Impact of respiratory movement on the computed tomographic images of small lung tumors in three-dimensional (3D) radiotherapy

Feasibility of insertion/implantation of 2.0-mm-diameter gold internal fiducial markers for precise setup and real-time tumor tracking in radiotherapy

PURPOSE

To examine the feasibility and reliability of insertion of internal fiducial markers into various organs for precise setup and real-time tumor tracking in radiotherapy (RT).

MATERIALS AND METHODS

Equipment and techniques for the insertion of 2.0-mm-diameter gold markers into or near the tumor were developed for spinal/paraspinal lesions, prostate tumors, and liver and lung tumors. Three markers were used to adjust the center of the mass of the target volume to the planned position in spinal/paraspinal lesions and prostate tumors (the three-marker method). The feasibility of the marker insertion and the stability of the position of markers were tested using stopping rules in the clinical protocol (i.e., the procedure was abandoned if 2 of 3 or 3 of 6 patients experienced marker dropping or migration). After the evaluation of the feasibility, the stability of the marker positions was monitored in those patients who entered the dose-escalation study.

RESULTS

Each of the following was shown to be feasible: bronchoscopic insertion for the peripheral lung; image-guided transcutaneous insertion for the liver; cystoscopic and image-guided percutaneous insertion for the prostate; and surgical implantation for spinal/paraspinal lesions. Transcutaneous insertion of markers for spinal/paraspinal lesions and bronchoscopic insertion for central lung lesions were abandoned. Overall, marker implantation was successful and was used for real-time tumor tracking in RT in 90 (90%) of 100 lesions. No serious complications related to the marker insertion were noted for any of the 100 lesions. Using three markers surgically implanted into the vertebral bone, the mean +/- standard deviation in distance among the three markers was within 0.2 +/- 0.6 mm (range -1.4 to 0.8) through the treatment period of 30 days. The distance between the three markers gradually decreased during RT in five of six prostate cancers, consistent with a mean rate of volume regression of 9.3% (range 0.015-13%) in 10 days.

CONCLUSIONS

Internal 2.0-mm-diameter gold markers can be safely inserted into various organs for real-time tumor tracking in RT using the prescribed equipment and techniques. The three-marker method has been shown to be a useful technique for precise setup for spinal/paraspinal lesions and prostate tumors.

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.

Can PET provide the 3D extent of tumor motion for individualized internal target volumes? A phantom study of the limitations of CT and the promise of PET

PURPOSE

To characterize the limitations of fast, spiral computed tomography (CT) when imaging a moving object and to investigate whether positron emission tomography (PET) can predict the internal target volume (ITV) and ultimately improve the planning target volume (PTV) for moving tumors.

METHODS AND MATERIALS

To mimic tumors, three fillable spheres were imaged while both stationary and during periodic motion using spiral CT and PET. CT- and PET-imaged volumes were defined quantitatively using voxel values. Ideal PTVs for each scenario were calculated. CT-based PTVs were generated using margins of 7.5, 10, and 15 mm to account for both organ motion and setup uncertainties. PET-based PTVs were derived with the assumption that motion was captured in the PET images and only a margin (7.5 mm) for setup errors was necessary. Comparisons between CT-based and PET-based PTVs with ideal PTVs were performed.

RESULTS

CT imaging of moving spheres resulted in significant distortions in the three-dimensional (3D) image-based representations, and did not, in general, result in images well representative of either moving or stationary spheres. PET images were similar to the ideal capsular shape encompassing the sphere and its motion. In all cases, CT-imaged volumes were larger than that for the stationary sphere (range of excess volume from 0.4 to 29 cm(3) for stationary volumes of 2.14 to 172 cm(3)), but smaller than that for the true motion volume. PET-imaged volumes were larger than the true motion volume (difference from ideal ranged from 3 to 94 cm(3) for motion volumes of 1.2 to 243 cm(3)) and much larger than the stationary volume. Using CT data, geographic miss of some part of the ideal PTV occurred for 0 of 24 cases, 11 of 24 cases, and 18 of 24 cases using a 15-mm, 10-mm, and 7.5-mm margin, respectively. Geographic miss did not occur in any case for the PET-based PTV. The amount of "normal tissue" included in CT-based PTVs was dramatically greater than that included in PET-based PTVs.

CONCLUSION

Fast CT imaging of a moving tumor can result in poor representation of the time-averaged position and shape of the tumor. PET imaging can provide a more accurate representation of the 3D volume encompassing motion of model tumors and has potential to provide patient-specific motion volumes for an individualized ITV.

Portal imaging to assess set-up errors, tumor motion and tumor shrinkage during conformal radiotherapy of non-small cell lung cancer

PURPOSE

To investigate patient set-up, tumor movement and shrinkage during 3D conformal radiotherapy for non-small cell lung cancer.

