Frank Lohr

Volumetric modulated arc therapy (VMAT) vs. serial tomotherapy, step-and-shoot IMRT and 3D-conformal RT for treatment of prostate cancer

INTRODUCTION Volumetric modulated arc therapy (VMAT), a complex treatment strategy for intensity-modulated radiation therapy, may increase treatment efficiency and has recently been established clinically. This analysis compares VMAT against established IMRT and 3D-conformal radiation therapy (3D-CRT) delivery techniques. METHODS Based on CT datasets of 9 patients treated for prostate cancer step-and-shoot IMRT, serial tomotherapy (MIMiC), 3D-CRT and VMAT were compared with regard to plan quality and treatment efficiency. Two VMAT approaches (one rotation (VMAT1x) and one rotation plus a second 200 degrees rotation (VMAT2x)) were calculated for the plan comparison. Plan quality was assessed by calculating homogeneity and conformity index (HI and CI), dose to normal tissue (non-target) and D(95%) (dose encompassing 95% of the target volume). For plan efficiency evaluation, treatment time and number of monitor units (MU) were considered. RESULTS For MIMiC/IMRT(MLC)/VMAT2x/VMAT1x/3D-CRT, mean CI was 1.5/1.23/1.45/1.51/1.46 and HI was 1.19/1.1/1.09/1.11/1.04. For a prescribed dose of 76 Gy, mean doses to organs-at-risk (OAR) were 50.69 Gy/53.99 Gy/60.29 Gy/61.59 Gy/66.33 Gy for the anterior half of the rectum and 31.85 Gy/34.89 Gy/38.75 Gy/38.57 Gy/55.43 Gy for the posterior rectum. Volumes of non-target normal tissue receiving > or =70% of prescribed dose (53 Gy) were 337 ml/284 ml/482 ml/505 ml/414 ml, for > or =50% (38 Gy) 869 ml/933 ml/1155 ml/1231 ml/1993 ml and for > or =30% (23 Gy) 2819 ml/3414 ml/3340 ml/3438 ml /3061 ml. D(95%) was 69.79 Gy/70.51 Gy/71,7 Gy/71.59 Gy/73.42 Gy. Mean treatment time was 12 min/6 min/3.7 min/1.8 min/2.5 min. CONCLUSION All approaches yield treatment plans of improved quality when compared to 3D-conformal treatments, with serial tomotherapy providing best OAR sparing and VMAT being the most efficient treatment option in our comparison. Plans which were calculated with 3D-CRT provided good target coverage but resulted in higher dose to the rectum.

EXTRACRANIAL STEREOTACTIC RADIATION THERAPY: SET-UP ACCURACY OF PATIENTS TREATED FOR LIVER METASTASES

PURPOSE Patients with liver metastases might benefit from high-dose conformal radiation therapy. A high accuracy of repositioning and a reduction of target movement are necessary for such an approach. The set-up accuracy of patients with liver metastases treated with stereotactic single dose radiation was evaluated. METHODS AND MATERIALS Twenty-four patients with liver metastases were treated with single dose radiation therapy on 26 occasions using a self-developed stereotactic frame. Liver movement was reduced by abdominal pressure. The effectiveness was evaluated under fluoroscopy. CT scans were performed on the planning day and directly before treatment. Representative reference marks were chosen and the coordinates were calculated. In addition, the target displacement was quantitatively evaluated after treatment. RESULTS Diaphragmal movement was reduced to median 7 mm (range: 3-13 mm). The final set-up accuracy of the body was limited to all of median 1.8 mm in latero-lateral direction (range: 0.3-5.0 mm) and 2.0 mm in anterior-posterior direction (0.8-3.8 mm). Deviations of the body in cranio-caudal direction were always less than the thickness of one CT slice (<5 mm). However, a repositioning was necessary in 16 occasions. The final target shift was median 1.6 mm (0.2-7.0 mm) in latero-lateral and 2.3 mm in anterior-posterior direction (0.0-6.3 mm). The median shift in cranio-caudal direction was 4.4 mm (0.0-10.0 mm). CONCLUSIONS In patients with liver metastases, a high set-up accuracy of the body and the target can be achieved. This allows a high-dose focal radiotherapy of these lesions. However, a control CT scan should be performed directly before therapy to confirm set-up accuracy and possibly prompt necessary corrections.

