Thomas Krieger

Is a single arc sufficient in volumetric-modulated arc therapy (VMAT) for complex-shaped target volumes?

PURPOSE To compare step-and-shoot intensity-modulated radiotherapy (ss-IMRT) with volumetric-modulated arc therapy (VMAT) for complex-shaped target volumes with a simultaneous integrated boost (SIB). MATERIALS AND METHODS This retrospective planning study was based on 20 patients composed of prostate cancer (n=5), postoperative (n=5) or primary (n=5) radiotherapy for pharyngeal cancer and for cancer of the paranasal sinuses (n=5); a SIB with two or three dose levels was planned in all patients. For each patient, one ss-IMRT plan with direct-machine-parameter optimization (DMPO) and VMAT plans with one to three arcs (SmartArc technique) were generated in the Pinnacle planning system. RESULTS Single arc VMAT improved target coverage and dose homogeneity in radiotherapy for prostate cancer. Two and three VMAT arcs were required to achieve equivalent results compared to ss-IMRT in postoperative and primary radiotherapy for pharyngeal cancer, respectively. In radiotherapy for cancer of the paranasal sinuses, multiarc VMAT resulted in increased spread of low doses to the lenses and decreased target coverage in the region between the orbits. CONCLUSIONS The complexity of the target volume determined whether single arc VMAT was equivalent to ss-IMRT. Multiple arc VMAT improved results compared to single arc VMAT at cost of increased delivery times, increased monitor unites and increased spread of low doses.

Dose–Response Relationship for Image-Guided Stereotactic Body Radiotherapy of Pulmonary Tumors: Relevance of 4D Dose Calculation

PURPOSE To evaluate outcome after image-guided stereotactic body radiotherapy (SBRT) for early-stage non-small-cell lung cancer (NSCLC) and pulmonary metastases. METHODS AND MATERIALS A total of 124 patients with 159 pulmonary lesions (metastases n = 118; NSCLC, n = 41; Stage IA, n = 13; Stage IB, n = 19; T3N0, n = 9) were treated with SBRT. Patients were treated with hypofractionated schemata (one to eight fractions of 6-26 Gy); biologic effective doses (BED) to the clinical target volume (CTV) were calculated based on four-dimensional (4D) dose calculation. The position of the pulmonary target was verified using volume imaging before all treatments. RESULTS With mean/median follow-up of 18/14 months, actuarial local control was 83% at 36 months with no difference between NSCLC and metastases. The dose to the CTV based on 4D dose calculation was closely correlated with local control: local control rates were 89% and 62% at 36 months for >100 Gy and <100 Gy BED (p = 0.0001), respectively. Actuarial freedom from regional and systemic progression was 34% at 36 months for primary NSCLC group; crude rate of regional failure was 15%. Three-year overall survival was 37% for primary NSCLC and 16% for metastases; no dose-response relationship for survival was observed. Exacerbation of comorbidities was the most frequent cause of death for primary NSCLC. CONCLUSIONS Doses of >100 Gy BED to the CTV based on 4D dose calculation resulted in excellent local control rates. This cutoff dose is not specific to the treatment technique and protocol of our study and may serve as a general recommendation.

Potential of image-guidance, gating and real-time tracking to improve accuracy in pulmonary stereotactic body radiotherapy

PURPOSE To evaluate the potential of image-guidance, gating and real-time tumor tracking to improve accuracy in pulmonary stereotactic body radiotherapy (SBRT). MATERIALS AND METHODS Safety margins for compensation of inter- and intra-fractional uncertainties of the target position were calculated based on SBRT treatments of 43 patients with pre- and post-treatment cone-beam CT imaging. Safety margins for compensation of breathing motion were evaluated for 17 pulmonary tumors using respiratory correlated CT, model-based segmentation of 4D-CT images and voxel-based dose accumulation; the target in the mid-ventilation position was the reference. RESULTS Because of large inter-fractional base-line shifts of the tumor, stereotactic patient positioning and image-guidance based on the bony anatomy required safety margins of 12 mm and 9 mm, respectively. Four-dimensional image-guidance targeting the tumor itself and intra-fractional tumor tracking reduced margins to <5 mm and <3 mm, respectively. Additional safety margins are required to compensate for breathing motion. A quadratic relationship between tumor motion and margins for motion compensation was observed: safety margins of 2.4mm and 6mm were calculated for compensation of 10 mm and 20 mm motion amplitudes in cranio-caudal direction, respectively. CONCLUSION Four-dimensional image-guidance with pre-treatment verification of the target position and online correction of errors reduced safety margins most effectively in pulmonary SBRT.

