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

Markerless liver online adaptive stereotactic radiotherapy: feasibility analysisCervantes

Objective. Radio-opaque markers are recommended for image-guided radiotherapy in liver stereotactic ablative radiotherapy (SABR), but their implantation is invasive. We evaluate in thisin-silicostudy the feasibility of cone-beam computed tomography-guided stereotactic online-adaptive radiotherapy (CBCT-STAR) to propagate the target volumes without implanting radio-opaque markers and assess its consequence on the margin that should be used in that context.Approach. An emulator of a CBCT-STAR-dedicated treatment planning system was used to generate plans for 32 liver SABR patients. Three target volume propagation strategies were compared, analysing the volume difference between the GTVPropagatedand the GTVConventional, the vector lengths between their centres of mass (lCoM), and the 95th percentile of the Hausdorff distance between these two volumes (HD95). These propagation strategies were: (1) structure-guided deformable registration with deformable GTV propagation; (2) rigid registration with rigid GTV propagation; and (3) image-guided deformable registration with rigid GTV propagation. Adaptive margin calculation integrated propagation errors, while interfraction position errors were removed. Scheduled plans (PlanNon-adaptive) and daily-adapted plans (PlanAdaptive) were compared for each treatment fraction.Main results.The image-guided deformable registration with rigid GTV propagation was the best propagation strategy regarding tolCoM(mean: 4.3 +/- 2.1 mm), HD95 (mean 4.8 +/- 3.2 mm) and volume preservation between GTVPropagatedand GTVConventional. This resulted in a planning target volume (PTV) margin increase (+69.1% in volume on average). Online adaptation (PlanAdaptive) reduced the violation rate of the most important dose constraints ('priority 1 constraints', 4.2 versus 0.9%, respectively;p< 0.001) and even improved target volume coverage compared to non-adaptive plans (PlanNon-adaptive).Significance. Markerless CBCT-STAR for liver tumours is feasible using Image-guided deformable registration with rigid GTV propagation. Despite the cost in terms of PTV volumes, daily adaptation reduces constraints violation and restores target volumes coverage.

Applying the N-isopropylacrylamide gel dosimeter to quantify dynamic dose effects: A feasibility study

BACKGROUND:

The gel dosimeter is a chemical as well as a relative dosimeter.

OBJECTIVE:

To evaluate the feasibility of using N-isopropylacrylamide (NIPAM) gel dosimeter to observe the dynamic dose effects and quantification of the respiration, and to help determine the safety margins.

METHODS:

The NIPAM gel dosimeter combined with the dynamic phantom was used to simulate radiotherapy of lung or upper abdominal tumor. The field set to 4 × 5 cm2, simulate respiratory rate of 4 sec/cycle, and motion range 2 cm. MRI was used for reading, and MATLAB was used for analysis. The 3%/3 mm gamma passing rate > 95% was used as a clinical basis for evaluation.

RESULTS:

The dynamic dose curve was compared with 4 × 5, 4 × 4, 4 × 3 cm2 TPS, and gamma passing rates were 74.32%, 54.83%, 30.18%. Gamma mapping demonstrated that the highest dose region was similar to the result of the 4 × 4 cm2 TPS. After appropriate selection and comparing that the ⩾ 60% part of the dose curve with TPS, the gamma passing rate was 96.49%.

CONCLUSIONS:

Using the NIPAM gel dosimeter with dynamic phantom to simulate organ motion during respiration for dynamic dose measurement and quantified the dynamic dose effect is feasible. The results are consistent with clinical evaluation standards.

Using NIPAM gel dosimeter and concentric swing machine to simulate the dose distribution during breathing: A feasibility study

BACKGROUND:

Radiotherapy plays an important role in cancer treatment today. Successful radiotherapy includes precise positioning and accurate dosimetry.

OBJECTIVE:

To use NIPAM gel dosimeter and concentric swing machine to simulate and evaluate the feasibility of lung or upper abdominal tumor dose distribution during breathing.

METHODS:

We used a concentric swing machine to simulate actual radiotherapy for lung or upper abdomen tumors. A 4 × 4 cm2 irradiation field area was set and MRI was performed. Next, readout analysis was performed using MATLAB and the 3 mm, 3% gamma passing rate > 95% was used as a basis for evaluation.

