Short-term and long-term reproducibility of lung tumor position using active breathing control (ABC)

Comparative assessment of radiation therapy-induced vasculitis using [18F]FDG-PET/CT in patients with non-small cell lung cancer treated with proton versus photon radiotherapy

PURPOSE

To assess radiation therapy (RT)-induced vasculitis in patients with non-small cell lung cancer (NSCLC) by examining changes in the uptake of 18F-fluoro-D-deoxyglucose ([18F]FDG) by positron emission tomography/computed tomography (PET/CT) images of the ascending aorta (AA), descending aorta (DA), and aortic arch (AoA) before and after proton and photon RT.

METHOD

Thirty-five consecutive locally advanced NSCLC patients were definitively treated with proton (n = 27) or photon (n = 8) RT and concurrent chemotherapy. The patients were prospectively enrolled to undergo [18F]FDG-PET/CT imaging before and 3 months after RT. An adaptive contrast-oriented thresholding algorithm was applied to generate mean standardized uptake values (SUVmean) for regions of interest (ROIs) 3 mm outside and 3 mm inside the outer perimeter of the AA, DA, and AoA. These ROIs were employed to exclusively select the aortic wall and remove the influence of blood pool activity. SUVmeans before and after RT were compared using two-tailed paired t-tests.

RESULTS

RT treatments were associated with increased SUVmeans in the AA, DA, and AoA-1.9%, 0.3%, and 1.3% for proton and 15.8%, 9.5%, and 15.5% for photon, respectively. There was a statistically significant difference in the ∆SUVmean (post-RT SUVmean - pre-RT SUVmean) in patients treated with photon RT when compared to ∆SUVmean in patients treated with proton RT in the AA (p = 0.043) and AoA (p = 0.015). There was an average increase in SUVmean that was related to dose for photon patients (across structures), but that was not seen for proton patients, although the increase was not statistically significant.

CONCLUSION

Our results suggest that patients treated with photon RT for NSCLC may exhibit significantly more RT-induced inflammation (measured as ∆SUVmean) in the AA and AoA when compared to patients who received proton RT. Knowledge gained from further analyses in larger cohorts could aid in treatment planning and help prevent the significant morbidity and mortality associated with RT-induced vascular complications.

TRIAL REGISTRATION

NCT02135679.

A modern review of the uncertainties in volumetric imaging of respiratory-induced target motion in lung radiotherapy

Radiotherapy has become a critical component for the treatment of all stages and types of lung cancer, often times being the primary gateway to a cure. However, given that radiation can cause harmful side effects depending on how much surrounding healthy tissue is exposed, treatment of the lung can be particularly challenging due to the presence of moving targets. Careful implementation of every step in the radiotherapy process is absolutely integral for attaining optimal clinical outcomes. With the advent and now widespread use of stereotactic body radiation therapy (SBRT), where extremely large doses are delivered, accurate, and precise dose targeting is especially vital to achieve an optimal risk to benefit ratio. This has largely become possible due to the rapid development of image-guided technology. Although imaging is critical to the success of radiotherapy, it can often be plagued with uncertainties due to respiratory-induced target motion. There has and continues to be an immense research effort aimed at acknowledging and addressing these uncertainties to further our abilities to more precisely target radiation treatment. Thus, the goal of this article is to provide a detailed review of the prevailing uncertainties that remain to be investigated across the different imaging modalities, as well as to highlight the more modern solutions to imaging motion and their role in addressing the current challenges.

Radiotherapy treatment for lung cancer: Current status and future directions

Radiotherapy is an important modality used for the treatment of lung cancer. Seventy-seven percent of all patients with lung cancer have an evidence-based indication for radiotherapy, although it is often underutilized. Radiotherapy can be used as curative or palliative treatment across all stages of disease. Technological advances have allowed better radiotherapy targeting of tumours and reduced incidental irradiation of surrounding normal tissues. This has expanded the indications for radiotherapy in lung cancer and improved outcomes both in terms of increasing survival and reducing toxicity. This review examines the current role of radiotherapy in lung cancer, discusses the evidence behind this and identifies future directions in the radiotherapy treatment of lung cancer.

Setup Management for Stereotactic Body Radiation Therapy of Patients With Pancreatic Cancer Treated via the Breath-Hold Technique

PURPOSE

Active Breathing Coordinator (Elekta AB, Crawley, UK) is a motion management strategy for radiation treatment. During setup, aligning the patient to the bony spine alone does not necessarily lead to an accurate alignment to soft tissue targets, and further adjustment is necessary. Determining a safe range of values for such adjustments is an important quality assurance measure and was the purpose of this study, with focus on stereotactic body radiation therapy in patients with pancreatic cancer.

METHODS AND MATERIALS

The retrospective study included 19 previously treated patients. For each fraction, a free-breathing cone beam computed tomography scan was registered to a reference breath-hold computed tomography for alignment to the spine. Two perpendicular breath-hold kV projection images were then acquired and compared with corresponding reference digitally reconstructed radiographs for additional alignment with a surrogate fiducial marker. By comparing the breath-hold kV projection images from subsequent treatment fractions with those from the first fraction, we derived the 3-dimensional variability of the fiducial position with respect to the reference image.

RESULTS

We observed intrafraction setup error to be within 2.0 mm. For interfraction, we observed average reproducibility of 1.7 ± 0.8 mm, 2.0 ± 1.4 mm, and 3.2 ± 2.5 mm in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions, respectively. The average excursion values from free breathing spine to breath-hold fiducial alignment were 1.5 ± 1.4 mm, 2.0 ± 1.9 mm, and 3.0 ± 2.0 mm in the LR, AP and SI directions, respectively. The observed ranges of average excursions among all patients were 0.2 to 5.1 mm, 0.1 to 5. 9 mm, and 0.6 to 7.8 mm in the LR, AP, and SI directions, respectively.

CONCLUSIONS

This study demonstrates that intrafraction targeting errors can be within 2 mm, and interfraction shifts from free-breathing spine to Active Breathing Coordinator breath-hold target can be as high as 8 mm. Values that deviate significantly would need further investigation to rule out factors such as local progression, bowel gas, or fiducial shift before treatment.

In-vivo treatment accuracy analysis of active motion-compensated liver SBRT through registration of plan dose to post-therapeutic MRI-morphologic alterations

BACKGROUND/PURPOSE

In-vivo-accuracy analysis (IVA) of dose-delivery with active motion-management (gating/tracking) was performed based on registration of post-radiotherapeutic MRI-morphologic-alterations (MMA) to the corresponding dose-distributions of gantry-based/robotic SBRT-plans.

METHODS

Forty targets in two patient cohorts were evaluated: (1) gantry-based SBRT (deep-inspiratory breath-hold-gating; GS) and (2) robotic SBRT (online fiducial-tracking; RS). The planning-CT was deformably registered to the first post-treatment contrast-enhanced T1-weighted MRI. An isodose-structure cropped to the liver (ISL) and corresponding to the contoured MMA was created. Structure and statistical analysis regarding volumes, surface-distance, conformity metrics and center-of-mass-differences (CoMD) was performed.

RESULTS

Liver volume-reduction was -43.1 ± 148.2 cc post-RS and -55.8 ± 174.3 cc post-GS. The mean surface-distance between MMA and ISL was 2.3 ± 0.8 mm (RS) and 2.8 ± 1.1 mm (GS). ISL and MMA volumes diverged by 5.1 ± 23.3 cc (RS) and 16.5 ± 34.1 cc (GS); the median conformity index of both structures was 0.83 (RS) and 0.80 (GS). The average relative directional errors were ≤0.7 mm (RS) and ≤0.3 mm (GS); the median absolute 3D-CoMD was 3.8 mm (RS) and 4.2 mm (GS) without statistically significant differences between the two techniques. Factors influencing the IVA included GTV and PTV (p = 0.041 and p = 0.020). Four local relapses occurred without correlation to IVA.