MATERIALS AND METHODS

In 97 patients, electronic portal images (EPIs) were acquired and corrected for set-up using an off-line correction protocol based on a shrinking action level. For 25 selected patients, the orthogonal EPIs (taken at random points in the breathing cycle) throughout the 6-7 week course of treatment were assessed to establish the tumor position in each image using both an overlay and a delineation technique. The range of movement in each direction was calculated. The position of the tumor in the digitally reconstructed radiograph (DRR) was compared to the average position of the lesion in the EPIs. In addition, tumor shrinkage was assessed.

RESULTS

The mean overall set-up errors after correction were 0, 0.6 and 0.2 mm in the x (left-right), y (cranial-caudal) and z (anterior-posterior) directions, respectively. After correction, the standard deviations (SDs) of systematic errors were 1.4, 1.5 and 1.3 mm and the SDs of random errors were 2.9, 3.1 and 2.0 mm in the x-, y- and z-directions, respectively. Without correction, 41% of patients had a set-up error of more than 5 mm vector length, but with the set-up correction protocol this percentage was reduced to 1%. The mean amplitude of tumor motion was 7.3 (SD 2.7), 12.5 (SD 7.3) and 9.4 mm (SD 5.2) in the x-, y- and z-directions, respectively. Tumor motion was greatest in the y-direction and in particular for lower lobe tumors. In 40% of the patients, the projected area of the tumor regressed by more than 20% during treatment in at least one projection. In 16 patients it was possible to define the position of the center of the tumor in the DRR. There was a mean difference of 6 mm vector length between the tumor position in the DRR and the average position in the portal images.

CONCLUSIONS

The application of the correction protocol resulted in a significant improvement in the set-up accuracy. There was wide variation in the observed tumor motion with more movement of lower lobe lesions. Tumor shrinkage was observed. The position of the tumor on the planning CT scan did not always coincide with the average position as measured during treatment.

Improvement of three-dimensional treatment planning models of small lung targets using high-speed multi-slice computed tomographic imaging

PURPOSE

To improve the reliability of the patient model and reduce treatment volume by acquiring multi-slice computed tomographic (CT) data with the patients' single holding of breath at normal inhalation and exhalation.

METHODS AND MATERIALS

Seven patients with nine small peripheral lung cancer tumors underwent CT scanning under three respiration conditions using multi-slice CT: free breathing (FB), shallow inspiration (SI), and shallow expiration (SE). To compare the treatment plan created using the two-respiratory-phase images (SI + SE) with the plans created using only SE images or using only FB images, we attempted to calculate the true dosimetric characteristics for three-dimensional treatment planning taking respiratory movement into consideration. Minimum dose to the gross tumor volume (GTV) and ipsilateral lung dose-volume histogram (DVH) were calculated for the inhalation and exhalation positions of shallow breathing.

RESULTS

There was no significant difference between minimum doses of the GTV in the three treatment plans when using anteroposterior/posteroanterior parallel-opposed fields. However, there was a significant difference between the minimum doses of the GTV in the two-phase treatment plan and the minimum dose in the other treatment plans when using the four-field technique, consisting of shaped anterior, posterior, right and left lateral fields (p = 0.03, 0.04). Comparison of the percent volume of ipsilateral lung receiving a dose exceeding 20 Gy (V(20)) based on inhalation and exhalation CT data revealed that the V(20) of the two-phase plan was the smallest of the three treatment planning fields (p < 0.001).

CONCLUSION

Two-phase planning using multi-slice CT provides an immediate reduction in the amount of normal tissue treated and improved reliability of patient data for DVH modeling.

Real-time tumor-tracking radiation therapy for lung carcinoma by the aid of insertion of a gold marker using bronchofiberscopy

BACKGROUND

The authors developed fluoroscopic real-time tumor-tracking radiation therapy (RTRT) by insertion of a gold marker using bronchofiberscopy to reduce uncertainties in organ motion and set-up error in external radiotherapy for moving tumors. The purpose of the current study was to evaluate RTRT's feasibility in lung carcinoma treatment.

METHODS

The three-dimensional position of a 1.0-2.0 mm gold marker in or near the tumor was detected by two sets of fluoroscopies every 0.03 seconds. The treatment beam was gated to irradiate the tumor only when the position of the marker coincided with its planned position using the RTRT system. Bronchofiberscopic equipment for insertion of the marker into the lung tumor was developed and used for 20 lung tumors in 18 patients. Patients were given high dose hypofractionated focal irradiation (35-48 Gy in 4-8 fractions in 4-10 days) with a planning target volume margin of 5 mm for the tumor.

RESULTS

The markers were successfully inserted and maintained at the inserted position during and after the radiotherapy in 14 (88%) of 16 peripheral-type lung tumors and in none of four central-type lung tumors, indicating that this method of RTRT was not feasible for central-type lung tumors. Tracking of the marker was successfully performed in 1 of 2 tumors with a 1.0 mm marker and in all of 12 tumors with a 1.5-2.0 mm marker. On the whole, 13 (65%) of the 20 tumors were successfully treated with RTRT. Local tumor control was achieved and maintained for all 12 patients (13 tumors), who were treated with RTRT, with a median followup of 9 months (range, 5-15). Localized radiation pneumonitis was found radiographically at the lung volume that was irradiated with about 20 Gy, without symptoms in all but one patient.