Monte Carlo- versus pencil-beam-/collapsed-cone-dose calculation in a heterogeneous multi-layer phantom.

The aim of this work was to evaluate the accuracy of dose predicted in heterogeneous media by a pencil beam (PB), a collapsed cone (CC) and a Monte Carlo (MC) algorithm. For this purpose, a simple multi-layer phantom composed of Styrofoam and white polystyrene was irradiated with 10 x 10 cm2 as well as 20 x 20 cm2 open 6 MV photon fields. The beam axis was aligned parallel to the layers and various field offsets were applied. Thereby, the amount of lateral scatter was controlled. Dose measurements were performed with an ionization chamber positioned both in the central layer of white polystyrene and the adjacent layers of Styrofoam. It was found that, in white polystyrene, both MC and CC calculations agreed satisfactorily with the measurements whereas the PB algorithm calculated 12% higher doses on average. By studying off-axis dose profiles the observed differences in the calculation results increased dramatically for the three algorithms. In the regions of low density CC calculated 10% (8%) lower doses for the 10 x 10 cm2 (20 x 20 cm2) fields than MC. The MC data on the other hand agreed well with the measurements, presuming that proper replacement correction for the ionization chamber embedded in Styrofoam was performed. PB results evidently did not account for the scattering geometry and were therefore not really comparable. Our investigations showed that the PB algorithm generates very large errors for the dose in the vicinity of interfaces and within low-density regions. We also found that for the used CC algorithm large deviations for the absolute dose (dose/monitor unit) occur in regions of electronic disequilibrium. The performance might be improved by better adapted parameters. Therefore, we recommend a careful investigation of the accuracy for dose calculations in heterogeneous media for each beam data set and algorithm.

Dose–response relationship for radiation-induced pneumonitis after pulmonary stereotactic body radiotherapy

PURPOSE To evaluate dosimetric factors predictive for radiation-induced pneumonitis (RP) after pulmonary stereotactic body radiotherapy (SBRT). MATERIALS AND METHODS A retrospective analysis was performed based on 59 consecutive patients treated with cone-beam CT-based image-guided SBRT for primary NSCLC (n=21) or pulmonary metastases (n=54). The majority of patients were treated with radiosurgery of 26 Gy to 80% (n=29) or three fractions of 12.5 Gy to 65% (n=40). To correct for different single fraction doses, local doses were converted to 2 Gy equivalent normalized total doses (NTDs) using α/β ratio of 3 Gy for RP. Dose-volume parameters and incidences of RP ≥ grade II SWOG were fitted using NTCP models. RESULTS Eleven patients developed RP grade II. With an average MLD of 10.3±5.6 Gy to the ipsilateral lung, a significant dose-response relationship was observed: the MLD was 12.5±4.3 Gy and 9.9±5.8 Gy for patients with and without development of RP, respectively. Additionally, volumes of the lung exposed to minimum doses between 2.5 and 50 Gy (V(2.5)-V(50)) were correlated with incidences of RP with a continuous decrease of the goodness of fit for higher doses. CONCLUSIONS The MLD and V(2.5)-V(50) of the ipsilateral lung were correlated with incidences of RP after pulmonary SBRT.

Image-Guided Radiotherapy for Liver Cancer Using Respiratory-Correlated Computed Tomography and Cone-Beam Computed Tomography

PURPOSE To evaluate a novel four-dimensional (4D) image-guided radiotherapy (IGRT) technique in stereotactic body RT for liver tumors. METHODS AND MATERIALS For 11 patients with 13 intrahepatic tumors, a respiratory-correlated 4D computed tomography (CT) scan was acquired at treatment planning. The target was defined using CT series reconstructed at end-inhalation and end-exhalation. The liver was delineated on these two CT series and served as a reference for image guidance. A cone-beam CT scan was acquired after patient positioning; the blurred diaphragm dome was interpreted as a probability density function showing the motion range of the liver. Manual contour matching of the liver structures from the planning 4D CT scan with the cone-beam CT scan was performed. Inter- and intrafractional uncertainties of target position and motion range were evaluated, and interobserver variability of the 4D-IGRT technique was tested. RESULTS The workflow of 4D-IGRT was successfully practiced in all patients. The absolute error in the liver position and error in relation to the bony anatomy was 8 +/- 4 mm and 5 +/- 2 mm (three-dimensional vector), respectively. Margins of 4-6 mm were calculated for compensation of the intrafractional drifts of the liver. The motion range of the diaphragm dome was reproducible within 5 mm for 11 of 13 lesions, and the interobserver variability of the 4D-IGRT technique was small (standard deviation, 1.5 mm). In 4 patients, the position of the intrahepatic lesion was directly verified using a mobile in-room CT scanner after application of intravenous contrast. CONCLUSION The results of our study have shown that 4D image guidance using liver contour matching between respiratory-correlated CT and cone-beam CT scans increased the accuracy compared with stereotactic positioning and compared with IGRT without consideration of breathing motion.