COMPARISON OF INTENSITY-MODULATED RADIOTHERAPY WITH CONVENTIONAL CONFORMAL RADIOTHERAPY FOR COMPLEX-SHAPED TUMORS

PURPOSE Conformal and intensity-modulated radiotherapy (IMRT) plans for 9 patients were compared based on characterization of plan quality and effects on the oncology department. METHODS AND MATERIALS These clinical cases, treated originally with conformal radiotherapy (CRT), required extraordinary effort to produce conformal treatment plans using nonmodulated, shaped noncoplanar fields with multileaf collimators (MLCs). IMRT plans created for comparison included rotational treatments with slit collimator, and fixed-field MLC treatments using equispaced coplanar, and noncoplanar fields. Plans were compared based upon target coverage, target conformality, dose homogeneity, monitor units (MU), user-interactive planning time, and treatment delivery time. The results were subjected to a statistical analysis. RESULTS IMRT increased target coverage an average of 36% and conformality by 10%. Where dose escalation was a goal, IMRT increased mean dose by 4-6 Gy and target coverage by 19% with the same degree of conformality. Rotational IMRT was slightly superior to fixed-field IMRT. All IMRT techniques increased integral dose and target dose heterogeneity. IMRT planning times were significantly less, whereas MU increased significantly; estimated delivery times were similar. CONCLUSION IMRT techniques increase dose and target coverage while continuing to spare organs-at-risk, and can be delivered in a time frame comparable to other sophisticated techniques.

NONINVASIVE PATIENT FIXATION FOR EXTRACRANIAL STEREOTACTIC RADIOTHERAPY

PURPOSE To evaluate the setup accuracy that can be achieved with a novel noninvasive patient fixation technique based on a body cast attached to a recently developed stereotactic body frame during fractionated extracranial stereotactic radiotherapy. METHODS AND MATERIALS Thirty-one CT studies (> or = 20 slices, thickness: 3 mm) from 5 patients who were immobilized in a body cast attached to a stereotactic body frame for treatment of paramedullary tumors in the thoracic or lumbar spine were evaluated with respect to setup accuracy. The immobilization device consisted of a custom-made wrap-around body cast that extended from the neck to the thighs and a separate head mask, both made from Scotchcast. Each CT study was performed immediately before or after every second or third actual treatment fraction without repositioning the patient between CT and treatment. The stereotactic localization system was mounted and the isocenter as initially located stereotactically was marked with fiducials for each CT study. Deviation of the treated isocenter as compared to the planned position was measured in all three dimensions. RESULTS The immobilization device can be easily handled, attached to and removed from the stereotactic frame and thus enables treatment of multiple patients with the same stereotactic frame each day. Mean patient movements of 1.6 mm+/-1.2 mm (laterolateral [LL]), 1.4 mm+/-1.0 mm (anterior-posterior [AP]), 2.3 mm+/-1.3 mm (transversal vectorial error [VE]) and < slice thickness = 3 mm (craniocaudal [CC]) were recorded for the targets in the thoracic spine and 1.4 mm+/-1.0 mm (LL), 1.2 mm+/-0.7 mm (AP), 1.8 mm+/-1.2 mm (VE), and < 3 mm (CC) for the lumbar spine. The worst case deviation was 3.9 mm for the first patient with the target in the thoracic spine (in the LL direction). Combining those numbers (mean transversal VE for both locations and maximum CC error of 3 mm), the mean three-dimensional vectorial patient movement and thus the mean overall accuracy can be safely estimated to be < or = 3.6 mm. CONCLUSION The presented combination of a body cast and head mask system in a rigid stereotactic body frame ensures reliable noninvasive patient fixation for fractionated extracranial stereotactic radiotherapy and may enable dose escalation for less radioresponsive tumors that are near the spinal cord or otherwise critically located while minimizing the risk of late sequelae.