CONCLUSIONS

The insertion of a gold marker into or near peripheral-type lung tumors using bronchofiberscopy is a feasible and safe technique. Excellent initial response and low incidence of clinical complications suggest that the high dose hypofractionated focal irradiation using the RTRT system can be a good local treatment for peripheral-type lung tumors.

Small-volume image-guided radiotherapy using hypofractionated, coplanar, and noncoplanar multiple fields for patients with inoperable Stage I nonsmall cell lung carcinomas

BACKGROUND

Occasionally, medically compromised and/or elderly patients with nonsmall cell lung carcinomas (NSCLCs) cannot be treated surgically. We investigated small-volume hypofractionated image-guided radiotherapy (IGRT) without the need for breath control in patients with inoperable Stage I NSCLCs.

METHODS

Between September 1996 and September 1999, 22 patients with Stage I NSCLCs, including 19 males and 3 females, were treated with IGRT. Among these patients, there were 13 Stage IA and 9 Stage IB tumors. The tumors ranged in size from 14.2 to 58.5 mm, with a median size of 26.7 mm. Of the 22 patients, 19 were unfit for surgical treatment due to poor pulmonary function, complications, and/or advanced age and 3 refused surgery. Computed tomographic scans (CT) of the primary tumor were taken during three respiratory phases and they were analyzed to determine the planning target volume, which included only the primary tumor with allowances for respiratory movement. The radiation doses administered at the edge of the moving tumor during normal breathing were 80% of the prescribed dose, either 48 or 60 Gy given in eight fractions over 2 weeks. Clinical evaluation, chest CT scan, and pulmonary function tests were performed before irradiation and at regular intervals for the post-IGRT follow-up. The median follow-up period was 24 months (range, 2-44 months; mean, 21.8 months) (at least 24 months for survivors).

RESULTS

Of 17 tumors assessed at the initial follow-up 2-6 months after treatment (5 complete responses, 11 partial responses, and 1 progressive disease), 16 (94%) were controlled locally. One local recurrence was observed during the follow-up. The lung carcinoma-specific survival rate at 1 year was 94% and the 1-year actuarial recurrence-free survival rate was 71%. The lung carcinoma-specific survival rate at 2 years was 73% and the 2-year actuarial recurrence-free survival rate was 67%. The treatment was well tolerated and no major side effects were observed. Localized radiation pneumonitis was observed in all patients who were examined by CT scan, but the patients were asymptomatic. Parameters of pulmonary function, including vital capacity, total lung capacity, and diffusion capacity for carbon monoxide, decreased very little or not at all, indicating that IGRT rarely deteriorated pulmonary functions.

CONCLUSIONS

Small-volume hypofractionated IGRT without breath control is a feasible and beneficial method for the curative treatment of patients with Stage I NSCLCs. It has the potential of a high local tumor control rate and low morbidity.

Open low-field magnetic resonance imaging in radiation therapy treatment planning

PURPOSE

To evaluate the possibilities of an open low-field magnetic resonance imaging (MRI) scanner in external beam radiotherapy treatment (RT) planning.

METHODS AND MATERIALS

A custom-made flat tabletop was constructed for the open MR, which was compatible with standard therapy positioning devices. To assess and correct image distortion in low-field MRI, a custom-made phantom was constructed and a software algorithm was developed. A total of 243 patients (43 patients with non-small-cell lung cancer, 155 patients with prostate cancer, and 45 patients with brain tumors) received low-field MR imaging in addition to computed tomographic (CT) planning imaging between January 1998 and September 2001 before the start of the irradiation.

RESULTS

Open low-field MRI provided adequate images for RT planning in nearly 95% of the examined patients. The mean and the maximal distortions 15 cm around the isocenter were reduced from 2.5 mm to 0.9 mm and from 6.1 mm to 2.1 mm respectively. The MRI-assisted planning led to better discrimination of tumor extent in two-thirds of the patients and to an optimization in lung cancer RT planning in one-third of the patients. In prostate cancer planning, low-field MRI resulted in significant reduction (40%) of organ volume and clinical target volume (CTV) compared with CT and to a reduction of the mean percentage of rectal dose of 15%. In brain tumors, low-field MR image quality was superior compared with CT in 39/45 patients for planning purposes.

CONCLUSIONS

The data presented here show that low-field MRI is feasible in RT treatment planning when image correction regarding system-induced distortions is performed and by selecting MR imaging protocol parameters with the emphasis on adequate images for RT planning.

