Dosimetric consequences of tumor mobility in radiotherapy of stage I non-small cell lung cancer--an analysis of data generated using 'slow' CT scans

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.

Impact of CT slice thickness on volume and dose evaluation during thoracic cancer radiotherapy

Introduction

Accurate delineation of targets and organs at risk (OAR) is required to ensure treatment efficacy and minimize risk of normal tissue toxicity with radiotherapy. Therefore, we evaluated the impacts of computed tomography (CT) slice thickness and reconstruction methods on the volume and dose evaluations of targets and OAR.

Patients and methods

Eleven CT datasets from patients with thoracic cancer were included. 3D images with a slice thickness of 2 mm (2–CT) were created automatically. Images of other slice thickness (4–CT, 6–CT, 8–CT, 10–CT) were reconstructed manually by the selected 2D images using two methods; internal tumor information and external CT Reference markers. Structures and plans on 2–CT images, as a reference data, were copied to the reconstructed images.

Results

The maximum error of volume was 84.6% for the smallest target in 10–CT, and the maximum error (≥20 cm³) was 10.1%, 14.8% for the two reconstruction methods, internal tumor information and external CT Reference, respectively. Changes in conformity index for a target of <20 cm³ were 5.4% and 17.5% in 8–CT. Changes on V₃₀ and V₄₀ of the heart were considerable. In the internal tumor information method, volumes of hearts decreased by 3.2% in 6–CT, while V₃₀ and V₄₀ increased by 18.4% and 46.6%.

Conclusion

The image reconstruction method by internal tumor information was less affected by slice thickness than the image reconstruction method by external CT Reference markers. This study suggested that before positioning scanning, the largest section through the target should be determined and the optimal slice thickness should be estimated.

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.

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.

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.

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.

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.

The potential for undertaking slow CT using a modern CT scanner

Respiratory motion complicates target volume definition for patients with lung cancer. The use of slow CT to aid in the definition of moving target volumes was investigated. Standard and slow scans of an oscillating phantom were acquired using gantry rotation periods of 0.8 and 1.5 s and pitches of 0.95 and 0.50, respectively. The resultant images of three spheres within the phantom, labelled as A, B and C with diameters of 3.7, 2.8 and 2.2 cm, were analysed. The central co-ordinates of each volume were determined, and the ratio of the target volume outlined on CT (TV(CT)) to the true target volume (TV) was calculated. For 1.5 cm peak-to-trough (PTT) motion, standard CT mean ratios of 0.8, 0.8 and 0.7 were obtained for spheres A, B and C, respectively, whereas slow CT resulted in a mean ratio of 0.9 for all three spheres. For 2.5 cm motion, standard CT mean ratios of 0.8, 0.7 and 0.7 were obtained, whereas the slow CT mean ratios were 0.9, 0.9 and 0.8. The deviation of the central co-ordinate for the slow CT volumes was within 0.1 cm whereas deviations of up to 0.7 cm were seen using standard CT. This study indicates the potential benefit of using slow CT, even on modern scanners capable of rotation periods only down to 1.5 s, to define moving target volumes more accurately and reproducibly moving target volumes, and aid in the management of respiratory motion for patients with lung cancer.

Exceptionally high incidence of symptomatic grade 2-5 radiation pneumonitis after stereotactic radiation therapy for lung tumors

BACKGROUND

To determine the usefulness of dose volume histogram (DVH) factors for predicting the occurrence of radiation pneumonitis (RP) after application of stereotactic radiation therapy (SRT) for lung tumors, DVH factors were measured before irradiation.

METHODS

From May 2004 to April 2006, 25 patients were treated with SRT at the University of Tokyo Hospital. Eighteen patients had primary lung cancer and seven had metastatic lung cancer. SRT was given in 6-7 fields with an isocenter dose of 48 Gy in four fractions over 5-8 days by linear accelerator.

RESULTS

Seven of the 25 patients suffered from RP of symptomatic grade 2-5 according to the NCI-CTC version 3.0. The overall incidence rate of RP grade2 or more was 29% at 18 months after completing SRT and three patients died from RP. RP occurred at significantly increased frequencies in patients with higher conformity index (CI) (p = 0.0394). Mean lung dose (MLD) showed a significant correlation with V5-V20 (irradiated lung volume) (p < 0.001) but showed no correlation with CI. RP did not statistically correlate with MLD. MLD had the strongest correlation with V5.

CONCLUSION

Even in SRT, when large volumes of lung parenchyma are irradiated to such high doses as the minimum dose within planning target volume, the incidence of lung toxicity can become high.