RESULTS:

The concentric dynamic dose curve for a simulated respiratory rate of 3 seconds/breath and 4 × 4 cm2 field was compared with 4 × 4, 3 × 3, and 2 × 2 cm2 treatment planning systems (TPS), and the 3 mm, 3% gamma passing rate was 42.87%, 54.96%, and 49.92%, respectively. Pre-simulation showed that the high-dose region dose curve was similar to the 2 × 2 cm2 TPS result. After appropriate selection and comparison, we found that the 3 mm, 3% gamma passing rate was 97.92% on comparing the > 60% dose curve with the 2 × 2 cm2 TPS.

CONCLUSIONS:

NIPAM gel dosimeter and concentric swing machine use is feasible to simulate dose distribution during breathing and results conforming to clinical evaluation standards.

Target coverage of daily cone-beam computed tomography in breath-hold image-guided radiotherapy for gastric lymphoma

Objectives

We evaluated retrospectively the daily target coverage using cone-beam computed tomography (CBCT) in breath-hold image-guided radiotherapy (BH-IGRT) for gastric lymphoma.

Methods

BH-IGRT was performed using a prescribed dose of 30.6 Gy in 17 fractions for the whole stomach. We assessed the target coverage of the whole stomach on daily CBCT images [daily clinical target volume (CTV)], which was delineated individually by two observers. We evaluated V_95% (percentage of volume receiving ≥95% of the prescribed dose) of daily CTV.

Results

In total, 102 fractions from 6 patients were assessed. The mean V_95% of daily CTV was 97.2%, which was over 95%. In two of six patients, the V_95% of daily CTV was over 95% for either observer in all fractions. One patient had significant interobserver variation (p = 0.013). In 95 fractions (93%), the V_95% of daily CTV was over 95% for either observer.

Conclusion

Daily target coverage for CTV in BH-IGRT for gastric lymphoma seems to be favorable, even when using CBCT.

Advances in knowledge

A previous study ascertained good daily target coverage in BH-IGRT for gastric lymphoma using in-room CT. Even when using CBCT in our study, daily target coverage for CTV in BH-IGRT for gastric lymphoma seems to be favorable.

Safely achieving single prolonged breath-holds of > 5 minutes for radiotherapy in the prone, front crawl position

OBJECTIVE

Breast cancer radiotherapy is increasingly delivered supine with multiple, short breath-holds. There may be heart and lung sparing advantages for locoregional breast cancer of both prone treatment and in a single breath-hold. We test here whether single prolonged breath-holds are possible in the prone, front crawl position.

METHODS

19 healthy volunteers were trained to deliver supine, single prolonged breath-holds with pre-oxygenation and hypocapnia. We tested whether all could achieve the same durations in the prone, front crawl position.

RESULTS

19 healthy volunteers achieved supine, single prolonged breath-holds for mean of 6.2 ± 0.3 min. All were able to hold safely for the same duration while prone (6.1 ± 0.2 min ns. by paired ANOVA). With prone, the increased weight on the chest did not impede chest inflation, nor the ability to hold air in the chest. Thus, the rate of chest deflation (mean anteroposterior deflation movement of three craniocaudally arranged surface markers on the spinal cord) was the same (1.2 ± 0.2, 2.0 ± 0.4 and 1.2 ± 0.4 mm/min) as found previously during supine prolonged breath-holds. No leakage of carbon dioxide or air was detectable into the facemask.

CONCLUSION

Single prolonged (>5 min) breath-holds are equally possible in the prone, front crawl position.

ADVANCES IN KNOWLEDGE

Prolonged breath-holds in the front crawl position are possible and have the same durations as in the supine position. Such training would therefore be feasible for some patients with breast cancer requiring loco-regional irradiation. It would have obvious advantages for hypofractionation.

A Review on Advances in Intra-operative Imaging for Surgery and Therapy: Imagining the Operating Room of the Future

With the advent of Minimally Invasive Surgery (MIS), intra-operative imaging has become crucial for surgery and therapy guidance, allowing to partially compensate for the lack of information typical of MIS. This paper reviews the advancements in both classical (i.e. ultrasounds, X-ray, optical coherence tomography and magnetic resonance imaging) and more recent (i.e. multispectral, photoacoustic and Raman imaging) intra-operative imaging modalities. Each imaging modality was analyzed, focusing on benefits and disadvantages in terms of compatibility with the operating room, costs, acquisition time and image characteristics. Tables are included to summarize this information. New generation of hybrid surgical room and algorithms for real time/in room image processing were also investigated. Each imaging modality has its own (site- and procedure-specific) peculiarities in terms of spatial and temporal resolution, field of view and contrasted tissues. Besides the benefits that each technique offers for guidance, considerations about operators and patient risk, costs, and extra time required for surgical procedures have to be considered. The current trend is to equip surgical rooms with multimodal imaging systems, so as to integrate multiple information for real-time data extraction and computer-assisted processing. The future of surgery is to enhance surgeons eye to minimize intra- and after-surgery adverse events and provide surgeons with all possible support to objectify and optimize the care-delivery process.

