Corine van Vliet-Vroegindeweij

Volumetric-Modulated Arc Therapy for Stereotactic Body Radiotherapy of Lung Tumors: A Comparison With Intensity-Modulated Radiotherapy Techniques

PURPOSE To demonstrate the potential of volumetric-modulated arc therapy (VMAT) compared with intensity-modulated radiotherapy (IMRT) techniques with a limited number of segments for stereotactic body radiotherapy (SBRT) for early-stage lung cancer. METHODS AND MATERIALS For a random selection of 27 patients eligible for SBRT, coplanar and noncoplanar IMRT and coplanar VMAT (using SmartArc) treatment plans were generated in Pinnacle(3) and compared. In addition, film measurements were performed using an anthropomorphic phantom to evaluate the skin dose for the different treatment techniques. RESULTS Using VMAT, the delivery times could be reduced to an average of 6.6 min compared with 23.7 min with noncoplanar IMRT. The mean dose to the healthy lung was 4.1 Gy for VMAT and noncoplanar IMRT and 4.2 Gy for coplanar IMRT. The volume of healthy lung receiving>5 Gy and >20 Gy was 18.0% and 5.4% for VMAT, 18.5% and 5.0% for noncoplanar IMRT, and 19.4% and 5.7% for coplanar IMRT, respectively. The dose conformity at 100% and 50% of the prescribed dose of 54 Gy was 1.13 and 5.17 for VMAT, 1.11 and 4.80 for noncoplanar IMRT and 1.12 and 5.31 for coplanar IMRT, respectively. The measured skin doses were comparable for VMAT and noncoplanar IMRT and slightly greater for coplanar IMRT. CONCLUSIONS Coplanar VMAT for SBRT for early-stage lung cancer achieved plan quality and skin dose levels comparable to those using noncoplanar IMRT and slightly better than those with coplanar IMRT. In addition, the delivery time could be reduced by ≤70% with VMAT.

CLINICAL RESULTS OF IMAGE-GUIDED DEEP INSPIRATION BREATH HOLD BREAST IRRADIATION

PURPOSE To evaluate the feasibility, cardiac dose reduction, and the influence of the setup error on the delivered dose for fluoroscopy-guided deep inspiration breath hold (DIBH) irradiation using a cone-beam CT for irradiation of left-sided breast cancer patients. METHODS AND MATERIALS Nineteen patients treated according to the DIBH protocol were evaluated regarding dose to the ipsilateral breast (or thoracic wall), heart, (left ventricle [LV] and left anterior descending artery [LAD]), and lung. The DIBH treatment plan was compared to the free-breathing (FB) treatment planning and to the dose data in which setup error was taken into account (i.e., actual delivered dose). RESULTS The largest setup variability was observed in the direction perpendicular to the RT field (μ = -0.8 mm, Σ = 2.9 mm, σ = 2.0 mm). The mean (D(mean)) and maximum (D(max)) doses of the DIBH treatment plan was significantly lower compared with the FB treatment plan for the heart (34% and 25%, p < 0.001), LV (71% and 28%, p < 0.001), and LAD (52% and 39.8%, p < 0.001). For some patients, large differences were observed between the heart D(max) according to the DIBH treatment plan and the actual delivered dose (up to 71%), although D(max) was always smaller than the planned FB dose (mean group reduction = 29%, p < 0.001). CONCLUSION The image-guided DIBH treatment protocol is a feasible irradiation method with small setup variability that significantly reduces the dose to the heart, LV, and LAD.

Multiinstitutional study on target volume delineation variation in breast radiotherapy in the presence of guidelines