The Use of Gated and 4D CT Imaging in Planning for Stereotactic Body Radiation Therapy

The localization of treatment targets is of utmost importance for patients receiving stereotactic body radiation therapy (SBRT), where the dose per fraction is large. While both setup or respiration-induced motion components affect the localization of the treatment volume, the purpose of this work is to describe our management of the intrafraction localization uncertainty induced by normal respiration. At our institution, we have implemented gated computed tomography (CT) acquisition with an active breathing control system (ABC), and 4-dimensional (4D) CT using a skin-based marker and retrospective respiration phase-based image sorting. During gated simulation, 3D CT images were acquired corresponding to end-inhalation and end-exhalation. For 4D CT imaging, 3D CT images were acquired corresponding to 8 phases of the respiratory cycle. In addition to gated or 4D CT images, we acquired a conventional free-breathing CT (FB). For both gated and 4D CT images, the target contours were registered to the FB scan in the planning system. These contours were then combined in the FB image set to form the internal target volume (ITV). Dynamic conformal arc treatment plans were generated for the ITV using the FB scan and the gated or 4D scans with an additional 7-mm margin for patient setup uncertainty. We have described our results for a pancreas and a lung tumor case. Plans were normalized so that the PTV received 95% of the prescription dose. The dose distribution for all the critical structures in the pancreas and lung tumor cases resulted in increased sparing when the ITV was defined using gated or 4D CT images than when the FB scan was used. Our results show that patient-specific target definition using gated or 4D CT scans lead to improved normal tissue sparing.

The management of respiratory motion in radiation oncology report of AAPM Task Group 76

This document is the report of a task group of the AAPM and has been prepared primarily to advise medical physicists involved in the external-beam radiation therapy of patients with thoracic, abdominal, and pelvic tumors affected by respiratory motion. This report describes the magnitude of respiratory motion, discusses radiotherapy specific problems caused by respiratory motion, explains techniques that explicitly manage respiratory motion during radiotherapy and gives recommendations in the application of these techniques for patient care, including quality assurance (QA) guidelines for these devices and their use with conformal and intensity modulated radiotherapy. The technologies covered by this report are motion-encompassing methods, respiratory gated techniques, breath-hold techniques, forced shallow-breathing methods, and respiration-synchronized techniques. The main outcome of this report is a clinical process guide for managing respiratory motion. Included in this guide is the recommendation that tumor motion should be measured (when possible) for each patient for whom respiratory motion is a concern. If target motion is greater than 5 mm, a method of respiratory motion management is available, and if the patient can tolerate the procedure, respiratory motion management technology is appropriate. Respiratory motion management is also appropriate when the procedure will increase normal tissue sparing. Respiratory motion management involves further resources, education and the development of and adherence to QA procedures.

Reproducibility of target volumes generated using uncoached 4-dimensional CT scans for peripheral lung cancer

Background

4-dimensional CT (4DCT) scans are increasingly used to account for mobility during radiotherapy planning. As variations in respiratory patterns can alter observed motion, with consequent changes in the generated target volumes, we evaluated the reproducibility of 4D target volumes generated during repeat uncoached quiet respiration.

Methods

A retrospective analysis was performed on two successive scans (4DCT1 and 4DCT2) generated at the same scanning session for 26 patients with peripheral lung cancer treated with stereotactic radiotherapy (SRT). The volume and position of planning target volumes (PTV_4DCT1 and PTV_4DCT2) contoured on both scans were compared, and a dosimetric analysis performed. A SRT plan optimized for each PTV was sequentially applied to the other PTV, and coverage by the 80% isodose was evaluated. Color intensity projections (CIP) were used to evaluate regions of underdosage.

Results

No significant volumetric differences were observed between the two PTVs (t-Test p = 0.60). The average displacement of the center of mass between corresponding PTVs was 1.4 ± 1.0 mm, but differences in position were 2.0 mm or greater in 5 cases (19%). Coverage of both PTVs by the 80% prescription isodose exceeded 90% for all but one patient. For the latter, the prescription isodose covered only 82.5% of PTV_4DCT1. CIP analysis revealed that the region of underdosage was an end-inspiratory position occupied by the tumor for only 10–20% of the respiratory cycle.

Conclusion

In nearly all patients with stage I lung cancer, the PTV derived from a single uncoached 4DCT achieves dosimetric coverage that is similar to that achieved using two such consecutive scans.

Quality assurance of thoracic radiotherapy in EORTC 08941: A randomised trial of surgery versus thoracic radiotherapy in patients with stage IIIA non-small-cell lung cancer (NSCLC) after response to induction chemotherapy

The aim of this study was to investigate the improvement of quality of radiotherapy and compliance to the protocol amendment of EORTC study 08941. The radiotherapy-specific data were analysed from 154 patients with stage IIIA-N2 Non-Small-Cell Lung Cancer who were actually irradiated after response to 3 cycles of platinum-based induction chemotherapy. The parameters of quality, assessed in 93 patients before and in 61 after protocol amendment, included: time interval between last chemotherapy course and start of thoracic radiotherapy, the use of a 3-D planning CT, dose and fractionation scheme to the primary tumour, the involved and uninvolved mediastinum, duration of radiotherapy and toxicity. A significant improvement of all quality parameters was noted, except for the overall treatment time, which decreased slightly. Protocol amendment resulted in an improvement of the quality and the compliance of most observed parameters, at the cost of some increase in overall treatment time. The latter reflects logistical problems rather than poor compliance.