CONCLUSIONS

For the first time a method for IVA was presented, which can serve as a benchmarking-tool for other treatment techniques. Both techniques have shown median deviations <5 mm of planned dose and MMA. However, IVA also revealed treatments with errors ≥5 mm, suggesting a necessity for patient-specific safety-margins. Nevertheless, the treatment accuracy of well-performed active motion-compensated liver SBRT seems not to be a driving factor for local treatment failure.

Automatic calibration of an arbitrarily-set near-infrared camera for patient surface respiratory monitoring

PURPOSE

A patient's respiratory monitoring is one of the key techniques in radiotherapy for a moving target. Generally, such monitoring systems are permanently set to a fixed geometry during the installation. This study aims to enable a temporary setup of such a monitoring system by developing a fast method to automatically calibrate the geometrical position by a quick measurement of calibration markers.

METHODS

One calibration marker was placed on the isocenter and the other six markers were placed at positions 5-cm apart from the isocenter to the left, right, anterior, posterior, superior, and inferior directions. A near-infrared (NIR) camera (NIC) [Kinect v2 (Microsoft Corp.)] was arbitrarily set with ten different angles around the calibration phantom with a fixed tilting-down angle at approximately 45° in a linear accelerator treatment vault. The three-dimensional (3D) coordinates in the camera (Cam) coordinate system (CS; x and y are the horizontal and vertical coordinates of the image, respectively, and z is a coordinate along the NIR time-of-flight) were taken for 1 min with 30 frames per second. The data corresponding to the measurement times of 1, 3, 10, 30, and 60 s were created to mimic various measurement times. These data were used to calculate the initial matrix elements, which included six parameters of the pitching, yawing, and rolling angles; horizontal two-dimensional translation in the treatment room; and the source-to-axis distance of NIC, for a conversion from the Cam CS to the treatment room CS for which the origin was defined at the isocenter (Iso coordinate). The six parameters were then optimized to minimize the displacements of the calculated marker coordinates from the actual positions in the Iso CS. The 3D positional accuracy and angular accuracy of the conversion were evaluated. The random error of the Iso coordinates was analyzed through a relation with the angle of each measurement setup.

RESULTS

Three angles of NIC and relative translation vectors were successfully calculated from the measurement data of the calibration markers. The achieved spatial and angular accuracies were 0.02 mm and 1.6°, respectively, after the optimization. Among the mimicked measurement times investigated in this study, both spatial and angular accuracies had no dependence on the measurement time. The average random error of a static marker was 0.46 mm after the optimization.

CONCLUSION

We developed an automatic method to calibrate the 3D patient surface monitoring system. The procedure developed in this study enabled a quick calibration of NIC, which can be easily repeated multiple times for a frequent and quick setup of the monitoring system.

Automated ultrafast kilovoltage-megavoltage cone-beam CT for image guided radiotherapy of lung cancer: System description and real-time results

PURPOSE

To establish a fully automated kV-MV CBCT imaging method on a clinical linear accelerator that allows image acquisition of thoracic targets for patient positioning within one breath-hold (∼15s) under realistic clinical conditions.

METHODS AND MATERIALS

Our previously developed FPGA-based hardware unit which allows synchronized kV-MV CBCT projection acquisition is connected to a clinical linear accelerator system via a multi-pin switch; i.e. either kV-MV imaging or conventional clinical mode can be selected. An application program was developed to control the relevant linac parameters automatically and to manage the MV detector readout as well as the gantry angle capture for each MV projection. The kV projections are acquired with the conventional CBCT system. GPU-accelerated filtered backprojection is performed separately for both data sets. After appropriate grayscale normalization both modalities are combined and the final kV-MV volume is re-imported in the CBCT system to enable image matching. To demonstrate adequate geometrical accuracy of the novel imaging system the Penta-Guide phantom QA procedure is performed. Furthermore, a human plastinate and different tumor shapes in a thorax phantom are scanned. Diameters of the known tumor shapes are measured in the kV-MV reconstruction.

RESULTS

An automated kV-MV CBCT workflow was successfully established in a clinical environment. The overall procedure, from starting the data acquisition until the reconstructed volume is available for registration, requires ∼90s including 17s acquisition time for 100° rotation. It is very simple and allows target positioning in the same way as for conventional CBCT. Registration accuracy of the QA phantom is within ±1mm. The average deviation from the known tumor dimensions measured in the thorax phantom was 0.7mm which corresponds to an improvement of 36% compared to our previous kV-MV imaging system.

CONCLUSIONS

Due to automation the kV-MV CBCT workflow is speeded up by a factor of >10 compared to the manual approach. Thus, the system allows a simple, fast and reliable imaging procedure and fulfills all requirements to be successfully introduced into the clinical workflow now, enabling single-breath-hold volume imaging.

Intra- and inter-fractional liver and lung tumor motions treated with SBRT under active breathing control

Purpose

To assess intra‐ and inter‐fractional motions of liver and lung tumors using active breathing control (ABC).

Methods and Materials

Nineteen patients with liver cancer and 15 patients with lung cancer treated with stereotactic body radiotherapy (SBRT) were included in this retrospective study. All patients received a series of three CTs at simulation to test breath‐hold reproducibility. The centroids of the whole livers and of the lung tumors from the three CTs were compared to assess intra‐fraction variability. For 15 patients (8 liver, 7 lung), ABC‐gated kilovoltage cone‐beam CTs (kV‐CBCTs) were acquired prior to each treatment, and the centroids of the whole livers and of the lung tumors were also compared to those in the planning CTs to assess inter‐fraction variability.

Results

Liver intra‐fractional systematic/random errors were 0.75/0.39 mm, 1.36/0.97 mm, and 1.55/1.41 mm at medial‐lateral (ML), anterior‐posterior (AP), and superior‐inferior (SI) directions, respectively. Lung intra‐fractional systematic/random errors were 0.71/0.54 mm (ML), 1.45/1.10 mm (AP), and 3.95/1.93 mm (SI), respectively. Substantial intra‐fraction motions (>3 mm) were observed in 26.3% of liver cancer patients and in 46.7% of lung cancer patients. For both liver and lung tumors, most inter‐fractional systematic and random errors were larger than the corresponding intra‐fractional errors. However, these inter‐fractional errors were mostly corrected by the treatment team prior to each treatment based on kV CBCT‐guided soft tissue alignment, thereby eliminating their effects on the treatment planning margins.

Conclusions

Intra‐fractional motion is the key to determine the planning margins since inter‐fractional motion can be compensated based on daily gated soft tissue imaging guidance of CBCT. Patient‐specific treatment planning margins instead of recipe‐based margins were suggested, which can benefit mostly for the patients with small intra‐fractional motions.

Interobserver variability of patient positioning using four different CT datasets for image registration in lung stereotactic body radiotherapy

PURPOSE

To assess the impact of different reference CT datasets on manual image registration with free-breathing three-dimensional (3D) cone beam CTs (FB-CBCT) for patient positioning by several observers.

METHODS

For 48 patients with lung lesions, manual image registration with FB-CBCTs was performed by four observers. A slow planning CT (PCT), average intensity projection (AIP), maximum intensity projection (MIP), and midventilation CT (MidV) were used as reference images. Couch shift differences between the four reference CT datasets for each observer as well as shift differences between the observers for the same reference CT dataset were determined. Statistical analyses were performed and correlations between the registration differences and the 3D tumor motion and the CBCT score were calculated.

