start, middle and end of treatment). Edges of prostate, rectum and bladder were measured in relation to bony reference structures and compared for both examination series (with and without balloon).ResultsAn increase of the distance between the prostate and the posterior rectal wall of 8 mm was observed at the base of the prostate when using the rectum balloon (Figures la,b and 2). Moreover prostate motion in the ventrodorsal direction ≥ 4 mm (1 SD) was reduced from 6/10 patients (60%) to 1/10 patients (10%) using the rectal balloon (Table 3, Figure 3). In general, deviations in the latero-lateral and cranio-caudal directions were less (mean ≤ 2 mm, 1 SD), no difference between both examination series (with and without balloon) was observed.ConclusionRectal balloon catheter offers a possibility to reduce prostate motion and rectum filling variations during treatment course. In addition it enables an increase in the distance between prostate and posterior rectal wall, which could enable an improved protection of the posterior rectal wall.

Moderate risk-adapted dose escalation with three-dimensional conformal radiotherapy of localized prostate cancer from 70 to 74 Gy

Purpose:Evaluation of late side effects and biochemical control (bNED) 5 years after three-dimensional radiotherapy with moderate, risk-adapted dose escalation.Patients and Methods:From 03/1999 to 07/2002, 486 patients have been registered in the prospective Austrian-German multicenter phase II trial (AUGE). 399 (82%) localized prostate cancer patients (T1–3 Nx/N0 M0) were evaluated. The low- and intermediate-risk groups were treated with 70 Gy, the high-risk group with 74 Gy, respectively. Additional hormonal therapy (HT) was recommended for intermediate- and high-risk group patients. Late toxicity (EORTC/RTOG) and bNED (ASTRO and Phoenix) were prospectively assessed.Results:Median follow-up was 65 months. Distribution concerning risk groups (low-, intermediate-, high-risk group) showed 29%, 50% and 21% of patients, respectively. HT was given in 87% of patients. The 5-year actuarial rates of late side effects grade ≥ 2 for 70 Gy/74 Gy were 28%/30% (gastrointestinal; p = 0.73) and 19%/34% (urogenital; p = 0,06). The 5-year actuarial bNED rate stratified by risk groups (low-, intermediate-, high-risk group) was 74%, 66% and 50% (ASTRO), and 81%, 80% and 60% (Phoenix), respectively. Within multivariate analysis T-stage and initial prostate specific antigen were significant factors influencing bNED (ASTRO) whereas Gleason Score and duration of HT were not.Conclusion:Dose escalation within standard three-dimensional conformal radiotherapy (3D-CRT) up to a level of 74 Gy did not result in significantly increased gastrointestinal side effects, whereas urogenital side effects showed an increase close to significance. However, the total number of patients with severe toxicity was low. To achieve high tumor control rates with acceptable treatment-related morbidity, local doses of at least 74 Gy should be considered, in particular for intermediate- or high-risk patients applying 3D-CRT.Ziel:Bestimmung von Spätnebenwirkungen und biochemischer Kontrolle (bNED) nach risikoadaptierter Dosiseskalation im Rahmen einer prospektiven österreichisch-deutschen Phase-II-Multicenterstudie.Patienten und Methodik:Von 03/1999 bis 07/2002 wurden 486 Patienten mit Prostatakarzinom (T1–3 Nx/N0 M0) gemeldet, und 399 (82%) kamen zur Auswertung. Patienten der Niedrig- und Intermediärrisikogruppe wurden mit 70 Gy, die Hochrisikogruppe mit 74 Gy bestrahlt (Tabelle 1). Eine begleitende Hormontherapie wurde für Patienten der Intermediär- und Hochrisikogruppe empfohlen. Spätnebenwirkungen (EORTC/RTOG) und bNED (ASTRO/Phoenix) wurden ermittelt.Ergebnisse:Der mittlere Nachbeobachtungszeitraum betrug 65 Monate. Hinsichtlich der Risikogruppen (Niedrig-, Intermediär-, Hochrisikogruppe) fanden sich 29%, 50%, und 21% Patienten. Eine begleitende Hormontherapie erhielten 87% der Patienten. Detaillierte Patientendaten sind in Tabelle 2 aufgeführt. Die 5-Jahres-Raten an Spätnebenwirkungen Grad ≥ 2 für 70 Gy/74 Gy lagen bei 28%/30% (gastrointestinal; p = 0,73) und 19%/34% (urogenital; p = 0,06; Abbildungen 1 und 2). Die 5-Jahres-bNED-Raten entsprechend den Risikogruppen (Niedrig-, Intermediär-, Hochrisikogruppe) lagen bei 74%, 66% und 50% (ASTRO; Abbildung 3) bzw. 81%, 80% und 60% (Phoenix; Abbildung 4). In der multivariaten Analyse zeigten sich T-Stadium und initiales prostataspezifisches Antigen als signifikant bezüglich bNED (ASTRO) und Gleason-Score sowie die Dauer der Hormontherapie als nicht signifikant (Tabelle 4).Schlussfolgerung:Die Dosissteigerung auf 74 Gy führt zu keinen signifikant erhöhten Raten an gastrointestinalen Spätnebenwirkungen. Die Rate an urogenitalen Spätnebenwirkungen ist hingegen erhöht. Insgesamt finden sich jedoch nur wenige schwere Grad-3-Spätnebenwirkungen (Tabelle 3). Um respektable Tumorkontrollraten (Abbildung 5) zu erreichen, sollte, vor allem für Patienten der Intermediär- und Hochrisikogruppe, eine lokale Dosis von zumindest 74 Gy appliziert werden.