Quantification of lung tumor volume and rotation at 3D dynamic parallel MR imaging with view sharing: preliminary results

The purpose of this study was to prospectively evaluate the volumes and rotations of pulmonary nodules during respiration by using three-dimensional fast low-angle shot dynamic magnetic resonance (MR) imaging (1.5/0.6 [repetition time msec/echo time msec], 3.8 x 3.8 x 3.8-mm voxel size, imaging time per three-dimensional data set of 1 second). The feasibility of the technique was verified by using 130-, 40-, and 12-cm3 phantoms made of meatballs and in five patients with solitary intrapulmonary tumors (four men, one woman; median age, 60 years) at computed tomography and histologic analysis. All patients provided written informed consent, and the study was institutional review board approved. It was proved that there were no substantial differences among the 21 algorithms used to correct partial volume effects. The most precise algorithm (r > 0.9, P < .01) used to correct partial volume effects--with which mean phantom volumes of 120.8 cm3 +/- 4.1, 36.1 cm3 +/- 3.98, and 13.1 cm3 +/- 1.5 were calculated--yielded a root mean square error of 14%. The MR imaging-derived nodule volume and rotation during respiration could be quantified by using oriented bounding box techniques.

A novel four-dimensional radiotherapy method for lung cancer: imaging, treatment planning and delivery

We present treatment planning methods based on four-dimensional computed tomography (4D-CT) to incorporate tumour motion using (1) a static field and (2) a dynamic field. Static 4D fields are determined to include the target in all breathing phases, whereas dynamic 4D fields are determined to follow the shape of the tumour assessed from 4D-CT images with a dynamic weighting factor. The weighting factor selection depends on the reliability of patient breathing and limitations of the delivery system. The static 4D method is compared with our standard protocol for gross tumour volume (GTV) coverage, mean lung dose and V20. It was found that the GTV delineated on helical CT without incorporating breathing motion does not adequately represent the target compared to the GTV delineated from 4D-CT. Dosimetric analysis indicates that the static 4D-CT based technique results in a reduction of the mean lung dose compared with the standard protocol. Measurements on a moving phantom and simulations indicated that 4D radiotherapy (4D-RT) synchronized with respiration-induced motion further reduces mean lung dose and V20, and may allow safe application of dose escalation and CRT/IMRT. The motions of the chest cavity, tumour and thoracic structures of 24 lung cancer patients are also analysed.

A dosimetric analysis of respiration-gated radiotherapy in patients with stage III lung cancer

Background

Respiration-gated radiotherapy can permit the irradiation of smaller target volumes. 4DCT scans performed for routine treatment were retrospectively analyzed to establish the benefits of gating in stage III non-small cell lung cancer (NSCLC).

Materials and methods

Gross tumor volumes (GTVs) were contoured in all 10 respiratory phases of a 4DCT scan in 15 patients with stage III NSCLC. Treatment planning was performed using different planning target volumes (PTVs), namely: (i) PTV_routine, derived from a single GTV plus 'conventional' margins; (ii) PTV_{all phases} incorporating all 3D mobility captured by the 4DCT; (iii) PTV_gating, incorporating residual 3D mobility in 3–4 phases at end-expiration. Mixed effect models were constructed in order to estimate the reductions in risk of lung toxicity for the different PTVs.

Results

Individual GTVs ranged from 41.5 – 235.0 cm³. With patient-specific mobility data (PTV_{all phases}), smaller PTVs were derived than when 'standard' conventional margins were used (p < 0.001). The average residual 3D tumor mobility within the gating window was 4.0 ± 3.5 mm, which was 5.5 mm less than non-gated tumor mobility (p < 0.001). The reductions in mean lung dose were 9.7% and 4.9%, respectively, for PTV_{all phases} versus PTV_routine, and PTV_gating versus PTV_{all phases}. The corresponding reductions in V₂₀ were 9.8% and 7.0%, respectively. Dosimetric gains were smaller for primary tumors of the upper lobe versus other locations (p = 0.02). Respiratory gating also reduced the risks of radiation-induced esophagitis.

Conclusion

Respiration-gated radiotherapy can reduce the risk of pulmonary toxicity but the benefits are particularly evident for tumors of the middle and lower lobes.

Time trends in target volumes for stage I non-small-cell lung cancer after stereotactic radiotherapy

PURPOSE

To identify potential time trends in target volumes and tumor mobility after stereotactic radiotherapy (SRT) for Stage I non-small-cell lung cancer.

PATIENTS AND METHODS

Repeat planning computed tomography (CT) scans were performed for 40 tumors during fractionated SRT delivered in either three (n = 21), five (n = 14), or eight fractions (n = 5). The planning CT scans used to define internal target volumes (ITVs) consisted of either six multislice CT scans or a single four-dimensional CT scan. All repeat CT scans were coregistered with the initial (D0) scan to determine volumetric or spatial changes in target volume, and tumor mobility vectors were determined from each scan.