RESULTS

The mean 3D shift difference between different reference CT datasets was the smallest for AIPvsMIP (range 1.1-2.2 mm) and the largest for MidVvsPCT (2.8-3.5 mm) with differences >10 mm. The 3D shifts showed partially significant correlations to 3D tumor motion and CBCT score. The interobserver comparison for the same reference CTs resulted in the smallest ∆3D mean differences and mean ∆3D standard deviation for ∆AIP (1.5 ± 0.7 mm, 0.7 ± 0.4 mm). The maximal 3D shift difference between observers was 10.4 mm (∆MidV). Both 3D tumor motion and mean CBCT score correlated with the shift differences (R_s = 0.336-0.740).

CONCLUSION

The applied reference CT dataset impacts image registration and causes interobserver variabilities. The 3D tumor motion and CBCT quality affect shift differences. The smallest differences were found for AIP which might be the most appropriate CT dataset for image registration with FB-CBCT.

Feasibility of using single photon counting X-ray for lung tumor position estimation based on 4D-CT

PURPOSE

In stereotactic body radiation therapy of lung tumors, reliable position estimation of the tumor is necessary in order to minimize normal tissue complication rate. While kV X-ray imaging is frequently used, continuous application during radiotherapy sessions is often not possible due to concerns about the additional dose. Thus, ultra low-dose (ULD) kV X-ray imaging based on a single photon counting detector is suggested. This paper addresses the lower limit of photons to locate the tumor reliably with an accuracy in the range of state-of-the-art methods, i.e. a few millimeters.

METHOD

18 patient cases with four dimensional CT (4D-CT), which serves as a-priori information, are included in the study. ULD cone beam projections are simulated from the 4D-CTs including Poisson noise. The projections from the breathing phases which correspond to different tumor positions are compared to the ULD projection by means of Poisson log-likelihood (PML) and correlation coefficient (CC), and template matching under these metrics.

RESULTS

The results indicate that in full thorax imaging five photons per pixel suffice for a standard deviation in tumor positions of less than half a breathing phase. Around 50 photons per pixel are needed to achieve this accuracy with the field of view restricted to the tumor region. Compared to CC, PML tends to perform better for low photon counts and shifts in patient setup. Template matching only improves the position estimation in high photon counts. The quality of the reconstruction is independent of the projection angle.

CONCLUSIONS

The accuracy of the proposed ULD single photon counting system is in the range of a few millimeters and therefore comparable to state-of-the-art tumor tracking methods. At the same time, a reduction in photons per pixel by three to four orders of magnitude relative to commercial systems with flatpanel detectors can be achieved. This enables continuous kV image-based position estimation during all fractions since the additional dose to the patient is negligible.

Advances in radiotherapy techniques and delivery for non-small cell lung cancer: benefits of intensity-modulated radiation therapy, proton therapy, and stereotactic body radiation therapy

The 21st century has seen several paradigm shifts in the treatment of non-small cell lung cancer (NSCLC) in early-stage inoperable disease, definitive locally advanced disease, and the postoperative setting. A key driver in improvement of local disease control has been the significant evolution of radiation therapy techniques in the last three decades, allowing for delivery of definitive radiation doses while limiting exposure of normal tissues. For patients with locally-advanced NSCLC, the advent of volumetric imaging techniques has allowed a shift from 2-dimensional approaches to 3-dimensional conformal radiation therapy (3DCRT). The next generation of 3DCRT, intensity-modulated radiation therapy and volumetric-modulated arc therapy (VMAT), have enabled even more conformal radiation delivery. Clinical evidence has shown that this can improve the quality of life for patients undergoing definitive management of lung cancer. In the early-stage setting, conventional fractionation led to poor outcomes. Evaluation of altered dose fractionation with the previously noted technology advances led to advent of stereotactic body radiation therapy (SBRT). This technique has dramatically improved local control and expanded treatment options for inoperable, early-stage patients. The recent development of proton therapy has opened new avenues for improving conformity and the therapeutic ratio. Evolution of newer proton therapy techniques, such as pencil-beam scanning (PBS), could improve tolerability and possibly allow reexamination of dose escalation. These new progresses, along with significant advances in systemic therapies, have improved survival for lung cancer patients across the spectrum of non-metastatic disease. They have also brought to light new challenges and avenues for further research and improvement.

Registration uncertainties between 3D cone beam computed tomography and different reference CT datasets in lung stereotactic body radiation therapy

Background

The aim of this study was to analyze differences in couch shifts (setup errors) resulting from image registration of different CT datasets with free breathing cone beam CTs (FB-CBCT). As well automatic as manual image registrations were performed and registration results were correlated to tumor characteristics.

Methods

FB-CBCT image registration was performed for 49 patients with lung lesions using slow planning CT (PCT), average intensity projection (AIP), maximum intensity projection (MIP) and mid-ventilation CTs (MidV) as reference images. Both, automatic and manual image registrations were applied. Shift differences were evaluated between the registered CT datasets for automatic and manual registration, respectively. Furthermore, differences between automatic and manual registration were analyzed for the same CT datasets. The registration results were statistically analyzed and correlated to tumor characteristics (3D tumor motion, tumor volume, superior-inferior (SI) distance, tumor environment).

Results

Median 3D shift differences over all patients were between 0.5 mm (AIPvsMIP) and 1.9 mm (MIPvsPCT and MidVvsPCT) for the automatic registration and between 1.8 mm (AIPvsPCT) and 2.8 mm (MIPvsPCT and MidVvsPCT) for the manual registration. For some patients, large shift differences (>5.0 mm) were found (maximum 10.5 mm, automatic registration).

Comparing automatic vs manual registrations for the same reference CTs, ∆AIP achieved the smallest (1.1 mm) and ∆MIP the largest (1.9 mm) median 3D shift differences. The standard deviation (variability) for the 3D shift differences was also the smallest for ∆AIP (1.1 mm). Significant correlations (p < 0.01) between 3D shift difference and 3D tumor motion (AIPvsMIP, MIPvsMidV) and SI distance (AIPvsMIP) (automatic) and also for 3D tumor motion (∆PCT, ∆MidV; automatic vs manual) were found.

Conclusions

Using different CT datasets for image registration with FB-CBCTs can result in different 3D couch shifts. Manual registrations achieved partly different 3D shifts than automatic registrations. AIP CTs yielded the smallest shift differences and might be the most appropriate CT dataset for registration with 3D FB-CBCTs.

MRI morphologic alterations after liver SBRT : Direct dose correlation with intermodal matching

AIM

CT morphologic and histopathologic alterations have been reported after SBRT. We analyzed the correlation of MRI morphologic alterations with radiation doses to assess the potential for MRI-based dose-effect correlation in healthy liver tissue.

PATIENTS AND METHODS

MRI data of 24 patients with liver metastases 7±3 weeks after image-guided SBRT in deep-inspiration breath-hold were retrospectively analyzed. MRI images were intermodally matched to the planning CT and corresponding dose distribution. Absolute doses were converted to EQD2,α/β =x with α/β values of 2, 3 for healthy liver tissue, 8 Gy for modelled predamaged liver tissue and 10 Gy for tumor tissue.

