Sonja Dieterich

Loyola University Maryland, Baltimore, Maryland, United States

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Publications (133)296.1 Total impact

  • Sonja Dieterich, Paul J Keall, Colin G Orton
    Medical Physics 10/2013; 40(10):100601. · 2.91 Impact Factor
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    ABSTRACT: Purpose: To determine how best to time respiratory surrogate-based tumor motion model updates by comparing a novel technique based on external measurements alone to three direct measurement methods.Methods: Concurrently measured tumor and respiratory surrogate positions from 166 treatment fractions for lung or pancreas lesions were analyzed. Partial-least-squares regression models of tumor position from marker motion were created from the first six measurements in each dataset. Successive tumor localizations were obtained at a rate of once per minute on average. Model updates were timed according to four methods: never, respiratory surrogate-based (when metrics based on respiratory surrogate measurements exceeded confidence limits), error-based (when localization error ≥3 mm), and always (approximately once per minute).Results: Radial tumor displacement prediction errors (mean ± standard deviation) for the four schema described above were 2.4 ± 1.2, 1.9 ± 0.9, 1.9 ± 0.8, and 1.7 ± 0.8 mm, respectively. The never-update error was significantly larger than errors of the other methods. Mean update counts over 20 min were 0, 4, 9, and 24, respectively.Conclusions: The same improvement in tumor localization accuracy could be achieved through any of the three update methods, but significantly fewer updates were required when the respiratory surrogate method was utilized. This study establishes the feasibility of timing image acquisitions for updating respiratory surrogate models without direct tumor localization.
    Medical Physics 07/2013; 40(7):071709. · 2.91 Impact Factor
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    International journal of radiation oncology, biology, physics 05/2013; · 4.59 Impact Factor
  • Tewfik Bichay, Sonja Dieterich, Colin G Orton
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    ABSTRACT: OVERVIEW With most external beam radiotherapy treatments an accuracy of ±3 mm is usually considered desirable and achievable. With stereotactic radiotherapy, however, a somewhat greater accuracy is desired and, with modern techniques, can be achieved, and some claim that even submillimeter accuracy is achievable. This is the topic debated in this month’s Point/Counterpoint.
    Medical Physics 05/2013; 40(5):050601. · 2.91 Impact Factor
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    ABSTRACT: The purpose of this study was to quantify postimplantation migration of percu-taneously implanted cylindrical gold seeds ("seeds") and platinum endovascular embolization coils ("coils") for tumor tracking in pulmonary stereotactic ablative radiotherapy (SABR). We retrospectively analyzed the migration of markers in 32 consecutive patients with computed tomography scans postimplantation and at simulation. We implanted 147 markers (59 seeds, 88 coils) in or around 34 pulmonary tumors over 32 procedures, with one lesion implanted twice. Marker coordinates were rigidly aligned by minimizing fiducial registration error (FRE), the root mean square of the differences in marker locations for each tumor between scans. To also evaluate whether single markers were responsible for most migra-tion, we aligned with and without the outlier causing the largest FRE increase per tumor. We applied the resultant transformation to all markers. We evaluated migration of individual markers and FRE of each group. Median scan interval was 8 days. Median individual marker migration was 1.28 mm (interquartile range [IQR] 0.78–2.63 mm). Median lesion FRE was 1.56 mm (IQR 0.92–2.95 mm). Outlier identification yielded 1.03 mm median migration (IQR 0.52–2.21 mm) and 1.97 mm median FRE (IQR 1.44–4.32 mm). Outliers caused a mean and median shift in the centroid of 1.22 and 0.80 mm (95th percentile 2.52 mm). Seeds and coils had no statistically significant difference. Univariate analysis suggested no correlation of migration with the number of markers, contact with the chest wall, or time elapsed. Marker migration between implantation and simulation is limited and unlikely to cause geometric miss during tracking.