RESULTS

A significant decrease in target volumes (ITVs and gross tumor volumes) relative to baseline values was observed starting at the fourth week of SRT (p = 0.015). No trends in tumor mobility were detected during SRT. Significant positional shifts in the ITV, of more than 5 mm, were seen in 26-43% of patients at different times during SRT.

CONCLUSION

Significant changes in target volumes can occur during SRT for Stage I non-small-cell lung cancer. A failure to account for such changes e.g., by repeat CT planning or verification using on-board volumetric imaging can lead to inadequate target coverage.

Use of maximum intensity projections (MIP) for target volume generation in 4DCT scans for lung cancer

PURPOSE

Single four-dimensional CT (4DCT) scans reliably capture intrafractional tumor mobility for radiotherapy planning, but generating internal target volumes (ITVs) requires the contouring of gross tumor volumes (GTVs) in up to 10 phases of a 4DCT scan, as is routinely performed in our department. We investigated the use of maximum intensity projection (MIP) protocols for rapid generation of ITVs.

METHODS AND MATERIALS

4DCT data from a mobile phantom and from 12 patients with Stage I lung cancer were analyzed. A single clinician contoured GTVs in all respiratory phases of a 4DCT, as well as in three consecutive phases selected for respiratory gating. MIP images were generated from both phantom and patient data, and ITVs were derived from encompassing volumes of the respective GTVs.

RESULTS

In the phantom study, the ratio between ITVs generated from all 10 phases and those from MIP scans was 1.04. The corresponding center of mass of both ITVs differed by less than 1 mm. In scans from patients, good agreement was observed between ITVs derived from 10 and 3 (gating) phases and corresponding MIPs, with ratios of 1.07 +/- 0.05 and 0.98 +/- 0.05, respectively. In addition, the center of mass of the respective ITVs differed by only 0.4 and 0.5 mm.

CONCLUSION

MIPs are a reliable clinical tool for generating ITVs from 4DCT data sets, thereby permitting rapid assessment of mobility for both gated and nongated 4D radiotherapy in lung cancer.

Small lung tumors: long-scan-time CT for planning of hypofractionated stereotactic radiation therapy--initial findings

PURPOSE

To prospectively use long-scan-time computed tomography (CT) to visualize the trajectory of tumor movements or the internal target volume.

MATERIALS AND METHODS

The study was approved by the institutional review board. Written informed consent was obtained from participants after the study and the role of procedures were explained fully. During the planning of stereotactic radiation therapy for 10 patients (nine men, one woman; mean age, 77 years; range, 69-89 years) with small lung tumors (mean volume, 9.0 cm3; range, 3.6-24.9 cm3), fluoroscopic imaging, long-scan-time CT, and thin-section CT were performed. The tumor and the partial-volume-averaging effects that resulted from tumor movement were delineated on each section at long-scan-time CT performed during the patient's steady breathing with scan time of 8 seconds per image. Visualized internal target volume was defined by integrating the sections. A simple model was examined for estimating internal target volume on the basis of respiratory motion and gross target volume delineated on thin-section CT images. Visualized internal target volume and estimated internal target volume were compared quantitatively and graphically. The Mann-Whitney test was used to analyze the relation between gross target volume delineated on thin-section CT images and the ratio of visualized internal target volume to the defined gross target volume.

RESULTS

The correlation coefficient between visualized internal target volume and estimated internal target volume was r = 0.98 (P < .001). The mean relative error +/- standard deviation was 1.9% +/- 19.0 (range, -11.0% to 56.4%). Excluding one case with an irregularly shaped tumor (56.4%), the mean relative error was -4.1% +/- 4.1. In patients with small tumors (defined gross target volume, < or = 10 cm3), the ratio of the visualized internal target volume to the defined gross tumor volume was significantly larger than that in patients with larger tumors (1.2-2.0 vs 1.0-1.2; P < .05). In some cases in which marginal spiculation depicted on thin-section CT images was blurred on long-scan-time CT images, the blurred area was erroneously excluded from the target volume.

CONCLUSION

In most cases, values for visualized internal target volume and estimated internal target volume were similar and long-scan-time CT depicted virtually the entire tumor trajectory.

Benefit of respiration-gated stereotactic radiotherapy for stage I lung cancer: An analysis of 4DCT datasets

PURPOSE

High local control rates have been reported with stereotactic radiotherapy (SRT) for Stage I non-small-cell lung cancer. Because high-dose fractions are used, reduction in treatment portals will reduce the risk of toxicity to adjacent structures. Respiratory gating can allow reduced field sizes and planning four-dimensional computed tomography scans were retrospectively analyzed to study the benefits for gated SRT and identify patients who derive significant benefit from this approach.

