Eva Maria Stoiber

Accuracy quantification of a deformable image registration tool applied in a clinical setting.

The purpose of this study was to test the accuracy of a commercially available deformable image registration tool in a clinical situation. In addition, to demonstrate a method to evaluate the resulting transformation of such a tool to a reference defined by multiple experts. For 16 patients (seven head and neck, four thoracic, five abdominal), 30‐50 anatomical landmarks were defined on recognizable spots of a planning CT and a corresponding fraction CT. A commercially available deformable image registration tool, Velocity AI, was used to align all fraction CTs with the respective planning CTs. The registration accuracy was quantified by means of the target registration error in respect to expert‐defined landmarks, considering the interobserver variation of five observers. The interobserver uncertainty of the landmark definition in our data sets is found to be 1.2±1.1mm. In general the deformable image registration tool decreases the extent of observable misalignments from 4‐8 mm to 1‐4 mm for nearly 50% of the landmarks (to 77% in sum). Only small differences are observed in the alignment quality of scans with different tumor location. Smallest residual deviations were achieved in scans of the head and neck region (79%,≤4mm) and the thoracic cases (79%,≤4mm), followed by the abdominal cases (59%,≤4mm). No difference is observed in the alignment quality of different tissue types (bony vs. soft tissue). The investigated commercially available deformable image registration tool is capable of reducing a mean target registration error to a level that is clinically acceptable for the evaluation of retreatment plans and replanning in case of gross tumor change during treatment. Yet, since the alignment quality needs to be improved further, the individual result of the deformable image registration tool has still to be judged by the physician prior to application. PACS numbers: 87.57.nj, 87.57.N‐, 87.55.‐x

Local setup errors in image-guided radiotherapy for head and neck cancer patients immobilized with a custom-made device.

PURPOSE To evaluate the local positioning uncertainties during fractionated radiotherapy of head-and-neck cancer patients immobilized using a custom-made fixation device and discuss the effect of possible patient correction strategies for these uncertainties. METHODS AND MATERIALS A total of 45 head-and-neck patients underwent regular control computed tomography scanning using an in-room computed tomography scanner. The local and global positioning variations of all patients were evaluated by applying a rigid registration algorithm. One bounding box around the complete target volume and nine local registration boxes containing relevant anatomic structures were introduced. The resulting uncertainties for a stereotactic setup and the deformations referenced to one anatomic local registration box were determined. Local deformations of the patients immobilized using our custom-made device were compared with previously published results. Several patient positioning correction strategies were simulated, and the residual local uncertainties were calculated. RESULTS The patient anatomy in the stereotactic setup showed local systematic positioning deviations of 1-4 mm. The deformations referenced to a particular anatomic local registration box were similar to the reported deformations assessed from patients immobilized with commercially available Aquaplast masks. A global correction, including the rotational error compensation, decreased the remaining local translational errors. Depending on the chosen patient positioning strategy, the remaining local uncertainties varied considerably. CONCLUSIONS Local deformations in head-and-neck patients occur even if an elaborate, custom-made patient fixation method is used. A rotational error correction decreased the required margins considerably. None of the considered correction strategies achieved perfect alignment. Therefore, weighting of anatomic subregions to obtain the optimal correction vector should be investigated in the future.

Intensity modulated radiotherapy (IMRT) in the treatment of children and Adolescents - a single institution's experience and a review of the literature

BackgroundWhile IMRT is widely used in treating complex oncological cases in adults, it is not commonly used in pediatric radiation oncology for a variety of reasons. This report evaluates our 9 year experience using stereotactic-guided, inverse planned intensity-modulated radiotherapy (IMRT) in children and adolescents in the context of the current literature.MethodsBetween 1999 and 2008 thirty-one children and adolescents with a mean age of 14.2 years (1.5 - 20.5) were treated with IMRT in our department. This heterogeneous group of patients consisted of 20 different tumor entities, with Ewings sarcoma being the largest (5 patients), followed by juvenile nasopharyngeal fibroma, esthesioneuroblastoma and rhabdomyosarcoma (3 patients each). In addition a review of the available literature reporting on technology, quality, toxicity, outcome and concerns of IMRT was performed.ResultsWith IMRT individualized dose distributions and excellent sparing of organs at risk were obtained in the most challenging cases. This was achieved at the cost of an increased volume of normal tissue receiving low radiation doses. Local control was achieved in 21 patients. 5 patients died due to progressive distant metastases. No severe acute or chronic toxicity was observed.ConclusionIMRT in the treatment of children and adolescents is feasible and was applied safely within the last 9 years at our institution. Several reports in literature show the excellent possibilities of IMRT in selective sparing of organs at risk and achieving local control. In selected cases the quality of IMRT plans increases the therapeutic ratio and outweighs the risk of potentially increased rates of secondary malignancies by the augmented low dose exposure.

Quantitative assessment of image-guided radiotherapy for paraspinal tumors.

