Multiple "slow" CT scans for incorporating lung tumor mobility in radiotherapy planning

Film measurement and analytical approach for assessing treatment accuracy and latency in a magnetic resonance-guided radiotherapy system

PURPOSE

We measure the dose distribution of gated delivery for different target motions and estimate the gating latency in a magnetic resonance-guided radiotherapy (MRgRT) system.

METHOD

The dose distribution accuracy of the gated MRgRT system (MRIdian, Viewray) was investigated using an in-house-developed phantom that was compatible with the magnetic field and gating method. This phantom contains a simulated tumor and a radiochromic film (EBT3, Ashland, Inc.). To investigate the effect of the number of beam switching and target velocity on the dose distribution, two types of target motions were applied. One is that the target was periodically moved at a constant velocity of 5 mm/s with different pause times (0, 1, 3, 10, and 20 s) between the motions. During different pause times, different numbers of beams were switched on/off. The other one is that the target was moved at velocities of 3, 5, 8, and 10 mm/s without any pause (i.e., continuous motion). The gated method was applied to these motions at MRIdian, and the dose distributions in each condition were measured using films. To investigate the relation between target motion and dose distribution in the gating method, we compared the results of the gamma analysis of the calculated and measured dose distributions. Moreover, we analytically estimated the gating latencies from the dose distributions measured using films and the gamma analysis results.

RESULTS

The gamma pass rate linearly decreased with increasing beam switching and target velocity. The overall gating latencies of beam-hold and beam-on were 0.51 ± 0.17 and 0.35 ± 0.05 s, respectively.

CONCLUSIONS

Film measurements highlighted the factors affecting the treatment accuracy of the gated MRgRT system. Our analytical approach, employing gamma analysis on films, can be used to estimate the overall latency of the gated MRgRT system.

Role of Stereotactic Radiation Therapy in Operable and Inoperable Early-Stage Non-small Cell Lung Cancer

OPINION STATEMENT

Radiation therapy is becoming an increasingly important part of non-small cell lung cancer (NSCLC) management. Approximately 60% of all cancer patients require radiation therapy (RT) as part of their treatment. For lung cancer, this number is even higher, reaching approximately 77% of all patients, from radical to palliative modalities of RT. This percentage may even be underestimated, as it may not account for the more recent use of RT in oligometastatic lung cancer patients. Thus, we can estimate that each year there will be approximately 21,890 new lung cancer patients in the USA requiring RT. These numbers are expected to continue to rise, as lung cancer radiation techniques continue to improve. There is growing interest in determining the best treatment options for early-stage NSCLC patients. There is well-established data showing the benefit of RT for inoperable patients, and more recent encouraging data even in operable patients.

Dynamic hybrid-phase computed tomography simulation in lung stereotactic body radiotherapy: A feasibility study

To assess the feasibility of dynamic hybrid-phase computed tomography (CT_DHP) simulation when patients undergo lung stereotactic body radiation therapy (SBRT). Eighteen non-small-cell lung-cancer patients were immobilised in a stereotactic body frame with abdominal compression. All underwent dynamic hybrid-phase CT scans that were compared with cone-beam CT (CBCT). We also determined the internal target volume (ITV) and evaluated the following four metrics: the "AND" function in the Boolean module of Eclipse, volume overlap (VO), Dice similarity coefficient (DSC), and dose-volume histogram. The average ITV values of 4DCT_DHP and 3D-CBCT were respectively 12.82±10.42 and 14.6±12.18 cm³ (n=72, p<0.001), and the average ITV value of AND was 11.7±10.1 cm³. The average planning target volume (PTV) of 4DCT_DHP and 3D-CBCT was 25.63±18.04 and 28.00±19.82 cm³ (n=72, p<0.001). The median AND difference between ITV and PTV was significant (p<0.01) and had a significantly linear distribution (R²=0.991 for ITV, R²=0.972 for PTV). The average VO of PTV was greater than that of ITV (0.81±0.096; 0.78±0.11). We also observed that the average DSC in PTV (0.83±0.066) was greater than that in ITV (0.81±0.084). The average results indicated that 97.9%±3.44 of ITV_CBCT was covered by 95% of the prescribed dose. The average minimum, maximum and mean percentage doses of ITV_CBCT were 87.9%±9.46, 107.3%±1.57, and 101.3%±1.12, respectively. This paper has demonstrated that dynamic hybrid-phase CT simulation for patients undergoing lung SBRT and also published evaluation metrics in scientific analysis. Our approach also has the advantage of adequate margin and fewer phases in CT simulation.

Variation of Tumor Volume During Moderate Hypo-Fractionated Stereotactic Body Radiation Therapy for Lung Cancer

Aim To investigate the variation of tumor volume during moderate hypo-fractionated stereotactic body radiation therapy (SBRT). Patients and Methods Twenty patients, who received SBRT at our institution, were included in the analysis. A prescribed dose was 56 Gy at iso-center in seven fractions. Tumor volumes before and during SBRT were calculated. In order to investigate factors affecting the variation of tumor volume in RT 2 (after first irradiation) and RT 7 (after last irradiation), various parameters were verified by the Mann-Whitney U test. Results With regard to the low maximum standardized uptake values (SUVmax) group, transient increase of tumor volume was found in RT 2, and tumor volume reduction was hardly found in RT 7. With regard to the high SUVmax group, a transient increase was not found, and a definite reduction was found in the treatment course. Conclusion Accurate prediction of tumor volume variation is required for more accurate treatment, such as adaptive radiation therapy.

Target motion management in breast cancer radiation therapy

Background

Over the last two decades, breast cancer remains the main cause of cancer deaths in women. To treat this type of cancer, radiation therapy (RT) has proved to be efficient. RT for breast cancer is, however, challenged by intrafractional motion caused by respiration. The problem is more severe for the left-sided breast cancer due to the proximity to the heart as an organ-at-risk. While particle therapy results in superior dose characteristics than conventional RT, due to the physics of particle interactions in the body, particle therapy is more sensitive to target motion.