The feasibility, safety and optimization of multiple prolonged breath-holds for radiotherapy

BACKGROUND & PURPOSE

Multiple, short breath-holds are now used in single radiotherapy treatment sessions. Here we investigated the feasibility and safety of multiple prolonged breath-holds in a single session. We measured how long is a second breath-hold if we prematurely terminate a single, prolonged breath-hold of >5 min either by using a single breath of oxygen (O₂), or by reintroducing preoxygenation and hypocapnia. We also investigated the feasibility and safety of undertaking 9 prolonged breath-holds in a row.

MATERIALS & METHODS

30 healthy volunteers with no previous breath-holding experience were trained to perform single prolonged breath-holds safely.

RESULTS

Their mean single, prolonged breath-hold duration was 6.1 ± 0.3 se minutes (n = 30). In 18/18 subjects, premature termination (at 5.1 ± 0.2 min) with a single breath of 60% O₂, enabled a 2nd safe breath-hold lasting 3.3 ± 0.2 min. In 18/18 subjects, premature termination at 5.3 ± 0.2 min) by reintroducing preoxygenation and hypocapnia, enabled a 2nd safe breath-hold lasting 5.8 ± 0.3 min. 17/17 subjects could safely perform 9 successive prolonged breath-holds, each terminated (at 4.3 ± 0.2 min) by reintroducing preoxygenation and hypocapnia for 3.1 ± 0.2 min. The 9th unconstrained breath-hold (mean of 6.0 ± 0.3 min) lasted as long as their single breath-hold.

CONCLUSIONS

Multiple prolonged breath-holds are possible and safe. In a ∼19 min treatment session, it would therefore be possible to have ∼13 min for radiotherapy treatment (3 breath-holds) and ∼6 min for setup and recovery. In a 65 min session, it would be possible to have 41 min for radiotherapy and 25 min for setup and recovery.

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.

Interfractional diaphragm changes during breath-holding in stereotactic body radiotherapy for liver cancer

Aim and background

IGRT based on bone matching may produce a large target positioning error in terms of the reproducibility of expiration breath-holding on SBRT for liver cancer. We evaluated the intrafractional and interfractional errors using the diaphragm position at the end of expiration by utilising Abches and analysed the factor of the interfractional error.

Materials and methods

Intrafractional and interfractional errors were measured using a couple of frontal kV images, planning computed tomography (pCT) and daily cone-beam computed tomography (CBCT). Moreover, max-min diaphragm position within daily CBCT image sets with respect to pCT and the maximum value of diaphragm position difference between CBCT and pCT were calculated.

Results

The mean ± SD (standard deviation) of the intra-fraction diaphragm position variation in the frontal kV images was 1.0 ± 0.7 mm in the C-C direction. The inter-fractional diaphragm changes were 0.4 ± 4.6 mm in the C-C direction, 1.4 ± 2.2 mm in the A-P direction, and -0.6 ± 1.8 mm in the L-R direction. There were no significant differences between the maximum value of the max-min diaphragm position within daily CBCT image sets with respect to pCT and the maximum value of diaphragm position difference between CBCT and pCT.

Conclusions

Residual intrafractional variability of diaphragm position is minimal, but large interfractional diaphragm changes were observed. There was a small effect in the patient condition difference between pCT and CBCT. The impact of the difference in daily breath-holds on the interfractional diaphragm position was large or the difference in daily breath-holding heavily influenced the interfractional diaphragm change.

Safely prolonging single breath-holds to >5 min in patients with cancer; feasibility and applications for radiotherapy

OBJECTIVE

Multiple, short and deep inspiratory breath-holds with air of approximately 20 s are now used in radiotherapy to reduce the influence of ventilatory motion and damage to healthy tissue. There may be further clinical advantages in delivering each treatment session in only one single, prolonged breath-hold. We have previously developed techniques enabling healthy subjects to breath-hold for 7 min. Here, we demonstrate their successful application in patients with cancer.

