S. Gaede

Intensity modulated radiotherapy of non-small-cell lung cancer incorporating SPECT ventilation imaging.

PURPOSEnThe authors performed this retrospective study to investigate the impact of using ventilation scans obtained from single photon emission computed tomography (SPECT) in selecting beam directions in intensity modulated radiation therapy (IMRT) planning in lung cancer radiotherapy to spare dosimetrically well ventilated lung.nnnMETHODSnFor ten consecutive stage III non-small-cell lung cancer patients, the authors obtained both ventilation/perfusion SPECT scans and four-dimensional CT scans for treatment planning purposes. Each ventilation scan was registered with the corresponding planning CT and ventilation volumes corresponding to either > or = 50% (vv50) or > or = 70% (vv70) of the maximum SPECT count were automatically segmented. For each patient, three IMRT plans were generated: One using nine equally spaced beams optimized according to nonfunctional lung based mean lung dose and lung v20; a second using nine equally spaced beams optimized to avoid vv50 and vv70; and a third plan using only three beams with gantry angles chosen based on minimum mean ventilated lung dose calculated for each conformal beam at every 10 degrees gantry angle avoiding vv50 and vv70. Resultant dose volume histogram indices were calculated for each plan and were compared with respect to calculated SPECT-based ventilation parameters in order to quantify the potential utility of ventilation SPECT in this setting.nnnRESULTSnTwo patient groups were identified based on (i) the overlap volume between PTV and vv50 and (ii) the average angular mean ventilated lung dose (AAMvLD). The first parameter quantifies the proximity of the PTV to well ventilated lung and the second parameter quantifies the degree of ventilation that surrounds the PTV. For group 1 patients, < or = 5% of the vv50 overlapped with the PTV. For group 2 patients, > 5% of the vv50 overlapped the PTV. Group 1 was further classified into subgroups 1A and 1B: For subgroup 1A, AAMvLD is >18 Gy, implying that the functional lung surrounds the PTV; for subgroup 1B, AAMvLD is <18 Gy, implying that the well ventilated lung does not completely surround PTV. For subgroup 1A, the plans generated using ventilated lung avoidance reduced dose to vv50 and vv70, with below tolerance dose to normal lung and acceptable coverage of the PTV. For subgroup 1B, the dose to the total lung and well ventilated lung are reduced with the beam direction optimization for the three-beam plan. For group 2, there was no significant dosimetric advantage of using SPECT-based ventilation information in IMRT plan optimization.nnnCONCLUSIONSnIn conclusion, it is feasible to use SPECT ventilation scans to optimize IMRT beam direction and, subsequently, to reduce dose to ventilated lung when overlap of the PTV and the ventilated lung is minimal and that the PTV is not surrounded by the ventilated lung. The potential benefit of ventilation SPECT scanning can be determined by preplanning assessment of overlap volumes and the AAMvLD.

Development of a novel ArcCHECK™ insert for routine quality assurance of VMAT delivery including dose calculation with inhomogeneities