Conclusions

This review highlights current and emerging strategies for the management of intrafractional target motion in breast cancer treatment with an emphasis on particle therapy, as a modern RT technique. There are major challenges associated with transferring real-time motion monitoring technologies from photon to particles beams. Surface imaging would be the dominant imaging modality for real-time intrafractional motion monitoring for breast cancer. The magnetic resonance imaging (MRI) guidance and ultra high dose rate (FLASH)-RT seem to be state-of-the-art approaches to deal with 4D RT for breast cancer.

Application of discrete cosine transform to assess the effect of tumor motion variations on the definition of ITV in lung and liver SBRT

PURPOSE

To use Discrete Cosine Transform to include tumor motion variations on ITV definition of SBRT patients.

METHODS

Data from 66 patients was collected. 2D planar fluoroscopy images (FI) were available for 54 patients. Daily CBCT projections (CBCTp) from 29 patients were employed to measure interfraction amplitude variability. Systematic amplitude variations were obtained from 17 patients with data from both FI and CBCTp. Tumor motion curves obtained from FI were characterized with a Cosine model (CM), based on cosine functions to the power of 2, 4 or 6, and DCT. Performance of both models was evaluated by means of R² coefficient and by comparing their results on Internal Target Volume (ITV) margins against those calculated from original tumor motion curves. Amplitude variations from CBCTp, as well as estimations of baseline shift variations were added to the DCT model to account for their effect on ITV margins.

RESULTS

DCT replicated tumor motion curves with a mean R² values for all patients of 0.86, 0.91 and 0.96 for the lateral (LAT), anterior-posterior (AP) and cranio-caudal (CC) directions respectively. CM yielded worst results, with R² values of 0.64, 0.61 and 0.74 in the three directions. Interfraction amplitude variation increased ITV margins by a 9%, while baseline shift variability implied a 40% and 80-100% increase for normalized values of baseline shift of 0.2 and 0.4 respectively.

CONCLUSIONS

Probability distribution functions of tumor positions can be successfully characterized with DCT. This permits to include tumor motion variablilities obtained from patient population into patient specific ITVs.

Tumour motion management in lung cancer: a narrative review

Respiratory motion is one of the geometrical uncertainties that may affect the accuracy of thoracic radiotherapy in the treatment of lung cancer. Accounting for tumour motion may allow reducing treatment volumes, irradiated healthy tissue and possibly toxicity, and finally enabling dose escalation. Historically, large population-based margins were used to encompass tumour motion. A paradigmatic change happened in the last decades led to the development of modern imaging techniques during the simulation and the delivery, such as the 4-dimensional (4D) computed tomography (CT) or the 4D-cone beam CT scan, has contributed to a better understanding of lung tumour motion and to the widespread use of individualised margins (with either an internal tumour volume approach or a mid-position/ventilation approach). Moreover, recent technological advances in the delivery of radiotherapy treatments (with a variety of commercial solution allowing tumour tracking, gating or treatments in deep-inspiration breath-hold) conjugate the necessity of minimising treatment volumes while maximizing the patient comfort with less invasive techniques. In this narrative review, we provided an introduction on the intra-fraction tumour motion (in both lung tumours and mediastinal lymph-nodes), and summarized the principal motion management strategies (in both the imaging and the treatment delivery) in thoracic radiotherapy for lung cancer, with an eye on the clinical outcomes.

Comparison of internal target volumes defined by three-dimensional, four-dimensional, and cone-beam computed tomography images of a motion phantom

Background

To explore the variations of the gross tumor volume (GTV) from different three-dimensional computed tomography (3DCT) scan modes and the consistency of internal target volume (ITV) between different 3DCT, cone-beam computed tomography (CBCT) and four-dimensional computed tomography (4DCT) scan, a study using a motion phantom simulating sinusoidal movement was conducted.

Methods

For three 3DCT scan modes: the GTV was contoured, and ITV_I was generated on the basis of GTV with a 10-mm margin while ITV_II and ITV_III with a 0-mm margin on the motion direction. ITV_CBCT and ITV_MIP were contoured on the images of CBCT and maximum-intensity projection (MIP) reconstructed 4DCT images. The centroid position shifts of ITVs were analyzed. The volume consistency between ITV_I, ITV_II, ITV_III and ITV_MIP were evaluated by calculating the Dice similarity coefficient (Dsc) and the value of Δ Volume (ΔV). Furthermore, the 3DCT and CBCT images from 12 NSCLC patients were retrospectively collected, then the Dsc and ΔV were calculated.

Results

The mean ± standard deviation of centroid position of ITV_I, ITV_II and ITV_III were 2.3±4.7, 2.6±4.0, and 1.0±1.4 mm, respectively. The mean ± standard deviation of Dsc between ITV_I, ITV_II, ITV_III and ITV_MIP were 0.78±0.77, 0.86±0.1, and 0.94±0.05, respectively. The ΔV of ITV_I, ITV_II, ITV_III were 29.67%, 17.22%, and 6.46%, respectively. The ITV from CBCT showed a deduction rate of 3.1-9.3% compared to 4DCT. For the patients, the mean Dsc andΔV between ITV_I and ITV_CBCT were 0.50 and 60.76%.

Conclusions

The GTV acquired from 3DCT scan mode I possessed great deviation of centroid position and target volume. ITV on the basis of this GTV was significantly larger than ITV_MIP. A good similarity was showed between ITV_III and ITV_MIP, 4DCT is still a golden standard for the ITV delineation, but in the absence of 4DCT, image from 3DCT scan mode III and KV-CBCT may be considered for ITV delineation with caution.

Definition of internal target volumes based on planar X-ray fluoroscopic images for lung and hepatic stereotactic body radiation therapy. Comparison to inhale/exhale CT technique

PURPOSE

To compare tumor motion amplitudes measured with 2D fluoroscopic images (FI) and with an inhale/exhale CT (IECT) technique MATERIALS AND METHODS: Tumor motion of 52 patients (39 lung patients and 13 liver patients) was obtained with both FI and IECT. For FI, tumor detection and tracking was performed by means of a software developed by the authors. Motion amplitude and, thus, internal target volume (ITV), were defined to cover the positions where the tumor spends 95% of the time. The algorithm was validated against two different respiratory motion phantoms. Motion amplitude in IECT was defined as the difference in the position of the centroid of the gross tumor volume in the image sets of both treatments.