METHODS

15 patients aged 37-74 years undergoing radiotherapy for breast cancer were trained to breath-hold safely with pre-oxygenation and mechanically induced hypocapnia under simulated radiotherapy treatment conditions.

RESULTS

The mean breath-hold duration was 5.3 ± 0.2 min. At breakpoint, all patients were normocapnic and normoxic [mean end-tidal partial pressure of carbon dioxide was 36 ± 1 standard error millimetre of mercury, (mmHg) and mean oxygen saturation was 100 ± 0 standard error %]. None were distressed, nor had gasping, dizziness or disturbed breathing in the post-breath-hold period. Mean blood pressure had risen significantly from 125 ± 3 to 166 ± 4 mmHg at breakpoint (without heart rate falling), but normalized within approximately 20 s of the breakpoint. During breath-holding, the mean linear anteroposterior displacement slope of the L breast marker was <2 mm min(-1).

CONCLUSION

Patients with cancer can be trained to breath-hold safely and under simulated radiotherapy treatment conditions for longer than the typical beam-on time of a single fraction. We discuss the important applications of this technique for radiotherapy.

ADVANCES IN KNOWLEDGE

We demonstrate for the first time a technique enabling patients with cancer to deliver safely a single prolonged breath-hold of >5 min (10 times longer than currently used in radiotherapy practice), under simulated radiotherapy treatment conditions.

Deep inspiration breath-hold radiotherapy for lung cancer: impact on image quality and registration uncertainty in cone beam CT image guidance

OBJECTIVE

We investigated the impact of deep inspiration breath-hold (DIBH) and tumour baseline shifts on image quality and registration uncertainty in image-guided DIBH radiotherapy (RT) for locally advanced lung cancer.

METHODS

Patients treated with daily cone beam CT (CBCT)-guided free-breathing (FB) RT had an additional CBCT in DIBH at three fractions. These CBCT scans were offline rigidly registered (on tumour) to FB and DIBH CT scans acquired at planning. All registrations were repeated to evaluate the intraobserver uncertainty. CBCT scans were scored on degree of streak artefacts and visualization of tumour and anatomical structures. We examined the impact of tumour baseline shift between consecutive DIBHs on CBCT image quality.

RESULTS

CBCT scans from 15 patients were analysed. Intraobserver image registration uncertainty was approximately 2 mm in both FB and DIBH, except for the craniocaudal direction in FB, where it was >3 mm. On the 31st fraction, the intraobserver uncertainty increased compared with the second fraction. This increase was more pronounced in FB. Image quality scores improved in DIBH compared with FB for all parameters in all patients. Simulated tumour baseline shifts ≤2 mm did not affect the CBCT image quality considerably.

CONCLUSION

DIBH CBCT improved image quality and reduced registration uncertainty in the craniocaudal direction in image-guided RT of locally advanced lung cancer. Baseline shifts ≤2 mm in DIBH during CBCT acquisition did not affect image quality. Advances in knowledge: DIBH RT has dosimetric advantages over FB; this work demonstrates an additional benefit of DIBH in terms of registration accuracy because of improved image quality.

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.

Analysis of the setup errors of medical image registration-based cone-beam CT for lung cancer

PURPOSE

This study aimed to investigate the feasibility of efficiently using a rigid image registration (RIR) algorithm or a deformable image registration (DIR) algorithm to match medical images and evaluate the impact of setup errors on intensity modulated radiation therapy of lung cancer patients.

METHODS

Ten lung cancer patients were chosen randomly each day and were subjected to image-guided radiotherapy. The clinical registration between cone-beam computed tomography (CBCT) images and treatment planning system CT images was performed by applying both RIR and DIR; the clinical registration was evaluated on the basis of the contour index, including dice similarity coefficient, sensitivity, and positive predictive value; the optimal scheme of image registration was selected to ensure that the actual irradiation isocenter was consistent with the treatment planning isocenter. In each patient, the translational errors in the right-left (x), superior-inferior (y), and anterior-posterior (z) directions and the rotational errors in the u, υ, and w directions formed by the x, y, and z directions were calculated and analyzed daily in the whole course of treatment; margins were calculated according to this equation: M = 2.5∑+ 0.7δ.