PURPOSE This study aims to determine magnitude, causes and consequences of post-operative breast tumour target volume delineation variation among radiation oncologists in the presence of guidelines. MATERIALS AND METHODS Excision cavities, CTVs and PTVs of eight breast cancer patients were delineated on CT scans by 13 Dutch radiation oncologists (observers) from 12 Dutch institutes participating in the international Young Boost Trial. Delineated volumes and conformity indices were determined. CTV delineation variation (SD) was determined for anatomically relevant regions. Non-parametric statistics were performed to establish effects of observers, patient characteristics and regions on delineation variation. RESULTS Even in the presence of delineation guidelines considerable delineation variation is present (0.24<SD<1.22 cm). Presence of clips or seroma reduced interobserver variation (0.24<SD<0.62 cm). Region-specific analysis showed distinct regions of higher variability per patient. This could not always be ascribed to anatomical features, suggesting interobserver variation is not solely due to lack of image quality. CONCLUSIONS In this study, interobserver delineation variation in breast tumour target volume delineation is larger than, e.g. setup inaccuracies and results from limited reliable visual guidance as well as interpretation differences between observers, despite guidelines. Reduction of delineation variation is essential in view of current developments in planning techniques, particularly for External Partial Breast Irradiation.

Breast Patient Setup Error Assessment: Comparison of Electronic Portal Image Devices and Cone-Beam Computed Tomography Matching Results

PURPOSE To quantify the differences in setup errors measured with the cone-beam computed tomography (CBCT) and electronic portal image devices (EPID) in breast cancer patients. METHODS AND MATERIALS Repeat CBCT scan were acquired for routine offline setup verification in 20 breast cancer patients. During the CBCT imaging fractions, EPID images of the treatment beams were recorded. Registrations of the bony anatomy for CBCT to planning CT and EPID to digitally reconstructed-radiographs (DRRs) were compared. In addition, similar measurements of an anthropomorphic thorax phantom were acquired. Bland-Altman and linear regression analysis were performed for clinical and phantom registrations. Systematic and random setup errors were quantified for CBCT and EPID-driven correction protocols in the EPID coordinate system (U, V), with V parallel to the cranial-caudal axis and U perpendicular to V and the central beam axis. RESULTS Bland-Altman analysis of clinical EPID and CBCT registrations yielded 4 to 6-mm limits of agreement, indicating that both methods were not compatible. The EPID-based setup errors were smaller than the CBCT-based setup errors. Phantom measurements showed that CBCT accurately measures setup error whereas EPID underestimates setup errors in the cranial-caudal direction. In the clinical measurements, the residual bony anatomy setup errors after offline CBCT-based corrections were Σ(U) = 1.4 mm, Σ(V) = 1.7 mm, and σ(U) = 2.6 mm, σ(V) = 3.1 mm. Residual setup errors of EPID driven corrections corrected for underestimation were estimated at Σ(U) = 2.2mm, Σ(V) = 3.3 mm, and σ(U) = 2.9 mm, σ(V) = 2.9 mm. CONCLUSION EPID registration underestimated the actual bony anatomy setup error in breast cancer patients by 20% to 50%. Using CBCT decreased setup uncertainties significantly.

Effects of Setup Errors and Shape Changes on Breast Radiotherapy

PURPOSE The purpose of the present study was to quantify the robustness of the dose distributions from three whole-breast radiotherapy (RT) techniques involving different levels of intensity modulation against whole patient setup inaccuracies and breast shape changes. METHODS AND MATERIALS For 19 patients (one computed tomography scan and five cone beam computed tomography scans each), three treatment plans were made (wedge, simple intensity-modulated RT [IMRT], and full IMRT). For each treatment plan, four dose distributions were calculated. The first dose distribution was the original plan. The other three included the effects of patient setup errors (rigid displacement of the bony anatomy) or breast errors (e.g., rotations and shape changes of the breast with respect to the bony anatomy), or both, and were obtained through deformable image registration and dose accumulation. Subsequently, the effects of the plan type and error sources on target volume coverage, mean lung dose, and excess dose were determined. RESULTS Systematic errors of 1-2 mm and random errors of 2-3 mm (standard deviation) were observed for both patient- and breast-related errors. Planning techniques involving glancing fields (wedge and simple IMRT) were primarily affected by patient errors (∼6% loss of coverage near the dorsal field edge and ∼2% near the skin). In contrast, plan deterioration due to breast errors was primarily observed in planning techniques without glancing fields (full IMRT, ∼2% loss of coverage near the dorsal field edge and ∼4% near the skin). CONCLUSION The influences of patient and breast errors on the dose distributions are comparable in magnitude for whole breast RT plans, including glancing open fields, rendering simple IMRT the preferred technique. Dose distributions from planning techniques without glancing open fields were more seriously affected by shape changes of the breast, demanding specific attention in partial breast planning techniques.