METHODS AND MATERIALS

A total of 31 consecutive patients underwent a four-dimensional computed tomography scan, in which three-dimensional computed tomography datasets for 10 phase bins of the respiratory cycle were acquired during free breathing. For a total of 34 tumors, the three planning target volumes (PTVs) were analyzed, namely (1) PTV(10bins), derived from an internal target volume (ITV) that incorporated all observed mobility (ITV(10bins)), with the addition of a 3-mm isotropic setup margin; (2) PTV(gating), derived from an ITV generated from mobility observed in three consecutive phases ("bins") during tidal-expiration, plus addition of a 3-mm isotropic margin; and (3) PTV(10 mm), derived from the addition of a 10-mm isotropic margin to the most central gross tumor volumes in the three bins selected for gating.

RESULTS

The PTV(10bins) and PTV(gating) were, on average, 48.2% and 33.3% of the PTV(10 mm), and respective mean volumes of normal tissue (outside the PTV) receiving the prescribed doses were 57.1% and 39.1%, respectively, of that of PTV(10 mm). A significant correlation was seen between the extent of tumor mobility (i.e., a three-dimensional mobility vector of at least 1 cm) and reduction in normal tissue irradiation achieved with gating. The ratio of the intersecting and the encompassing volumes of GTVs at extreme phases of tidal respiration predicted for the benefits of gated respiration.

CONCLUSION

The use of "standard population-based" margins for SRT leads to unnecessary normal tissue irradiation. The risk of toxicity is further reduced if respiration-gated radiotherapy is used to treat mobile tumors. These findings suggest that gated SRT will be of clinical relevance in selected patients with mobile tumors.

Radiotherapy planning for lung cancer: slow CTs allow the drawing of tighter margins

BACKGROUND AND PURPOSE

Evaluation of the use of planning CTs with slow revolution time (4s/slice; 'slow CTs') in the planning procedure of radiotherapy for lung cancer patients in comparison to commonly used 'fast' planning CTs; impact on margin assessment of planning target volume (PTV) design.

PATIENTS AND METHODS

Eighteen lung cancer patients (six upper, lower lobe and central tumors, respectively) have been scanned each by three series of slow CTs and one fast CT (spiral CT). Patients have been freely breathing. The largest transversal tumor diameters in slow and fast CTs have been measured. Tumor edge positions have been determined for six spatial directions in all slices of the three slow CT series.

RESULTS

Slow CTs show larger dimensions of the visible tumor than fast CTs. The median difference of the diameter for all tumors is 2mm (range 0-4mm). Slow CTs deliver constant depictions of lung tumors within a range of 1.6mm in all directions. This margin is considered to be sufficient to compensate for tumor movements by respiration and cardiovascular motions (internal margin). A margin of 7 mm added to the GTV of a single slow CT series to draw the PTV is proposed.

CONCLUSIONS

Slow planning CTs show larger, but highly constant depictions of lung tumors in comparison to conventional fast CT scanning, yielding an integral delineation of almost all positions of the moving tumors. Thus the use of slow planning CTs enables the drawing of tighter margins in external beam treatment planning of lung cancer.

Measurement of tumor diameter-dependent mobility of lung tumors by dynamic MRI

BACKGROUND AND PURPOSE

To assess the influence of tumor diameter on tumor mobility and motion of the tumor bearing hemithorax during the whole breathing cycle in patients with stage I non-small-cell lung cancer (NSCLC) using dynamic MRI.

PATIENTS AND METHODS

Breathing cycles of thirty-nine patients with solitary NSCLCs were examined using a trueFISP sequence (three images per second). Patients were divided into three groups according to the maximal tumor diameter in the transverse plane (<3, 3-5 and >5 cm). Continuous time-distance curves and deep inspiratory and expiratory positions of the chest wall, the diaphragm and the tumor were measured in three planes. Motion of tumor-bearing and corresponding contralateral non-tumor bearing regions was compared.

RESULTS

Patients with a tumor >3 cm showed a significantly lower diaphragmatic motion of the tumor bearing compared with the non-tumor bearing hemithorax in the craniocaudal (CC) directions (tumors 3-5 cm: 23.4+/-1.2 vs 21.1+/-1.5 cm (P<0.05); tumors >5 cm: 23.4+/-1.2 vs 20.1+/-1.6 cm (P<0.01). Tumors >5 cm in the lower lung region showed a significantly lower mobility compared with tumors <3 cm (1.8+/-1.0 vs 3.8+/-0.7 cm, P<0.01) in the CC directions.

CONCLUSIONS

Dynamic MRI is a simple non-invasive method to differentiate mobility of tumors with different diameters and its influence on the surrounding tissue. Tumor diameter has a significant influence on tumor mobility and this might be taken into account in future radiotherapy planning.

Four-dimensional CT scans for treatment planning in stereotactic radiotherapy for stage I lung cancer

PURPOSE

Hypofractionated stereotactic radiotherapy (SRT) for Stage I non-small-cell lung cancer requires that meticulous attention be paid toward ensuring optimal target definition. Two computed tomography (CT) scan techniques for defining internal target volumes (ITV) were evaluated.