Integration of digital fluoroscopy with CT-based radiation therapy planning of lung tumors

Radiation dose escalation may be a means to increase the local control rate of inoperable lung tumors. Treatment plans involve the creation of a uniform planning target volume (PTV) to ensure proper coverage despite patient breathing and setup error. This may lead to unnecessary radiation of normal tissue in shallow breathers or target underdosing for patients with excess internal motion. Therefore, the nature of tumor motion for each patient should be measured in 3D, something that cannot be done with CT alone. We have developed a method that acquires 2D real-time fluoroscopic images (loops) and coregisters them with 2D digitally reconstructed radiographs (DRR) formed from the CT scan. The limitations of CT to encompass motion can be overcome by merging the two modalities together. The accuracy of the coregistration method is tested with a stationary grid of radio-opaque markers at various spatial positions. The in-plane (at-depth) displacement between markers on the fluoroscopic image versus the DRR varies with position across the image due to slight misalignments between the x-ray source used in fluoroscopy and the virtual source used for the DRR relative to the test object. At clinically relevant positions, the maximum, measured in-plane displacement, is 1.1 mm. The method is applied to the thorax of an anthropomorphic phantom and a good fit is observed between the appearances of the bony anatomical structures on the coregistered image. Finally, a series of motion measurements are carried out on two oscillating cylindrical objects. The degree of motion as measured by fluoroscopy is accurate to within 1.0 mm, whereas the DRR is inconsistent in predicting motion. The coregistration of fluoroscopic loops with the DRR shows at what point within the oscillation the DRR fails to encompass motion. For any treatment site involving target motion, this real-time imaging is a useful asset in the planning stage.

Precise and real-time measurement of 3D tumor motion in lung due to breathing and heartbeat, measured during radiotherapy

PURPOSE

In this work, three-dimensional (3D) motion of lung tumors during radiotherapy in real time was investigated. Understanding the behavior of tumor motion in lung tissue to model tumor movement is necessary for accurate (gated or breath-hold) radiotherapy or CT scanning.

METHODS

Twenty patients were included in this study. Before treatment, a 2-mm gold marker was implanted in or near the tumor. A real-time tumor tracking system using two fluoroscopy image processor units was installed in the treatment room. The 3D position of the implanted gold marker was determined by using real-time pattern recognition and a calibrated projection geometry. The linear accelerator was triggered to irradiate the tumor only when the gold marker was located within a certain volume. The system provided the coordinates of the gold marker during beam-on and beam-off time in all directions simultaneously, at a sample rate of 30 images per second. The recorded tumor motion was analyzed in terms of the amplitude and curvature of the tumor motion in three directions, the differences in breathing level during treatment, hysteresis (the difference between the inhalation and exhalation trajectory of the tumor), and the amplitude of tumor motion induced by cardiac motion.

RESULTS

The average amplitude of the tumor motion was greatest (12 +/- 2 mm [SD]) in the cranial-caudal direction for tumors situated in the lower lobes and not attached to rigid structures such as the chest wall or vertebrae. For the lateral and anterior-posterior directions, tumor motion was small both for upper- and lower-lobe tumors (2 +/- 1 mm). The time-averaged tumor position was closer to the exhale position, because the tumor spent more time in the exhalation than in the inhalation phase. The tumor motion was modeled as a sinusoidal movement with varying asymmetry. The tumor position in the exhale phase was more stable than the tumor position in the inhale phase during individual treatment fields. However, in many patients, shifts in the exhale tumor position were observed intra- and interfractionally. These shifts are the result of patient relaxation, gravity (posterior direction), setup errors, and/or patient movement.The 3D trajectory of the tumor showed hysteresis for 10 of the 21 tumors, which ranged from 1 to 5 mm. The extent of hysteresis and the amplitude of the tumor motion remained fairly constant during the entire treatment. Changes in shape of the trajectory of the tumor were observed between subsequent treatment days for only one patient. Fourier analysis revealed that for 7 of the 21 tumors, a measurable motion in the range 1-4 mm was caused by the cardiac beat. These tumors were located near the heart or attached to the aortic arch. The motion due to the heartbeat was greatest in the lateral direction. Tumor motion due to hysteresis and heartbeat can lower treatment efficiency in real-time tumor tracking-gated treatments or lead to a geographic miss in conventional or active breathing controlled treatments.

CONCLUSION

The real-time tumor tracking system measured the tumor position in all three directions simultaneously, at a sampling rate that enabled detection of tumor motion due to heartbeat as well as hysteresis. Tumor motion and hysteresis could be modeled with an asymmetric function with varying asymmetry. Tumor motion due to breathing was greatest in the cranial-caudal direction for lower-lobe unfixed tumors.

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.