RESULTS

Important differences exist when defining ITVs with FI and IECT. Overall, differences larger than 5 mm were obtained for 49%, 31%, and 9.6% of the patients in Superior-Inferior (SI), Anterior-Posterior (AP), and Lateral (LAT) directions, respectively. For tumor location, larger differences were found for tumors in the liver (73.6% SI, 27.3% AP, and 6.7% in LAT had differences larger than 5 mm), while tumors in the upper lobe benefitted less using FI (differences larger than 5 mm were only present in 27.6% (SI), 36.7% (AP), and 0% (LAT) of the patients).

CONCLUSIONS

Use of FI with the linac built-in CBCT system is feasible for ITV definition. Large differences between motion amplitudes detected with FI and IECT methods were found. The method presented in this work based on FI could represent an improvement in ITV definition compared to the method based on IECT due to FI permits tumor motion acquisition in a more realistic situation than IECT.

Electromagnetic Transponder Based Tracking and Gating in the Radiotherapeutic Treatment of Thoracic Malignancies

PURPOSE

This report details our institutional workflow and technique for use of the Calypso electromagnetic transponder system with respiratory gating for localization and tracking of lung tumors during stereotactic radiation therapy for early stage thoracic malignancies.

METHODS AND MATERIALS

Sixteen patients underwent bronchoscopic fiducial placement of 3 transponders in small airways in proximity to the primary tumor. Transponders were placed <19 cm from the most anterior skin location of the patient for appropriate tracking functionality. Patients underwent simulation with 4-dimensional assessment and were treated with transponder based positional gating if tumors moved >5 mm in any direction. Tumor motion <5 mm was not gated and treated using an internal target volume approach. A 5 mm uniform planning target volume was used. Before treatment, fiducial placement and tumor location were verified by daily kilovoltage (kV) and cone beam computed tomography image guidance. Tracking limits were placed based on the movement of the transponders from the centroid of the structures on the maximum intensity projection image. The Calypso treatment system paused treatment automatically if beacons shifted beyond the predefined tracking limits.

RESULTS

All 16 patients underwent successful implantation of the electromagnetic transponders. Eight patients exhibited tumor motion sufficient to require respiratory gating, and the other 8 patients were treated using a free breathing internal target volume technique. Difficulty with transponder sensing was experienced in 3 patients as a result of anatomic interference with the placement of the sensing arrays; each of these cases was successfully treated after making setup modifications. Triggered imaging of fiducials during treatment was consistent with real-time positioning determined by the Calypso tracking system.

CONCLUSIONS

Respiratory gated electromagnetic based transponder guided stereotactic body radiation therapy using the workflow described is feasible and well tolerated in selected patients with early stage lung malignancies.

Selection of patient for gated treatment based on the information from 4DCT imaging in stereotactic body radiotherapy of non-small cell lung cancer

Purpose

Stereotactic body radiotherapy (SBRT) is widely used for the treatment of stage-I non-small cell lung cancer (NSCLC). Patient-specific motion correlated with 4DCT could be essential for hypofractionated SBRT. All patients undergoing SBRT do not require motion management during the dose delivery. The objective of this study was to evaluate which patient may benefit from Gated SBRT.

Materials and methods

Treatment planning of 20 patients of stage-I NSCLC was analysed. Conventional and 4DCT scans were taken. Internal target volume as well as planning target volume (ITV and PTV) were determined in the CT data sets. PTVall phases created using 4DCT data sets and PTV15mm created using conventional CT data were compared. Also, ITVall phases were compared with ITV created from maximum intensity projections (ITVMIP). Suitability of patients for motion management-based treatment delivery was also evaluated.

Results

The average ITVMIP to ITVall phases ratio is 1·06 indicating good agreement between them. Based on the ratio of intensity projections, 9 out of 17 patients were found suitable for our existing gated treatment.

Conclusion

4D CT is the main requirement in SBRT to identify the patients who can benefit from motion management during the dose delivery.

The Practicality of ICRU and Considerations for Future ICRU Definitions

The International Commission on Radiation Units and Measurements (ICRU) volumes are standardized volume definitions used in radiation oncology practice that have evolved over time to account for advancements in technology and radiation planning. The current definitions have strengths but also practical limitations. The main limitation is related to the process of accounting for tumor motion during treatment. As radiotherapeutic techniques become more precise, motion interplay effects and anatomical changes during treatment must be taken into account to ensure accurate and safe delivery of treatment. Adaptive replanning can help to mitigate the effect of these uncertainties and widen the therapeutic ratio by maximizing dose to the tumor and protecting critical normal structures. As adaptive replanning becomes more common, standardization of how adaptive therapy is implemented and reported will become necessary.

Advances in the use of motion management and image guidance in radiation therapy treatment for lung cancer

The development of advanced radiation technologies, including intensity-modulated radiation therapy (IMRT), stereotactic body radiation therapy (SBRT) and proton therapy, has resulted in increasingly conformal radiation treatments. Recent evidence for the importance of minimizing dose to normal critical structures including the heart and lungs has led to incorporation of these advanced treatment modalities into radiation therapy (RT) for non-small cell lung cancer (NSCLC). While such technologies have allowed for improved dose delivery, implementation requires improved target accuracy with treatments, placing increasing importance on evaluating tumor motion at the time of planning and verifying tumor position at the time of treatment. In this review article, we describe issues and updates related both to motion management and image guidance in the treatment of NSCLC.

The impact of technology on the changing practice of lung SBRT

Stereotactic body radiotherapy (SBRT) for lung tumours has been gaining wide acceptance in lung cancer. Here, we review the technological evolution of SBRT delivery in lung cancer, from the first treatments using the stereotactic body frame in the 1990's to modern developments in image guidance and motion management. Finally, we discuss the impact of current technological approaches on the requirements for quality assurance as well as future technological developments.