RESULTS

A central nonenhancing area was observed within the isodose lines of nominally 48.2 ± 15.2 Gy, EQD2Gy/α/β =10 92.5 ± 27.7 Gy. Contrast-enhancement around the central nonenhancing area was observed within the isodose lines of nominally 46.9 ± 15.3 Gy, EQD2Gy/α/β =10 90.5 ± 28.3 Gy. Outside the high-dose volume, in the beam path, characteristic sharply defined, nonblurred MRI morphologic alterations were observed that corresponded with the following isodose lines: T1-intensity changes occurred at isodose lines of nominally 21.9 ± 6.7 Gy (EQD2,α/β =2 42.5 ± 8.7 Gy, EQD2,α/β =3 38.5 ± 7.6 Gy, EQD2,α/β =8 30.2 ±6.3 Gy). T2-hyper/hypointensity was observed within isodose lines of nominally 22.4 ± 6.6 Gy (EQD2,α/β=2 42.7 ± 8.1 Gy, EQD2,α/β=3 38.7 ± 7 Gy; EQD2,α/β=8 30.5 ± 5.9 Gy).

CONCLUSIONS

Using deformable matching, direct spatial/dosimetric correlation of SBRT-induced changes in liver tissue was possible. In the PTV high-dose region, a central nonenhancing area and peripheral contrast medium accumulation was observed. Beam path doses of 38-42 Gy (EQD2,α/β =2-3) induce characteristic MRI morphologic alterations.

Stereotactic body radiotherapy: current strategies and future development

Stereotactic body radiotherapy (SBRT) has emerged as the standard treatment for medically inoperable early-staged non-small cell lung cancer (NSCLC). The local control rate after SBRT is over 90%. Some forms of tumour motion management and image-guided radiation delivery techniques are the prerequisites for fulfilment of its goal to deliver a high radiation dose to the tumour target without overdosing surrounding normal tissues. In this review, the current strategies of tumour motion management will be discussed, followed by an overview of various image-guided radiotherapy (RT) systems and devices available for clinical practice. Besides medically inoperable stage I NSCLC, SBRT has also been widely adopted for treatment of oligometastasis involving the lungs. Its possible applications in various other cancer illnesses are under extensive exploration. The progress of SBRT is critically technology-dependent. With advancement of technology, the ideal of personalised, effective and yet safe SBRT is already on the horizon.

Geometric uncertainties in voluntary deep inspiration breath hold radiotherapy for locally advanced lung cancer

BACKGROUND AND PURPOSE

Deep inspiration breath hold (DIBH) increases lung volume and can potentially reduce treatment-related toxicity in locally advanced lung cancer. We estimated geometric uncertainties in visually guided voluntary DIBH and derived the appropriate treatment margins for different image-guidance strategies.

MATERIAL AND METHODS

Seventeen patients were included prospectively. An optical marker-based respiratory monitoring with visual guidance enabled comfortable DIBHs, adjusted to each patient's performance. All patients had three consecutive DIBH CTs at each of the treatment fractions 2, 16 and 31. DIBH reproducibility was evaluated as inter- and intra-fractional variations in lung volume, tumour position and differential motion between primary tumour and mediastinal lymph nodes.

RESULTS

Lung volume increased by median 60% in DIBH. Inter- and intra-fractional lung volume variations were median 2.1% and 1.1%, respectively. Inter- and intra-fractional uncertainties in 3D tumour position were 4.8 ± 2.8 mm and 1.7 ± 1.4 mm (mean ± SD). Inter- and intra-fractional differential motion was 4.8 ± 3.3 mm and 0.0 ± 1.1 mm.

CONCLUSIONS

For single targets, visually guided voluntary DIBH radiotherapy is highly reproducible provided an image-guidance strategy with tumour registration is performed. If the primary tumour is separated from the mediastinal lymph nodes, inter-fractional differential motion remains a challenge and margins must be adapted to reflect the image registration strategy.

Towards clinical implementation of ultrafast combined kV-MV CBCT for IGRT of lung cancer : Evaluation of registration accuracy based on phantom study

PURPOSE

Combined kV-MV cone-beam CT (CBCT) is a promising approach to accelerate imaging for patients with lung tumors treated with deep inspiration breath-hold. During a single breath-hold (15 s), a 3D kV-MV CBCT can be acquired, thus minimizing motion artifacts and increasing patient comfort. Prior to clinical implementation, positioning accuracy was evaluated and compared to clinically established imaging techniques.

METHODS AND MATERIALS

An inhomogeneous thorax phantom with four tumor-mimicking inlays was imaged in 10 predefined positions and registered to a planning CT. Novel kV-MV CBCT imaging (90° arc) was compared to clinically established kV-chest CBCT (360°) as well as nonclinical kV-CBCT and low-dose MV-CBCT (each 180°). Manual registration, automatic registration provided by the manufacturer and an additional in-house developed manufacturer-independent framework based on the MATLAB registration toolkit were applied.

RESULTS

Systematic setup error was reduced to 0.05 mm by high-precision phantom positioning with optical tracking. Stochastic mean displacement errors were 0.5 ± 0.3 mm in right-left, 0.4  ± 0.4 mm in anteroposterior and 0.0 ± 0.4 mm in craniocaudal directions for kV-MV CBCT with manual registration (maximum errors of no more than 1.4 mm). Clinical kV-chest CBCT resulted in mean errors of 0.2 mm (other modalities: 0.4-0.8 mm). Similar results were achieved with both automatic registration methods.

CONCLUSION

The comparison study of repositioning accuracy between novel kV-MV CBCT and clinically established volume imaging demonstrated that registration accuracy is maintained below 1 mm. Since imaging time is reduced to one breath-hold, kV-MV CBCT is ideal for image guidance, e.g., in lung stereotactic ablative radiotherapy.

Deep Inspiration Breath Hold-Based Radiation Therapy: A Clinical Review

Several recent developments in linear accelerator-based radiation therapy (RT) such as fast multileaf collimators, accelerated intensity modulation paradigms like volumeric modulated arc therapy and flattening filter-free (FFF) high-dose-rate therapy have dramatically shortened the duration of treatment fractions. Deliverable photon dose distributions have approached physical complexity limits as a consequence of precise dose calculation algorithms and online 3-dimensional image guided patient positioning (image guided RT). Simultaneously, beam quality and treatment speed have continuously been improved in particle beam therapy, especially for scanned particle beams. Applying complex treatment plans with steep dose gradients requires strategies to mitigate and compensate for motion effects in general, particularly breathing motion. Intrafractional breathing-related motion results in uncertainties in dose delivery and thus in target coverage. As a consequence, generous margins have been used, which, in turn, increases exposure to organs at risk. Particle therapy, particularly with scanned beams, poses additional problems such as interplay effects and range uncertainties. Among advanced strategies to compensate breathing motion such as beam gating and tracking, deep inspiration breath hold (DIBH) gating is particularly advantageous in several respects, not only for hypofractionated, high single-dose stereotactic body RT of lung, liver, and upper abdominal lesions but also for normofractionated treatment of thoracic tumors such as lung cancer, mediastinal lymphomas, and breast cancer. This review provides an in-depth discussion of the rationale and technical implementation of DIBH gating for hypofractionated and normofractionated RT of intrathoracic and upper abdominal tumors in photon and proton RT.

Are three doses of stereotactic ablative radiotherapy (SABR) more effective than 30 doses of conventional radiotherapy?

In early stage non-small cell lung cancer (NSCLC) definitive radiation therapy is an appropriate alternative to surgery. Recent studies show, that in such patients hypofractionation schedules (for example 3 times 18 Gy or 5 times 12 Gy), can be safely applied, without causing severe toxicities and achieving high local control rates of up to 90% and more. In the last couple of years a lot of knowledge about the cancer biology, technical aspects, clinical outcomes and toxicities has been accumulated from different clinical trials. The purpose of this review is to summarize recent outcomes and developments in stereotactic radiation therapy for patients with early stage NSCLC.