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    ABSTRACT: The purpose of this study was to quantify postimplantation migration of percu-taneously implanted cylindrical gold seeds ("seeds") and platinum endovascular embolization coils ("coils") for tumor tracking in pulmonary stereotactic ablative radiotherapy (SABR). We retrospectively analyzed the migration of markers in 32 consecutive patients with computed tomography scans postimplantation and at simulation. We implanted 147 markers (59 seeds, 88 coils) in or around 34 pulmonary tumors over 32 procedures, with one lesion implanted twice. Marker coordinates were rigidly aligned by minimizing fiducial registration error (FRE), the root mean square of the differences in marker locations for each tumor between scans. To also evaluate whether single markers were responsible for most migra-tion, we aligned with and without the outlier causing the largest FRE increase per tumor. We applied the resultant transformation to all markers. We evaluated migration of individual markers and FRE of each group. Median scan interval was 8 days. Median individual marker migration was 1.28 mm (interquartile range [IQR] 0.78–2.63 mm). Median lesion FRE was 1.56 mm (IQR 0.92–2.95 mm). Outlier identification yielded 1.03 mm median migration (IQR 0.52–2.21 mm) and 1.97 mm median FRE (IQR 1.44–4.32 mm). Outliers caused a mean and median shift in the centroid of 1.22 and 0.80 mm (95th percentile 2.52 mm). Seeds and coils had no statistically significant difference. Univariate analysis suggested no correlation of migration with the number of markers, contact with the chest wall, or time elapsed. Marker migration between implantation and simulation is limited and unlikely to cause geometric miss during tracking.
    Journal of Applied Clinical Medical Physics 03/2013; 14(2):77. · 0.96 Impact Factor
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    ABSTRACT: The purpose of this study was to quantify postimplantation migration of percu-taneously implanted cylindrical gold seeds ("seeds") and platinum endovascular embolization coils ("coils") for tumor tracking in pulmonary stereotactic ablative radiotherapy (SABR). We retrospectively analyzed the migration of markers in 32 consecutive patients with computed tomography scans postimplantation and at simulation. We implanted 147 markers (59 seeds, 88 coils) in or around 34 pulmonary tumors over 32 procedures, with one lesion implanted twice. Marker coordinates were rigidly aligned by minimizing fiducial registration error (FRE), the root mean square of the differences in marker locations for each tumor between scans. To also evaluate whether single markers were responsible for most migra-tion, we aligned with and without the outlier causing the largest FRE increase per tumor. We applied the resultant transformation to all markers. We evaluated migration of individual markers and FRE of each group. Median scan interval was 8 days. Median individual marker migration was 1.28 mm (interquartile range [IQR] 0.78–2.63 mm). Median lesion FRE was 1.56 mm (IQR 0.92–2.95 mm). Outlier identification yielded 1.03 mm median migration (IQR 0.52–2.21 mm) and 1.97 mm median FRE (IQR 1.44–4.32 mm). Outliers caused a mean and median shift in the centroid of 1.22 and 0.80 mm (95th percentile 2.52 mm). Seeds and coils had no statistically significant difference. Univariate analysis suggested no correlation of migration with the number of markers, contact with the chest wall, or time elapsed. Marker migration between implantation and simulation is limited and unlikely to cause geometric miss during tracking.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of this study was to quantify postimplantation migration of percu-taneously implanted cylindrical gold seeds ("seeds") and platinum endovascular embolization coils ("coils") for tumor tracking in pulmonary stereotactic ablative radiotherapy (SABR). We retrospectively analyzed the migration of markers in 32 consecutive patients with computed tomography scans postimplantation and at simulation. We implanted 147 markers (59 seeds, 88 coils) in or around 34 pulmonary tumors over 32 procedures, with one lesion implanted twice. Marker coordinates were rigidly aligned by minimizing fiducial registration error (FRE), the root mean square of the differences in marker locations for each tumor between scans. To also evaluate whether single markers were responsible for most migra-tion, we aligned with and without the outlier causing the largest FRE increase per tumor. We applied the resultant transformation to all markers. We evaluated migration of individual markers and FRE of each group. Median scan interval was 8 days. Median individual marker migration was 1.28 mm (interquartile range [IQR] 0.78–2.63 mm). Median lesion FRE was 1.56 mm (IQR 0.92–2.95 mm). Outlier identification yielded 1.03 mm median migration (IQR 0.52–2.21 mm) and 1.97 mm median FRE (IQR 1.44–4.32 mm). Outliers caused a mean and median shift in the centroid of 1.22 and 0.80 mm (95th percentile 2.52 mm). Seeds and coils had no statistically significant difference. Univariate analysis suggested no correlation of migration with the number of markers, contact with the chest wall, or time elapsed. Marker migration between implantation and simulation is limited and unlikely to cause geometric miss during tracking.