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

Effects of reconstruction methods on dose distribution for lung stereotactic body radiotherapy treatment plans

The aim of the present study was to investigate the effect of tumour motion on various imaging strategies as well as on treatment plan accuracy for lung stereotactic body radiotherapy treatment (SBRT) cases. The ExacTrac gating phantom and paraffin were used to investigate respiratory motion and represent a lung tumour, respectively. Four-dimensional computed tomography (4DCT) imaging was performed, while the phantom was moving sinusoidally with 4 s cycling time with three different amplitudes of 8, 16, and 24 mm. Reconstructions were done with maximum (MIP) and average intensity projection (AIP) methods. Comparisons of target density and volume were performed using two reconstruction techniques and references values. Volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) were planned based on reconstructed computed tomography (CT) sets, and it was examined how density variations affect the dose-volume histogram (DVH) parameters. 4D cone beam computed tomography (CBCT) was performed with the Elekta Versa HD linac imaging system before irradiation and compared with 3D CBCT. Thus, various combinations of 4DCT reconstruction methods and treatment alignment methods have been investigated. Point measurements as well as 2 and 3D dose measurements were done by optically stimulated luminescence (OSL), gafchromic films, and electronic portal imaging devices (EPIDs), respectively. The mean volume reduction was 7.8% for the AIP and 2.6% for the MIP method. The obtained Hounsfield Unit (HU) values were lower for AIP and higher for MIP when compared with the reference volume density. In DVH analysis, there were no statistical differences for D_95%, D_98%, and D_mean (p > 0.05). However, D_2% was significantly affected by HU changes (p < 0.01). A positional variation was obtained up to 2 mm in moving direction when 4D CBCT was applied after 3D CBCT. Dosimetric measurements showed that the main part of the observed dose deviation was due to movement. In lung SBRT treatment plans, D_2% doses differ significantly according to the reconstruction method. Additionally, it has been observed that setups based on 3D imaging can cause a positional error of up to 2 mm compared to setups based on 4D imaging. It is concluded that MIP has advantages over AIP in defining internal target volume (ITV) in lung SBRT applications. In addition, 4D CBCT and 3D EPID dosimetry are recommended for lung SBRT treatments.

Computed Tomography-Based Evaluation of Volume and Position Changes of the Target Region and Organs at Risk During Radiotherapy for Esophageal Cancer: A Pilot Study

Objective

To analyze changes in volume and position of target regions and organs at risk (OARs) during radiotherapy for esophageal cancer patients.

Methods

Overall, 16 esophageal cancer patients who underwent radiotherapy, including 10 cases of intensity-modulated radiation therapy (IMRT) and six of three-dimensional conformal radiotherapy (3D-CRT), were enrolled. The prescription doses for the planning target volumes (PTVs) were as follows: PTV1, 64 Gy/32 fractions; and PTV2, 46 Gy/23 fractions. Repeat computed tomography (CT) was performed for patients after the 5th, 10th, 15th, 20th, and 25th fractions. Delineation of the gross tumor volume (GTV) and OAR volume was determined using five repeat CTs performed by the same physician. The target and OAR volumes and centroid positions were recorded and used to analyze volume change ratio (VCR), center displacement (ΔD), and changes in the distance from the OAR centroid positions to the planned radiotherapy isocenter (distance to isocenter, DTI) during treatment.

Results

No patient showed significant changes in target volume (TV) after the first week of radiotherapy (five fractions). However, TV gradually decreased over the following weeks, with the rate slowing after the fourth week (40 Gy). The comparison of TV from baseline to 40 Gy (20 fractions) showed that average GTVs decreased from 130.7 ± 63.1 cc to 92.1 ± 47.2 cc, with a VCR of −29.21 ± 13.96% (p<0.01), while the clinical target volume (CTV1) decreased from 276.7 ± 98.2 cc to 246.7 ± 87.2 cc, with a VCR of −10.34 ± 7.58% (p<0.01). As TVs decreased, ΔD increased and DTI decreased. After the fourth week of radiotherapy (40 Gy), centroids of GTV, CTV1, and prophylactic CTV (CTV2) showed average deviations in ΔD of 7.6 ± 4.0, 6.9 ± 3.4, and 6.0 ± 3.0 mm, respectively. The average DTI of the heart decreased by 4.53 mm (from 15.61 ± 2.96 cm to 15.16 ± 2.27 cm).