PURPOSEnTo design a versatile, nonhomogeneous insert for the dose verification phantom ArcCHECK(™) (Sun Nuclear Corp., FL) and to demonstrate its usefulness for the verification of dose distributions in inhomogeneous media. As an example, we demonstrate it can be used clinically for routine quality assurance of two volumetric modulated arc therapy (VMAT) systems for lung stereotactic body radiation therapy (SBRT): SmartArc(®) (Pinnacle(3), Philips Radiation Oncology Systems, Fitchburg, WI) and RapidArc(®) (Eclipse(™), Varian Medical Systems, Palo Alto, CA).nnnMETHODSnThe cylindrical detector array ArcCHECK(™) has a retractable homogeneous acrylic insert. In this work, we designed and manufactured a customized heterogeneous insert with densities that simulate soft tissue, lung, bone, and air. The insert offers several possible heterogeneity configurations and multiple locations for point dose measurements. SmartArc(®) and RapidArc(®) plans for lung SBRT were generated and copied to ArcCHECK(™) for each inhomogeneity configuration. Dose delivery was done on a Varian 2100 ix linac. The evaluation of dose distributions was based on gamma analysis of the diode measurements and point doses measurements at different positions near the inhomogeneities.nnnRESULTSnThe insert was successfully manufactured and tested with different measurements of VMAT plans. Dose distributions measured with the homogeneous insert showed gamma passing rates similar to our clinical results (∼99%) for both treatment-planning systems. Using nonhomogeneous inserts decreased the passing rates by up to 3.6% in the examples studied. Overall, SmartArc(®) plans showed better gamma passing rates for nonhomogeneous measurements. The discrepancy between calculated and measured point doses was increased up to 6.5% for the nonhomogeneous insert depending on the inhomogeneity configuration and measurement location. SmartArc(®) and RapidArc(®) plans had similar plan quality but RapidArc(®) plans had significantly higher monitor units (up to 70%).nnnCONCLUSIONSnA versatile, nonhomogeneous insert was developed for ArcCHECK(™) for an easy and quick evaluation of dose calculations with nonhomogeneous media and for comparison of different treatment planning systems. The device was tested for SmartArc(®) and RapidArc(®) plans for lung SBRT, showing the uncertainties of dose calculations with inhomogeneities. The new insert combines the convenience of the ArcCHECK(™) and the possibility of assessing dose distributions in inhomogeneous media.PURPOSEnTo design a versatile, nonhomogeneous insert for the dose verification phantom ArcCHECK™ (Sun Nuclear Corp., FL) and to demonstrate its usefulness for the verification of dose distributions in inhomogeneous media. As an example, we demonstrate it can be used clinically for routine quality assurance of two volumetric modulated arc therapy (VMAT) systems for lung stereotactic body radiation therapy (SBRT): SmartArc® (Pinnacle3 , Philips Radiation Oncology Systems, Fitchburg, WI) and RapidArc® (Eclipse™ , Varian Medical Systems, Palo Alto, CA).nnnMETHODSnThe cylindrical detector array ArcCHECK™ has a retractable homogeneous acrylic insert. In this work, we designed and manufactured a customized heterogeneous insert with densities that simulate soft tissue, lung, bone, and air. The insert offers several possible heterogeneity configurations and multiple locations for point dose measurements. SmartArc® and RapidArc® plans for lung SBRT were generated and copied to ArcCHECK™ for each inhomogeneity configuration. Dose delivery was done on a Varian 2100 ix linac. The evaluation of dose distributions was based on gamma analysis of the diode measurements and point doses measurements at different positions near the inhomogeneities.nnnRESULTSnThe insert was successfully manufactured and tested with different measurements of VMAT plans. Dose distributions measured with the homogeneous insert showed gamma passing rates similar to our clinical results (∼99%) for both treatment-planning systems. Using nonhomogeneous inserts decreased the passing rates by up to 3.6% in the examples studied. Overall, SmartArc® plans showed better gamma passing rates for nonhomogeneous measurements. The discrepancy between calculated and measured point doses was increased up to 6.5% for the nonhomogeneous insert depending on the inhomogeneity configuration and measurement location. SmartArc® and RapidArc® plans had similar plan quality but RapidArc® plans had significantly higher monitor units (up to 70%).nnnCONCLUSIONSnA versatile, nonhomogeneous insert was developed for ArcCHECK™ for an easy and quick evaluation of dose calculations with nonhomogeneous media and for comparison of different treatment planning systems. The device was tested for SmartArc® and RapidArc® plans for lung SBRT, showing the uncertainties of dose calculations with inhomogeneities. The new insert combines the convenience of the ArcCHECK™ and the possibility of assessing dose distributions in inhomogeneous media.