Multi-institutional comparison of volumetric modulated arc therapy vs. intensity-modulated radiation therapy for head-and-neck cancer: a planning study

BackgroundCompared to static beam Intensity-Modulated Radiation Therapy (IMRT), the main advantage of Volumetric Modulated Arc Therapy (VMAT) is a shortened delivery time, which leads to improved patient comfort and possibly smaller intra-fraction movements. This study aims at a treatment planner-independent comparison of radiotherapy treatment planning of IMRT and VMAT for head-and-neck cancer performed by several institutes and based on the same CT- and contouring data.MethodsFive institutes generated IMRT and VMAT plans for five oropharyngeal cancer patients using either Pinnacle3 or Oncentra Masterplan to be delivered on Elekta linear accelerators.ResultsComparison of VMAT and IMRT plans within the same patient and institute showed significantly better sparing for almost all OARs with VMAT. The average mean dose to the parotid glands and oral cavity was reduced from 27.2 Gy and 39.4 Gy for IMRT to 25.0 Gy and 36.7 Gy for VMAT, respectively. The dose conformity at 95% of the prescribed dose for PTVboost and PTVtotal was 1.45 and 1.62 for IMRT and 1.37 and 1.50 for VMAT, respectively. The average effective delivery time was reduced from 13:15 min for IMRT to 5:54 min for VMAT.ConclusionsIndependently of institution-specific optimization strategies, the quality of the VMAT plans including double arcs was superior to step-and-shoot IMRT plans including 5–9 beam ports, while the effective treatment delivery time was shortened by ~50% with VMAT.

Assessment of set-up variability during deep inspiration breath hold radiotherapy for breast cancer patients by 3D-surface imaging.

PURPOSE To quantify set-up uncertainties during voluntary deep inspiration breath hold (DIBH) radiotherapy using 3D-surface imaging in patients with left sided breast cancer. MATERIAL AND METHODS Nineteen patients were included. Cone-beam CT-scan (CBCT) was used for online set-up correction while patients were instructed to perform a voluntary DIBH. The reproducibility of the DIBH during treatment was monitored with 2D-fluoroscopy and portal imaging. Simultaneously, a surface imaging system was used to capture 3D-surfaces throughout CBCT acquisition and delivery of treatment beams. Retrospectively, all captured surfaces were registered to the planning-CT surface. Interfraction, intra-fraction and intra-beam set-up variability were quantified in left-right, cranio-caudal and anterior-posterior direction. RESULTS Inter-fraction systematic (Σ) and random (σ) translational errors (1SD) before and after set-up correction were between 0.20-0.50 cm and 0.09-0.22 cm, respectively, whereas rotational Σ and σ errors were between 0.08 and 1.56°. The intra-fraction Σ and σ errors were ≤ 0.14 cm and ≤ 0.47°. The intra-beam SD variability was ≤ 0.08 cm and ≤ 0.28° in all directions. CONCLUSION Quantification of 3D set-up variability in DIBH RT showed that patients are able to perform a very stable and reproducible DIBH within a treatment fraction. However, relatively large inter-fraction variability requires online image guided set-up corrections.