Model-guided respiratory organ motion prediction of the liver from 2D ultrasound

With the availability of new and more accurate tumour treatment modalities such as high-intensity focused ultrasound or proton therapy, accurate target location prediction has become a key issue. Various approaches for diverse application scenarios have been proposed over the last decade. Whereas external surrogate markers such as a breathing belt work to some extent, knowledge about the internal motion of the organs inherently provides more accurate results. In this paper, we combine a population-based statistical motion model and information from 2d ultrasound sequences in order to predict the respiratory motion of the right liver lobe. For this, the motion model is fitted to a 3d exhalation breath-hold scan of the liver acquired before prediction. Anatomical landmarks tracked in the ultrasound images together with the model are then used to reconstruct the complete organ position over time. The prediction is both spatial and temporal, can be computed in real-time and is evaluated on ground truth over long time scales (5.5 min). The method is quantitatively validated on eight volunteers where the ultrasound images are synchronously acquired with 4D-MRI, which provides ground-truth motion. With an average spatial prediction accuracy of 2.4 mm, we can predict tumour locations within clinically acceptable margins.

Clinical outcome of hypofractionated breath-hold image-guided SABR of primary lung tumors and lung metastases

Background

Stereotactic Ablative RadioTherapy (SABR) of lung tumors/metastases has been shown to be an effective treatment modality with low toxicity. Outcome and toxicity were retrospectively evaluated in a unique single-institution cohort treated with intensity-modulated image-guided breath-hold SABR (igSABR) without external immobilization. The dose–response relationship is analyzed based on Biologically Equivalent Dose (BED).

Patients and methods

50 lesions in 43 patients with primary NSCLC (n = 27) or lung-metastases of various primaries (n = 16) were consecutively treated with igSABR with Active-Breathing-Coordinator (ABC®) and repeat-breath-hold cone-beam-CT. After an initial dose-finding/-escalation period, 5x12 Gy for peripheral lesions and single doses of 5 Gy to varying dose levels for central lesions were applied. Overall-survival (OS), progression-free-survival (PFS), progression pattern, local control (LC) and toxicity were analyzed.

Results

The median BED2 was 83 Gy. 12 lesions were treated with a BED2 of <80 Gy, and 38 lesions with a BED2 of >80 Gy. Median follow-up was 15 months. Actuarial 1- and 2-year OS were 67% and 43%; respectively. Cause of death was non-disease-related in 27%. Actuarial 1- and 2-year PFS was 42% and 28%. Progression site was predominantly distant. Actuarial 1- and 2 year LC was 90% and 85%. LC showed a trend for a correlation to BED2 (p = 0.1167). Pneumonitis requiring conservative treatment occurred in 23%.

Conclusion

Intensity-modulated breath-hold igSABR results in high LC-rates and low toxicity in this unfavorable patient cohort with inoperable lung tumors or metastases. A BED2 of <80 Gy was associated with reduced local control.

Flattening-filter-free intensity modulated breath-hold image-guided SABR (Stereotactic ABlative Radiotherapy) can be applied in a 15-min treatment slot

Hypofractionated image-guided stereotactic ablative radiotherapy (igSABR) is effective in small lung/liver lesions. Computer-assisted breath-hold reduces intrafraction motion but, as every gating/triggering strategy, reduces the duty cycle, resulting in long fraction times if combined with intensity-modulated radiotherapy (IMRT). 10 MV flattening-filter-free IMRT reduces daily fraction duration to <10 min for single doses of 5-20 Gy.

Challenges and opportunities in patient-specific, motion-managed and PET/CT-guided radiation therapy of lung cancer: review and perspective

The increasing interest in combined positron emission tomography (PET) and computed tomography (CT) to guide lung cancer radiation therapy planning has been well documented. Motion management strategies during treatment simulation PET/CT imaging and treatment delivery have been proposed to improve the precision and accuracy of radiotherapy. In light of these research advances, why has translation of motion-managed PET/CT to clinical radiotherapy been slow and infrequent? Solutions to this problem are as complex as they are numerous, driven by large inter-patient variability in tumor motion trajectories across a highly heterogeneous population. Such variation dictates a comprehensive and patient-specific incorporation of motion management strategies into PET/CT-guided radiotherapy rather than a one-size-fits-all tactic. This review summarizes challenges and opportunities for clinical translation of advances in PET/CT-guided radiotherapy, as well as in respiratory motion-managed radiotherapy of lung cancer. These two concepts are then integrated into proposed patient-specific workflows that span classification schemes, PET/CT image formation, treatment planning, and adaptive image-guided radiotherapy delivery techniques.

[Image-guided radiation therapy]

Radiotherapy technology has improved rapidly over the past two decades. New imaging modalities, such as positron emission (computed) tomography (PET, PET-CT) and high-resolution morphological and functional magnetic resonance imaging (MRI) have been introduced into the treatment planning process. Image-guided radiation therapy (IGRT) with 3D soft tissue depiction directly imaging target and normal structures, is currently replacing patient positioning based on patient surface markers, frame-based intracranial and extracranial stereotactic treatment and partially also 2D field verification methods. On-line 3D soft tissue-based position correction unlocked the full potential of new delivery techniques, such as intensity-modulated radiotherapy, by safely delivering highly conformal dose distributions that facilitate dose escalation and hypofractionation. These strategies have already resulted in better clinical outcomes, e.g. in prostate and lung cancer and are expected to further improve radiotherapy results.

Hypofractionated image-guided breath-hold SABR (stereotactic ablative body radiotherapy) of liver metastases--clinical results

Purpose

Stereotactic Ablative Body Radiotherapy (SABR) is a non-invasive therapy option for inoperable liver oligometastases. Outcome and toxicity were retrospectively evaluated in a single-institution patient cohort who had undergone ultrasound-guided breath-hold SABR.

Patients and methods

19 patients with liver metastases of various primary tumors consecutively treated with SABR (image-guidance with stereotactic ultrasound in combination with computer-controlled breath-hold) were analysed regarding overall-survival (OS), progression-free-survival (PFS), progression pattern, local control (LC), acute and late toxicity.

Results

PTV (planning target volume)-size was 108 ± 109cm³ (median 67.4 cm³). BED2 (Biologically effective dose in 2 Gy fraction) was 83.3 ± 26.2 Gy (median 78 Gy). Median follow-up and median OS were 12 months. Actuarial 2-year-OS-rate was 31%. Median PFS was 4 months, actuarial 1-year-PFS-rate was 20%. Site of first progression was predominantly distant. Regression of irradiated lesions was observed in 84% (median time to detection of regression was 2 months). Actuarial 6-month-LC-rate was 92%, 1- and 2-years-LC-rate 57%, respectively. BED2 influenced LC. When a cut-off of BED2 = 78 Gy was used, the higher BED2 values resulted in improved local control with a statistical trend to significance (p = 0.0999). Larger PTV-sizes, inversely correlated with applied dose, resulted in lower local control, also with a trend to significance (p-value = 0.08) when a volume cut-off of 67 cm³ was used.

No local relapse was observed at PTV-sizes < 67 cm³ and BED2 > 78 Gy. No acute clinical toxicity > °2 was observed. Late toxicity was also ≤ °2 with the exception of one gastrointestinal bleeding-episode 1 year post-SABR. A statistically significant elevation in the acute phase was observed for alkaline-phosphatase; in the chronic phase for alkaline-phosphatase, bilirubine, cholinesterase and C-reactive protein.