ASSESSMENT OF FOCAL LIVER REACTION BY MULTIPHASIC CT AFTER STEREOTACTIC SINGLE-DOSE RADIOTHERAPY OF LIVER TUMORS

PURPOSE To characterize and quantitatively assess focal radiation reactions in the liver after stereotactic single-dose radiotherapy for liver malignancies. METHODS AND MATERIALS A total of 131 multiphasic CT scans were performed in 36 patients before and after stereotactic radiotherapy for liver tumors. The examination protocol included a nonenhanced scan and contrast-enhanced scans at different times after contrast injection. The volume of the reaction was determined in each scan and the threshold dose calculated using the dose-volume histogram of the treatment plan. RESULTS Every patient showed a focal radiation reaction on at least one follow-up examination. In 74% of the posttherapeutic scans, a sharply demarcated hypodense area surrounded the treated tumor in the nonenhanced scans. The reaction occurred at a median of 1.8 months (range 1.2-4.6) after radiotherapy. The median threshold dose was 13.7 Gy (range 8.9-19.2). The threshold dose strongly correlated with the time of detection after therapy (r = 0.7). Radiologically, three reaction types were found on the enhanced scans: type 1, portal-venous phase: hypodense and late phase: isodense; type 2, portal-venous phase: hypodense and late phase: hyperdense; and type 3, portal-venous phase: isodense/hyperdense and late phase: hyperdense. Type 1 or 2 reactions were observed significantly earlier than type 3 (p <0.05). The median threshold dose for type 1 or 2 reactions was significantly lower than for type 3 (p <0.05). The reaction volume decreased with longer follow-up (2-4 months: median 40% of initial volume). The reaction types shifted with follow-up: 58% were of type 1 at the initial manifestation and 58% were of type 3 at the next examination thereafter. CONCLUSION A focal radiation reaction occurs after stereotactic single-dose therapy in the liver. The volume of the reaction decreases and changes its radiologic appearance during follow-up. This reaction has to be differentiated from recurrent tumor.

CONVENTIONALLY FRACTIONATED STEREOTACTIC RADIOTHERAPY (FSRT) FOR ACOUSTIC NEUROMAS

PURPOSE Analysis of local tumor control and functional outcome following conventionally fractionated stereotactic radiotherapy (FSRT) for acoustic neuromas. PATIENTS AND METHODS From 11/1989 to 9/1999 51 patients with acoustic neuromas have been treated by FSRT. Mean total dose was 57.6 +/- 2.5 Gy. Forty-two patients have been followed for at least 12 months and were subject of an outcome analysis. Mean follow-up was 42 months. We analyzed local control, hearing preservation, and facial and trigeminal nerve functional preservation. We evaluated influences of tumor size, age, and association with neurofibromatosis Type 2 (NF2) on outcome and treatment related toxicity. RESULTS Actuarial 2- and 5-year tumor control rates were 100% and 97.7%, respectively. Actuarial useful hearing preservation rate was 85% at 2 and 5 years. New hearing loss was diagnosed in 4 NF2 patients. Pretreatment normal facial nerve function was preserved in all cases. Two cases of new or impaired trigeminal nerve dysesthesia required medication. No other cranial nerve deficit was observed. In Patients without NF2 tumor size or age had no influence on tumor control and cranial nerve toxicity. Diagnosis of NF2 was associated with higher risk of hearing impairment (p = 0.0002), the hearing preservation rate in this subgroup was 60%. CONCLUSION FSRT has been shown to be an effective means of local tumor control. Excellent hearing preservation rates and 5th and 7th nerve functional preservation rates were achieved. The results support the conclusion that FSRT can be recommended to patients with acoustic neuromas where special attention has to be taken to preserve useful hearing and normal cranial nerve function. For NF2 patients, FSRT may be the treatment of choice with superior functional outcome compared to treatment alternatives.

kV cone-beam CT-based IGRT: a clinical review.