PURPOSE To evaluate stereotactic positioning uncertainties of patients with paraspinal tumors treated with fractionated intensity-modulated radiotherapy; and to determine whether target-point correction via rigid registration is sufficient for daily patient positioning. PATIENTS AND METHODS Forty-five patients with tumors at the cervical, thoracic, and lumbar spine received regular control computed-tomography (CT) scans using an in-room CT scanner. All patients were immobilized with the combination of Scotch cast torso and head masks. The positioning was evaluated regarding translational and rotational errors by applying a rigid registration algorithm based on mutual information. The registration box was fitted to the target volume for optimal registration in the high-dose area. To evaluate the suitability of the rigid registration result for correcting the target volume position we subsequently registered three small subsections of the upper, middle, and lower target volume. The resulting residual deviations reflect the extent of the elastic deformations, which cannot be covered by the rigid-body registration procedure. RESULTS A total of 321 control CT scans were evaluated. The rotational errors were negligible. Translational errors were smallest for cervical tumors (-0.1 +/- 1.1, 0.3 +/- 0.8, and 0.1 +/- 0.9 mm along left-right, anterior-posterior, and superior-inferior axes), followed by thoracic (0.8 +/- 1.1, 0.3 +/- 0.8, and 1.1 +/- 1.3 mm) and lumbar tumors (-0.7 +/- 1.3, 0.0 +/- 0.9, and 0.5 +/- 1.6 mm). The residual deviations of the three subsections were <1 mm. CONCLUSIONS The applied stereotactic patient setup resulted in small rotational errors. However, considerable translational positioning errors may occur; thus, on the basis of these data daily control CT scans are recommended. Rigid transformation is adequate for correcting the target volume position.

The frequency of re-planning and its variability dependent on the modification of the re-planning criteria and IGRT correction strategy in head and neck IMRT

BackgroundTo analyse the frequency of re-planning and its variability dependent on the IGRT correction strategy and on the modification of the dosimetric criteria for re-planning for the spinal cord in head and neck IG-IMRT.MethodsDaily kV-control-CTs of six head and neck patients (=175 CTs) were analysed. All volumes of interest were re-contoured using deformable image registration. Three IGRT correction strategies were simulated and the resulting dose distributions were computed for all fractions. Different sets of criteria with varying dose thresholds for re-planning were investigated. All sets of criteria ensure equivalent target coverage of both CTVs, but vary in the tolerance threshold of the spinal cord.ResultsThe variations of the D95 and D2 in respect to the planned values ranged from -7% to +3% for both CTVs, and -2% to +6% for the spinal cord. Despite different correction vectors of the three IGRT strategies, the dosimetric differences were small. The number of fractions not requiring re-planning varied between 0% and 11% dependent on the applied IGRT correction strategy. In contrast, this number ranged between 32% and 70% dependent on the dosimetric thresholds, even though these thresholds were only gently modified.ConclusionsThe more precise the planned dose needs to be maintained over the treatment course, the more frequently re-planning is required. The influence of different IGRT correction strategies, even though geometrically notable, was found to be of only limited relevance for the re-planning frequency. In contrast, the definition and modification of thresholds for re-planning have a major impact on the re-planning frequency.

Treatment of Recurrent Bronchial Carcinoma: The Role of High-Dose-Rate Endoluminal Brachytherapy

PURPOSE This studys aim was to assess outcome and toxicity of high-dose-rate endoluminal brachytherapy (HDREB) for recurrent bronchial carcinoma. METHODS AND MATERIALS From 1987 to 2005, 41 patients were treated with HDREB for symptomatic recurrent bronchial carcinoma. All patients had previously undergone external beam radiotherapy (EBRT) with a median dose of 56 Gy (range, 30-70 Gy). The median HDREB dose applied was 15 Gy (range, 5-29 Gy). The median time interval between primary EBRT and reirradiation was 9 months (range, 2-54 months). RESULTS After a median follow-up of 6.7 months, the 6-, 12-, and 24-month overall survival rates were 58%, 18%, and 7%, respectively. The median overall survival time was 6.7 months. Local remission was achieved in 73% of patients (n = 30). A total of 24% of patients (n = 10) showed no response or progressive disease within 8 weeks after treatment. In 1 patient, treatment response was not documented. The 6-, 12-, and 24-month local control rates were 38%, 17%, and 3%, respectively. The median local progression-free survival time was 4 months (range, 1-23 months). Prognostic factors were a total dose of >or=15 Gy of HDREB (p = 0.029) and a Karnofsky performance score of >or=80% (p = 0.0012). The cause of death was locoregional progression in 27% of patients (n = 11), distant metastases in 24% of patients (n = 10), fatal hemorrhage in 15% of patients (n = 6), and other causes in 29% of patients (n = 12). None of the patients with locally controlled disease showed grade 3 or 4 late effects. CONCLUSIONS Palliative treatment of symptomatic, locally recurrent bronchial carcinoma with HDREB can effectively relieve symptoms in the majority of patients while causing only few complications. Still, time to progression is short.