Conclusions

A trend to statistically significant correlation of local progression was observed for BED2 and PTV-size. Dose-levels BED2 > 78 Gy cannot be reached in large lesions constituting a significant fraction of this series. Image-guided SABR (igSABR) is therefore an effective non-invasive treatment modality with low toxicity in patients with small inoperable liver metastases.

[Advances of precise radiotherapy for lung cancer]

目前肺部肿瘤的放射治疗已进入精确放疗时代。实施精确放疗的具体方法主要包括：调强放疗（intensity modulated radiotherapy, IMRT）、图像引导放射治疗（image-guided radiotherapy, IGRT）和体部立体定向放射治疗（stereotactic body radiotherapy, SBRT）。在实施精确放疗过程中，对于以下问题：患者体位固定、肺部肿瘤运动的控制、影像技术的使用、PTV边界、剂量的处方和报道、射野的安排、剂量体积的控制和治疗的实施等，应给予充分的考虑和注意，以确保精确放疗能够精确执行。

Lung tumor reproducibility with active breath control (ABC) in image-guided radiotherapy based on cone-beam computed tomography with two registration methods

PURPOSE

To study the inter- and intrafraction tumor reproducibility with active breath control (ABC) utilizing cone-beam computed tomography (CBCT), and compare validity of registration with two different regions of interest (ROI).

METHODS AND MATERIALS

Thirty-one lung tumors in 19 patients received conventional or stereotactic body radiotherapy with ABC. During each treatment, patients had three CBCT scanned before and after online position correction and after treatment. These CBCT images were aligned to the planning CT using the gray scale registration of tumor and bony registration of the thorax, and tumor position uncertainties were then determined.

RESULTS

The interfraction systematic and random translation errors in the left-right (LR), superior-inferior (SI) and anterior-posterior (AP) directions were 3.6, 4.8, and 2.9mm; 2.5, 4.5, and 3.5mm, respectively, with gray scale alignment; 1.9, 4.3, 2.0mm and 2.5, 4.4, 2.9mm, respectively, with bony alignment. The interfraction systematic and random rotation errors with gray scale and bony alignment groups ranged from 1.4° to 3.0° and 0.8° to 2.3°, respectively. The intrafraction systematic and random errors with gray scale registration in LR, SI, AP directions were 0.9, 2.0, 1.8mm and 1.5, 1.7, 2.9mm, respectively, for translation; 1.5°, 0.9°, 1.0° and 1.2°, 2.2°, 1.8°, respectively, for rotation. The translational errors in SI direction with bony alignment were significantly larger than that of gray scale (p<0.05).

CONCLUSIONS

With CBCT guided online correction the interfraction positioning errors can be markedly reduced. The intrafraction errors were not diminished by the use of ABC. Rotation errors were not very remarkable both inter- and intrafraction. Gray scale alignment of tumor may provide a better registration in SI direction.

Multiple breath-hold CBCT for online image guided radiotherapy of lung tumors: simulation with a dynamic phantom and first patient data

BACKGROUND AND PURPOSE

Computer controlled breath-hold effectively reduces organ motion for image-guided precision radiotherapy of lung tumors. However, the acquisition time of 3D cone-beam-CT (CBCT) exceeds maximum breath-hold times. We have developed an approach enabling online verification using CBCT image acquisition with ABC®-based breath-hold.

METHODS

Patient CBCT images were acquired with ABC®-based repeat breath-hold. The clinical situation was also simulated with a Motion Phantom. Reconstruction of patient and phantom images with selection of free-breathing and breath-hold projections only was performed.

RESULTS

CBCT-imaging in repeat breath-hold resulted in a precisely spherical appearance of a tumor-mimicking structure in the phantom. A faint "ghost" structure (free-breathing phases) can be clearly discriminated. Mean percentage of patient breath-hold time was 66%. Reconstruction based on free-breathing-only shows blurring of both tumor and diaphragm, reconstruction based on breath-hold projections only resulted in sharp contours of the same structures. From the phantom experiments, a maximal repositioning error of 1mm in each direction can be estimated.

DISCUSSION AND CONCLUSION

CBCT during repetitive breath hold provides reliable soft-tissue-based positioning. Fast 3D-imaging during one breath-hold is currently under development and has the potential to accelerate clinical linac-based volume imaging.

Extra-cranial Stereotactic Radiation Therapy (ESRT) in the treatment of inoperable stage 1 & 2 non-small-cell lung cancer patients with highly mobile tumours: a literature review

Objective: Extra-cranial Stereotactic Radiation Therapy (ESRT) techniques and equipment utilised in the treatment of Stage 1 or 2 inoperable non-small-cell lung cancer (NSCLC); accounting for Respiratory Induced Tumour Motion (RITM).

Methods: A narrative review of current world literature.

Results: Four main strategies are employed to address RITM: (1) tumour movement minimisation/immobilisation; (2) integration of respiratory movements into planning; (3) respiratory-gating techniques; and (iv) tumour-tracking techniques.

Discussion: Analysis of data gathered suggests that due to inherent difficulties with respiratory function, combined with co-morbidities and the level of dose escalation facilitated by ESRT: techniques that do not require patient ability to comply are more likely to be effective with a wider range of patients. Similarly, treatment planning must incorporate accurate four-dimensional (4D) data to ensure target coverage, although setup and verification should be controlled to smaller margins for error.

Conclusion: The disparate nature of reporting methods restricts statistical comparison. However, this paper suggests that the ESRT technique using abdominal compression (AC), free-breathing respiratory-gating (FBRG), 4D computed tomography (4DCT) planning, combined with daily on board kV cone beam computed tomography (CBCT) imaging for setup and target verification, is a possible candidate for further treatment regime assessments in large multi-centre trials.

Positional reproducibility of pancreatic tumors under end-exhalation breath-hold conditions using a visual feedback technique

PURPOSE

To assess positional reproducibility of pancreatic tumors under end-exhalation (EE) breath-hold (BH) conditions with a visual feedback technique based on computed tomography (CT) images.

METHODS AND MATERIALS

Ten patients with pancreatic cancer were enrolled in an institutional review board-approved trial. All patients were placed in a supine position on an individualized vacuum pillow with both arms raised. At the time of CT scan, they held their breath at EE with the aid of video goggles displaying their abdominal displacement. Each three-consecutive helical CT data set was acquired four times (sessions 1-4; session 1 corresponded to the time of CT simulation). The point of interest within or in proximity to a gross tumor volume was defined based on certain structural features. The positional variations in point of interest and margin size required to cover positional variations were assessed.

RESULTS

The means ± standard deviations (SDs) of intrafraction positional variations were 0.0 ± 1.1, 0.1 ± 1.2, and 0.1 ± 1.0 mm in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions, respectively (p = 0.726). The means ± SDs of interfraction positional variations were 0.3 ± 2.0, 0.8 ± 1.8, and 0.3 ± 1.8 mm in the LR, AP, and SI directions, respectively (p = 0.533). Population-based margin sizes required to cover 95th percentiles of the overall positional variations were 4.7, 5.3, and 4.9 mm in the LR, AP, and SI directions, respectively.

CONCLUSIONS

A margin size of 5 mm was needed to cover the 95th percentiles of the overall positional variations under EE-BH conditions, using this noninvasive approach to motion management for pancreatic tumors.