Introduction of audio gating to further reduce organ motion in breathing synchronized radiotherapy

With breathing synchronized radiotherapy (BSRT), a voltage signal derived from an organ displacement detector is usually displayed on the vertical axis whereas the elapsed time is shown on the horizontal axis. The voltage gate window is set on the breathing voltage signal. Whenever the breathing signal falls between the two gate levels, a gate pulse is produced to enable the treatment machine. In this paper a new gating mechanism, audio (or time-sequence) gating, is introduced and is integrated into the existing voltage gating system. The audio gating takes advantage of the repetitive nature of the breathing signal when repetitive audio instruction is given to the patient. The audio gating is aimed at removing the regions of sharp rises and falls in the breathing signal that cannot be removed by the voltage gating. When the breathing signal falls between voltage gate levels as well as between audio-gate levels, the voltage- and audio-gated radiotherapy (ART) system will generate an AND gate pulse. When this gate pulse is received by a linear accelerator, the linear accelerator becomes "enabled" for beam delivery and will deliver the beam when all other interlocks are removed. This paper describes a new gating mechanism and a method of recording beam-on signal, both of which are, configured into a laptop computer. The paper also presents evidence of some clinical advantages achieved with the ART system.

Potential radiotherapy improvements with respiratory gating

Gating is a relatively new and potentially useful therapeutic addition to external beam radiotherapy applied to regions affected by intra-fraction motion. The impact was of gating on treatment margins, image artifacts, and volume and positional accuracy was investigated by CT imaging of sinusoidally moving spheres. The motion of the spheres simulates target motion. During the CT imaging of dynamically moving spheres, gating reproduced the static volume to within 1%, whereas errors of over 20% were observed where gating was not used. Using a theoretical analysis of margins, gating alone or in combination with an electronic portal imaging device may allow a 2-11 mm reduction in the CTV to PTV margin, and thus less healthy tissue need be irradiated. Gating may allow a reduction of treatment margins, an improvement in image quality, and an improvement in positional and volumetric accuracy of the gross tumor volume.

The impact of (18)FDG-PET on target and critical organs in CT-based treatment planning of patients with poorly defined non-small-cell lung carcinoma: a prospective study

PURPOSE

To prospectively study the impact of coregistering (18)F-fluoro-deoxy-2-glucose hybrid positron emission tomographic (FDG-PET) images with CT images on the planning target volume (PTV), target coverage, and critical organ dose in radiation therapy planning of non-small-cell lung carcinoma.

METHODS AND MATERIALS

Thirty patients with poorly defined tumors on CT, referred for radical radiation therapy, underwent both FDG-PET and CT simulation procedures on the same day, in radiation treatment position. Image sets were coregistered using external fiducial markers. Three radiation oncologists independently defined the gross tumor volumes, using first CT data alone and then coregistered CT and FDG-PET data. Standard margins were applied to each gross tumor volume to generate a PTV, and standardized treatment plans were designed and calculated for each PTV. Dose-volume histograms were used to evaluate the relative effect of FDG information on target coverage and on normal tissue dose.

RESULTS

In 7 of 30 (23%) cases, FDG-PET information changed management strategy from radical to palliative. In 5 of the remaining 23 (22%) cases, new FDG-avid nodes were found within 5 cm of the primary tumor and were included in the PTV. The PTV defined using coregistered CT and FDG-PET would have been poorly covered by the CT-based treatment plan in 17--29% of cases, depending on the physician, implying a geographic miss had only CT information been available. The effect of FDG-PET on target definition varied with the physician, leading to a reduction in PTV in 24-70% of cases and an increase in 30-76% of cases. The relative change in PTV ranged from 0.40 to 1.86. On average, FDG-PET information led to a reduction in spinal cord dose but not in total lung dose, although large differences in dose to the lung were seen for a few individuals.

CONCLUSION

The coregistration of planning CT and FDG-PET images made significant alterations to patient management and to the PTV. Ultimately, changes to the PTV resulted in changes to the radiation treatment plans for the majority of cases. Where possible, we would recommend that FDG-PET data be integrated into treatment planning of non-small-cell lung carcinoma, particularly for three-dimensional conformal techniques.

[Radiotherapy of lung cancer: the inspiration breath hold with spirometric monitoring]

A CT acquisition during a free breathing examination generates images of poor quality. It creates an uncertainty on the reconstructed gross tumour volume and dose distribution. The aim of this study is to test the feasibility of a breath hold method applied in all preparation and treatment days. Five patients received a thoracic radiotherapy with the benefit of this procedure. The breathing of the patient was measured with a spirometer. The patient was coached to reproduce a constant level of breath-hold in a deep inspiration. Video glasses helped the patients to fix the breath-hold at the reference level. The patients followed the coaching during preparation and treatment, without any difficulty. The better quality of the CT reconstructed images resulted in an easier contouring. No movements of the gross tumour volume lead to a better coverage. The deep breath hold decreased the volume of irradiated lung. This method improves the reproducibility of the thoracic irradiation. The decrease of irradiated lung volume offers prospects in dose escalation and intensity modulation radiotherapy.

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

PURPOSE

The high local recurrence rates after radiotherapy in early-stage lung cancer may be due to geometric errors that arise when target volumes are generated using fast spiral CT scanners. A "slow" CT technique that generates more representative target volumes was evaluated.