METHODS AND MATERIALS

Ten consecutive patients treated with SRT underwent six "standard" rapid multislice CT scans to generate an ITV(6 CT) and one four-dimensional CT (4DCT) scan that generated volumetric datasets for 10 phases of the respiratory cycle, all of which were used to generate an ITV(4DCT). Geometric and dosimetric analyses were performed for (1) PTV(4DCT), derived from the ITV(4DCT) with the addition of a 3-mm margin; (2) PTV(6 CT), derived from the ITV(6 CT) with the addition of a 3-mm margin; and (3) 6 PTV(10 mm), derived from each separate GTV(6 CT), to which a three-dimensional margin of 10 mm was added.

RESULTS

The ITV(4DCT) was not significantly different from the ITV(6 CT) in 8 patients, but was considerably larger in 2 patients whose tumors exhibited the greatest mobility. On average, the ITV(6 CT) missed on average 22% of the volume encompassing both ITVs, in contrast to a corresponding mean value of only 8.3% for ITV(4DCT). Plans based on PTV(4DCT) resulted in coverage of the PTV(6 CT) by the 80% isodose in all patients. However, plans based on use of PTV(6 CT) led to a mean PTV(4DCT) coverage of only 92.5%, with a minimum of 77.7% and 77.5% for the two most mobile tumors. PTVs derived from a single multislice CT expanded with a margin of 10 mm were on average twice the size of PTVs derived using the other methods, but still led to an underdosing in the two most mobile tumors.

CONCLUSIONS

Individualized ITVs can improve target definition for SRT of Stage I non-small-cell lung cancer, and use of only a single CT scan with a 10-mm margin is inappropriate. A single 4D scan generates comparable or larger ITVs than are generated using six unmonitored rapid CT scans, a finding related to the ability to account for all respiration-correlated mobility.

Literature-based recommendations for treatment planning and execution in high-dose radiotherapy for lung cancer

BACKGROUND AND PURPOSE

To review the literature on techniques used in high-dose radiotherapy of lung cancer in order to develop recommendations for clinical practice and for use in research protocols.

PATIENTS AND METHODS

A literature search was performed for articles and abstracts that were considered both clinically relevant and practical to use. The relevant information was arbitrarily categorized under the following headings: patient positioning, CT scanning, incorporating tumour mobility, definition of target volumes, radiotherapy planning, treatment delivery, and scoring of response and toxicity.

RESULTS

Recommendations were made for each of the above steps from the published literature. Although most of the recommended techniques have yet to be evaluated in multicenter clinical trials, their use in high-dose radiotherapy to the thorax appears to be rational on the basis of current evidence.

CONCLUSIONS

Recommendations for the clinical implementation of high-dose conformal radiotherapy for lung tumours were identified in the literature. Procedures that are still considered to be investigational were also highlighted.

Intrathoracic tumour motion estimation from CT imaging using the 3D optical flow method

The purpose of this work was to develop and validate an automated method for intrathoracic tumour motion estimation from breath-hold computed tomography (BH CT) imaging using the three-dimensional optical flow method (3D OFM). A modified 3D OFM algorithm provided 3D displacement vectors for each voxel which were used to map tumour voxels on expiration BH CT onto inspiration BH CT images. A thoracic phantom and simulated expiration/inspiration BH CT pairs were used for validation. The 3D OFM was applied to the measured inspiration and expiration BH CT images from one lung cancer and one oesophageal cancer patient. The resulting displacements were plotted in histogram format and analysed to provide insight regarding the tumour motion. The phantom tumour displacement was measured as 1.20 and 2.40 cm with full-width at tenth maximum (FWTM) for the distribution of displacement estimates of 0.008 and 0.006 cm, respectively. The maximum error of any single voxel's motion estimate was 1.1 mm along the z-dimension or approximately one-third of the z-dimension voxel size. The simulated BH CT pairs revealed an rms error of less than 0.25 mm. The displacement of the oesophageal tumours was nonuniform and up to 1.4 cm, this was a new finding. A lung tumour maximum displacement of 2.4 cm was found in the case evaluated. In conclusion, 3D OFM provided an accurate estimation of intrathoracic tumour motion, with estimated errors less than the voxel dimension in a simulated motion phantom study. Surprisingly, oesophageal tumour motion was large and nonuniform, with greatest motion occurring at the gastro-oesophageal junction.

Acquiring 4D thoracic CT scans using a multislice helical method

Respiratory motion degrades anatomic position reproducibility during imaging, necessitates larger margins during radiotherapy planning and causes errors during radiation delivery. Computed tomography (CT) scans acquired synchronously with the respiratory signal can be used to reconstruct 4D CT scans, which can be employed for 4D treatment planning to explicitly account for respiratory motion. The aim of this research was to develop, test and clinically implement a method to acquire 4D thoracic CT scans using a multislice helical method. A commercial position-monitoring system used for respiratory-gated radiotherapy was interfaced with a third generation multislice scanner. 4D cardiac reconstruction methods were modified to allow 4D thoracic CT acquisition. The technique was tested on a phantom under different conditions: stationary, periodic motion and non-periodic motion. 4D CT was also implemented for a lung cancer patient with audio-visual breathing coaching. For all cases, 4D CT images were successfully acquired from eight discrete breathing phases, however, some limitations of the system in terms of respiration reproducibility and breathing period relative to scanner settings were evident. Lung mass for the 4D CT patient scan was reproducible to within 2.1% over the eight phases, though the lung volume changed by 20% between end inspiration and end expiration (870 cm3). 4D CT can be used for 4D radiotherapy, respiration-gated radiotherapy, 'slow' CT acquisition and tumour motion studies.