Conclusion

During radiotherapy for esophageal cancer, Targets and OARs change significantly in volume and position during the 2^nd–4^th weeks. Image-guidance and evaluation of dosimetric changes are recommended for these fractions of treatment to appropriate adjust treatment plans.

Tumor volume shrinkage during stereotactic body radiotherapy is related to better prognoses in patients with stage I non-small-cell lung cancer

The purpose of the study was to investigate the association between tumor volume changes during stereotactic body radiation therapy (SBRT) and prognoses in stage I non-small-cell lung cancer (NSCLC). This retrospective review included stage I NSCLC patients in whom SBRT was performed at a total dose of 48.0-50.5 Gy in four or five fractions. The tumor volumes observed on computed tomography (CT) simulation and on the CT performed at the last treatment session using a CT-on-rails system were measured and compared. Then, the tumor volume changes during the SBRT period were measured and assessed for their association with prognoses (overall survival, local control, lymph node metastases and distant metastases). A total of 98 patients with a mean age of 78.6 years were enrolled in the study. The T-stage was T1a in 42%, T1b in 32% and T2a in 26% of the cases. The gross tumor volume (GTV) shrank and increased ≥10% in 23 (23.5%) and 36 (36.7%) of the cases, respectively. The 5-year local control and overall survival rates in the groups with a tumor shrinkage of ≥10% vs the group with a shrinkage of <10% were 94.7 vs 70.8% and 85.4 vs 47.6%, respectively; these differences were significant, with a P-value < 0.05. During a short SBRT period, the tumor shrank or enlarged in a small number of cases. A decrease of ≥10% in the GTV during SBRT was significantly related to better overall survival and local control.

Local Control and Toxicity of Adaptive Radiotherapy Using Weekly CT Imaging: Results from the LARTIA Trial in Stage III NSCLC

INTRODUCTION

Anatomical change of tumor during radiotherapy contributes to target missing. However, in the case of tumor shrinkage, adaptation of volume could result in an increased incidence of recurrence in the area of target reduction. This study aims to investigate the incidence of failure of the adaptive approach and, in particular, the risk for local recurrence in the area excluded after replanning.

METHODS

In this prospective study, patients with locally advanced NSCLC treated with concomitant chemoradiation underwent weekly chest computed tomography simulation during treatment. In the case of tumor shrinkage, a new tumor volume was delineated and a new treatment plan outlined (replanning). Toxicity was evaluated with the Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer scale. Patterns of failures were classified as in field (dimensional and/or metabolic progression within the replanning planning target volume [PTV]), marginal (recurrence in initial the PTV excluded from the replanning PTV), and out of field (recurrence outside the initial PTV).

RESULTS

Replanning was outlined in 50 patients selected from a total of 217 patients subjected to weekly simulation computed tomography in our center from 2012 to 2014. With a median follow-up of 20.5 months, acute grade 3 or higher pulmonary and esophageal toxicity were reported in 2% and 4% of cases and late toxicity in 4% and 2%, respectively. Marginal relapse was recorded in 6% of patients, and 20% and 4% of patients experienced in-field and out-of-field local failure, respectively.

CONCLUSIONS

The reduced toxicity and the documented low rate of marginal failures make the adaptive approach a modern option for future randomized studies. The best scenario to confirm its application is probably in neoadjuvant chemoradiation trials.

Inter-Fraction Tumor Volume Response during Lung Stereotactic Body Radiation Therapy Correlated to Patient Variables

Purpose

Analyze inter-fraction volumetric changes of lung tumors treated with stereotactic body radiation therapy (SBRT) and determine if the volume changes during treatment can be predicted and thus considered in treatment planning.