Optimizing immobilization, margins, and imaging for lung stereotactic body radiation therapy

The simultaneous advancement of technologies for the delivery of precisely targeted radiation therapy and the paradigm shift to substantial hypofractionation have led to significant improvements in the treatment of early stage non-small cell lung cancer (ES-NSCLC). Stereotactic body radiation therapy (SBRT) has become a well-established option for the treatment of ES-NSCLC and is now becoming widely available within the radiation oncology community. Implementation of this technique, however, requires highly accurate target delineation, thorough evaluation of tumor motion, and improved on-board imaging at the time of treatment for patient alignment, each of which is critical for successful tumor control and mitigation of risks to normal tissues. In this article, we review updates and issues related to immobilization and image guidance for SBRT in the treatment of ES-NSCLC.

Gross tumor volume dependency on phase sorting methods of four-dimensional computed tomography images for lung cancer

Purpose

To see the gross tumor volume (GTV) dependency according to the phase selection and reconstruction methods, we measured and analyzed the changes of tumor volume and motion at each phase in 20 cases with lung cancer patients who underwent image-guided radiotherapy.

Materials and Methods

We retrospectively analyzed four-dimensional computed tomography (4D-CT) images in 20 cases of 19 patients who underwent image-guided radiotherapy. The 4D-CT images were reconstructed by the maximum intensity projection (MIP) and the minimum intensity projection (Min-IP) method after sorting phase as 40%–60%, 30%–70%, and 0%–90%. We analyzed the relationship between the range of motion and the change of GTV according to the reconstruction method.

Results

The motion ranges of GTVs are statistically significant only for the tumor motion in craniocaudal direction. The discrepancies of GTV volume and motion between MIP and Min-IP increased rapidly as the wider ranges of duty cycles are selected.

Conclusion

As narrow as possible duty cycle such as 40%–60% and MIP reconstruction was suitable for lung cancer if the respiration was stable. Selecting the reconstruction methods and duty cycle is important for small size and for large motion range tumors.

Magnitude, Impact, and Management of Respiration-induced Target Motion in Radiotherapy Treatment: A Comprehensive Review

Tumors in thoracic and upper abdomen regions such as lungs, liver, pancreas, esophagus, and breast move due to respiration. Respiration-induced motion introduces uncertainties in radiotherapy treatments of these sites and is regarded as a significant bottleneck in achieving highly conformal dose distributions. Recent developments in radiation therapy have resulted in (i) motion-encompassing, (ii) respiratory gating, and (iii) tracking methods for adapting the radiation beam aperture to account for the respiration-induced target motion. The purpose of this review is to discuss the magnitude, impact, and management of respiration-induced tumor motion.

Variations of target volume definition and daily target volume localization in stereotactic body radiotherapy for early-stage non-small cell lung cancer patients under abdominal compression

We aimed to compare gross tumor volumes (GTV) in 3-dimensional computed tomography (3DCT) simulation and daily cone beam CT (CBCT) with the internal target volume (ITV) in 4-dimensional CT (4DCT) simulation in stereotactic body radiotherapy (SBRT) treatment of patients with early-stage non-small cell lung cancer (NSCLC) under abdominal compression. We retrospectively selected 10 patients with NSCLC who received image-guided SBRT treatments under abdominal compression with daily CBCT imaging. GTVs were contoured as visible gross tumor on the planning 3DCT and daily CBCT, and ITVs were contoured using maximum intensity projection (MIP) images of the planning 4DCT. Daily CBCTs were registered with 3DCT and MIP images by matching of bony landmarks in the thoracic region to evaluate interfractional GTV position variations. Relative to MIP-based ITVs, the average 3DCT-based GTV volume was 66.3 ± 17.1% (range: 37.5% to 92.0%) (p < 0.01 in paired t-test), and the average CBCT-based GTV volume was 90.0 ± 6.7% (daily range: 75.7% to 107.1%) (p = 0.02). Based on bony anatomy matching, the center-of-mass coordinates for CBCT-based GTVs had maximum absolute shift of 2.4 mm (left-right), 7.0 mm (anterior-posterior [AP]), and 5.2 mm (superior-inferior [SI]) relative to the MIP-based ITV. CBCT-based GTVs had average overlapping ratio of 81.3 ± 11.2% (range: 45.1% to 98.9%) with the MIP-based ITV, and 57.7 ± 13.7% (range: 35.1% to 83.2%) with the 3DCT-based GTV. Even with abdominal compression, both 3DCT simulations and daily CBCT scans significantly underestimated the full range of tumor motion. In daily image-guided patient setup corrections, automatic bony anatomy-based image registration could lead to target misalignment. Soft tissue-based image registration should be performed for accurate treatment delivery.

A comparative study of the target volume definition in radiotherapy with «Slow CT Scan» vs. 4D PET/CT Scan in early stages non-small cell lung cancer

OBJECTIVES

To evaluate the use of 4D PET/CT to quantify tumor respiratory motion compared to the «Slow»-CT (CTs) in the radiotherapy planning process.

MATERIAL AND METHODS

A total of 25 patients with inoperable early stage non small cell lung cancer (NSCLC) were included in the study. Each patient was imaged with a CTs (4s/slice) and 4D PET/CT. The adequacy of each technique for respiratory motion capture was evaluated using the volume definition for each of the following: Internal target volume (ITV) 4D and ITVslow in relation with the volume defined by the encompassing volume of 4D PET/CT and CTs (ITVtotal). The maximum distance between the edges of the volume defined by each technique to that of the total volume was measured in orthogonal beam's eye view.

RESULTS

The ITV4D showed less differences in relation with the ITVtotal in both the cranio-caudal and the antero-posterior axis compared to the ITVslow. The maximum differences were 0.36mm in 4D PET/CTand 0.57mm in CTs in the antero-posterior axis. 4D PET/CT resulted in the definition of more accurate (ITV4D/ITVtotal 0.78 vs. ITVs/ITVtotal 0.63), and larger ITVs (19.9 cc vs. 16.3 cc) than those obtained with CTs.

CONCLUSION

Planning with 4D PET/CT in comparison with CTs, allows incorporating tumor respiratory motion and improving planning radiotherapy of patients in early stages of lung cancer.