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of this study was to quantify postimplantation migration of percu-taneously implanted cylindrical gold seeds ("seeds") and platinum endovascular embolization coils ("coils") for tumor tracking in pulmonary stereotactic ablative radiotherapy (SABR). We retrospectively analyzed the migration of markers in 32 consecutive patients with computed tomography scans postimplantation and at simulation. We implanted 147 markers (59 seeds, 88 coils) in or around 34 pulmonary tumors over 32 procedures, with one lesion implanted twice. Marker coordinates were rigidly aligned by minimizing fiducial registration error (FRE), the root mean square of the differences in marker locations for each tumor between scans. To also evaluate whether single markers were responsible for most migra-tion, we aligned with and without the outlier causing the largest FRE increase per tumor. We applied the resultant transformation to all markers. We evaluated migration of individual markers and FRE of each group. Median scan interval was 8 days. Median individual marker migration was 1.28 mm (interquartile range [IQR] 0.78–2.63 mm). Median lesion FRE was 1.56 mm (IQR 0.92–2.95 mm). Outlier identification yielded 1.03 mm median migration (IQR 0.52–2.21 mm) and 1.97 mm median FRE (IQR 1.44–4.32 mm). Outliers caused a mean and median shift in the centroid of 1.22 and 0.80 mm (95th percentile 2.52 mm). Seeds and coils had no statistically significant difference. Univariate analysis suggested no correlation of migration with the number of markers, contact with the chest wall, or time elapsed. Marker migration between implantation and simulation is limited and unlikely to cause geometric miss during tracking.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of this study was to quantify postimplantation migration of percu-taneously implanted cylindrical gold seeds ("seeds") and platinum endovascular embolization coils ("coils") for tumor tracking in pulmonary stereotactic ablative radiotherapy (SABR). We retrospectively analyzed the migration of markers in 32 consecutive patients with computed tomography scans postimplantation and at simulation. We implanted 147 markers (59 seeds, 88 coils) in or around 34 pulmonary tumors over 32 procedures, with one lesion implanted twice. Marker coordinates were rigidly aligned by minimizing fiducial registration error (FRE), the root mean square of the differences in marker locations for each tumor between scans. To also evaluate whether single markers were responsible for most migra-tion, we aligned with and without the outlier causing the largest FRE increase per tumor. We applied the resultant transformation to all markers. We evaluated migration of individual markers and FRE of each group. Median scan interval was 8 days. Median individual marker migration was 1.28 mm (interquartile range [IQR] 0.78–2.63 mm). Median lesion FRE was 1.56 mm (IQR 0.92–2.95 mm). Outlier identification yielded 1.03 mm median migration (IQR 0.52–2.21 mm) and 1.97 mm median FRE (IQR 1.44–4.32 mm). Outliers caused a mean and median shift in the centroid of 1.22 and 0.80 mm (95th percentile 2.52 mm). Seeds and coils had no statistically significant difference. Univariate analysis suggested no correlation of migration with the number of markers, contact with the chest wall, or time elapsed. Marker migration between implantation and simulation is limited and unlikely to cause geometric miss during tracking.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of this study was to quantify postimplantation migration of percu-taneously implanted cylindrical gold seeds ("seeds") and platinum endovascular embolization coils ("coils") for tumor tracking in pulmonary stereotactic ablative radiotherapy (SABR). We retrospectively analyzed the migration of markers in 32 consecutive patients with computed tomography scans postimplantation and at simulation. We implanted 147 markers (59 seeds, 88 coils) in or around 34 pulmonary tumors over 32 procedures, with one lesion implanted twice. Marker coordinates were rigidly aligned by minimizing fiducial registration error (FRE), the root mean square of the differences in marker locations for each tumor between scans. To also evaluate whether single markers were responsible for most migra-tion, we aligned with and without the outlier causing the largest FRE increase per tumor. We applied the resultant transformation to all markers. We evaluated migration of