METHODS AND MATERIALS

Planning CT scans (slice thickness 3 mm, reconstruction index 2.5 mm) were performed during quiet respiration in 10 patients with peripheral lung lesions. Planning CT scans were repeated twice, followed by three slow CT scans (slice thickness 4 mm, index 3 mm, revolution time 4 s/slice). All, except the first scan, were limited to the tumor region. Three-dimensional registration of all scans was performed. The reproducibility of the imaged volumes was evaluated with each technique using (1) the common overlapping volume (COM), the component of the clinical target volume (CTV) covered by all three CT scans, and (2) the encompassing volume (SUM), which is the volume enveloped by all CTVs.

RESULTS

In all patients, the target volumes generated using slow CT scans were larger than those derived using planning scans (mean ratio of planning-CTV:slow-CTV of 88.8% +/- 5.6%), and also more reproducible. The mean ratio of the respective COM:SUM volumes was 62.6% +/- 10.8% and 54.9% +/- 12.9%.

CONCLUSIONS

Larger, and more reproducible, target volumes are generated for peripheral lung tumors with the use of slow CT scans, thereby indicating that slow scans can better capture tumor movement.

Conformal radiotherapy (CRT) planning for lung cancer: analysis of intrathoracic organ motion during extreme phases of breathing

PURPOSE

Conformal radiotherapy beams are defined on the basis of static computed tomography acquisitions by taking into account setup errors and organ/tumor motion during breathing. In the absence of precise data, the size of the margins is estimated arbitrarily. The objective of this study was to evaluate the amplitude of maximum intrathoracic organ motion during breathing.

METHODS AND MATERIALS

Twenty patients treated for non-small-cell lung cancer were included in the study: 10 patients at the Institut Curie with a personalized alpha cradle immobilization and 10 patients at Tenon Hospital with just the Posirest device below their arms. Three computed tomography acquisitions were performed in the treatment position: the first during free breathing and the other two during deep breath-hold inspiration and expiration. For each acquisition, the displacements of the various intrathoracic structures were measured in three dimensions.

RESULTS

Patients from the two centers were comparable in terms of age, weight, height, tumor site, and stage. In the overall population, the greatest displacements were observed for the diaphragm, and the smallest displacements were observed for the lung apices and carina. The relative amplitude of motion was comparable between the two centers. The use of a personalized immobilization device reduced lateral thoracic movements (p < 0.02) and lung apex movements (p < 0.02).

CONCLUSION

Intrathoracic organ movements during extreme phases of breathing are considerable. Quantification of organ motion is necessary for definition of the safety margins. A personalized immobilization device appears to effectively reduce apical and lateral displacement.

Three-Dimensional Conformal Radiation Therapy (3D-CRT) for Early-Stage Non–Small-Cell Lung Cancer

The standard treatment for early-stage non-small-cell lung cancer is surgical resection. However, many patients are inoperable due to medical comorbidities. Thirty-two medically inoperable patients with early-stage non-small-cell lung cancer were treated with 3-dimensional conformal radiation therapy between January 1991 and December 2000. The median dose was 70.2 Gy, and the median follow-up time in survivors was 30 months. The 2-year actuarial local control, overall survival, and cancer-specific survival rates were 43%, 54%, and 57%, respectively. The 5-year actuarial local control, overall survival, and cancer-specific survival rates were 43%, 33%, and 39%, respectively. This report suggests that local control is improved with high-dose conformal radiation therapy when compared to other institutions' retrospective experiences.

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

BACKGROUND

The target coverage for radiotherapy of early-stage lung cancer was evaluated using two different CT techniques.

MATERIALS AND METHODS

A conventional planning CT scan and two limited scans of the tumor region were performed in seven patients with peripheral tumors. Three 'slow' scans (slice thickness 4mm, index 3mm, revolution time 4s/slice) were then performed, followed by three-dimensional image registration. Planning target volumes (PTV) were generated using these GTV-PTV margins: (a) 1cm (PTV1.0); (b) 1.5 cm (PTV1.5); and (c) 0.9, 1.0, and 0.9 cm ('PTV(clinical)') when set-up errors are avoided.

RESULTS

PTVs derived from three 'slow' scans missed 1.9% of the volume derived from three planning scans for an immobile tumor and 9.3% in the case of a mobile tumor. For an immobile tumor, PTV1.5 achieved comparable coverage to that achieved using PTVclinical, which was generated from three 'slow' scans and a planning scan. For a mobile tumor, PTV(1.5) covered only 89% of the volume captured by PTVclinical. PTV1.0 resulted in inadequate target coverage in all the patients. Reductions in potential lung toxicity (V20) were achievable in six patients despite the larger GTVclinical when treatment set-up errors were minimized.

CONCLUSIONS

PTVs derived using 'slow' CT scans consistently produce superior target coverage than that using conventional scans. This may account for the poor local control observed in stage I lung cancer.

Detection of lung tumor movement in real-time tumor-tracking radiotherapy

PURPOSE

External radiotherapy for lung tumors requires reducing the uncertainty due to setup error and organ motion. We investigated the three-dimensional movement of lung tumors through an inserted internal marker using a real-time tumor-tracking system and evaluated the efficacy of this system at reducing the internal margin.