Methods and Materials

Kilo-voltage cone-beam CT (kV-CBCT) images obtained immediately prior to each fraction were used to monitor inter-fraction volumetric changes of 15 consecutive patients (18 lung nodules) treated with lung SBRT at our institution (45–54 Gy in 3–5 fractions) in the year of 2011–2012. Spearman's (ρ) correlation and Spearman's partial correlation analysis was performed with respect to patient/tumor and treatment characteristics. Multiple hypothesis correction was performed using False Discovery Rate (FDR) and q-values were reported.

Results

All tumors studied experienced volume change during treatment. Tumor increased in volume by an average of 15% and regressed by an average of 11%. The overall volume increase during treatment is contained within the planning target volume (PTV) for all tumors. Larger tumors increased in volume more than smaller tumors during treatment (q = 0.0029). The volume increase on CBCT was correlated to the treatment planning gross target volume (GTV) as well as internal target volumes (ITV) (q = 0.0085 and q = 0.0039 respectively) and could be predicted for tumors with a GTV less than 22 mL. The volume increase was correlated to the integral dose (ID) in the ITV at every fraction (q = 0.0049). The peak inter-fraction volume occurred at an earlier fraction in younger patients (q = 0.0122).

Conclusions

We introduced a new analysis method to follow inter-fraction tumor volume changes and determined that the observed changes during lung SBRT treatment are correlated to the initial tumor volume, integral dose (ID), and patient age. Furthermore, the volume increase during treatment of tumors less than 22mL can be predicted during treatment planning. The volume increase remained significantly less than the overall PTV expansion, and radiation re-planning was therefore not required for the purpose of tumor control. The presence of the studied correlations suggests that the observed volumetric changes may reflect some underlying biologic process rather than random fluctuations.

Evaluation of interfractional variation of the centroid position and volume of internal target volume during stereotactic body radiotherapy of lung cancer using cone-beam computed tomography

The purpose of this study was to determine interfractional variation of the centroid position and volume of internal target volume (ITV) during stereotactic body radiation therapy (SBRT) of lung cancer. From January 2014 to August 2014, a total of 32 patients with 37 primary or metastatic lung tumors were enrolled in our study. All patients received SBRT treatment in 4-5 fractions to a median dose of 48 Gy. Both 3D CT and 4D CT scans were used for radiotherapy treatment planning. 3D CBCT was acquired prior to treatment delivery to verify patient positioning. A total of 163 3D CBCT images were available for evaluation. 3D CBCT scans acquired for verification were registered with simulation CT scans. The ITVs were contoured on all verification 3D CBCT scans and compared to the initial gross target volume (GTV) or ITV in treatment planning system. GTV was based on 3D CT while ITV was based on both 3D CT and 4D CT. To assess the interfractional variation of ITV centroid position, we used vertebrae body adja-cent to the tumor as reference point when performing the registration procedure. To eliminate the effect of time on tumor volume between simulation CT scan and the first fraction, the interfractional variation of ITV was evaluated from the first fraction to the last fraction. The overall 3D vector shift was 4.4 ± 2.5 mm (range: 0.4-13.8 mm). The interfractional variation of ITV centroid position in superior-inferior, anterior-posterior, and left-right directions were -0.7 ± 2.7 mm, -1.4 ± 3.4 mm, and -0.5 ± 2.2 mm, respectively. No significant difference was observed between three directions (p = 0.147). Large interfractional variations (≥ 5 mm) were observed in 12 fractions (9.3%) in superior-inferior direction, 24 fractions (18.6%) in anterior-posterior direction, and 5 fractions (3.9%) in left-right direction. No time trend of tumor volume change measured in 3D CBCT was detected during four fractions (p = 0.074). A significant (p = 0.010) time trend was detected when evaluating the time trend of ITV change during 5 fractions and diameter was found to be significantly correlated with the ITV change (p = 0.000). ITV did not show significant regression during SBRT treatment, but interfractional variation in the ITV centroid position was observed, especially in anterior-posterior direc-tion. An isotropic margin of 7 mm around ITV might be necessary for adequate coverage of interfractional variation of ITV centroid position, but only in case no soft tissue-based setup is performed during SBRT treatment.