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.

Interobserver comparison of CT and MRI-based prostate apex definition. Clinical relevance for conformal radiotherapy treatment planning.

Background: CT is widely used for conformal radiotherapy treatment planning of prostate carcinoma. Its limitations are especially at the prostatic apex which cannot be separated from the urogenital diaphragm. The aim of this study was to compare the localization of the prostatic apex in CT and axial MRI to the sagittal MRI in an interobserver analysis. Patients and Methods: 22 patients with pathologically proven prostatic carcinoma were included in the analysis. In all patients sagittal and axial T2-weighted MRI and conventional CT were performed. The position of the MRI and CT apices were localized independently by three observers in relation to the intertrochanteric line. Additional subjective judgment of the ability to define the apical border of the prostatic gland was performed by a five-scaled score. Results: The apex of the prostate could be discriminated statistically significant (p < 0.001) better in the MRI as compared to CT with best judgment for the sagittal MRI. The interobserver variation for the definition of the prostatic apex was statistically significant (p = 0.009) smaler for the sagittal MRI compared to axial MRI and CT. On the average the apex as determined by sagittal MRI, axial MRI and CT was located 29 mm, 27 mm and 24 mm above the intertrochanteric line. The apex defined by CT would have led to an additional treatment of 6–13 mm in 10/22 patients compared to the sagittal MRI, defined by axial MRI only in five patients. Conclusion: Additional MRI provides a superior anatomic information especially in the apical portion of the prostate. It should be recommended for every single patient in the treatment planning process. It helps to avoid an unnecessary irradiation of healthy tissue and could lead to a decrease of anal side effects and radiation-induced impotency due to a reduction of the extent of irradiated penile structures.Hintergrund: Die Computertomographie (CT) stellt den Standard in der konformalen Strahlentherapieplanung des Prostatakarzinoms dar. Vor allem im Bereich des Apex der Prostata stößt die CT durch die fehlende Abgrenzbarkeit vom Diaphragma urogenitale an ihre Grenzen. Ziel dieser Studie war es, die Lokalisation des Apex im konventionellen CT und im axialen MRT mit jener im sagittalen MRT zu vergleichen. Patienten und Methode: 22 Patienten mit histologisch verifiziertem Prostatakarzinom wurden in die Auswerung einbezogen. Bei allen Patienten wurde eine axiale und sagittale T2-gewichtete MRT und eine konventionelle CT unter Planungsbedingungen durchgeführt. Die Lokalisation des Apex wurde in allen drei Schnittbildmodalitäten von drei Untersuchern in Relation zur Linea intertrochanterica festgelegt. Zusätzlich wurde die subjektive Abgrenzbarkeit des Apex nach einer fünfrangigen Skala beurteilt. Ergebnisse: Die subjektive Abgrenzbarkeit des Apex wurde im MRT statistisch signifikant (p < 0,001) besser beurteilt als im CT, mit der besten Beurteilung für das sagittale MRT (Abbildung 1). Die Interobserver-Abweichung der Apexlokalisation war für das sagittale MRT statistisch signifikant (p = 0,009) kleiner im Vergleich zum axialen MRT und CT. Im Mittel wurde der Apex im sagittalen MRT, axialen MRT und CT 29 mm, 27 mm und 24 mm oberhalb der Linea intertrochanterica lokalisiert (Abbildungen 2 bis 4). Eine Apexdefinition auf Basis des CT hätte im Vergleich zum sagittalen MRT bei 10/22 Patienten zu einer zusätzlichen Bestrahlung von gesundem Gewebe geführt, auf Basis der axialen MRT nur bei fünf Patienten. Schlussfolgerung: Die Kernspintomographie bildet die Anatomie im Bereich des Prostataapex deutlich besser ab als die CT und sollte deshalb zusätzlich durchgeführt werden (Abbildung 6). Sie erlaubt eine adäquate Apexdefinition im Rahmen der konformalen Bestrahlungsplanung des Prostatakarzinoms und hilft so, eine unnötige Bestrahlung gesunder analer oder peniler Strukturen zu vermeiden. Dies kann sowohl zu einer Reduktion von radiogenen analen Nebenwirkungen als auch zu einer Verminderung von radiogenen Potenzstörungen beitragen.