An optimised IGRT correction vector determined from a displacement vector field: A proof of principle of a decision-making aid for re-planning

Abstract Background. To present a new method that determines an optimised IGRT couch correction vector from a displacement vector field (DVF). The DVF is computed by a deformable image registration (DIR) method. The proposed method can improve the quality of volume-of-interest (VOI) alignment in image guided radiation therapy (IGRT), and can serve as a decision-making aid for re-planning. Material and methods. The proposed method was demonstrated using the CT data sets of 11 head-and-neck cancer patients with daily kilovoltage control-CTs. A DVF was computed for each control-CT using a DIR method. The DVF was used for voxel tracking and re-contouring of the VOIs in the control-CTs. Then a rigid body transformation, which could be used as couch correction vector, was optimised. The aim of the optimisation process was to find a vector and rotations that map the deformed VOIs into a specified territory. This territory was defined by a margin extension of the VOIs at the time of the planning process. Within this extension, VOI motion and deformation was tolerated. The objective function in the optimisation process was the sum of all volume fractions outside the defined territories. Results. The proposed method was able to find a correction vector, which resulted in a coverage of the target volumes of at least 98% in 52.3% of all fractions. In contrast, a standard IGRT correction using a rigid registration method only fulfilled this criterion in 22.6% of all fractions. The optimisation process took an average of 1.5 minutes per fraction. Conclusion. The knowledge of the deformation of the anatomy allows the determination of an optimised rigid correction vector using our method. The method ensures controlled mapping of the VOIs despite small deformations. If no optimised vector can be determined, re-planning should be considered. Thus, our method can also serve as a decision-making aid for re-planning.

Comparison of two IGRT correction strategies in postoperative head-and-neck IMRT patients.

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IGRT versus non-IGRT for postoperative head-and-neck IMRT patients: dosimetric consequences arising from a PTV margin reduction

BackgroundTo evaluate the impact of image-guided radiation therapy (IGRT) versus non-image-guided radiation therapy (non-IGRT) on the dose to the clinical target volume (CTV) and the cervical spinal cord during fractionated intensity-modulated radiation therapy (IMRT) for head-and-neck cancer (HNC) patients.Material and MethodsFor detailed investigation, 4 exemplary patients with daily control-CT scans (total 118 CT scans) were analyzed. For the IGRT approach a target point correction (TPC) derived from a rigid registration focused to the high-dose region was used. In the non-IGRT setting, instead of a TPC, an additional cohort-based safety margin was applied. The dose distributions of the CTV and spinal cord were calculated on each control-CT and the resulting dose volume histograms (DVHs) were compared with the planned ones fraction by fraction. The D50 and D98 values for the CTV and the D5 values of the spinal cord were additionally reported.ResultsIn general, the D50 and D98 histograms show no remarkable difference between both strategies. Yet, our detailed analysis also reveals differences in individual dose coverage worth inspection. Using IGRT, the D5 histograms show that the spinal cord less frequently receives a higher dose than planned compared to the non-IGRT setting. This effect is even more pronounced when looking at the curve progressions of the respective DVHs.ConclusionsBoth approaches are equally effective in maintaining CTV coverage. However, IGRT is beneficial in spinal cord sparing. The use of an additional margin in the non-IGRT approach frequently results in a higher dose to the spinal cord than originally planned. This implies that a margin reduction combined with an IGRT correction helps to maintain spinal cord dose sparing best as possible. Yet, a detailed analysis of the dosimetric consequences dependent on the used strategy is required, to detect single fractions with unacceptable dosimetric deviations.

Primary radiotherapy with endobronchial high-dose-rate brachytherapy boost for inoperable lung cancer: long-term results.

BACKGROUND To retrospectively evaluate the outcome of patients with inoperable non-small-cell lung cancer treated with primary external beam radiotherapy combined with high-dose-rate endobronchial brachytherapy boost. PATIENTS AND METHODS Between 1988 and 2005, 35 patients with non-small-cell lung cancer (stage I-III) ineligible for surgical resection and/or chemotherapy, were primarily treated with external beam radiotherapy with a median total dose of 50 Gy (range, 46-60). A median of 3 fractions high-dose-rate endobronchial brachytherapy was applied as a boost after external beam radiotherapy, the median total dose was 15 Gy (range, 8-20). High-dose-rate endobronchial brachytherapy was carried out with iridium-192 sources (370 GBq) and prescribed to 1 cm distance from the source axis. RESULTS With a median follow-up of 26 months from the first fraction of high-dose-rate endobronchial brachytherapy, the 1-, 2- and 5-year overall (local progression-free) survival rates were 76% (76%), 61% (57%) and 28% (42%), respectively. Complete or partial remission rates 6 to 8 weeks after treatment were 57% and 17%, respectively. Significant prognostic favorable factors were a complete remission 6-8 weeks after treatment and a negative nodal status. In patients without mediastinal node involvement, a long-term local control could be achieved with 56% 5-year local progression-free survival. Common Toxicity Criteria grade 3 toxicities were hemoptysis (n = 2) and necrosis (n = 1). One fatal hemoptysis occurred in combination with a local tumor recurrence. CONCLUSIONS The combination of external beam radiotherapy with high-dose-rate endobronchial brachytherapy boost is an effective primary treatment with acceptable toxicity in patients with non-small-cell lung cancer ineligible for surgical resection and/or chemotherapy.