RESULTS

The tumors and the surrounding soft tissues of the patients are shown more clearly in the CBCT images than in the CT images. DIR can be applied more efficiently than RIR to determine the morphological and positional changes in the organs shown in the images with the same or different modalities in the different period. The setup errors in translation in the x, y and z axes were 0.05±0.16, 0.09±0.32 and -0.02±0.13 cm, respectively; by contrast, the setup errors in rotation in u, υ and w directions were (0.41±0.64)°, (-0.08±0.57)° and (-0.03±0.62)°, respectively. The setup errors in the x, y and z axes of the patients indicated that the margins expansions were 0.82, 1.15 and 0.72 cm, respectively.

CONCLUSION

CBCT with DIR can measure and correct the setup errors online; as a result, setup errors in lung cancer treatments can be significantly reduced and the accuracy of radiotherapy can be enhanced.

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.

Automatically gated image-guided breath-hold IMRT is a fast, precise, and dosimetrically robust treatment for lung cancer patients

BACKGROUND

High-dose radiotherapy of lung cancer is challenging. Tumors may move by up to 2 cm in craniocaudal and anteroposterior directions as a function of breathing cycle. Tumor displacement increases with treatment time, which consequentially increases the treatment uncertainty.

OBJECTIVE

This study analyzed whether automatically gated cone-beam-CT (CBCT)-controlled intensity modulated fast deep inspiration breath hold (DIBH) stereotactic body radiation therapy (SBRT) in flattening filter free (FFF) technique and normofractionated lung DIBH intensity-modulated radiotherapy (IMRT)/volumetric-modulated arc therapy (VMAT) treatments delivered with a flattening filter can be applied with sufficient accuracy within a clinically acceptable timeslot.

MATERIALS AND METHODS

Plans of 34 patients with lung tumors were analyzed. Of these patients, 17 received computer-controlled fast DIBH SBRT with a dose of 60 Gy (5 fractions of 12 Gy or 12 fractions of 5 Gy) in an FFF VMAT technique (FFF-SBRT) every other day and 17 received conventional VMAT with a flattening filter (conv-VMAT) and 2-Gy daily fractional doses (cumulative dose 50-70 Gy).

RESULTS

FFF-SBRT plans required more monitor units (MU) than conv-VMAT plans (2956.6 ± 885.3 MU for 12 Gy/fraction and 1148.7 ± 289.2 MU for 5 Gy/fraction vs. 608.4 ± 157.5 MU for 2 Gy/fraction). Total treatment and net beam-on times were shorter for FFF-SBRT plans than conv-VMAT plans (268.0 ± 74.4 s vs. 330.2 ± 93.6 s and 85.8 ± 25.3 s vs. 117.2 ± 29.6 s, respectively). Total slot time was 13.0 min for FFF-SBRT and 14.0 min for conv-VMAT. All modalities could be delivered accurately despite multiple beam-on/-off cycles and were robust against multiple interruptions.

CONCLUSION

Automatically gated CBCT-controlled fast DIBH SBRT in VMAT FFF technique and normofractionated lung DIBH VMAT can be applied with a low number of breath-holds in a short timeslot, with excellent dosimetric accuracy. In clinical routine, these approaches combine optimally reduced lung tissue irradiation with maximal delivery precision for patients with small and larger lung tumors.

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.

Visualization of data in radiotherapy using web services for optimization of workflow

BACKGROUND

Every day a large amount of data is produced within a radiotherapy department. Although this data is available in one form or other within the centralised systems, it is often not in the form which is of interest to the departmental staff. This work presents a flexible browser based reporting and visualization system for clinical and scientific use, not currently found in commercially available software such as MOSAIQ(TM) or ARIA(TM). Moreover, the majority of user merely wish to retrieve data and not record and/or modify data. Thus the idea was conceived, to present the user with all relevant information in a simple and effective manner in the form of web-services. Due to the widespread availability of the internet, most people can master the use of a web-browser. Ultimately the aim is to optimize clinical procedures, enhance transparency and improve revenue.

METHODS

Our working group (BAS) examined many internal procedures, to find out whether relevant information suitable for our purposes lay therein. After the results were collated, it was necessary to select an effective software platform. After a more detailed analysis of all data, it became clear that the implementation of web-services was appropriate. In our institute several such web-based information services had already been developed over the last few years, with which we gained invaluable experience. Moreover, we strived for high acceptance amongst staff members.