individual markers and FRE of each group. Median scan interval was 8 days. Median individual marker migration was 1.28 mm (interquartile range [IQR] 0.78–2.63 mm). Median lesion FRE was 1.56 mm (IQR 0.92–2.95 mm). Outlier identification yielded 1.03 mm median migration (IQR 0.52–2.21 mm) and 1.97 mm median FRE (IQR 1.44–4.32 mm). Outliers caused a mean and median shift in the centroid of 1.22 and 0.80 mm (95th percentile 2.52 mm). Seeds and coils had no statistically significant difference. Univariate analysis suggested no correlation of migration with the number of markers, contact with the chest wall, or time elapsed. Marker migration between implantation and simulation is limited and unlikely to cause geometric miss during tracking. PACS number: 87.57.N-; 87.57.nm; 87.53.Ly Key words: implanted fiducial marker migration, stereotactic ablative radiotherapy (SABR), stereotactic body radiotherapy (SBRT), endovascular embolization coils, gold seed fiducial markers Conflict of Interest statement: BL and PM have received speaking honoraria from Varian Medical Systems and General Electric Medical Systems, and research fund-ing from Varian Medical Systems to the Department of Radiation Oncology.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of this study was to quantify postimplantation migration of percu-taneously implanted cylindrical gold seeds ("seeds") and platinum endovascular embolization coils ("coils") for tumor tracking in pulmonary stereotactic ablative radiotherapy (SABR). We retrospectively analyzed the migration of markers in 32 consecutive patients with computed tomography scans postimplantation and at simulation. We implanted 147 markers (59 seeds, 88 coils) in or around 34 pulmonary tumors over 32 procedures, with one lesion implanted twice. Marker coordinates were rigidly aligned by minimizing fiducial registration error (FRE), the root mean square of the differences in marker locations for each tumor between scans. To also evaluate whether single markers were responsible for most migra-tion, we aligned with and without the outlier causing the largest FRE increase per tumor. We applied the resultant transformation to all markers. We evaluated migration of individual markers and FRE of each group. Median scan interval was 8 days. Median individual marker migration was 1.28 mm (interquartile range [IQR] 0.78–2.63 mm). Median lesion FRE was 1.56 mm (IQR 0.92–2.95 mm). Outlier identification yielded 1.03 mm median migration (IQR 0.52–2.21 mm) and 1.97 mm median FRE (IQR 1.44–4.32 mm). Outliers caused a mean and median shift in the centroid of 1.22 and 0.80 mm (95th percentile 2.52 mm). Seeds and coils had no statistically significant difference. Univariate analysis suggested no correlation of migration with the number of markers, contact with the chest wall, or time elapsed. Marker migration between implantation and simulation is limited and unlikely to cause geometric miss during tracking.
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    ABSTRACT: To determine the clinical impact of calculated dose differences between effective path length (EPL) and Monte Carlo (MC) algorithms in stereotactic ablative radiation therapy (SABR) of lung tumors. We retrospectively analyzed the treatment plans and clinical outcomes of 77 consecutive patients treated with SABR for 82 lung tumors between 2003 and 2009 at our institution. Sixty treatments were originally planned using EPL, and 22 using MC. All plans were recalculated for the same beam specifications using MC and EPL, respectively. The doses covering 95%, 50%, and 5% (D95, D50, D5, respectively) of the target volumes were compared between EPL and MC (assumed to be the actual delivered dose), both as physical dose and biologically effective dose. Time to local recurrence was correlated with dose by Cox regression analysis. The relationship between tumor control probability (TCP) and biologically effective dose was determined via logistic regression and used to estimate the TCP decrements due to prescribing by EPL calculations. EPL overestimated dose compared with MC in all tumor dose-volume histogram parameters in all plans. The difference was >10% of the MC D95 to the planning target volume and gross tumor volume in 60 of 82 (73%) and 52 of 82 plans (63%), respectively. Local recurrence occurred in 13 of 82 tumors. Controlling for gross tumor volume, higher physical and biologically effective planning target volume D95 correlated significantly with local control (P = .007 and P = .045, respectively). Compared with MC, prescribing based on EPL translated to a median TCP decrement of 4.3% (range, 1.2%-37%) and a >5% decrement in 46% of tumors. Clinical follow-up for local lung tumor control in a sizable cohort of patients treated with SABR demonstrates that EPL overestimates dose by amounts that substantially decrease TCP in a large proportion. EPL algorithms should be avoided for lung tumor SABR.