Analysis of precision in tumor tracking based on optical positioning system during radiotherapy

Tumor tracking is performed during patient set-up and monitoring of respiratory motion in radiotherapy. In the clinical setting, there are several types of equipment for this set-up such as the Electronic Portal imaging Device (EPID) and Cone Beam CT (CBCT). Technically, an optical positioning system tracks the difference between the infra ball reflected from body and machine isocenter. Our objective is to compare the clinical positioning error of patient setup between Cone Beam CT (CBCT) with the Optical Positioning System (OPS), and to evaluate the traditional positioning systems and OPS based on our proposed approach of patient positioning. In our experiments, a phantom was used, and we measured its setup errors in three directions. Specifically, the deviations in the left-to-right (LR), anterior-to-posterior (AP) and inferior-to-superior (IS) directions were measured by vernier caliper on a graph paper using the Varian Linear accelerator. Then, we verified the accuracy of OPS based on this experimental study. In order to verify the accuracy of phantom experiment, 40 patients were selected in our radiotherapy experiment. To illustrate the precise of optical positioning system, we designed clinical trials using EPID. From our radiotherapy procedure, we can conclude that OPS has higher precise than conventional positioning methods, and is a comparatively fast and efficient positioning method with respect to the CBCT guidance system.

Hypofractionated 3D radiotherapy for inoperable T1-3 N0-1 non-small-cell lung cancer

OBJECTIVE

This study assessed the toxicity and clinical outcomes of three-dimensional (3D) hypofractionated radiotherapy (HFRT) for medically inoperable T1-3 N0-1 non-small-cell lung cancer (NSCLC).

METHODS

34 patients with inoperable early-stage NSCLC were treated from August 2008 to April 2013. Prior to enrolment, patients were required to be evaluated by an experienced thoracic surgeon to determine the "operability". All received 57 Gy in 19 fractions followed by escalated doses of 3-Gy fractions, up to a total dose of 66 Gy using a 3D conformal technique. Toxicities were measured using the Common Terminology Criteria for Adverse Effects v. 4.0.

RESULTS

The median follow-up was 33 months (7-74 months). Toxicity grades ≥3 were not observed. Local control (LC) was 80.4% at 2 years, whereas regional control (RC) was 78%. The overall survival (OS), time to progression (TTP) and time to distant metastasis (TTM) at 2 years were 60%, 59% and 80%, respectively. For patients with T1-2 N0 and a tumour size <45 mm (n = 19), rates of OS, TTP and TTM at 2 years were 71%, 75% and 94%, respectively. LC and RC at 2 years were 85% and 94%, respectively.

CONCLUSION

HFRT using 3.0-Gy fractions amounting to a total dose of 66 Gy is the recommended dose. A Phase 2 trial is warranted in order to assess the safety and efficacy of this fractionation scheme.

ADVANCES IN KNOWLEDGE

HFRT results in a favourable outcome in early-stage lung cancer without the usual restrictions in tumour size and/or location associated with previous treatment methods. No special equipment is required, therefore permitting its application in any centre.

A forward planned treatment planning technique for non-small-cell lung cancer stereotactic ablative body radiotherapy based on a systematic review of literature

Purpose and Method

A systematic literature review of six computerised databases was undertaken in order to review and summarise a forward planned lung stereotactic ablative body radiotherapy (SABR) treatment planning (TP) technique as a starting point for clinical implementation in the author’s department based on current empirical research. The data were abstracted and content analysed to synthesise the findings based upon a SIGN quality checklist tool.

Findings

A four-dimensional computed tomography scan should be performed upon which the internal target volume and organs at risk (OAR) are drawn. A set-up margin of 5 mm is applied to account for inter-fraction motion. The field arrangement consists of a combination of 7–13 coplanar and non-coplanar beams all evenly spaced. Beam modifiers are used to assist in the homogeneity of the beam, although a 20% planning target volume dose homogeneity is acceptable. The recommended fractionations by the UK SABR Consortium are 54 Gy in 3 fractions (standard), 55–60 Gy in 5 fractions (conservative) and 50–60 Gy in 8–10 fractions (very conservative). Conformity indices for both the target volume and OAR will be used to assess the planned distribution.

Conclusion

An overview of a clinically acceptable forward planned lung SABR TP technique based on current literature as a starting point, with a view to inverse planning with support from the UK SABR Consortium mentoring scheme.

Molecular Imaging to Plan Radiotherapy and Evaluate Its Efficacy

Molecular imaging plays a central role in the management of radiation oncology patients. Specific uses of imaging, particularly to plan radiotherapy and assess its efficacy, require an additional level of reproducibility and image quality beyond what is required for diagnostic imaging. Specific requirements include proper patient preparation, adequate technologist training, careful imaging protocol design, reliable scanner technology, reproducible software algorithms, and reliable data analysis methods. As uncertainty in target definition is arguably the greatest challenge facing radiation oncology, the greatest impact that molecular imaging can have may be in the reduction of interobserver variability in target volume delineation and in providing greater conformity between target volume boundaries and true tumor boundaries. Several automatic and semiautomatic contouring methods based on molecular imaging are available but still need sufficient validation to be widely adopted. Biologically conformal radiotherapy (dose painting) based on molecular imaging-assessed tumor heterogeneity is being investigated, but many challenges remain to fully exploring its potential. Molecular imaging also plays increasingly important roles in both early (during treatment) and late (after treatment) response assessment as both a predictive and a prognostic tool. Because of potentially confounding effects of radiation-induced inflammation, treatment response assessment requires careful interpretation. Although molecular imaging is already strongly embedded in radiotherapy, the path to widespread and all-inclusive use is still long. The lack of solid clinical evidence is the main impediment to broader use. Recommendations for practicing physicians are still rather scarce. (18)F-FDG PET/CT remains the main molecular imaging modality in radiation oncology applications. Although other molecular imaging options (e.g., proliferation imaging) are becoming more common, their widespread use is limited by lack of tracer availability and inadequate reimbursement models. With the increasing presence of molecular imaging in radiation oncology, special emphasis should be placed on adequate training of radiation oncology personnel to understand the potential, and particularly the limitations, of quantitative molecular imaging applications. Similarly, radiologists and nuclear medicine specialists should be sensitized to the special need of the radiation oncologist in terms of quantification and reproducibility. Furthermore, strong collaboration between radiation oncology, nuclear medicine/radiology, and medical physics teams is necessary, as optimal and safe use of molecular imaging can be ensured only within appropriate interdisciplinary teams.