Fast kilovoltage/megavoltage (kVMV) breathhold cone-beam CT for image-guided radiotherapy of lung cancer

Long image acquisition times of 60-120 s for cone-beam CT (CBCT) limit the number of patients with lung cancer who can undergo volume image guidance under breathhold. We developed a low-dose dual-energy kilovoltage-megavoltage-cone-beam CT (kVMV-CBCT) based on a clinical treatment unit reducing imaging time to < or =15 s. Simultaneous kVMV-imaging was achieved by dedicated synchronization hardware controlling the output of the linear accelerator (linac) based on detector panel readout signals, preventing imaging artifacts from interference of the linac's MV-irradiation and panel readouts. Optimization was performed to minimize the imaging dose. Single MV-projections, reconstructed MV-CBCT images and images of simultaneous 90 degrees kV- and 90 degrees MV-CBCT (180 degrees kVMV-CBCT) were acquired with different parameters. Image quality and imaging dose were evaluated and compared to kV-imaging. Hardware-based kVMV synchronization resulted in artifact-free projections. A combined 180 degrees kVMV-CBCT scan with a total MV-dose of 5 monitor units was acquired in 15 s and with sufficient image quality. The resolution was 5-6 line pairs cm(-1) (Catphan phantom). The combined kVMV-scan dose was equivalent to a kV-radiation scan dose of approximately 33 mGy. kVMV-CBCT based on a standard linac is promising and can provide ultra-fast online volume image guidance with low imaging dose and sufficient image quality for fast and accurate patient positioning for patients with lung cancer under breathhold.

Anatomic and pathologic variability during radiotherapy for a hybrid active breath-hold gating technique

PURPOSE

To evaluate intra- and interfraction variability of tumor and lung volume and position using a hybrid active breath-hold gating technique.

METHODS AND MATERIALS

A total of 159 repeat normal inspiration active breath-hold CTs were acquired weekly during radiotherapy for 9 lung cancer patients (12-21 scans per patient). A physician delineated the gross tumor volume (GTV), lungs, and spinal cord on the first breath-hold CT, and contours were propagated semiautomatically. Intra- and interfraction variability of tumor and lung position and volume were evaluated. Tumor centroid and border variability were quantified.

RESULTS

On average, intrafraction variability of lung and GTV centroid position was <2.0 mm. Interfraction population variability was 3.6-6.7 mm (systematic) and 3.1-3.9 mm (random) for the GTV centroid and 1.0-3.3 mm (systematic) and 1.5-2.6 mm (random) for the lungs. Tumor volume regressed 44.6% +/- 23.2%. Gross tumor volume border variability was patient specific and demonstrated anisotropic shape change in some subjects. Interfraction GTV positional variability was associated with tumor volume regression and contralateral lung volume (p < 0.05). Inter-breath-hold reproducibility was unaffected by time point in the treatment course (p > 0.1). Increases in free-breathing tidal volume were associated with increases in breath-hold ipsilateral lung volume (p < 0.05).

CONCLUSIONS

The breath-hold technique was reproducible within 2 mm during each fraction. Interfraction variability of GTV position and shape was substantial because of tumor volume and breath-hold lung volume change during therapy. These results support the feasibility of a hybrid breath-hold gating technique and suggest that online image guidance would be beneficial.

Hypofractionated radiotherapy for lung tumors with online cone beam CT guidance and active breathing control

Background

To study the set-up errors, PTV margin and toxicity of cone beam CT (CBCT) guided hypofractionated radiotherapy with active breathing control (ABC) for patients with non-small cell lung cancer (NSCLC) or metastatic tumors in lung.

Methods

32 tumors in 20 patients were treated. Based on the location of tumor, dose per fraction given to tumor was divided into three groups: 12 Gy, 8 Gy and 6 Gy. ABC is applied for every patient. During each treatment, patients receive CBCT scan for online set-up correction. The pre- and post-correction setup errors between fractions, the interfractional and intrafractional, set-up errors, PTV margin as well as toxicity are analyzed.

Results

The pre-correction systematic and random errors in the left-right (LR), superior-inferior (SI), anterior-posterior (AP) directions were 3.7 mm and 5.3 mm, 3.1 mm and 2.1 mm, 3.7 mm and 2.8 mm, respectively, while the post-correction residual errors were 0.6 mm and 0.8 mm, 0.8 mm and 0.8 mm, 1.2 mm and 1.3 mm, respectively. There was an obvious intrafractional shift of tumor position. The pre-correction PTV margin was 9.5 mm in LR, 14.1 mm in SI and 8.2 mm in AP direction. After CBCT guided online correction, the PTV margin was markedly reduced in all three directions. The post-correction margins ranged 1.5 to 2.1 mm. The treatment was well tolerated by patients, of whom there were 4 (20%) grade1-2 acute pneumonitis, 3 (15%) grade1 acute esophagitis, 2 (10%) grade1 late pneumonitis and 1 (5%) grade 1 late esophagitis.

Conclusion

The positioning errors for lung SBRT using ABC were significant. Online correction with CBCT image guidance should be applied to reduce setup errors and PTV margin, which may reduce radiotherapy toxicity of tissues when ABC was used.

Feasibility of the use of the Active Breathing Co ordinator (ABC) in patients receiving radical radiotherapy for non-small cell lung cancer (NSCLC)

INTRODUCTION

One method to overcome the problem of lung tumour movement in patients treated with radiotherapy is to restrict tumour motion with an active breathing control (ABC) device. This study evaluated the feasibility of using ABC in patients receiving radical radiotherapy for non-small cell lung cancer.

METHODS

Eighteen patients, median (range) age of 66 (44-82) years, consented to the study. A training session was conducted to establish the patient's breath hold level and breath hold time. Three planning scans were acquired using the ABC device. Reproducibility of breath hold was assessed by comparing lung volumes measured from the planning scans and the volume recorded by ABC. Patients were treated with a 3-field coplanar beam arrangement and treatment time (patient on and off the bed) and number of breath holds recorded. The tolerability of the device was assessed by weekly questionnaire. Quality assurance was performed on the two ABC devices used.

RESULTS

17/18 patients completed 32 fractions of radiotherapy using ABC. All patients tolerated a maximum breath hold time >15s. The mean (SD) patient training time was 13.8 (4.8)min and no patient found the ABC very uncomfortable. Six to thirteen breath holds of 10-14 s were required per session. The mean treatment time was 15.8 min (5.8 min). The breath hold volumes were reproducible during treatment and also between the two ABC devices.

CONCLUSION

The use of ABC in patients receiving radical radiotherapy for NSCLC is feasible. It was not possible to predict a patient's ability to hold breath. A minimum tolerated breath hold time of 15 s is recommended prior to commencing treatment.

Image-guided respiratory-gated lung stereotactic body radiotherapy: which target definition is optimal?