    Practical radiation oncology. 10/2012; 3(4):294-300.
  • G Kalantzis, A Lo, S Dieterich
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    ABSTRACT: Purpose: : Stereotactic radiosurgery (SRS) procedures are known to deliver a very high dose per fraction and thus, the increased risk of secondary types of cancer due to increased peripheral dose could be a limiting factor for the long term survival of the patients. The aim of this study is to evaluate the peripheral dose (PD) received at preselected anatomical sites in an anthropomorphic phantom for treatments of intracranial lesions with the CyberRnife. Methods: Eight patients treated using the CyberRnife were selected for this study. Organs at risk and target were delineated on volumetric CT data and treatment planning (Multiplan v.4.5.0) was optimized accordingly, in order to achieve the required prescribed target dose and critical structures sparing for each patient. The final treatment plan was delivered with a CyberRnife VIS (Accuray, Inc., Sunnyvale, CA) operating with a dose rate of 1000 MU/min at a flattening filter free mode and upgraded shielding. We performed our measurements using a male anthropomorphic RANDO phantom (Alderson Research Laboratories, Inc., Stamford, CT). Groups of three TLD 100 were placed anteriorly inside RANDO at a depth of 5 cm at locations corresponding to the thyroid, breast or lung, uterus and inferior abdomen for each treatment plan. Results: The average percentage dose normalized to the prescribed dose for the thyroid gland was 0.92+0.23 % with a max of 1.95%. The maximum reduction of the PD (expressed as percentage of the prescribed dose) was 80% between the thyroid gland and the lower pelvic area. Similarly the PD normalized to the number of MU showed an average of 0.84×10-3 (cGy/MU), with a max of 0.0025 (cGy/MU) for the thyroid gland region. Conclusions: It is evident that the PD is proportional to the number of MU as well as to the prescribed dose. These correlations can be utilized to estimate the PD during intracranial treatments.
    Medical Physics 06/2012; 39(6):3800-3801. · 2.91 Impact Factor
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    ABSTRACT: OBJECTIVES:: To report outcomes, failure patterns, and toxicity after stereotactic radiosurgery (SRS) for recurrent head and neck cutaneous squamous cell carcinoma with gross perineural invasion (GPNI). METHODS:: Ten patients who received SRS as part of retreatment for recurrent head and neck cutaneous squamous cell carcinoma with GPNI were included. All patients exhibited clinical and radiologic evidence of GPNI before SRS. Previous treatments included surgery alone in 3 patients and surgery with adjuvant external beam radiotherapy (EBRT) in 7 patients. Retreatment included SRS alone in 2 and EBRT boosted with SRS in 8 patients. Magnetic resonance images were obtained every 3 to 6 months after SRS to track failure patterns. RESULTS:: At a median 22-month follow-up, the 2-year progression-free and overall survival rates were 20% and 50%, respectively. Seven patients exhibited local failures, all of which occurred outside both SRS and EBRT fields. Five local failures occurred in previously clinically uninvolved cranial nerves (CNs). CN disease spreads through 3 distinct patterns: among different branches of CN V; between CNs V and VII; and between V1 and CNs III, IV, and/or VI. Five patients experienced side effects potentially attributable to radiation. CONCLUSIONS:: Although there is excellent in-field control with this approach, the rate of out-of-field failures remains unacceptably high. We found that the majority of failures occurred in previously clinically uninvolved CNs often just outside treatment fields. Novel treatment strategies targeting this mode of perineural spread are needed.