The development of stereotactic body radiotherapy in the past decade: a global perspective

In the past 10 years, there has been an exponential increase in the incorporation of stereotactic body radiotherapy, also known as stereotactic ablative radiotherapy, into the armamentarium against various types of cancer in different settings worldwide. In this article in the 10th year anniversary issue of Future Oncology, representatives from the USA, Canada, Japan, Germany, The Netherlands, Australia and Singapore will provide individual perspectives of the development of stereotactic body radiotherapy in their respective countries.

The applications of corrected standardized uptake values in the diagnosis of peripheral lung lesions

Fluorine 18-fluorodeoxyglucose positron emission tomography/computed tomography (F-FDG PET/CT) imaging has been widely used to diagnose many types of tumors. However, many factors can affect the accuracy of standardized uptake values (SUVs). In this study, we aimed to explore the applications of corrected SUVs in the diagnosis of peripheral solitary pulmonary lesions.A retrospective study was undertaken in 69 patients with peripheral solitary pulmonary lesions. Whole-body PET/CT was acquired approximately 60 min after F-FDG injection. The lesions were found to be malignant in 57 cases and benign in 12 cases. Of the 69 cases, 68 were correctly diagnosed, and only 1 was misdiagnosed by the corrected SUVs. The diagnostic accuracy rate was 98.5%. The sensitivity, specificity, positive predictive value, and negative predictive value of the corrected SUV were 100%, 91.7%, 98.3%, and 100%, respectively.F-FDG PET/CT with corrected SUVs is of great value for improving diagnostic accuracy in peripheral lung lesions.

Stereotactic body radiotherapy for small lung tumors in the University of Tokyo Hospital

Our work on stereotactic body radiation therapy (SBRT) for primary and metastatic lung tumors will be described. The eligibility criteria for SBRT, our previous SBRT method, the definition of target volume, heterogeneity correction, the position adjustment using four-dimensional cone-beam computed tomography (4D CBCT) immediately before SBRT, volumetric modulated arc therapy (VMAT) method for SBRT, verifying of tumor position within internal target volume (ITV) using in-treatment 4D-CBCT during VMAT-SBRT, shortening of treatment time using flattening-filter-free (FFF) techniques, delivery of 4D dose calculation for lung-VMAT patients using in-treatment CBCT and LINAC log data with agility multileaf collimator, and SBRT method for centrally located lung tumors in our institution will be shown. In our institution, these efforts have been made with the goal of raising the local control rate and decreasing adverse effects after SBRT.

Applications of linac-mounted kilovoltage Cone-beam Computed Tomography in modern radiation therapy: A review

The use of Cone-beam Computed Tomography (CBCT) in radiotherapy is increasing due to the widespread implementation of kilovoltage systems on the currently available linear accelerators. Cone beam CT acts as an effective Image-Guided Radiotherapy (IGRT) tool for the verification of patient position. It also opens up the possibility of real-time re-optimization of treatment plans for Adaptive Radiotherapy (ART). This paper reviews the most prominent applications of CBCT (linac-mounted) in radiation therapy, focusing on CBCT-based planning and dose calculation studies. This is followed by a concise review of the main issues associated with CBCT, such as imaging artifacts, dose and image quality. It explores how medical physicists and oncologists can best apply CBCT for therapeutic applications.

Reconstitution of internal target volumes by combining four-dimensional computed tomography and a modified slow computed tomography scan in stereotactic body radiotherapy planning for lung cancer

Background

To evaluate the volumetric and geometric differences in the ITVs generated by four-dimensional (4D) computed tomography (CT), a modified slow CT scan, and a combination of these CT methods in lung cancer patients treated with stereotactic body radiotherapy (SBRT).

Methods

Both 4D CT and modified slow CT using a multi-slice CT scanner were performed for SBRT planning in 14 patients with 15 pulmonary targets. Volumetric and geometric analyses were performed for (1) ITVall, generated by combining the gross tumor volumes (GTVs) from all 8 phases of the 4D CT; (2) ITV2, generated by combining the GTVs from 2 extreme phases of the 4D CT; (3) ITVslow, derived from the GTV on the modified slow CT scan; (4) ITVall+slow, generated by combining ITVall and ITVslow; and (5) ITV2+slow, generated by combining ITV2 and ITVslow. Three SBRT plans were performed using 3 ITVs to assess the dosimetric effects on normal lung caused by the various target volumes.

Results

ITVall (11.8 ± 8.3 cm³) was significantly smaller than ITVall+slow (12.5 ± 8.9 cm³), with mean values of 5.8% for the percentage volume difference, and a mean of 7.5% of ITVslow was not encompassed in ITVall. The geometric coverages of ITV2 and ITVslow for ITVall were 84.7 ± 6.6% and 76.2 ± 9.3%, respectively, but the coverage for ITVall increased to 90.9 ± 5.9% by using the composite of these two ITVs. There were statistically significant increases in the lung-dose parameters of the plans based on ITVall+slow compared to the plans based on ITVall or ITV2+slow. However, the magnitudes of these differences were relatively small, with a value of less than 3% in all dosimetric parameters.

Conclusions

Due to its ability to provides additional motion information, the combination of 4D CT and a modified slow CT scan in SBRT planning for lung cancer can be used to reduce possible errors in true target delineation caused by breathing pattern variations.

Geometrical differences in gross target volumes between 3DCT and 4DCT imaging in radiotherapy for non-small-cell lung cancer