Development of a novel ArcCHECK{sup Trade-Mark-Sign} insert for routine quality assurance of VMAT delivery including dose calculation with inhomogeneities

PURPOSEnTo design a versatile, nonhomogeneous insert for the dose verification phantom ArcCHECK(™) (Sun Nuclear Corp., FL) and to demonstrate its usefulness for the verification of dose distributions in inhomogeneous media. As an example, we demonstrate it can be used clinically for routine quality assurance of two volumetric modulated arc therapy (VMAT) systems for lung stereotactic body radiation therapy (SBRT): SmartArc(®) (Pinnacle(3), Philips Radiation Oncology Systems, Fitchburg, WI) and RapidArc(®) (Eclipse(™), Varian Medical Systems, Palo Alto, CA).nnnMETHODSnThe cylindrical detector array ArcCHECK(™) has a retractable homogeneous acrylic insert. In this work, we designed and manufactured a customized heterogeneous insert with densities that simulate soft tissue, lung, bone, and air. The insert offers several possible heterogeneity configurations and multiple locations for point dose measurements. SmartArc(®) and RapidArc(®) plans for lung SBRT were generated and copied to ArcCHECK(™) for each inhomogeneity configuration. Dose delivery was done on a Varian 2100 ix linac. The evaluation of dose distributions was based on gamma analysis of the diode measurements and point doses measurements at different positions near the inhomogeneities.nnnRESULTSnThe insert was successfully manufactured and tested with different measurements of VMAT plans. Dose distributions measured with the homogeneous insert showed gamma passing rates similar to our clinical results (∼99%) for both treatment-planning systems. Using nonhomogeneous inserts decreased the passing rates by up to 3.6% in the examples studied. Overall, SmartArc(®) plans showed better gamma passing rates for nonhomogeneous measurements. The discrepancy between calculated and measured point doses was increased up to 6.5% for the nonhomogeneous insert depending on the inhomogeneity configuration and measurement location. SmartArc(®) and RapidArc(®) plans had similar plan quality but RapidArc(®) plans had significantly higher monitor units (up to 70%).nnnCONCLUSIONSnA versatile, nonhomogeneous insert was developed for ArcCHECK(™) for an easy and quick evaluation of dose calculations with nonhomogeneous media and for comparison of different treatment planning systems. The device was tested for SmartArc(®) and RapidArc(®) plans for lung SBRT, showing the uncertainties of dose calculations with inhomogeneities. The new insert combines the convenience of the ArcCHECK(™) and the possibility of assessing dose distributions in inhomogeneous media.PURPOSEnTo design a versatile, nonhomogeneous insert for the dose verification phantom ArcCHECK™ (Sun Nuclear Corp., FL) and to demonstrate its usefulness for the verification of dose distributions in inhomogeneous media. As an example, we demonstrate it can be used clinically for routine quality assurance of two volumetric modulated arc therapy (VMAT) systems for lung stereotactic body radiation therapy (SBRT): SmartArc® (Pinnacle3 , Philips Radiation Oncology Systems, Fitchburg, WI) and RapidArc® (Eclipse™ , Varian Medical Systems, Palo Alto, CA).nnnMETHODSnThe cylindrical detector array ArcCHECK™ has a retractable homogeneous acrylic insert. In this work, we designed and manufactured a customized heterogeneous insert with densities that simulate soft tissue, lung, bone, and air. The insert offers several possible heterogeneity configurations and multiple locations for point dose measurements. SmartArc® and RapidArc® plans for lung SBRT were generated and copied to ArcCHECK™ for each inhomogeneity configuration. Dose delivery was done on a Varian 2100 ix linac. The evaluation of dose distributions was based on gamma analysis of the diode measurements and point doses measurements at different positions near the inhomogeneities.nnnRESULTSnThe insert was successfully manufactured and tested with different measurements of VMAT plans. Dose distributions measured with the homogeneous insert showed gamma passing rates similar to our clinical results (∼99%) for both treatment-planning systems. Using nonhomogeneous inserts decreased the passing rates by up to 3.6% in the examples studied. Overall, SmartArc® plans showed better gamma passing rates for nonhomogeneous measurements. The discrepancy between calculated and measured point doses was increased up to 6.5% for the nonhomogeneous insert depending on the inhomogeneity configuration and measurement location. SmartArc® and RapidArc® plans had similar plan quality but RapidArc® plans had significantly higher monitor units (up to 70%).nnnCONCLUSIONSnA versatile, nonhomogeneous insert was developed for ArcCHECK™ for an easy and quick evaluation of dose calculations with nonhomogeneous media and for comparison of different treatment planning systems. The device was tested for SmartArc® and RapidArc® plans for lung SBRT, showing the uncertainties of dose calculations with inhomogeneities. The new insert combines the convenience of the ArcCHECK™ and the possibility of assessing dose distributions in inhomogeneous media.