    American journal of clinical oncology 04/2012; · 2.21 Impact Factor
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    ABSTRACT: To investigate the effect of tumor site, measurement precision, tumor-surrogate correlation, training data selection, model design, and interpatient and interfraction variations on the accuracy of external marker-based models of tumor position. Cyberknife Synchrony system log files comprising synchronously acquired positions of external markers and the tumor from 167 treatment fractions were analyzed. The accuracy of Synchrony, ordinary-least-squares regression, and partial-least-squares regression models for predicting the tumor position from the external markers was evaluated. The quantity and timing of the data used to build the predictive model were varied. The effects of tumor-surrogate correlation and the precision in both the tumor and the external surrogate position measurements were explored by adding noise to the data. The tumor position prediction errors increased during the duration of a fraction. Increasing the training data quantities did not always lead to more accurate models. Adding uncorrelated noise to the external marker-based inputs degraded the tumor-surrogate correlation models by 16% for partial-least-squares and 57% for ordinary-least-squares. External marker and tumor position measurement errors led to tumor position prediction changes 0.3-3.6 times the magnitude of the measurement errors, varying widely with model algorithm. The tumor position prediction errors were significantly associated with the patient index but not with the fraction index or tumor site. Partial-least-squares was as accurate as Synchrony and more accurate than ordinary-least-squares. The accuracy of surrogate-based inferential models of tumor position was affected by all the investigated factors, except for the tumor site and fraction index.
    International journal of radiation oncology, biology, physics 04/2012; 82(5):e709-16. · 4.59 Impact Factor
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    ABSTRACT: To evaluate Hotelling's T(2) statistic and the input variable squared prediction error (Q((X))) for detecting large respiratory surrogate-based tumor displacement prediction errors without directly measuring the tumor's position. Tumor and external marker positions from a database of 188 Cyberknife Synchrony™ lung, liver, and pancreas treatment fractions were analyzed. The first ten measurements of tumor position in each fraction were used to create fraction-specific models of tumor displacement using external surrogates as input; the models were used to predict tumor position from subsequent external marker measurements. A partial least squares (PLS) model with four scores was developed for each fraction to determine T(2) and Q((X)) confidence limits based on the first ten measurements in a fraction. The T(2) and Q((X)) statistics were then calculated for every set of external marker measurements. Correlations between model error and both T(2) and Q((X)) were determined. Receiver operating characteristic analysis was applied to evaluate sensitivities and specificities of T(2), Q((X)), and T(2)∪Q((X)) for predicting real-time tumor localization errors >3 mm over a range of T(2) and Q((X)) confidence limits. Sensitivity and specificity of detecting errors >3 mm varied with confidence limit selection. At 95% sensitivity, T(2)∪Q((X)) specificity was 15%, 2% higher than either T(2) or Q((X)) alone. The mean time to alarm for T(2)∪Q((X)) at 95% sensitivity was 5.3 min but varied with a standard deviation of 8.2 min. Results did not differ significantly by tumor site. The results of this study establish the feasibility of respiratory surrogate-based online monitoring of real-time respiration-induced tumor motion model accuracy for lung, liver, and pancreas tumors. The T(2) and Q((X)) statistics were able to indicate whether inferential model errors exceeded 3 mm with high sensitivity. Modest improvements in specificity were achieved by combining T(2) and Q((X)) results.
    Medical Physics 04/2012; 39(4):2042-8. · 2.91 Impact Factor
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    ABSTRACT: Current stereotactic ablative radiotherapy (SABR) protocols for lung tumors prescribe a uniform dose regimen irrespective of tumor size. We report the outcomes of a lung tumor volume-adapted SABR dosing strategy. We retrospectively reviewed the outcomes in 111 patients with a total of 138 primary or metastatic lung tumors treated by SABR, including local control, regional control, distant metastasis, overall survival, and treatment toxicity. We also performed subset analysis on 83 patients with 97 tumors treated with a volume-adapted dosing strategy in which small tumors (gross tumor volume <12 mL) received single-fraction regimens with biologically effective doses (BED) <100 Gy (total dose, 18-25 Gy) (Group 1), and larger tumors (gross tumor volume ≥12 mL) received multifraction regimens with BED ≥100 Gy (total dose, 50-60 Gy in three to four fractions) (Group 2). The median follow-up time was 13.5 months. Local control for Groups 1 and 2 was 91.4% and 92.5%, respectively (p = 0.24) at 12 months. For primary lung tumors only (excluding metastases), local control was 92.6% and 91.7%, respectively (p = 0.58). Regional control, freedom from distant metastasis, and overall survival did not differ significantly between Groups 1 and 2. Rates of radiation pneumonitis, chest wall toxicity, and esophagitis were low in both groups, but all Grade 3 toxicities developed in Group 2 (p = 0.02). A volume-adapted dosing approach for SABR of lung tumors seems to provide excellent local control for both small- and large-volume tumors and may reduce toxicity.