The aim of this study was to explore the characteristic of 3DCT scanning phases and estimate the comparative amount of respiration motion information included in 3DCT and 4DCT by comparing the volumetric and positional difference between the volumes from 3DCT and 4DCT for the radiotherapy of non-small-cell lung cancer (NSCLC). A total of 28 patients with NSCLC sequentially underwent 3DCT and 4DCT simulation scans of the thorax during free breathing. The 4DCT images with respiratory signal data were reconstructed and sorted into 10 phases throughout a respiratory cycle. GTV-3D from 3DCT, GTV-0%, GTV-20%, GTV-50% and GTV-70% from end-inspiration, mid-expiration, end-expiration and mid-inspiration of 4DCT, and the internal GTV (IGTV-10) from the fused phase of 4DCT were delineated based on the 50% phase image, respectively. The differences in the position, size, matching index (MI) and degree of inclusion (DI) for different volumes were evaluated. The variation in the centroid shifts of GTV-0% and GTV-3D, GTV-20% and GTV-3D, GTV-50% and GTV-3D, and GTV-90% and GTV-3D in the 3D direction was not significant (P = 0.990). The size ratios of GTV-0%, GTV-20%, GTV-50%, GTV-70% and IGTV-10 to GTV-3D were 0.94 ± 0.18, 0.95 ± 0.18, 0.98 ± 0.15, 1.00 ± 0.18 and 1.60 ± 0.55, respectively. DIs of GTV-3D in IGTV-10, and IGTV-10 in GTV-3D were 0.88 ± 0.14 and 0.59 ± 0.16 (P < 0.001). The 3DCT scanning phases are irregular. The CTV-to-ITV expansion should be isotropic when defining the ITV on the 3DCT. The internal GTV derived from 4DCT cannot completely include the GTV from 3DCT. An additional margin may be required when defining the ITV-based 4DCT.

Respiratory Gating for Radiotherapy: Main Technical Aspects and Clinical Benefits

Respiratory-gated radiotherapy offers a significant potential for improvement in the irradiation of tumor sites affected by respiratory motion such as lung, breast, and liver tumors. An increased conformality of irradiation fields leading to decreased complication rates of organs at risk is expected. Five main strategies are used to reduce respiratory motion effects: integration of respiratory movements into treatment planning, forced shallow breathing with abdominal compression, breath-hold techniques, respiratory gating techniques, and tracking techniques. Measurements of respiratory movements can be performed either in a representative sample of the general population, or directly on the patient before irradiation. Reduction of breathing motion can be achieved by using either abdominal compression, breath-hold techniques, or respiratory gating techniques. Abdominal compression can be used to reduce diaphragmatic excursions. Breath-hold can be achieved with active techniques, in which airflow of the patient is temporarily blocked by a valve, or passive techniques, in which the patient voluntarily breath-holds. Respiratory gating techniques use external devices to predict the phase of the breathing cycle while the patient breathes freely. Another approach is tumor-tracking technique, which consists of a real-time localization of a constantly moving tumor. This work describes these different strategies and gives an overview of the literature.

Motion management in positron emission tomography/computed tomography for radiation treatment planning

Hybrid positron emission tomography (PET)/computed tomography (CT) scanners combine, in a unique gantry, 2 of the most important diagnostic imaging systems, a CT and a PET tomograph, enabling anatomical (CT) and functional (PET) studies to be performed in a single study session. Furthermore, as the 2 scanners use the same spatial coordinate system, the reconstructed CT and PET images are spatially co-registered, allowing an accurate localization of the functional signal over the corresponding anatomical structure. This peculiarity of the hybrid PET/CT system results in improved tumor characterization for oncological applications, and more recently, it was found to be also useful for target volume definition (TVD) and treatment planning in radiotherapy (RT) applications. In fact, the use of combined PET/CT information has been shown to improve the RT treatment plan when compared with that obtained by a CT alone. A limiting factor to the accuracy of TVD by PET/CT is organ and tumor motion, which is mainly due to patient respiration. In fact, respiratory motion has a degrading effect on PET/CT image quality, and this is also critical for TVD, as it can lead to possible tumor missing or undertreatment. Thus, the management of respiratory motion is becoming an increasingly essential component in RT treatment planning; indeed, it has been recognized that the use of personalized motion information can improve TVD and, consequently, permit increased tumor dosage while sparing surrounding healthy tissues and organs at risk. This review describes the methods used for motion management in PET/CT for radiation treatment planning. The article covers the following: (1) problems caused by organ and lesion motion owing to respiration, and the artifacts generated on CT, PET, and PET/CT images; (2) data acquisition and processing techniques used to manage respiratory motion in PET/CT studies; and (3) the use of personalized motion information for TVD and radiation treatment planning.

Stereotactic ablative radiotherapy delivered by image-guided helical tomotherapy for extracranial oligometastases

PURPOSE

To investigate the outcomes and risk factors of patients treated with stereotactic ablative radiotherapy (SABR) delivered by image-guided helical tomotherapy (HT) for extracranial oligometastases.

METHODS

From August 2006 through July 2011, 42 consecutive patients (median age 69 years [range 16-87]) with oligometastases (≤3) received HT to all known cancer sites (lung, n = 28; liver, n = 12; adrenal, n = 2). Prognostic factors were assessed by Cox's proportional hazards regression analysis.

RESULTS

A total of 60 lesions were treated with hypofractionated HT (median dose 39 Gy [range 36-72.5]; median dose per fraction 12 Gy [range 5-20]). Complete or partial response was observed in 40 (54 %) patients. With a median follow-up period of 15 months, 1- and 2-year overall survival (OS) was 84 and 63 %, respectively; and 1- and 2-year local control (LC) was 92 and 86 %, respectively. Four patients had pneumonitis Grade ≥2 and two patients had lower gastrointestinal toxicity Grade ≥2. Only the lack of complete/partial response was associated with higher risk of mortality on univariate (HR = 3.8, P = 0.04) and multivariate (HR = 6.6, P = 0.01) analyses.

CONCLUSIONS

SABR delivered by image-guided HT is well tolerated and offers adequate LC with low acute morbidity in patients with extracranial oligometastatic disease. We found that the response to HT was the only predictor for OS.

Results of stereotactic radiotherapy for stage I non-small-cell lung cancer: is there a need for image guidance and highly sophisticated devices?

SUMMARY In stage I non-small-cell lung cancer, stereotactic body radiation therapy achieves a local control of 90%, by accurate dose delivery with stereotactic beam navigation and/or image-guided techniques, and extremely dose-escalated hypofractionated radiotherapy. Three-to-ten fractions over 1–2 weeks or one single fraction as radiosurgery are used. A broad spectrum of different techniques have also been introduced, some encouraged by electric companies, and heavily commercialized by institutions and physicians. Although a direct comparison of these techniques has been carried out only in technical and not within clinical trials; clinical data from the few prospective Phase I and II trials and the majority of retrospective evaluations have not shown superiority of either technique. Based on personal experiences, there are nearly no limitations for the use of very simple and cheap techniques, and the broad and increasing disposition of dedicated systems is questionable.