Breast-Conserving Therapy: Radiotherapy Margins for Breast Tumor Bed Boost

PURPOSE To quantify the interfraction position variability of the excision cavity (EC) and to compare the rib and breast surface as surrogates for the cavity. Additionally, we sought to determine the required margin for on-line, off-line and no correction protocols in external beam radiotherapy. METHODS AND MATERIALS A total of 20 patients were studied who had been treated in the supine position for 28 daily fractions. Cone-beam computed tomography scans were regularly acquired according to a shrinking action level setup correction protocol based on bony anatomy registration of the ribs and sternum. The position of the excision area was retrospectively analyzed by gray value cone-beam computed tomography-to-computed tomography registration. Subsequently, three setup correction strategies (on-line, off-line, and no corrections) were applied, according to the rib and breast surface registrations, to estimate the residual setup errors (systematic [Sigma] and random [sigma]) of the excision area. The required margins were calculated using a margin recipe. RESULTS The image quality of the cone-beam computed tomography scans was sufficient for localization of the EC. The margins required for the investigated setup correction protocols and the setup errors for the left-right, craniocaudal and anteroposterior directions were 8.3 mm (Sigma = 3.0, sigma = 2.6), 10.6 mm (Sigma = 3.8, sigma = 3.2), and 7.7 mm (Sigma = 2.7, sigma = 2.9) for the no correction strategy; 5.6 mm (Sigma = 2.0, Sigma = 1.8), 6.5 mm (Sigma = 2.3, sigma = 2.3), and 4.5 mm (Sigma = 1.5, sigma = 1.9) for the on-line rib strategy; and 5.1 mm (Sigma = 1.8, sigma = 1.7), 4.8 mm (Sigma = 1.7, sigma = 1.6), and 3.3 mm (Sigma = 1.1, sigma = 1.6) for the on-line surface strategy, respectively. CONCLUSION Considerable geometric uncertainties in the position of the EC relative to the bony anatomy and breast surface have been observed. By using registration of the breast surface, instead of the rib, the uncertainties in the position of the EC area were reduced.

Bowel exposure in rectal cancer IMRT using prone, supine, or a belly board

PURPOSE To investigate bowel exposure using prone, supine, or two different belly boards for rectal cancer intensity modulated RT plans using a full bladder protocol. METHODS AND MATERIALS For 11 volunteers four MR scans were acquired, on a flat table in prone, supine, and on two different belly boards (IT-V Medizintechnik GmbH® (BB1) and CIVCO® (BB2)), using a full bladder protocol. On each scan a 25×2 Gy IMRT plan was calculated. RESULTS BB2 led to an average bowel area volume reduction of 20-30% at any dose level compared to prone. BB1 showed a smaller dose reduction effect, while no differences between prone and supine were found. Differences between BB2 and prone, supine or BB1 were significant up to a level of respectively, 45, 35, and 30 Gy. The reducing effect varied among individuals, except for the 50 Gy region, where no effect was found. An increase in bladder volume of 100 cc led to a significant bowel area V15 reduction of 16% independent of scan type. CONCLUSIONS In the low and intermediate dose region a belly board still attributes to a significant bowel dose reduction when using IMRT and a full bladder protocol. A larger bladder volume resulted in a significant decreased bowel area dose.

Accuracy Evaluation of a 3-Dimensional Surface Imaging System for Guidance in Deep-Inspiration Breath-Hold Radiation Therapy

PURPOSE To investigate the applicability of 3-dimensional (3D) surface imaging for image guidance in deep-inspiration breath-hold radiation therapy (DIBH-RT) for patients with left-sided breast cancer. For this purpose, setup data based on captured 3D surfaces was compared with setup data based on cone beam computed tomography (CBCT). METHODS AND MATERIALS Twenty patients treated with DIBH-RT after breast-conserving surgery (BCS) were included. Before the start of treatment, each patient underwent a breath-hold CT scan for planning purposes. During treatment, dose delivery was preceded by setup verification using CBCT of the left breast. 3D surfaces were captured by a surface imaging system concurrently with the CBCT scan. Retrospectively, surface registrations were performed for CBCT to CT and for a captured 3D surface to CT. The resulting setup errors were compared with linear regression analysis. For the differences between setup errors, group mean, systematic error, random error, and 95% limits of agreement were calculated. Furthermore, receiver operating characteristic (ROC) analysis was performed. RESULTS Good correlation between setup errors was found: R(2)=0.70, 0.90, 0.82 in left-right, craniocaudal, and anterior-posterior directions, respectively. Systematic errors were ≤0.17 cm in all directions. Random errors were ≤0.15 cm. The limits of agreement were -0.34-0.48, -0.42-0.39, and -0.52-0.23 cm in left-right, craniocaudal, and anterior-posterior directions, respectively. ROC analysis showed that a threshold between 0.4 and 0.8 cm corresponds to promising true positive rates (0.78-0.95) and false positive rates (0.12-0.28). CONCLUSIONS The results support the application of 3D surface imaging for image guidance in DIBH-RT after BCS.