In stereotactic body radiotherapy (SBRT), the respiratory tumor motion makes target definition very important to achieve optimal clinical results for treatment of early stage lung cancer. In this article, the authors quantitatively evaluated the influence of different target definition strategies on image-guided respiratory-gated SBRT for lung cancer. Twelve lung cancer patients with 4D CT estimated target motion of >1 cm were selected for this retrospective study. An experienced physician contoured gross target volumes (GTVs) at each 4D CT phase for all patients. Three types of internal target volumes (ITVs) were generated based on the contoured GTVs:(1) ITVBH: GTV contoured on deep expiration breath-hold (BH) CT with an isotropic internal margin (IM) of 5 mm; (2) ITV50: GTV contoured at the end-expiration (50%) phase with an isotropic IM of 5 mm; (3) ITVGW: Composite volume of all GTVs within the gating window, defined as several phases around phase 50% with residual target motion of <5 mm. Planning target volumes (PTVs) were generated by adding 3 mm isotropic setup error margin to ITVs. Three treatment plans, namely, PlanBH, Plan50, and PlanGW, were created based on the three PTVs. Identical beam settings and planning constraints were used for all three plans for each patient. The prescription dose was 60 Gy in three fractions. The potential toxicities to the critical organs were quantified by mean lung dose (MLD), lung volume receiving >20 Gy (V20), mean heart dose (MHD), and spinal cord dose (SCD). It is shown that the tumor volume and dose coverage are comparable for PlanBH and Plan50. On average, PTVGW are 38% less than PTV50. Although for most patients PTV50 encompasses the entire PTVGW, up to 5.48 cm3 (6%) of PTVGW is outside PTV50. Compared to Plan50, prescribed percentage is about 2% higher for PlanGW, and the average dose decreases in critical organs are 0.78 Gy for MLD, 1.02% for V20, 0.61 Gy for MHD and 0.59 Gy for maximum SCD. For the cases receiving high lung and heart dose with Plan50, the dose reduction is 1.0 Gy for MLD and 1.14 Gy for MHD with PlanGW. Our preliminary results show that a patient-specific ITV, defined as the composite volume of all GTVs within the gating window, may be used to define PTV in image-guided respiratory-gated SBRT. This approach potentially reduces the irradiated volume of normal tissue further without sacrificing target dose coverage and thus may minimize the risk of treatment-related toxicities.

Interfractional changes in tumour volume and position during entire radiotherapy courses for lung cancer with respiratory gating and image guidance

INTRODUCTION

With the purpose of implementing gated radiotherapy for lung cancer patients, this study investigated the interfraction variations in tumour size and internal displacement over entire treatment courses. To explore the potential of image guided radiotherapy (IGRT) the variations were measured using a set-up strategy based on imaging of bony landmarks and compared to a strategy using in room lasers, skin tattoos and cupper landmarks.

MATERIALS AND METHODS

During their six week treatment course of 60Gy in 2Gy fractions, ten patients underwent 3 respiratory gated CT scans. The tumours were contoured on each CT scan to evaluate the variations in volumes and position. The lung tumours and the mediastinal tumours were contoured separately. The positional variations were measured as 3D mobility vectors and correlated to matching of the scans using the two different strategies.

RESULTS

The tumour size was significantly reduced from the first to the last CT scan. For the lung tumours the reduction was 19%, p=0.03, and for the mediastinal tumours the reduction was 34%, p=0.0007. The mean 3D mobility vector and the SD for the lung tumours was 0.51 cm (+/-0.21) for matching using bony landmarks and 0.85 cm (+/-0.54) for matching using skin tattoos. For the mediastinal tumours the corresponding vectors and SD's were 0.55 cm (+/-0.19) and 0.72 cm (+/-0.43). The differences between the vectors were significant for the lung tumours p=0.004. The interfractional overlap of lung tumours was 80-87% when matched using bony landmarks and 70-76% when matched using skin tattoos. The overlap of the mediastinal tumours were 60-65% and 41-47%, respectively.

CONCLUSIONS

Despite the use of gating the tumours varied considerably, regarding both position and volume. The variations in position were dependent on the set-up strategy. Set-up using IGRT was superior to set-up using skin tattoos.

Characterization of pancreatic tumor motion using cine MRI: surrogates for tumor position should be used with caution

PURPOSE

Our current understanding of intrafraction pancreatic tumor motion due to respiration is limited. In this study, we characterized pancreatic tumor motion and evaluated the application of several radiotherapy motion management strategies.

METHODS AND MATERIALS

Seventeen patients with unresectable pancreatic cancer were enrolled in a prospective internal review board-approved study and imaged during shallow free-breathing using cine MRI on a 3T scanner. Tumor borders were agreed on by a radiation oncologist and an abdominal MRI radiologist. Tumor motion and correlation with the potential surrogates of the diaphragm and abdominal wall were assessed. These data were also used to evaluate planning target volume margin construction, respiratory gating, and four-dimensional treatment planning for pancreatic tumors.

RESULTS

Tumor borders moved much more than expected. To provide 99% geometric coverage, margins of 20 mm inferiorly, 10 mm anteriorly, 7 mm superiorly, and 4 mm posteriorly are required. Tumor position correlated poorly with diaphragm and abdominal wall position, with patient-level Pearson correlation coefficients of -0.18-0.43. Sensitivity and specificity of gating with these surrogates was also poor, at 53%-68%, with overall error of 35%-38%, suggesting that the tumor may be underdosed and normal tissues overdosed.

CONCLUSIONS

Motion of pancreatic tumor borders is highly variable between patients and larger than expected. There is substantial deformation with breathing, and tumor border position does not correlate well with abdominal wall or diaphragmatic position. Current motion management strategies may not account fully for tumor motion and should be used with caution.

Quality and accuracy of cone beam computed tomography gated by active breathing control

The purpose of this study was to evaluate the quality and accuracy of cone beam computed tomography (CBCT) gated by active breathing control (ABC), which may be useful for image guidance in the presence of respiration. Comparisons were made between conventional ABC-CBCT (stop and go), fast ABC-CBCT (a method to speed up the acquisition by slowing the gantry instead of stopping during free breathing), and free breathing respiration correlated CBCT. Image quality was assessed in phantom. Accuracy of reconstructed voxel intensity, uniformity, and root mean square error were evaluated. Registration accuracy (bony and soft tissue) was quantified with both an anthropomorphic and a quality assurance phantom. Gantry angle accuracy was measured with respect to gantry speed modulation. Conventional ABC-CBCT scan time ranged from 2.3 to 5.8 min. Fast ABC-CBCT scan time ranged from 1.4 to 1.8 min, and respiratory correlated CBCT scans took 2.1 min to complete. Voxel intensity value for ABC gated scans was accurate relative to a normal clinical scan with all projections. Uniformity and root mean square error performance degraded as the number of projections used in the reconstruction of the fast ABC-CBCT scans decreased (shortest breath hold, longest free breathing segment). Registration accuracy for small, large, and rotational corrections was within 1 mm and 1 degrees. Gantry angle accuracy was within 1 degrees for all scans. For high-contrast targets, performance for image-guidance purposes was similar for fast and conventional ABC-CBCT scans and respiration correlated CBCT.

Real time transit dosimetry for the breath-hold radiotherapy technique: an initial experience

INTRODUCTION

The breath-hold is one of the techniques to obtain the dose escalation for lung tumors. However, the change of the patient's breath pattern can influence the stability of the inhaled air volume, IAV, used in this work as a surrogate parameter to assure the tumor position reproducibility during dose delivery.

MATERIALS AND METHOD

In this paper, an Elekta active breathing coordinator has been used for lung tumor irradiation. This device is not an absolute spirometer and the feasibility study here presented developed (i) the possibility to select a specific range epsilon of IAV values comfortable for the patient and (ii) the ability of a transit signal rate S(t), obtained by a small ion-chamber positioned on the portal image device, to supply in real time the in vivo isocenter dose reproducibility. Indeed, while the selection of the IAV range depends on the patient's ability to follow instructions for breath-hold, the S(t) monitoring can supply to the radiation therapist a surrogate of the tumor irradiation reproducibility.

RESULTS

The detection of the S(t) in real time during breath-hold was used to determine the interfraction isocenter dose variations due to the reproducibility of the patient's breathing pattern. The agreement between the reconstructed and planned isocenter dose in breath-hold at the interfraction level was well within 1.5%, while in free breathing a disagreement up to 8% was observed. The standard deviation of the S(t) in breath-hold observed at the intrafraction level is a bit higher than the one obtained without the patient and this can be justified by the presence of a small residual tumor motion as heartbeat.

CONCLUSION

The technique is simple and can be implemented for routine use in a busy clinic.