Tumor location cannot predict the mobility of lung tumors: a 3D analysis of data generated from multiple CT scans

PURPOSE

There is limited information available on the three-dimensional (3D) motion of lung tumors. Data derived from multiple planning computed tomographic (CT) scans were used to characterize the 3D movement of small peripheral lung tumors.

METHODS AND MATERIALS

A total of 29 data sets from patients with Stage I non-small-cell lung cancer (NSCLC), each of which consisted of three "rapid" and three "slow" planning CT scans, were analyzed. All six scans were coregistered, and contoured gross tumor volumes (GTVs) were expanded by 5 mm to derive clinical target volumes (CTVs). Two-dimensional and 3D displacement vectors of the individual CTVs, relative to an "optimal" CTV derived from all six scans, were generated. Tumor mobility was correlated with location. Three-dimensional margins, which had to be added to individual CTVs to ensure coverage of "optimal" CTVs, were determined.

RESULTS

No significant correlation was observed between the anatomic location of tumors and the extent of mobility in the x, y, and z axes. However, supradiaphragmatic lesions exhibited more mobility, particularly in the craniocaudal direction. The addition of a 3D margin of 5 mm to a single slow CTV ensured full coverage of the "optimal CTV".

CONCLUSIONS

Lung tumors demonstrate significant mobility in all directions, and this did not closely correlate with anatomic location. Individualized assessment of tumor mobility remains necessary, and is possible when the CTV derived from a single slow scan is used for radiotherapy planning.

Lung cancer 5: state of the art radiotherapy for lung cancer

Radiotherapy has a key role in curative and palliative treatments of patients with lung cancer. Important advances are described in the technique of treatment delivery and its integration with chemotherapy.

Are multiple CT scans required for planning curative radiotherapy in lung tumors of the lower lobe?

PURPOSE

Lung tumors located in the lower lobe are the most mobile. Multiple computed tomographic (CT) scans, which had been performed for radiotherapy planning, were analyzed to determine the minimal number of required scans.

METHODS AND MATERIALS

Six spiral CT scans (3 rapid and 3 slow) from 7 such patients were coregistered. Reproducibility of target volumes was defined as the ratio between the overlapping and encompassing volume (COM/SUM) from scans derived using one technique. Volumetric and dosimetric analyses were performed.

RESULTS

Slow CT scans generated larger and more reproducible target volumes than rapid planning scans, with a mean COM/SUM ratio of 71.9 +/- 8.7% and 58.0 +/- 12.7%, respectively. When only a single slow CT scan was used for planning, the addition of a symmetrical 3D margin of 5 mm ensured 99% coverage of the "optimal" target volume, which was derived from summation of target volumes from all six scans.

CONCLUSION

Planning target volumes (PTVs) derived from a single slow CT scan plus a 5-mm margin covered the "optimal" PTVs generated from six scans. Although these "slow PTVs" were larger, the increase in V(20) (the volume of lung tissue receiving a dose > or = 20 Gy) was limited. This indicates that only two CT scans, i.e., a full rapid scan of the entire thorax and a limited slow scan, are necessary for treatment planning in peripheral lung cancers.

Procedures for high precision setup verification and correction of lung cancer patients using CT-simulation and digitally reconstructed radiographs (DRR)

PURPOSE

In a recent study, large systematic setup errors were detected in patients with lung cancer when a conventional simulation procedure was used to define and mark the treatment isocenter. In the present study, we describe a procedure to omit the session at a conventional simulator to remove simulation errors entirely. Isocenter definition and verification was performed at a computed tomography (CT) simulator, and digitally reconstructed radiographs (DRRs) were used for setup verification and correction at the treatment unit.

METHODS AND MATERIALS

A CT simulation protocol was developed, in which radiopaque markers were used to verify the coincidence of the isocenter marked on the patients' skin with the isocenter defined in the planning CT scan. This protocol was evaluated for 20 patients. Subsequently, electronic portal images were acquired at the treatment unit. The three-dimensional setup error was established from a template match of the appropriate anatomy visible in two orthogonal beams with the corresponding anatomy in DRRs. An offline setup correction protocol was applied to reduce systematic setup errors.

RESULTS

For all patients, the skin marks defined the planning CT scan isocenter to within +/- 1.5 mm in each of the three main directions. Random setup errors at the treatment unit were 1.8, 2.0, and 1.9 mm (1 SD) for the lateral (x), the superior-inferior (y), and the anterior-posterior (z) directions, respectively. With the use of the correction protocol, the systematic errors for x, y, and z were 1.5, 1.5, and 1.3 mm (1 SD).