AbstractAims and Methods:Delivery of high radiation doses while simultaneously sparing organs at risk requires advanced imaging for target volume definition, highly conformal dose distributions of intensity modulated radiotherapy (IMRT), and narrow planning target volume (PTV) margins. Three-dimensional image-guided radiotherapy (IGRT) with cone-beam computer tomography (CBCT), which results in more precise target localization, is quickly replacing two-dimensional (2D) IGRT. An overview on the clinical applications of kilovoltage gantry-mounted CBCT systems with emphasis on the most frequently targeted body sites (prostate, lung, head and neck) is provided based on a review of the relevant literature. Alternative imaging methods and their advantages/disadvantages are discussed.Results:IGRT with soft tissue detection improves set-up accuracy and is currently replacing 2D verification and frame-based stereotactic treatments; safety margins are significantly reduced by this IGRT technology. In addition, systematic changes of tumor volume and shape and of the normal tissue can be monitored allowing for adaptation of radiotherapy. IGRT in combination with conformal treatment planning allows for hypofractionated dose escalation, which results in improved rates of local tumor control with low rates of toxicity.Conclusion:CBCT allows for daily pretreatment position verification and online correction of set-up errors which improves the precision of patient repositioning with the possibility of shrinking safety margins, sparing organs at risk, and escalating radiation doses. A trend for better clinical outcome can be observed.ZusammenfassungHintergrund und Methodik:Die Verwendung von eskalierten Bestrahlungsdosen bei gleichzeitiger Schonung der Risikoorgane setzt multimodale Bildgebung zur Zielvolumendefinition, hochkonformale Bestrahlungsplanung mittels intensitätsmodulierter Radiotherapie und enge Sicherheitssäume voraus. Bildgeführte Strahlentherapie (IGRT) dient der präzisen Lokalisation des Zielvolumens, und konventionelle 2D Techniken wie Feldkontrollaufnahmen werden aktuell insbesondere durch dreidimensionale Cone-beam-(CBCT-)Technik ersetzt. Dieser Artikel gibt einen Literaturüberblick über den aktuellen Stand der IGRT mittels CBCT. Schwerpunkte sind die praktische Anwendung und klinischen Resultate bei Prostatakarzinom, Bronchialkarzinom und Kopf-Hals-Tumoren. Ergebnisse: Schlussfolgerungen: Schlüsselwörter: Ergebnisse:IGRT mittels CBCT ist hocheffektiv zur Verifikation der Patientenpositionierung und insbesondere zur Verifikation der Tumorposition. Rahmenbasierte Stereotaxie kann durch IGRT ersetzt werden, sowohl kraniell als auch extrakraniell. Bei Verwendung von IGRT-Techniken ohne ausreichenden Weichteilkontrast müssen größere Sicherheitssäume verwendet werden, um ein Verfehlen des Zielvolumens zu vermeiden. Zusätzlich sind mittels 3D IGRT systematische Veränderungen von Tumorvolumen, Tumorform und Lagebeziehung zu Risikoorganen darstellbar, was zur Adaption des Bestrahlungsplanes genutzt werden kann. Mittels konformaler IMRT-Bestrahlungstechniken und präziser IGRT konnten hypofraktionierte, eskalierte Bestrahlungsdosen sicher appliziert werden, was in verbesserter lokaler Tumorkontrolle ohne erhöhte Toxizität resultierte.Schlussfolgerungen:CBCT ermöglicht die Verifikation der Tumorposition zur Online-Korrektur von Positionsfehlern vor der Behandlung, was die Anwendung von kleinen Sicherheitssäumen, Normalgewebsschonung und Dosiseskalation ermöglicht. Die Verbesserung klinischer Ergebnisse wird durch diese Techniken erwartet und ist z.T. bereits in der Literatur dokumentiert.