Stereotactic body radiotherapy for local boost irradiation in unfavourable locally recurrent gynaecological cancer

PURPOSE To evaluate outcome of radiotherapy for locally recurrent cervical and endometrial cancer. MATERIALS AND METHODS Nineteen patients were treated for a locally recurrent cervical (n=12) or endometrial (n=7) cancer median 26 months after initial surgery (n=18) or radiotherapy (n=1). The whole pelvis was irradiated with 50Gy conventionally fractionated radiotherapy (n=16). Because of large size of the recurrent cancer (median 4.5 cm) and peripheral location (n=12), stereotactic body radiotherapy (SBRT; median 3 fractions of 5Gy to 65%) was used for local dose escalation instead of (n=16) or combined with (n=3) vaginal brachytherapy. RESULTS After median follow-up of 22 months, 3-year overall survival was 34% with systemic progression the leading cause of death (7/10). Median time to systemic progression was 16 months. Three local recurrences resulted in a local control rate of 81% at 3 years. No correlation between survival, systemic or local control and any patient or treatment characteristic was observed. The rate of late toxicity>grade II was 25% at 3 years: two patients developed a grade IV intestino-vaginal fistula and one patient suffered from a grade IV small bowel ileus. CONCLUSION Image-guided SBRT for local dose escalation resulted in high rates of local control but was associated with significant late toxicity.

Comparison of Wedge versus Segmented Techniques in Whole Breast Irradiation

Purpose:To compare two irradiation techniques for whole breast irradiation: tangential wedged beams (WT) versus “open” fields (without wedges) with forward planned segments (ST).Patients and Methods:For 20 patients two comparative 3-D plans were defined using Pinnacle P3D and analyzed with respect to dose, dose homogeneity in the target volume, and scattered dose to organs at risk. The plans of six patients were reproduced in an Alderson phantom. Measurements were performed in the planning target volume (PTV), contralateral breast, lungs, heart, thyroid gland and in mid-pelvis.Results:Dose distribution in the PTV was nearly identical for WT and ST with the exception of D1. Scattered doses were significantly smaller for ST. In the contralateral breast the doses per 2-Gy fraction were 7.3 cGy ± 2.1 cGy (WT), and 4.7 cGy ± 1.9 cGy (ST; p < 0.01). Similar doses were measured for lung and heart. In mid pelvis the largest difference was observed (WT: 1.0 cGy ± 0.2 cGy, ST: 0.2 cGy ± 0.1 cGy; p < 0.01).Conclusion:Partial volume segments can replace wedges for improved dose coverage and homogeneity in the PTV. The ST causes significantly less scattered dose to extra-target organs. This may have implications for long-term risks after exposure to low radiation doses.Ziel:Vergleich zweier Bestrahlungstechniken für die Brustbestrahlung: tangentiale Keilfiltertechnik (WT) versus „offene“ Felder (ohne Keil) mit vorwärts geplanten Segmenten (ST).Patienten und Methodik:Bei 20 Patientinnen wurden je ein Bestrahlungsplan mit Keilfiltern und ein Plan mit segmentierten Feldern erstellt und bezüglich Dosis, Dosishomogenität im Zielvolumen und Streuanteil in Risikoorganen analysiert. Die Pläne von sechs Patientinnen wurden am Alderson-Phantom reproduziert. Messungen wurden im Zielvolumen (PTV), der kontralateralen Brust, den Lungen, dem Herzen, der Schilddrüse und im kleinen Becken durchgeführt.Ergebnisse:Die Dosisverteilung im Planungszielvolumen (PTV) war für WT und ST nahezu identisch mit Ausnahme von D1. Der Streuanteil für Risikoorgane war für die ST signifikant geringer. In der kontralateralen Mamma betrug die Dosis pro 2-Gy-Fraktion mit der WT 7,3 cGy ± 2,1 cGy und mit der ST 4,7 cGy ± 1,9 cGy (p < 0,01). Ähnliche Ergebnisse wurden für die Dosen in Lunge und Herz gemessen. Der größte Unterschied zwischen WT und ST zeigte sich im kleinen Becken (WT 1,0 cGy ± 0,2 cGy, ST 0,2 cGy ± 0,1 cGy; p < 0,01).Schlussfolgerung:Teilvolumensegmente können Keile in Bezug auf Zielvolumenabdeckung und Dosishomogenität im PTV ersetzen. Die ST verursacht signifikant weniger Streuanteil außerhalb des Zielvolumens. Dies kann Einfluss auf Langzeitrisiken nach Exposition niedriger Strahlendosen haben.