Four dimensional CT imaging: a review of current technologies and modalities

Organ motion is a substantial concern in the treatment of thoracic tumours using radiotherapy. A number of technologies have evolved in order to address this both during computed tomography (CT) imaging and radiation delivery. This review paper investigates the various technologies which have been developed in the field of CT scanning as well as their accuracy, cost and the implications of their clinical implementation. The scanning modalities covered include: slow CT, breath hold CT, gated CT and retrospectively correlated CT (4DCT). It was found that there are advantages and drawbacks to each of the mentioned techniques relating to patient dose, scan time, extra equipment and workload. Also some scanning techniques are only compatible with certain treatment modalities which would further influence the decision as to which technologies to implement.

Techniques for respiration-induced artifacts reductions in thoracic PET/CT

The advent of positron emission tomography/computed tomography (PET/CT) provides fusion of both anatomical and functional information. CT-based attenuation correction replaced (68)Ge-based attenuation correction for shortening acquisition time, improving image quality and quantitative accuracy. However, due to the temporal difference of PET and CT, mis-registration and motion artifacts are observed in the attenuation-corrected images mainly due to the respiratory motion. Reducing the spatial mismatch of the PET and CT reconstructed image remains a challenge. This review provides an introduction to various respiratory image artifacts reduction techniques especially for thoracic lesions, including breathing instruction based methods, CT protocol based methods and 4-dimensional PET/CT. The advantages and drawbacks of different methods are also discussed.

To study tumor motion and planning target volume margins using four dimensional computed tomography for cancer of the thorax and abdomen regions

In this study, four dimensional computed tomography (4DCT) scanning was performed during free breathing on a 16-slice Positron emission tomography PET /computed tomography (CT) for abdomen and thoracic patients. Images were sorted into 10 phases based on the temporal correlation between surface motion and data acquisition with an Advantage Workstation. Gross tumor volume gross tumor volume (GTV) s were manually contoured on all 10 phases of the 4DCT scan. GTVs in the multiple CT phases were called GTV4D. GTV4D plus an isotropic margin of 1.0 cm was called CTV4D. Two sets of planning target volume (PTV) 4D (PTV4D) were derived from the CTV4D, i.e. PTV4D_2cm = CTV4D plus 1 cm setup margin (SM) and 1 cm internal margin (IM) and PTV4D_1.5cm = CTV4D plus 1 cm SM and 0.5cm IM. PTV3D was derived from a CTV3D of the helical CT scan plus conventional margins of 2 cm. PTV_gated was generated only selecting three CT phases, with a total margin of 1.5 cm. All four volumes were compared. To quantify the extent of the motion, we selected the two phases where the tumor exhibited the greatest range of motion. We also studied the effect of different PTV volumes on dose to the surrounding critical structures. Volume of CTV4D was greater than that of CTV3D. We found, on an average, a reduction of 14% volume of PTV4D_1.5cm as compared with PTV3D and reduction of 10% volume of PTV_gated as compared with PTV4D_1.5cm. We found that 2 cm of margin was inadequate if true motion of tumor was not known. We observed greater sparing of critical structures for PTVs drawn taking into account the tumor motion.

Stereotactic radiotherapy of primary lung cancer and other targets: results of consultant meeting of the International Atomic Energy Agency

To evaluate the current status of stereotactic body radiotherapy (SBRT) and identify both advantages and disadvantages of its use in developing countries, a meeting composed of consultants of the International Atomic Energy Agency was held in Vienna in November 2006. Owing to continuous developments in the field, the meeting was extended by subsequent discussions and correspondence (2007-2010), which led to the summary presented here. The advantages and disadvantages of SBRT expected to be encountered in developing countries were identified. The definitions, typical treatment courses, and clinical results were presented. Thereafter, minimal methodology/technology requirements for SBRT were evaluated. Finally, characteristics of SBRT for developing countries were recommended. Patients for SBRT should be carefully selected, because single high-dose radiotherapy may cause serious complications in some serial organs at risk. Clinical experiences have been reported in some populations of lung cancer, lung oligometastases, liver cancer, pancreas cancer, and kidney cancer. Despite the disadvantages expected to be experienced in developing countries, SBRT using fewer fractions may be useful in selected patients with various extracranial cancers with favorable outcome and low toxicity.

Comparison of helical and average computed tomography for stereotactic body radiation treatment planning and normal tissue contouring in lung cancer

AIMS

To compare average computed tomography (CT(AVE)) datasets with free breathing helical computed tomography (CT(HEL)) for contouring organs at risk (OARs) and radiation treatment planning in patients receiving stereotactic body radiation therapy (SBRT) in the lung.

MATERIALS AND METHODS

Ten SBRT patients with peripheral stage I non-small cell lung cancer underwent a CT(HEL) and a four-dimensional computed tomography scan in the treatment position. CT(AVE) datasets were generated from the four-dimensional computed tomography scan. The following OARs were delineated on the CT(HEL) and CT(AVE) datasets of each patient: lung minus internal target volume, trachea/main bronchus, heart, oesophagus and spinal cord. Volumes and geometric centres of the OARs, as well as the dosimetric impact of planning with these different datasets, were examined.

RESULTS

There were no statistical differences in the OAR geometric centre coordinates nor in the OAR volumes between the CT(HEL) and CT(AVE) datasets, except that CT(AVE)-defined trachea/main bronchus and lung minus internal target volume mean volumes were larger than those defined on the CT(HEL) (46, 43 cm³ and 3516, 3378 cm³, respectively, P<0.05). Despite this, there were no significant differences in the mean and maximum doses to the OAR contours when using the CT(HEL) or CT(AVE) for planning (<4% average change in the maximum and mean doses for all OARs, P>0.05). There were also no significant differences in the locations of the hotspots within OARs among the CT(HEL) or CT(AVE) datasets (P>0.05).

CONCLUSIONS

CT(AVE) datasets may be used in place of CT(HEL) for OAR contouring and dose calculations. When four-dimensional computed tomography is available, it may not be necessary to acquire a separate CT(HEL) scan for OAR contouring or dosimetric purposes.