Potential Effect of Robust and Simple IMRT Approach for Left-Sided Breast Cancer on Cardiac Mortality

PURPOSE Three-dimensional (3D) treatment planning has reduced the cardiac dose in postoperative radiotherapy for breast cancer; however, the overall cardiac toxicity is still an issue because of more aggressive adjuvant treatment. Toxicity models have suggested that a reduction of the heart volume treated to high doses might be particularly advantageous. We compared aperture-based multifield intensity-modulated radiotherapy (IMRT) plans to 3D-planned tangent fields using dose-volume histograms, cardiac toxicity risk, and the robustness to positioning errors. METHODS AND MATERIALS For 14 computed tomography data sets of patients with left-sided breast cancer (unfavorable thoracic geometry), a 3D treatment plan and an IMRT plan were created. The dose-volume histograms were evaluated for the target and risk organs. Excess risk of cardiac mortality was calculated for both approaches using a relative seriality model. Positioning errors were simulated by moving the isocenter. RESULTS IMRT reduced the maximal dose to the left ventricle by a mean of 30.9% (49.14 vs. 33.97 Gy). The average heart volume exposed to >30 Gy was reduced from 45 cm(3) to 5.84 cm(3). The mean dose to the left ventricle was reduced by an average of 10.7% (10.86 vs. 9.7 Gy), and the mean heart dose increased by an average of 24% (from 6.85 to 8.52 Gy). The model-based reduction of the probability for excess therapy-associated cardiac death risk was from 6.03% for the 3D plans to 0.25% for the IMRT plans. CONCLUSION Aperture-based IMRT for left-sided breast cancer significantly reduces the maximal dose to the left ventricle, which might translate into reduced cardiac mortality. Biological modeling might aid in deciding to treat with IMRT but has to be validated prospectively.

kV Cone-Beam CT-Based IGRT

AbstractAims and Methods:Delivery of high radiation doses while simultaneously sparing organs at risk requires advanced imaging for target volume definition, highly conformal dose distributions of intensity modulated radiotherapy (IMRT), and narrow planning target volume (PTV) margins. Three-dimensional image-guided radiotherapy (IGRT) with cone-beam computer tomography (CBCT), which results in more precise target localization, is quickly replacing two-dimensional (2D) IGRT. An overview on the clinical applications of kilovoltage gantry-mounted CBCT systems with emphasis on the most frequently targeted body sites (prostate, lung, head and neck) is provided based on a review of the relevant literature. Alternative imaging methods and their advantages/disadvantages are discussed.Results:IGRT with soft tissue detection improves set-up accuracy and is currently replacing 2D verification and frame-based stereotactic treatments; safety margins are significantly reduced by this IGRT technology. In addition, systematic changes of tumor volume and shape and of the normal tissue can be monitored allowing for adaptation of radiotherapy. IGRT in combination with conformal treatment planning allows for hypofractionated dose escalation, which results in improved rates of local tumor control with low rates of toxicity.Conclusion:CBCT allows for daily pretreatment position verification and online correction of set-up errors which improves the precision of patient repositioning with the possibility of shrinking safety margins, sparing organs at risk, and escalating radiation doses. A trend for better clinical outcome can be observed.ZusammenfassungHintergrund und Methodik:Die Verwendung von eskalierten Bestrahlungsdosen bei gleichzeitiger Schonung der Risikoorgane setzt multimodale Bildgebung zur Zielvolumendefinition, hochkonformale Bestrahlungsplanung mittels intensitätsmodulierter Radiotherapie und enge Sicherheitssäume voraus. Bildgeführte Strahlentherapie (IGRT) dient der präzisen Lokalisation des Zielvolumens, und konventionelle 2D Techniken wie Feldkontrollaufnahmen werden aktuell insbesondere durch dreidimensionale Cone-beam-(CBCT-)Technik ersetzt. Dieser Artikel gibt einen Literaturüberblick über den aktuellen Stand der IGRT mittels CBCT. Schwerpunkte sind die praktische Anwendung und klinischen Resultate bei Prostatakarzinom, Bronchialkarzinom und Kopf-Hals-Tumoren. Ergebnisse: Schlussfolgerungen: Schlüsselwörter: Ergebnisse:IGRT mittels CBCT ist hocheffektiv zur Verifikation der Patientenpositionierung und insbesondere zur Verifikation der Tumorposition. Rahmenbasierte Stereotaxie kann durch IGRT ersetzt werden, sowohl kraniell als auch extrakraniell. Bei Verwendung von IGRT-Techniken ohne ausreichenden Weichteilkontrast müssen größere Sicherheitssäume verwendet werden, um ein Verfehlen des Zielvolumens zu vermeiden. Zusätzlich sind mittels 3D IGRT systematische Veränderungen von Tumorvolumen, Tumorform und Lagebeziehung zu Risikoorganen darstellbar, was zur Adaption des Bestrahlungsplanes genutzt werden kann. Mittels konformaler IMRT-Bestrahlungstechniken und präziser IGRT konnten hypofraktionierte, eskalierte Bestrahlungsdosen sicher appliziert werden, was in verbesserter lokaler Tumorkontrolle ohne erhöhte Toxizität resultierte.Schlussfolgerungen:CBCT ermöglicht die Verifikation der Tumorposition zur Online-Korrektur von Positionsfehlern vor der Behandlung, was die Anwendung von kleinen Sicherheitssäumen, Normalgewebsschonung und Dosiseskalation ermöglicht. Die Verbesserung klinischer Ergebnisse wird durch diese Techniken erwartet und ist z.T. bereits in der Literatur dokumentiert.