Influence of calculation algorithm on dose distribution in irradiation of non-small cell lung cancer (NSCLC) collapsed cone versus pencil beam.

Purpose:The influence of two different calculation algorithms (“pencil beam” [PB] versus “collapsed cone” [CC]) on dose distribution, as well as the dose-volume histograms (DVHs) of the planning target volume (PTV) and the organs at risk was analyzed for irradiation of lung cancer.Material and Methods:Between 10/2001 and 02/2002 three-dimensional treatment planning was done in ten patients with lung cancer (Helax, TMS®, V.6.01). The PTV, the ipsilateral lung (IL) and the contralateral lung (CL) were defined in each axial CT slice (slice thickness 1 cm). Dose distributions for three-dimensional multiple-field technique were calculated using a PB and a CC algorithm, respectively. Normalization was in accordance with ICRU 50. The DVHs were analyzed relating the minimum, maximum, median and mean dose to the volumes of interest (VOI).Results:Median PTV amounted to 774 cm3. Minimum dose within the PTV was 67.4% for CC and 75.6% for PB algorithm (p = 0.04). Using the CC algorithm, only 76.5% of the PTV was included by the 95% isodose, whereas 90.1% was included when the PB algorithm (p = 0.01) was used. Median volume of IL amounted to 1 953 cm3. Mean dose to IL was 43.0% for CC and 44.0% for PB algorithm (p = 0.02). Median volume of IL within the 80% isodose was 19.6% for CC and 24.1% for PB algorithm (p < 0.01). Median volume of CL amounted to 1 847 cm3. Mean dose to CL was 17.4% for CC and 18.1% for PB algorithm (p < 0.01). Volume of CL within the 80% isodose was 3.3% for CC and 4.1% for PB algorithm (p = 0.03).Conclusion:The CC and PB calculation algorithms result in different dose distributions in case of lung tumors. Particularly the minimum dose to the PTV, which may be relevant for tumor control, is significantly lower for CC. Since it is generally accepted that the CC algorithm describes secondary particle transport more exactly than PB models, the use of the latter should be critically evaluated in the treatment planning of lung cancer.Ziel:Der Einfluss zweier unterschiedlicher Rechenalgorithmen (“pencil beam” [PB] versus “collapsed cone” [CC]) auf die Dosisverteilung sowie die Dosis-Volumen-Histogramme (DVH) des Planungszielvolumens (PTV) und der Risikoorgane wird für die Bestrahlung des Lungenkarzinoms untersucht.Material und Methodik:Zwischen 10/2001 und 02/2002 wurde bei zehn Patienten mit Bronchialkarzinom eine dreidimensionale Bestrahlungsplanung durchgeführt (Helax, TMS®, V.6.01). Das PTV, die ipsilaterale Lunge (IL) und die kontralaterale Lunge (CL) wurden in jeder axialen CT-Schicht definiert (Schichtdicke 1 cm). Die Dosisverteilung für eine Mehrfeldertechnik wurde zunächst unter Verwendung des PB-Algorithmus optimiert. Anschließend wurde die Dosisverteilung der sich dabei ergebenden Bestrahlungspläne unter Beibehaltung der Feldparameter mittels des CC-Algorithmus erneut berechnet. Die Dosis wurde gemäß ICRU 50 normiert. Die DVH von PTV, IL und CL wurden analysiert.Ergebnisse:Das PTV betrug im Median 774 cm3. Die minimale Dosis im PTV war 67,4% für den CC- und 75,6% für den PB-Algorithmus (p = 0,04). Unter Verwendung von CC wurden lediglich 76,5% des PTV von der 95%-Isodose umschlossen, während dies unter Verwendung des PB bei 90,1% der Fall war (p = 0,01). Das mediane Volumen der IL war 1 953 cm3. Die mittlere Dosis in der IL betrug für den CC-Algorithmus 43,0% bzw. für den PB-Algorithmus 44,0% (p = 0,02). Das Volumen der IL innerhalb der 80%-Isodose betrug 19,6% für den CC- und 24,1% für den PB-Algorithmus (p < 0,01). Das mediane Volumen der CL lag bei 1 847 cm3. Die mittlere Dosis im Bereich der CL betrug 17,4% für den CC- und 18,1% für den PB-Algorithmus (p < 0,01). Das Volumen der CL innerhalb der 80%-Isodose war 3,3% für den CC- und 4,1% für den PB-Algorithmus (p = 0,03).Schlussfolgerung:Die Berechnung der Dosisverteilung mit dem CC- bzw. dem PB-Algorithmus führt bei gleicher Feldkonfiguration zu erheblich unterschiedlichen Ergebnissen. Insbesondere die sich dabei ergebende Minimaldosis im Bereich des PTV, welche für die Tumorkontrolle relevant sein kann, ist beim CC-Algorithmus signifikant niedriger. Da der CC-Algorithmus die tatsächlichen Streuungsverhältnisse im Gewebe unterschiedlicher Dichte genauer berücksichtigt als der PB-Algorithmus, sollte die Verwendung des PB-Algorithmus für die Bestrahlungsplanung des Bronchialkarzinoms sehr kritisch beurteilt werden.