A study of longitudinal tumor motion in helical tomotherapy using a cylindrical phantom.

Tumor motion during radiation treatment on a helical tomotherapy unit may create problems due to interplay with motion of the multileaf collimator, gantry rotation, and patient couch translation through the gantry. This study evaluated this interplay effect for typical clinical parameters using a cylindrical phantom consisting of 1386 diode detectors placed on a respiratory motion platform. All combinations of radiation field widths (1, 2.5, and 5 cm) and gantry rotation periods (16, 30, and 60 s) were considered for sinusoidal motions with a period of 4 s and amplitudes of 5, 6, 7, 8, 9, and 10 mm, as well as real patient breathing pattern. Gamma comparisons with 2% dose difference and 2 mm distance to agreement and dose profiles were used for evaluation. The required motion margins were determined for each set of parameters. The required margin size increased with decreasing field width and increasing tumor motion amplitude, but was not affected by rotation period. The plans with the smallest field width of 1 cm have required motion margins approximately equal to the amplitude of motion (±25%), while those with the largest field width of 5 cm had required motion margins approximately equal to 20% of the motion amplitude (±20%). For tumor motion amplitudes below 6 mm and field widths above 1 cm, the required additional motion margins were very small, at a maximum of 2.5 mm for sinusoidal breathing patterns and 1.2 mm for the real patient breathing pattern. PACS numbers: 87.55.km, 87.55.Qr, 87.56.Fc

Optimizing SABR delivery for synchronous multiple lung tumors using volumetric-modulated arc therapy

Abstract Background: Volumetric-modulated arc therapy (VMAT) delivery for stereotactic ablative radiotherapy (SABR) of multiple lung tumors allows for faster treatments. We report on clinical outcomes and describe a general approach for treatment planning. Material and methods: Patients undergoing multi iso-center VMAT-based SABR for ≥2 lung lesions between 2009 and 2014 were identified from the VU University Medical Center and London Health Sciences Centre. Patients were eligible if the start date of the SABR treatment for the different lesions was within a time range of 30 days. SABR was delivered using separate iso-centers for lesions at a substantial distance from each other. Tumors were either treated with a single fraction of 34u2009Gy, or using three risk-adapted dose-fractionation schemes, namely three fractions of 18u2009Gy, five fractions of 11u2009Gy, or eight fractions of 7.5u2009Gy, depending on the tumor size and the location. Multivariable analysis was performed to assess factors predictive of clinical outcomes. Results: Of 84 patients (188 lesions) identified, 46% were treated for multiple metastases and 54% for multiple primary NSCLC. About 97% were treated for two or three lesions, and 56% had bilateral disease. After a median follow-up of 28 months, median overall survival (OS) for primary tumors was 27.6 months, and not reached for metastatic lesions (pu2009=u2009.028). Grade ≥3 toxicity was observed in 2% of patients. Multivariable analysis showed that grade 2 or higher radiation pneumonitis (nu2009=u20099) was best predicted by a total lung V35Gy of ≥6.5% (in 2Gy/fraction equivalent) (pu2009=u2009.007). Conclusion: Severe toxicity was uncommon following SABR using VMAT for up to three lung tumors. Further investigations of planning parameters are needed in patients presenting with more lesions.