METHODS AND MATERIALS

Four patients with lung cancer were analyzed. A 2.0-mm gold marker was inserted into the tumor. The real-time tumor-tracking system calculates and stores three-dimensional coordinates of the marker 30 times/s. The system can trigger the linear accelerator to irradiate the tumor only when the marker is located within the predetermined "permitted dislocation." The value was set at +/-1 to +/-3 mm according to the patient's characteristics. We analyzed 10,413-14,893 data sets for each of the 4 patients. The range of marker movement during normal breathing (beam-off period) was compared with that during gated irradiation (beam-on period) by Student's t test.

RESULTS

The range of marker movement during the beam-off period was 5.5-10.0 mm in the lateral direction (x), 6.8-15.9 mm in the craniocaudal direction (y) and 8.1-14.6 mm in the ventrodorsal direction (z). The range during the beam-on period was reduced to within 5.3 mm in all directions in all 4 patients. A significant difference was found between the mean of the range during the beam-off period and the mean of the range during the beam-on period in the x (p = 0.007), y (p = 0.025), and z (p = 0.002) coordinates, respectively.

CONCLUSION

The real-time tumor-tracking radiotherapy system was useful to analyze the movement of an internal marker. Treatment with megavoltage X-rays was properly given when the tumor marker moved into the "permitted dislocation" zone from the planned position.

Determining parameters for respiration-gated radiotherapy

Respiration-gated radiotherapy for tumor sites affected by respiratory motion will potentially improve radiotherapy outcomes by allowing reduced treatment margins leading to decreased complication rates and/or increased tumor control. Furthermore, for intensity-modulated radiotherapy (IMRT), respiratory gating will minimize the hot and cold spot artifacts in dose distributions that may occur as a result of interplay between respiratory motion and leaf motion. Most implementations of respiration gating rely on the real time knowledge of the relative position of the internal anatomy being treated with respect to that of an external marker. A method to determine the amplitude of motion and account for any difference in phase between the internal tumor motion and external marker motion has been developed. Treating patients using gating requires several clinical decisions, such as whether to gate during inhale or exhale, whether to use phase or amplitude tracking of the respiratory signal, and by how much the intrafraction tumor motion can be decreased at the cost of increased delivery time. These parameters may change from patient to patient. A method has been developed to provide the data necessary to make decisions as to the CTV to PTV margins to apply to a gated treatment plan.

Respiratory-driven lung tumor motion is independent of tumor size, tumor location, and pulmonary function

PURPOSE

To determine whether superior-inferior lung tumor motion is predictable by tumor size or location, or pulmonary function test results.

METHODS AND MATERIALS

Superior-inferior tumor motion was measured on orthogonal radiographs taken during simulation of 22 patients with inoperable lung cancer diagnosed by orthogonal radiographs.

RESULTS

The tumor size averaged 5.5 +/- 3.1 cm (range 1.5-12 cm). Seven of 11 central tumors demonstrated some motion compared with 5 of 11 peripheral tumors. Four of 5 upper lobe tumors moved compared with 8 of 17 tumors that were either middle or lower lobe lesions. The mean fourth rib motion was 7.3 +/- 3.2 mm (range 2-15). The mean FeV(1) was 1.8 +/- 1.2 (range 0.55-5.33. The mean diffusing capacity of the lung for carbon monoxide was 14.0 +/- 6.5 (range 7.8-21.9). The mean total lung capacity was 6.5 +/- 1.2 (range 3.3-8.4). None of these parameters correlated with tumor motion. Although lateral tumor motion could not be consistently determined, 1 tumor moved 10 mm anterior-posteriorly.

CONCLUSIONS

Lung tumors often move significantly during respiration. Tumor motion is not predictable by tumor size or location, or pulmonary function test results. Therefore, tumor motion must be measured in all patients. Measurement in three dimensions will likely be necessary to maximize the irradiated lung volumes or choose beam arrangements parallel to the major axis of motion.

Dosimetric evaluation of lung tumor immobilization using breath hold at deep inspiration

PURPOSE

To examine the dosimetric benefit of self-gated radiotherapy at deep-inspiration breath hold (DIBH) in the treatment of patients with non-small-cell lung cancer (NSCLC). The relative contributions of tumor immobilization at breath hold (BH) and increased lung volume at deep inspiration (DI) in sparing high-dose lung irradiation (> or = 20 Gy) were examined.