RESULTS

By employing web-services, we attained high effectiveness, transparency and efficient information processing for the user. Furthermore, we achieved an almost maintenance-free and low support system. The aim of the project, making web-based information available to the user from the departmental system MOSAIQ, physician letter system MEDATEC(R) and the central finding server MiraPlus (laboratory, pathology and radiology) were implemented without restrictions.

CONCLUSION

Due to widespread use of web-based technology the training effort was effectively nil, since practically every member of staff can master the use of a web-browser. Moreover, we have achieved high acceptance amongst staff members and have improved our effectiveness resulting in a considerable time saving. The many MOSAIQ-specific parts of the system can be readily used by departments which use MOSAIQ as the departmental system.

Heart dose reduction by prone deep inspiration breath hold in left-sided breast irradiation

BACKGROUND AND PURPOSE

Cardiac disease has been related to heart dose after left-sided breast radiotherapy. This trial evaluates the heart sparing ability and feasibility of deep inspiration breath hold (DIBH) in the prone position for left-sided whole breast irradiation (WBI).

MATERIALS AND METHODS

Twelve patients underwent CT-simulation in supine shallow breathing (SB), supine DIBH, prone SB and prone DIBH. A validation cohort of 38 patients received prone SB and prone DIBH CT-scans; the last 30 patients were accepted for prone DIBH treatment. WBI was planned with a prescription dose of 40.05 Gy.

RESULTS

DIBH was able to reduce (p<0.001) heart dose in both positions, with results for prone DIBH at least as favorable as for supine DIBH. Mean heart dose was lowered from 2.2 Gy for prone SB to 1.3 Gy for prone DIBH (p<0.001), while preserving the lung sparing ability of prone positioning. Moreover prone DIBH nearly consistently reduced mean heart dose to less then 2 Gy, regardless of breast volume. All patients were able to perform the simulation procedure, 28/30 patients were treated with prone DIBH.

CONCLUSIONS

This trial demonstrates the ability and feasibility of prone DIBH to acquire optimal heart and lung sparing for left-sided WBI.

Improving radiotherapy planning, delivery accuracy, and normal tissue sparing using cutting edge technologies

In the United States, more than half of all new invasive cancers diagnosed are non-small cell lung cancer, with a significant number of these cases presenting at locally advanced stages, resulting in about one-third of all cancer deaths. While the advent of stereotactic ablative radiation therapy (SABR, also known as stereotactic body radiotherapy, or SBRT) for early-staged patients has improved local tumor control to >90%, survival results for locally advanced stage lung cancer remain grim. Significant challenges exist in lung cancer radiation therapy including tumor motion, accurate dose calculation in low density media, limiting dose to nearby organs at risk, and changing anatomy over the treatment course. However, many recent technological advancements have been introduced that can meet these challenges, including four-dimensional computed tomography (4DCT) and volumetric cone-beam computed tomography (CBCT) to enable more accurate target definition and precise tumor localization during radiation, respectively. In addition, advances in dose calculation algorithms have allowed for more accurate dosimetry in heterogeneous media, and intensity modulated and arc delivery techniques can help spare organs at risk. New delivery approaches, such as tumor tracking and gating, offer additional potential for further reducing target margins. Image-guided adaptive radiation therapy (IGART) introduces the potential for individualized plan adaptation based on imaging feedback, including bulky residual disease, tumor progression, and physiological changes that occur during the treatment course. This review provides an overview of the current state of the art technology for lung cancer volume definition, treatment planning, localization, and treatment plan adaptation.

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.

Evaluation of the geometric accuracy of anatomic landmarks as surrogates for intrapulmonary tumors in image-guided radiotherapy

OBJECTIVES

The purpose of this study was to evaluate the geometric accuracy of thoracic anatomic landmarks as target surrogates of intrapulmonary tumors for manual rigid registration during image-guided radiotherapy (IGRT).

METHODS

Kilovolt cone-beam computed tomography (CBCT) images acquired during IGRT for 29 lung cancer patients with 33 tumors, including 16 central and 17 peripheral lesions, were analyzed. We selected the "vertebrae", "carina", and "large bronchi" as the candidate surrogates for central targets, and the "vertebrae", "carina", and "ribs" as the candidate surrogates for peripheral lesions. Three to six pairs of small identifiable markers were noted in the tumors for the planning CT and Day 1 CBCT. The accuracy of the candidate surrogates was evaluated by comparing the distances of the corresponding markers after manual rigid matching based on the "tumor" and a particular surrogate. Differences between the surrogates were assessed using 1-way analysis of variance and post hoc least-significant-difference tests.