TU‐FF‐A1‐02: Commissioning Fast Monte Carlo Dose Calculation for Lung Treatment Planning

Purpose: To commission a commercial Monte Carlo (MC) simulation package, NXEGS (Numerix LLC), for photon beam dose calculations. We investigated within NXEGS the EGS4 compatibility mode, fast MC, and post processing (PostP). Method and Materials: We commissioned NXEGS and Pinnacle 6.2b with the same set of measured data. We compared its dose calculation accuracy and efficiency with the collapsed cone convolution algorithm in Pinnacle and the National Research Council EGS4. Dose distributions were compared in three phantoms: a water phantom to check the output and beam profiles; a water phantom with a lung slab to test the inhomogeneity correction; and a water phantom with 1- 3 cm diameter cylindrical air pockets to test the PostP algorithm. We also compared fast MC using PostP with Pinnacle for a three-field lung treatment plan. Number of histories is chosen to give +/− 2% dose accuracy at the isocenter. All doses were converted to cGy per MU. Results: Fast MC improves computational speed by a factor of ∼10 from the EGS4 compatibility mode. PostP decreases number of histories required and hence the computation time by another factor of ∼10. PostP adds ∼1 minute per 106 dose voxels. Inside the lung slab, fast MC with PostP differed from Pinnacle by ∼0.03cGy/MU with a misalignment of ∼2mm whereas fast MC with PostP agreed within 0.03cGy/MU of EGS4. PostP did not preserve the dose perturbation from ⩾1cm air inhomogeneities. Conclusion: Without PostP, the accuracy and computational time scaled with number of histories. When we specify ±2% accuracy in the target volume, the dose calculation time using fast MC with PostP is comparable to Pinnacle for a three-field lung plan. NXEGS fast MC with PostP predicts the dose spread due to electron transport in lung with good accuracy-to-speed ratio and is suitable for routine treatment planning.

A phase II trial to evaluate single-dose stereotactic body radiation therapy (SBRT) prior to surgery for early-stage breast carcinoma: SIGNAL (stereotactic image-guided neoadjuvant ablative radiation then lumpectomy) trial

AbstractBackgroundBreast-conserving therapy has become a preferred option in the treatment of early breast cancer. Current breast-conserving therapy includes 3–5xa0weeks of external beam radiotherapy to the whole breast, sometimes followed by a 1–2-week boost to the tumor bed. However, the duration of the radiation regimen can be prohibitive for the elderly, infirm or immobile patients, those patients who live far from the cancer center, or those who have difficulty taking an extended leave of absence. We propose to treat these patients with a single dose of radiation preoperatively, thereby shortening the total treatment time.MethodsThis is a single-arm phase II case series trial, conducted on 120 patients with early breast cancer who will be accrued from multidisciplinary breast cancer clinics. These patients will have research biopsies taken at the time of enrollment and will undergo radiation planning with CT simulation and PET/MRI. A single dose of 21xa0Gy will then be delivered in the prone position to the tumor. A second research biopsy will be taken, then lumpectomy will be performed. This entire procedure will be completed within 1xa0week (7xa0days). The primary endpoint is rate of toxicity (≥grade 2 fibrosis), and secondary endpoints include cosmetic results, quality of life, and rate of recurrence.DiscussionThis study will assess the toxicity associated with using a single preoperative dose of radiation as a replacement for standard adjuvant radiotherapy in breast-conserving therapy. Results of this trial will guide the design of a possible phase III study.n Trial registration: Clinicaltrials.gov identifier: NCT02212860

Poster — Thurs Eve‐40: The potential of using SPECT ventilation information with IMRT for functional lung avoidance in radiotherapy of non small cell lung cancer

We have investigated the feasibility of using ventilation scans obtained from single photon emission computed tomography (SPECT) in intensity-modulated radiation therapy (IMRT) planning in lung cancer radiotherapy to avoid well functioning lung. We fused SPECT ventilation scans acquired at GE Hawkeye SPECT-CT of ten stage-III lung radiotherapy patients with planning CT in treatment planning system (Pinnacle v8.0, Philips Medical Systems). We automatically segment out 50% and 70% ventilated volumes. For each patient, we generated IMRT plans using nine equally spaced beams with and without avoiding well ventilated volume. They were compared with three beam IMRT plans with beam directions chosen to minimize the mean dose to the ventilated lung volumes, while keeping cord dose below tolerance and dose uniformity in the target. The plans generated using functional lung avoidance information reduces the doses to the functioning lung. With both IMRT avoidance plans, we could not obtain better functional avoidance or lower V-20Gy (volume receiving 20Gy or more) for total lung when the planning target volume (PTV) was surrounded by functional lung volumes. We were able to achieve better ventilated lung avoidance and lower total lung V-20Gy when the PTV is close to, but not surrounded by functioning lung volumes. For patients with the PTV that is far from 50% and 70% functional lung volumes, three-field IMRT spare the ventilated lung as well as nine-field IMRT ventilation avoidance plan, with a lower total lung V20-Gy.