Tumor volume change with stereotactic body radiotherapy (SBRT) for early-stage lung cancer: evaluating the potential for adaptive SBRT

OBJECTIVES

To quantify gross tumor volume (GTV) change during stereotactic body radiotherapy (SBRT) and on first follow-up, as well as to evaluate for any predictive prognostic risk factors related to GTV decrease. An attempt was also made to identify the potential timing for adaptive SBRT.

METHODS

Twenty-five tumors in 24 consecutive patients were treated with SBRT to total dose of 50 Gy in 5 fractions. Median age was 72.5 years. Tumor stage was T1, 68%; T2, 20%; and other, 12%. The GTVs of on the 5 cone-beam computed tomographies (CBCT1-5) obtained before each fraction and the first follow-up CT (CTPOST) were analyzed.

RESULTS

Median time from diagnosis to initiation of radiotherapy was 64 days. GTV on CBCT1 was the baseline for comparison. GTV decreased by a mean of 7% on CBCT2 (P=0.148), 11% on CBCT3 (P=0.364), 19% on CBCT4 (P=0.0021), and 32% on CBCT5 (P=0.0004). Univariate analyses of GTV shrinkage was significantly associated with "time from CBCT5 to CTPOST" (P=0.027) and "T-stage" (P=0.002). In multivariate analyses, "T-stage" remained significant with T1 tumors showing greater GTV shrinkage than T2 tumors.

CONCLUSIONS

Significant decrease in GTV volume based on daily CBCT was demonstrated during SBRT treatment. Adaptive SBRT has the potential to minimize integral dose to the surrounding normal tissues without compromising GTV coverage.

Interfractional variations of tumor centroid position and tumor regression during stereotactic body radiotherapy for lung tumor

Purpose. To determine interfractional changes of lung tumor centroid position and tumor regression during stereotactic body radiation therapy (SBRT). Methods and Materials. 34 patients were treated by SBRT in 4-5 fractions to a median dose of 50 Gy. The CT scans acquired for verification were registered with simulation CT scans. The gross target volume (GTV) was contoured on all verification CT scans and compared to the initial GTV in treatment plan system. Results. The mean (±standard deviation, SD) three-dimension vector shift was 5.2 ± 3.1 mm. The mean (±SD) interfractional variations of tumor centroid position were −0.7 ± 4.5 mm in anterior-posterior (AP) direction, 0.2 ± 3.1 mm in superior-inferior (SI) direction, and 0.4 ± 2.4 mm in right-left (RL) direction. Large interfractional variations (≥5 mm) were observed in 5 fractions (3.3%) in RL direction, 16 fractions (10.5%) in SI direction, and 36 fractions (23.5%) in AP direction. Tumor volume did not decrease significantly during lung SBRT. Conclusions. Small but insignificant tumor volume regression was observed during lung SBRT. While the mean interfractional variations of tumor centroid position were minimal in three directions, variations more than 5 mm account for approximately a third of all, indicating additional margin for PTV, especially in AP direction.

Changes in volume of stage I non-small-cell lung cancer during stereotactic body radiotherapy

Background

The overall treatment time of stereotactic body radiotherapy (SBRT) for non-small-cell lung cancer is usually 3 to over 10 days. If it is longer than 7 days, tumor volume expansion during SBRT may jeopardize the target dose coverage. In this study, volume change of stage I NSCLC during SBRT was investigated.

Methods

Fifty patients undergoing 4-fraction SBRT with a total dose of 48 Gy (n = 36) or 52 Gy (n = 14) were analyzed. CT was taken for registration at the first and third SBRT sessions with an interval of 7 days in all patients. Patient age was 29–87 years (median, 77), and 39 were men. Histology was adenocarcinoma in 28, squamous cell carcinoma in 17, and others in 5. According to the UICC 7th classification, T-stage was T1a in 9 patients, T1b in 27, and T2a in 14. Tumor volumes on the first and 8th days were determined on CT images taken during the exhalation phase, by importing the data into the Dr. View/LINAX image analysis system. After determining the optimal threshold for distinguishing tumor from pulmonary parenchyma, the region above -250 HU was automatically extracted and the tumor volumes were calculated.