    International journal of radiation oncology, biology, physics 02/2012; 84(1):231-7. · 4.59 Impact Factor
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    ABSTRACT: The Varian's new digital linear accelerator (LINAC), TrueBeam STx, is equipped with a high dose rate flattening filter free (FFF) mode (6 MV and 10 MV), a high definition multileaf collimator (2.5 mm leaf width), as well as onboard imaging capabilities. A series of end-to-end phantom tests were performed, TrueBeam-based image guided radiation therapy (IGRT), to determine the geometric accuracy of the image-guided setup and dose delivery process for all beam modalities delivered using intensity modulated radiation therapy (IMRT) and RapidArc. In these tests, an anthropomorphic phantom with a Ball Cube II insert and the analysis software (FilmQA (3cognition)) were used to evaluate the accuracy of TrueBeam image-guided setup and dose delivery. Laser cut EBT2 films with 0.15 mm accuracy were embedded into the phantom. The phantom with the film inserted was first scanned with a GE Discovery-ST CT scanner, and the images were then imported to the planning system. Plans with steep dose fall off surrounding hypothetical targets of different sizes were created using RapidArc and IMRT with FFF and WFF (with flattening filter) beams. Four RapidArc plans (6 MV and 10 MV FFF) and five IMRT plans (6 MV and 10 MV FFF; 6 MV, 10 MV and 15 MV WFF) were studied. The RapidArc plans with 6 MV FFF were planned with target diameters of 1 cm (0.52 cc), 2 cm (4.2 cc) and 3 cm (14.1 cc), and all other plans with a target diameter of 3 cm. Both onboard planar and volumetric imaging procedures were used for phantom setup and target localization. The IMRT and RapidArc plans were then delivered, and the film measurements were compared with the original treatment plans using a gamma criteria of 3%/1 mm and 3%/2 mm. The shifts required in order to align the film measured dose with the calculated dose distributions was attributed to be the targeting error. Targeting accuracy of image-guided treatment using TrueBeam was found to be within 1 mm. For irradiation of the 3 cm target, the gammas (3%, 1 mm) were found to be above 90% in all plan deliveries. For irradiations of smaller targets (2 cm and 1 cm), similar accuracy was achieved for 6 MV and 10 MV beams. Slightly degraded accuracy was observed for irradiations with higher energy beam (15 MV). In general, gammas (3%, 2 mm) were found to be above 97% for all the plans. Our end-to-end tests showed an excellent relative dosimetric agreement and sub-millimeter targeting accuracy for 6 MV and 10 MV beams, using both FFF and WFF delivery methods. However, increased deviations in spatial and dosimetric accuracy were found when treating lesions smaller than 2 cm or with 15 MV beam.