TH‐D‐332‐08: A Fully Automated 4D‐CT Registration Algorithm for Lung Studies

Purpose: To develop an automated 4D‐CT registration algorithm that performs without the aid of data collected from an external respiratory surrogate. Method and Materials: 5 patients with lungcancer were scanned with a GE Healthcare 4‐Slice CT scanner using an overlapping cine protocol: the thorax was scanned with 4×2.5 mm cine scans. The couch was translated 7.5 mms between adjacent cine scans, resulting in a common 2.5 mm overlapping slice linking the two adjacent cine scans. A 4D‐CT dataset was produced by aligning entire 3D volumes at each phase of the breathing cycle: a reference couch position was selected, images at that position were truncated to 1 breathing cycle and then interpolated into 16 evenly spaced phases. To begin, the images of the reference couch position were matched to images from the adjacent couch position by maximizing the Normalized Cross Correlation of the overlapping slice. The process continued in a ‘daisy chain’ fashion through all couch positions using the selected images until an entire 3D volume was selected. The algorithm was repeated for all 16 phases to complete a 4D‐CT dataset. The data were also registered using a reference external marker 4D‐CT amplitude registration method. Image quality was quantified by calculating the mean difference of the registered overlapping slices from adjacent couch positions. Banding artifacts, as the result of image misalignment, cause higher mean differences. The values obtained from each registration method were compared using t‐statistics. Results: The NCC volumes showed a decrease of banding artifacts. Artifact correction was accompanied by a significant decrease in mean difference for 3 of the 5 patients (p < 0.01). The other patient data, that showed no initial artifacts, showed no significant differences. Conclusion: An automatic 4D‐CT registration method was developed and shown to perform as well or better than an external marker method.

WE‐C‐ValA‐03: The Use of CT Density Changes at Internal Tissue Interfaces to Monitor Respiratory Induced Lung Tumor Motion

Purpose: To describe a non‐invasive method to monitor the motion of internal organs affected by respiration without using external markers or spirometry, to apply the method to construct 4D‐CT datasets, to test the correlation with external markers, and to calculate any time shift between the datasets. Method and Materials: Ten lungcancer patients were CT scanned with a General Electric Fast 4‐Slice CT scanner operating in cine mode. An external signal was also acquired simultaneously using the Real‐Time Position Management (RPM) Respiratory Gating System (Varian Medical Systems). We retrospectively reconstructed the raw CT data to obtain consecutive 0.5s reconstructions at 0.1s intervals to increase image sampling. We defined regions of interest containing tissue interfaces that move due to breathing on each axial slice and measured the mean CT number as a function of respiratory phase. We constructed 4D‐CT data sets by retrospectively sorting each image set based on the respiratory phase determined by the mean CT number curve. The external marker and tumor motion were directly correlated using the sample coefficient of determination, r 2. Any time shift between the two data sets was calculated by shifting the tumor motion curve until r 2 was maximized. Results: Only three of the ten patients showed correlation higher than r2=0.80 between tumor motion and external marker position. However, after taking into account time shifts (ranging between 0s and 0.4s) between the two data sets, all ten patients showed correlation better than r2=0.8. Conclusions: 4D‐CT acquisition using an internal method improves the temporal registration of CTimages affected by respiratory motion without the need for external markers or spirometry. A non‐invasive method to directly correlate the motion of external markers and internal organs can be used to help guide decisions regarding the validity of the RPM system for respiratory gated radiotherapy on a patient‐specific basis.