CONCLUSIONS

Because the distributions of treatment setup errors measured against DRRs obtained in our CT simulation were equal to previously obtained distributions measured against simulator films, conventional simulation can be omitted and DRRs are well-suited for setup verification. By adopting our CT simulation procedure, the large systematic simulation setup errors, which remain hidden if a conventional simulation is performed, can be avoided.

What margins are necessary for incorporating mediastinal nodal mobility into involved-field radiotherapy for lung cancer?

PURPOSE

The mobility of mediastinal nodes was studied on multiple CT scans of the thorax from patients with non-small-cell lung cancer.

PATIENTS AND METHODS

A total of 10 enlarged mediastinal nodes/masses were identified in 8 patients with non-small-cell lung cancer. Nodal locations were classified using the Naruke/ATS-LCSG system, and between 3 and 6 scans were available for each site. The CT data sets were coregistered, and the contoured nodes were automatically projected onto the initial planning CT scan. An encompassing nodal volume (ENV) of all contours of a particular node was manually contoured on all scans. Individual nodal volumes were expanded in three dimensions to establish additional margins required to encompass the ENV.

RESULTS

The mean volume of nodes studied ranged from 0.8 to 23.2 cc. The addition to individual nodes of a margin of 5 mm was found to result in a mean ENV coverage of >or=95% at all sites. For individual nodes at locations N4R, N5, and N6, however, the coverage ranged from 87.8% to 92.6%.

CONCLUSION

The addition of a margin of 5 mm to individual mediastinal nodes seems to be adequate to account for variations in both contouring and mobility.

Has 3-D conformal radiotherapy (3D CRT) improved the local tumour control for stage I non-small cell lung cancer?

AIMS AND BACKGROUND

The high local failure rates observed after radiotherapy in stage I non-small cell lung cancer (NSCLC) may be improved by the use of 3-dimensional conformal radiotherapy (3D CRT).

MATERIALS AND METHODS

The case-records of 113 patients who were treated with curative 3D CRT between 1991 and 1999 were analysed. No elective nodal irradiation was performed, and doses of 60Gy or more, in once-daily fractions of between 2 and 3Gy, were prescribed.

RESULTS

The median actuarial survival of patients was 20 months, with 1-, 3- and 5-year survival of 71, 25 and 12%, respectively. Local disease progression was the cause of death in 30% of patients, and 22% patients died from distant metastases. Grade 2-3 acute radiation pneumonitis (SWOG) was observed in 6.2% of patients. The median actuarial local progression-free survival (LPFS) was 27 months, with 85 and 43% of patients free from local progression at 1 and 3 years, respectively. Endobronchial tumour extension significantly influenced LPFS, both on univariate (P=0.023) and multivariate analysis (P=0.023). The median actuarial cause-specific survival (CSS) was 19 months, and the respective 1- and 3-year rates were 72 and 30%. Multivariate analysis showed T2 classification (P=0.017) and the presence of endobronchial tumour extension (P=0.029) to be adverse prognostic factors for CSS. On multivariate analysis, T-stage significantly correlated with distant failure (P=0.005).

CONCLUSIONS

Local failure rates remain substantial despite the use of 3D CRT for stage I NSCLC. Additional improvements in local control can come about with the use of radiation dose escalation and approaches to address the problem of tumour mobility.

Curative radiotherapy for a second primary lung cancer arising after pneumonectomy -- techniques and results

BACKGROUND AND PURPOSE

Only limited data exist on the outcome of curative radiotherapy in patients who develop a second primary lung tumour after pneumonectomy. The treatment of eight such patients is described.

MATERIALS AND METHODS

The case records of patients who underwent curative radiotherapy for stage I non-small cell lung cancer after a previous pneumonectomy were reviewed. Treatment was delivered using 3D external radiotherapy to a dose of 50-70 Gy, in once-daily fractions of 2-2.5 Gy. An endobronchial brachytherapy boost was used in three patients. Original treatments were re-planned in an attempt to minimize the volume of irradiated lung.

RESULTS

A complete remission was achieved in five (of six) evaluable patients, but two patients subsequently developed a local relapse. All patients survived for a minimum of 1 year after treatment. Only one patient developed significant (grade 2) radiation pneumonitis. When treatments were re-planned to optimize beam arrangements, and when customized blocks were used, the mean lung volume receiving > or = 20 Gy (calculated for 70 Gy) decreased from 24.6+/-4.1 (range, 18-31%) to 17.3+/-5.1% (range, 12-26%). Similarly, the radiation conformity index improved from 0.44+/-0.11 to 0.61+/-0.06.

CONCLUSIONS

Involved-field radiotherapy can be curative in patients who develop a new lung tumour after pneumonectomy. Recent advances in defining target volumes, treatment planning and delivery are likely to improve upon these results.