METHODS AND MATERIALS

Ten consecutive patients undergoing radiotherapy for Stage I-IIIB NSCLC who met the screening criteria were entered on this study. Patients were instructed to BH at DI without the use of external monitors or breath-holding devices (self-gating). Computed tomography (CT) scans of the thorax were performed during free breathing (FB) and DIBH. Fluoroscopy screened for reproducible tumor position throughout DIBH, and determined the maximum superior-inferior (SI) tumor motion during both FB and DIBH. Margins used to define the planning target volume (PTV) from the clinical target volume included 1 cm for setup error and organ motion, plus an additional SI margin for tumor motion, as determined from fluoroscopy. Three conformal treatment plans were then generated for each patient, one from the FB scan with FB PTV margins, a second from the DIBH scan with FB PTV margins, and a third from the DIBH scan with DIBH PTV margins. The percent of total lung volume receiving > or = 20 Gy (using a prescription dose of 70.9 Gy to isocenter) was determined for each plan.

RESULTS

Self-gating at DIBH was possible for 8 of the 10 patients; 2 patients were excluded, because they were not able to perform a reproducible DIBH. For these 8 patients, the median BH time was 23 (range, 19-52) s. The mean percent of total lung volume receiving > or = 20 Gy under FB conditions (FB scan with FB PTV margins) was 12.8%. With increased lung volume alone (DIBH scan with FB PTV margins), this was reduced to 11.0%, tending toward a significant decrease in lung irradiation over FB (p = 0.086). With both increased lung volume and tumor immobilization (DIBH scan with DIBH PTV margins), the mean percent lung volume receiving > or = 20 Gy was further reduced to 8.8%, a significant decrease in lung irradiation compared to FB (p = 0.011). Furthermore, at DIBH, the additional benefit provided by tumor immobilization (i.e., using DIBH instead of FB PTV margins) was also significant (p = 0.006). The relative contributions of tumor immobilization and increased lung volume toward reducing the percent total lung volume receiving > or = 20 Gy were patient specific; however, all 8 of the patients analyzed showed a dosimetric benefit with this DIBH technique.

CONCLUSION

Compared to FB conditions, at DIBH the mean reduction in percent lung volume receiving > or = 20 Gy was 14.3% with the increase in lung volume alone, 22.1% with tumor immobilization alone, and 32.5% with the combined effect. The dosimetric benefit seen at DIBH was patient specific, and due to both the increased lung volume seen at DI and the PTV margin reduction seen with tumor immobilization.

Motion adaptive x-ray therapy: a feasibility study

Intrafraction motion caused by breathing requires increased treatment margins for chest and abdominal radiotherapy and may lead to 'motion artefacts' in dose distributions during intensity modulated radiotherapy (IMRT). Technologies such as gated radiotherapy may significantly increase the treatment time, while breath-hold techniques may be poorly tolerated by pulmonarily compromised patients. A solution that allows reduced margins and dose distribution artefacts, without compromising delivery time, is to synchronously follow the target motion by adapting the x-ray beam using a dynamic multileaf collimator (MLC), i.e. motion adaptive x-ray therapy, or MAX-T for short. Though the target is moving with time, in the MAX-T beam view the target is static. The MAX-T method superimposes the target motion due to respiration onto the beam originally planned for delivery. Thus during beam delivery the beam is dynamically changing position with respect to the isocentre using a dynamic MLC, the leaf positions of which are dependent upon the target position. Synchronization of the MLC motion and target motion occurs using respiration gated radiotherapy equipment. The concept and feasibility of MAX-T and the capability of the treatment machine to deliver such a treatment were investigated by performing measurements for uniform and IMRT fields using a mechanical sinusoidal oscillator to simulate target motion. Target dose measurements obtained using MAX-T for a moving target were found to be equivalent to those delivered to a static target by a static beam.

Physical aspects of a real-time tumor-tracking system for gated radiotherapy

PURPOSE

To reduce uncertainty due to setup error and organ motion during radiotherapy of tumors in or near the lung, by means of real-time tumor tracking and gating of a linear accelerator.

METHODS AND MATERIALS

The real-time tumor-tracking system consists of four sets of diagnostic X-ray television systems (two of which offer an unobstructed view of the patient at any time), an image processor unit, a gating control unit, and an image display unit. The system recognizes the position of a 2.0-mm gold marker in the human body 30 times per second using two X-ray television systems. The marker is inserted in or near the tumor using image guided implantation. The linear accelerator is gated to irradiate the tumor only when the marker is within a given tolerance from its planned coordinates relative to the isocenter. The accuracy of the system and the additional dose due to the diagnostic X-ray were examined in a phantom, and the geometric performance of the system was evaluated in 4 patients.

RESULTS

The phantom experiment demonstrated that the geometric accuracy of the tumor-tracking system is better than 1.5 mm for moving targets up to a speed of 40 mm/s. The dose due to the diagnostic X-ray monitoring ranged from 0.01% to 1% of the target dose for a 2.0-Gy irradiation of a chest phantom. In 4 patients with lung cancer, the range of the coordinates of the tumor marker during irradiation was 2.5-5.3 mm, which would have been 9.6-38.4 mm without tracking.

CONCLUSION

We successfully implemented and applied a tumor-tracking and gating system. The system significantly improves the accuracy of irradiation of targets in motion at the expense of an acceptable amount of diagnostic X-ray exposure.