Evaluation of Possible Prostate Displacement Induced by Pressure Applied during Transabdominal Ultrasound Image Acquisition

Background and Purpose:For accurate positioning of the prostate in external radiotherapy, transabdominal ultrasound localization and positioning systems are available. Reports have stated that probe pressure applied during image acquisition causes clinically relevant prostate displacement. The aim of this study was to investigate the prostate displacement due to the pressure applied during transabdominal ultrasound image acquisition with the BAT® ultrasound system.Material and Methods:For ten patients who had undergone iodine-125 seed implantation for brachytherapy of prostate cancer, X-ray simulations were performed before and during ultrasound image acquisition. The iodine seeds are visible on the X-ray images, representing the position of the prostate. The simulator’s crosshair, indicating the isocenter, was used as reference coordinate system. For each patient the change in prostate position was calculated based on the seed positions during and after ultrasound examination.Results:A maximum displacement of the prostate of 2.3 mm in anteroposterior and 1.9 mm in craniocaudal direction and a rotational change of up to 2.5° were observed. If the system was not handled correctly and too much pressure was applied, a shift of the prostate of up to 10 mm could be induced.Conclusion:Compared to the prostate displacement due to changes in rectal filling, which according to Crook et al. can be as much as 1.7 cm, the maximum displacement of less than 0.3 cm caused by the probe pressure is negligible. However, proper education of the staff and preparation of the patient are essential for the safe use of the system.Hintergrund und Ziel:Zur genauen Positionierung der Prostata in der Teletherapie stehen Ultraschall-Lokalisationssysteme zur Verfügung. Ziel der Studie war zu untersuchen, ob der Druck, der während der BAT®-Ultraschallaufnahme ausgeübt wird, eine klinisch relevante Verschiebung der Prostata bewirkt, die den Nutzen eines solchen Systems für die Patientenpositionierung in Frage stellt.Material und Methodik:Von zehn Patienten mit Iod-125-Seed-Implantaten wurden während und nach der Ultraschallaufnahme Röntgensimulationsaufnahmen angefertigt. Die in den Röntgenaufnahmen sichtbaren Seeds repräsentieren die Lage der Prostata. Das Fadenkreuz des Simulators wurde als Referenzkoordinatensystem verwendet. Für jeden Patienten wurde die Lageänderung der Prostata aus der Änderung der Seedpositionen bestimmt.Ergebnisse:Bei korrekter Anwendung des Ultraschallsystems wurde die Prostata maximal bis zu 2,3 mm in anteroposteriorer und 1,9 mm in kraniokaudaler Richtung verschoben und um maximal 2.5° rotiert. Durch falsche Handhabung des Systems mit zu hohem Druck konnte eine Verschiebung der Prostata um bis zu 10 mm bewirkt werden.Schlussfolgerung:Im Vergleich zu der natürlichen Lagevariation der Prostata durch unterschiedlich starke Rektumfüllung, die nach Crook et al. bis zu 1,7 cm betragen kann, ist eine maximale Verschiebung von weniger als 0,3 cm durch den Schallkopfdruck vernachlässigbar. Um das Potential des Systems voll zu nutzen, müssen eine korrekte Handhabung und Patientenvorbereitung gewährleistet sein.