Results

The median tumor volume was 7.3 ml (range, 0.5-35.7) on day 1 and 7.5 ml (range, 0.5-35.7) on day 8. Volume increase of over 10% was observed in 16 cases (32%); increases by >10 to ≤20%, >20 to ≤30%, and >30% were observed in 9, 5, and 2 cases, respectively. The increase in the estimated tumor diameter was over 2 mm in 3 cases and 1–2 mm in 6. A decrease of 10% or more was seen in 3 cases. Among the 16 tumors showing a volume increase of over 10%, T-stage was T1a in 2 patients, T1b in 9, and T2a in 5. Histology was adenocarcinoma in 10 patients, squamous cell carcinoma in 5, and others in 1.

Conclusions

Volume expansion >10% was observed in 32% of the tumors during the first week of SBRT, possibly due to edema or sustained tumor progression. When planning SBRT, this phenomenon should be taken into account.

Modeling of non-small cell lung cancer volume changes during CT-based image guided radiotherapy: patterns observed and clinical implications

Background. To characterize the lung tumor volume response during conventional and hypofractionated radiotherapy (RT) based on diagnostic quality CT images prior to each treatment fraction. Methods. Out of 26 consecutive patients who had received CT-on-rails IGRT to the lung from 2004 to 2008, 18 were selected because they had lung lesions that could be easily distinguished. The time course of the tumor volume for each patient was individually analyzed using a computer program. Results. The model fits of group L (conventional fractionation) patients were very close to experimental data, with a median Δ% (average percent difference between data and fit) of 5.1% (range 3.5-10.2%). The fits obtained in group S (hypofractionation) patients were generally good, with a median Δ% of 7.2% (range 3.7-23.9%) for the best fitting model. Four types of tumor responses were observed-Type A: "high" kill and "slow" dying rate; Type B: "high" kill and "fast" dying rate; Type C: "low" kill and "slow" dying rate; and Type D: "low" kill and "fast" dying rate. Conclusions. The models used in this study performed well in fitting the available dataset. The models provided useful insights into the possible underlying mechanisms responsible for the RT tumor volume response.

Detection of interfraction displacement and volume variance during radiotherapy of primary thoracic esophageal cancer based on repeated four-dimensional CT scans

Background

To investigate the interfraction displacement and volume variation of primary thoracic esophagus carcinoma with enhanced four-dimensional computed tomography (4DCT) scanning during fractionated radiotherapy.

Methods

4DCT data sets were acquired at the time of treatment simulation and every ten fraction for each of 32 patients throughout treatment. Scans were registered to baseline (simulation) 4DCT scans by using bony landmarks. The gross tumor volumes (GTVs) were delineated on each data set. Coordinates of the GTV centroids were acquired on each respiration phase. Distance between center of the GTV contour on the simulation scan and the centers on subsequent scans were used to assess interfraction displacement between fractions. Volumes were constructed using three approaches: The GTV delineated from the maximum intensity projection (MIP) was defined IGTV_MIP, all 10 GTVs were combined to form IGTV₁₀, GTV_mean was the average of all 10 phases of each GTV.

Results

Interfraction displacement in left-right (LR), anterior-posterior (AP), superior-inferior (SI) directions and 3D vector were 0.13 ± 0.09 cm, 0.16 ± 0.12 cm, 0.34 ± 0.26 cm and 0.43 ± 0.24 cm, respectively between the tenth fraction and simulation 4DCT scan. 0.14 ± 0.09 cm, 0.19 ± 0.16 cm, 0.45 ± 0.43 cm and 0.56 ± 0.40 cm in LR, AP, SI and 3D vector respectively between the twentieth fraction and simulation 4DCT scan. Displacement in SI direction was larger than LR and AP directions during treatment. For distal esophageal cancer, increased interfraction displacements were observed in SI direction and 3D vector (P = 0.002 and P = 0.001, respectively) during radiotherapy. The volume of GTV_mean, IGTV_MIP, and IGTV₁₀ decreased significantly at the twentieth fraction for middle (median: 34.01%, 33.09% and 28.71%, respectively) and distal (median: 22.76%, 25.27% and 23.96%, respectively) esophageal cancer, but for the upper third, no significant variation were observed during radiotherapy.