RESULTS

For central targets, the residual errors increased in the following ascending order: "tumor", "bronchi", "carina", and "vertebrae"; there was a significant difference between "tumor" and "vertebrae" (p=0.010). For peripheral diseases, the residual errors increased in the following ascending order: "tumor", "ribs", "vertebrae", and "carina". There was a significant difference between "tumor" and "carina" (p=0.005).

CONCLUSIONS

The "bronchi" and "carina" are the optimal surrogates for central lung targets, while "ribs" and "vertebrae" are the optimal surrogates for peripheral lung targets for manual matching of online and planned tumors.

[Integration of the radiotherapy irradiation planning in the digital workflow]

BACKGROUND AND PURPOSE

At the Clinic of Radiotherapy at the University Hospital Freiburg, all relevant workflow is paperless. After implementing the Operating Schedule System (OSS) as a framework, all processes are being implemented into the departmental system MOSAIQ. Designing a digital workflow for radiotherapy irradiation planning is a large challenge, it requires interdisciplinary expertise and therefore the interfaces between the professions also have to be interdisciplinary. For every single step of radiotherapy irradiation planning, distinct responsibilities have to be defined and documented. All aspects of digital storage, backup and long-term availability of data were considered and have already been realized during the OSS project.

METHOD

After an analysis of the complete workflow and the statutory requirements, a detailed project plan was designed. In an interdisciplinary workgroup, problems were discussed and a detailed flowchart was developed. The new functionalities were implemented in a testing environment by the Clinical and Administrative IT Department (CAI). After extensive tests they were integrated into the new modular department system.

RESULTS AND CONCLUSION

The Clinic of Radiotherapy succeeded in realizing a completely digital workflow for radiotherapy irradiation planning. During the testing phase, our digital workflow was examined and afterwards was approved by the responsible authority.

[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.

RapidArc combined with the active breathing coordinator provides an effective and accurate approach for the radiotherapy of hepatocellular carcinoma

PURPOSE

The goal of this research was to investigate the feasibility of volumetric modulated arc therapy, RapidArc (RA), in association with the active breathing coordinator (ABC) for the treatment of hepatocellular carcinoma (HCC) with radiotherapy.

PATIENTS AND MATERIALS

A total of 12 patients with HCC, after receiving transcatheter arterial chemoembolization (TACE) treatment, underwent three-dimensional computer tomography (3D-CT) scanning associated with ABC using end inspiration hold (EIH), end expiration hold (EEH), and free breathing (FB) techniques. The three-dimensional conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), and RA plans (three 135° arcs) were designed on different CT images, respectively. The liver volume, gross tumor volume (GTV), and planning target volume (PTV) of the three breath status and the dosimetric differences of the different plans were compared.

RESULTS

There were no significant differences in the volumes of live and GTV between the three breathing techniques (p > 0.05); the PTV in FB was greater than in the EEH and EIH (p < 0.05). The overall conformality index (CI) and homogeneity index (HI) for RA (CI 0.92, HI 0.90) were better than IMRT (CI 0.90, HI 0.89) and 3D-CRT (CI 0.70, HI 0.84) for the three breathing techniques (p< 0.05). The RA and IMRT significantly reduced the mean dose, V(20), V(30), and V(40) of normal liver compared to 3D-CRT, while the V(5) and V(10) in RA were higher than in IMRT. The mean values in mean dose, V(10), V(20), V(30), and V(40) of the normal liver were reduced from 13.12 Gy, 46%, 24%, 13%, and 8% in RA(FB) to 10.23 Gy, 35%, 16%, 8%, and 5% in RA(EEH) and 9.23 Gy, 32%, 16%, 8%, and 5% in RA(EIH ), respectively. In addition, the treatment time of RA was equal to 3D-CRT, which was significantly shorter than IMRT.

CONCLUSION

RA in conjunction with ABC for the treatment of HCC with radiotherapy can achieve better dose delivery and ensure the accuracy of the target volume, which spares more organs at risk, uses fewer monitor units, and shortens treatment time.

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.