Comparison of wedge versus segmented techniques in whole breast irradiation: effects on dose exposure outside the treatment volume.

Purpose:To compare two irradiation techniques for whole breast irradiation: tangential wedged beams (WT) versus “open” fields (without wedges) with forward planned segments (ST).Patients and Methods:For 20 patients two comparative 3-D plans were defined using Pinnacle P3D and analyzed with respect to dose, dose homogeneity in the target volume, and scattered dose to organs at risk. The plans of six patients were reproduced in an Alderson phantom. Measurements were performed in the planning target volume (PTV), contralateral breast, lungs, heart, thyroid gland and in mid-pelvis.Results:Dose distribution in the PTV was nearly identical for WT and ST with the exception of D1. Scattered doses were significantly smaller for ST. In the contralateral breast the doses per 2-Gy fraction were 7.3 cGy ± 2.1 cGy (WT), and 4.7 cGy ± 1.9 cGy (ST; p < 0.01). Similar doses were measured for lung and heart. In mid pelvis the largest difference was observed (WT: 1.0 cGy ± 0.2 cGy, ST: 0.2 cGy ± 0.1 cGy; p < 0.01).Conclusion:Partial volume segments can replace wedges for improved dose coverage and homogeneity in the PTV. The ST causes significantly less scattered dose to extra-target organs. This may have implications for long-term risks after exposure to low radiation doses.Ziel:Vergleich zweier Bestrahlungstechniken für die Brustbestrahlung: tangentiale Keilfiltertechnik (WT) versus „offene“ Felder (ohne Keil) mit vorwärts geplanten Segmenten (ST).Patienten und Methodik:Bei 20 Patientinnen wurden je ein Bestrahlungsplan mit Keilfiltern und ein Plan mit segmentierten Feldern erstellt und bezüglich Dosis, Dosishomogenität im Zielvolumen und Streuanteil in Risikoorganen analysiert. Die Pläne von sechs Patientinnen wurden am Alderson-Phantom reproduziert. Messungen wurden im Zielvolumen (PTV), der kontralateralen Brust, den Lungen, dem Herzen, der Schilddrüse und im kleinen Becken durchgeführt.Ergebnisse:Die Dosisverteilung im Planungszielvolumen (PTV) war für WT und ST nahezu identisch mit Ausnahme von D1. Der Streuanteil für Risikoorgane war für die ST signifikant geringer. In der kontralateralen Mamma betrug die Dosis pro 2-Gy-Fraktion mit der WT 7,3 cGy ± 2,1 cGy und mit der ST 4,7 cGy ± 1,9 cGy (p < 0,01). Ähnliche Ergebnisse wurden für die Dosen in Lunge und Herz gemessen. Der größte Unterschied zwischen WT und ST zeigte sich im kleinen Becken (WT 1,0 cGy ± 0,2 cGy, ST 0,2 cGy ± 0,1 cGy; p < 0,01).Schlussfolgerung:Teilvolumensegmente können Keile in Bezug auf Zielvolumenabdeckung und Dosishomogenität im PTV ersetzen. Die ST verursacht signifikant weniger Streuanteil außerhalb des Zielvolumens. Dies kann Einfluss auf Langzeitrisiken nach Exposition niedriger Strahlendosen haben.