Conclusions

Interfractional displacements in SI direction were larger than LR and AP directions. For distal location, significant changes were observed in SI direction and 3D vector during radiotherapy. For middle and distal locations, the best time to reset position should be selected at the twentieth fraction when the primary tumor target volume changed significantly, and it was preferable to guide target correction and planning modification.

[Image-guided and adaptive radiotherapy]

Image-guided radiotherapy (IGRT) aims to take into account anatomical variations occurring during irradiation by visualization of anatomical structures. It may consist of a rigid registration of the tumour by moving the patient, in case of prostatic irradiation for example. IGRT associated with intensity-modulated radiotherapy (IMRT) is strongly recommended when high-dose is delivered in the prostate, where it seems to reduce rectal and bladder toxicity. In case of significant anatomical deformations, as in head and neck tumours (tumour shrinking and decrease in volume of the salivary glands), replanning appears to be necessary, corresponding to the adaptive radiotherapy. This should ideally be "monitored" and possibly triggered based on a calculation of cumulative dose, session after session, compared to the initial planning dose, corresponding to the concept of dose-guided adaptive radiotherapy. The creation of "planning libraries" based on predictable organ positions (as in cervical cancer) is another way of adaptive radiotherapy. All of these strategies still appear very complex and expensive and therefore require stringent validation before being routinely applied.

Localization accuracy from automatic and semi-automatic rigid registration of locally-advanced lung cancer targets during image-guided radiation therapy

PURPOSE

To evaluate localization accuracy resulting from rigid registration of locally-advanced lung cancer targets using fully automatic and semi-automatic protocols for image-guided radiation therapy.

METHODS

Seventeen lung cancer patients, fourteen also presenting with involved lymph nodes, received computed tomography (CT) scans once per week throughout treatment under active breathing control. A physician contoured both lung and lymph node targets for all weekly scans. Various automatic and semi-automatic rigid registration techniques were then performed for both individual and simultaneous alignments of the primary gross tumor volume (GTV(P)) and involved lymph nodes (GTV(LN)) to simulate the localization process in image-guided radiation therapy. Techniques included "standard" (direct registration of weekly images to a planning CT), "seeded" (manual prealignment of targets to guide standard registration), "transitive-based" (alignment of pretreatment and planning CTs through one or more intermediate images), and "rereferenced" (designation of a new reference image for registration). Localization error (LE) was assessed as the residual centroid and border distances between targets from planning and weekly CTs after registration.

RESULTS

Initial bony alignment resulted in centroid LE of 7.3 ± 5.4 mm and 5.4 ± 3.4 mm for the GTV(P) and GTV(LN), respectively. Compared to bony alignment, transitive-based and seeded registrations significantly reduced GTV(P) centroid LE to 4.7 ± 3.7 mm (p = 0.011) and 4.3 ± 2.5 mm (p < 1 × 10(-3)), respectively, but the smallest GTV(P) LE of 2.4 ± 2.1 mm was provided by rereferenced registration (p < 1 × 10(-6)). Standard registration significantly reduced GTV(LN) centroid LE to 3.2 ± 2.5 mm (p < 1 × 10(-3)) compared to bony alignment, with little additional gain offered by the other registration techniques. For simultaneous target alignment, centroid LE as low as 3.9 ± 2.7 mm and 3.8 ± 2.3 mm were achieved for the GTV(P) and GTV(LN), respectively, using rereferenced registration.

CONCLUSIONS

Target shape, volume, and configuration changes during radiation therapy limited the accuracy of standard rigid registration for image-guided localization in locally-advanced lung cancer. Significant error reductions were possible using other rigid registration techniques, with LE approaching the lower limit imposed by interfraction target variability throughout treatment.