    Physics in Medicine and Biology 02/2012; 57(3):757-69. · 2.70 Impact Factor
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    ABSTRACT: Objectives: To successfully ablate a tumor in robotic radiotherapy, it is necessary to compensate the motion of inner organs caused by respiration. This can be achieved by tracking the body surface and correlation of the external movement to the tumor position, as it is implemented in Cyberknife Synchrony. A systematic error is produced from the delays, which arise from the data acquisition, signal processing and kinematical limitations of the system. The error can be decreased by predicting the time series of human respiration. A wavelet-based least mean square algorithm (wLMS) is evaluated on 17 patients and compared to the results of the Cyberknife Synchrony prediction algorithm and a multi-step linear method (MULIN). Methods: The algorithms were evaluated on 17 patients of the Cyberknife Center North Germany. The patients were treated with up to 5 fractions, in total 62 fractions. The fractions have a mean duration of 51 minutes. During the treatment, 3 markers were recorded at a frequency of 26 Hz. Besides respiratory movements, the data also contains movements due to the alignment of the patient. These periods have been cut out of the data. The prediction horizon was set to 4 samples (approx. 150 ms), which is in line with the latency of the Cyberknife. The wLMS prediction algorithm is based on the á trous wavelet decomposition. The signal is decomposed into J wavelet scales and a residual. With this decomposition it is possible to perform prediction on each individual scale. At each time step, a new weight vector is calculated depending on the past observations and is used to calculate the next prediction. The wavelet scale J was set to 3 according to previous experiments. The basic idea behind the MULIN algorithm is to compute the predicted signal from an expansion of the error signal. This linear prediction algorithm can be extended to the MULIN algorithm by taking higher derivatives into account. The algorithms are evaluated with respect to the relative root mean square error (RMS) and the relative Jitter of the predicted signal. The rel. RMS error is a measure of the accuracy of the prediction and is defined as the RMS error between the predicted signal and the real signal divided by the RMS error between the real signal and the real signal delayed by 4 samples. The Jitter is a measure of the stability and smoothness of the predicted signal. It is defined as the sum of the differences between the data points divided by the time steps. Results: Evaluating the data, the Cyberknife algorithm has the highest averaged rel. RMS error over all fractions. The mean averaged rel. RMS error for all fractions and the directions is 64.6%. The averaged rel. RMS error for the wLMS prediction algorithm is in average 13 % better (51.3%). Compared with the MULIN algorithm, the wLMS algorithm is in average 6 % better (57.2%). The standard deviation of the relative RMS error is also the highest for the Cyberknife algorithm. The standard deviation averaged over all 3 directions and all fractions is 25.5% for the Cyberknife, 17.7% for wLMS and 21.1% for the MULIN algorithm. In terms of the rel. Jitter, the results are very similar. The wLMS algorithm outperforms the Cyberknife algorithm. The mean average rel. Jitter over all fractions and direction is 141.6% for the Cyberknife, 114.5% wLMS and 125.1% for MULIN. In general all rel. Jitter values are above 100% for the 3 predictors above 100 %. This means that the delayed signal without prediction is smoother as the predicted signals. Conclusion: The evaluation clearly shows that the wLMS algorithm is superior compared to the MULIN algorithm and the Cyberknife. The wLMS algorithm has lowest rel. RMS error, standard deviation of the rel. RMS error and rel. Jitter. This means that the accuracy of the treatments and the smoothness of the robot control are increased.
    The SRS/SBRT Scientific Meeting; 02/2012

Publication Stats

829 Citations
296.10 Total Impact Points

Institutions

  • 2013
    • Loyola University Maryland
      Baltimore, Maryland, United States
    • University of California, Davis
      Davis, California, United States
  • 2011–2013
    • Trinity Health
      Livonia, Michigan, United States
    • Universität zu Lübeck
      • Institut für Robotik und Kognitive Systeme
      Lübeck, Schleswig-Holstein, Germany
  • 2007–2013
    • Stanford University
      • Department of Radiation Oncology
      Palo Alto, CA, United States
  • 2012
    • University of Maryland, Baltimore
      • Department of Radiation Oncology
      Baltimore, MD, United States
  • 2011–2012
    • Stanford Medicine
      • Department of Radiation Oncology
      Stanford, California, United States
  • 2005–2012
    • University of Maryland, College Park
      • Department of Physics
      Maryland, United States
  • 2001–2011
    • Rutgers, The State University of New Jersey
      New Brunswick, New Jersey, United States
  • 2009
    • University of Miami Miller School of Medicine
      • Department of Radiation Oncology
      Miami, FL, United States
  • 2003–2008
    • Georgetown University
      • • Department of Radiation Medicine
      • • Department of Radiology
      Washington, D. C., DC, United States
  • 2006–2007
    • Virginia Commonwealth University
      • Department of Radiation Oncology
      Richmond, VA, United States
  • 2003–2005
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
  • 2002
    • University of Illinois, Urbana-Champaign
      • Department of Physics
      Urbana, Illinois, United States
    • College of William and Mary
      • Department of Physics
      Williamsburg, Virginia, United States