Classifying geometric variability by dominant eigenmodes of deformation in regressing tumours during active breath-hold lung cancer radiotherapy

The purpose of this study is to develop and evaluate a lung tumour interfraction geometric variability classification scheme as a means to guide adaptive radiotherapy and improve measurement of treatment response. Principal component analysis (PCA) was used to generate statistical shape models of the gross tumour volume (GTV) for 12 patients with weekly breath hold CT scans. Each eigenmode of the PCA model was classified as 'trending' or 'non-trending' depending on whether its contribution to the overall GTV variability included a time trend over the treatment course. Trending eigenmodes were used to reconstruct the original semi-automatically delineated GTVs into a reduced model containing only time trends. Reduced models were compared to the original GTVs by analyzing the reconstruction error in the GTV and position. Both retrospective (all weekly images) and prospective (only the first four weekly images) were evaluated. The average volume difference from the original GTV was 4.3% ± 2.4% for the trending model. The positional variability of the GTV over the treatment course, as measured by the standard deviation of the GTV centroid, was 1.9 ± 1.4 mm for the original GTVs, which was reduced to 1.2 ± 0.6 mm for the trending-only model. In 3/13 cases, the dominant eigenmode changed class between the prospective and retrospective models. The trending-only model preserved GTV and shape relative to the original GTVs, while reducing spurious positional variability. The classification scheme appears feasible for separating types of geometric variability by time trend.

Localization accuracy of the clinical target volume during image-guided radiotherapy of lung cancer

PURPOSE

To evaluate the position and shape of the originally defined clinical target volume (CTV) over the treatment course, and to assess the impact of gross tumor volume (GTV)-based online computed tomography (CT) guidance on CTV localization accuracy.

METHODS AND MATERIALS

Weekly breath-hold CT scans were acquired in 17 patients undergoing radiotherapy. Deformable registration was used to propagate the GTV and CTV from the first weekly CT image to all other weekly CT images. The on-treatment CT scans were registered rigidly to the planning CT scan based on the GTV location to simulate online guidance, and residual error in the CTV centroids and borders was calculated.

RESULTS

The mean GTV after 5 weeks relative to volume at the beginning of treatment was 77% ± 20%, whereas for the prescribed CTV, it was 92% ± 10%. The mean absolute residual error magnitude in the CTV centroid position after a GTV-based localization was 2.9 ± 3.0 mm, and it varied from 0.3 to 20.0 mm over all patients. Residual error of the CTV centroid was associated with GTV regression and anisotropy of regression during treatment (p = 0.02 and p = 0.03, respectively; Spearman rank correlation). A residual error in CTV border position greater than 2 mm was present in 77% of patients and 50% of fractions. Among these fractions, residual error of the CTV borders was 3.5 ± 1.6 mm (left-right), 3.1 ± 0.9 mm (anterior-posterior), and 6.4 ± 7.5 mm (superior-inferior).

CONCLUSIONS

Online guidance based on the visible GTV produces substantial error in CTV localization, particularly for highly regressing tumors. The results of this study will be useful in designing margins for CTV localization or for developing new online CTV localization strategies.

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

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

Methods: A narrative review of current world literature.

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

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

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

Should patient setup in lung cancer be based on the primary tumor? An analysis of tumor coverage and normal tissue dose using repeated positron emission tomography/computed tomography imaging

PURPOSE

Evaluation of the dose distribution for lung cancer patients using a patient setup procedure based on the bony anatomy or the primary tumor.

METHODS AND MATERIALS

For 39 patients with non-small-cell lung cancer, the planning fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) scan was registered to a repeated FDG-PET/CT scan made in the second week of treatment. Two patient setup methods were analyzed based on the bony anatomy or the primary tumor. The original treatment plan was copied to the repeated scan, and target and normal tissue structures were delineated. Dose distributions were analyzed using dose-volume histograms for the primary tumor, lymph nodes, lungs, and spinal cord.

RESULTS

One patient showed decreased dose coverage of the primary tumor caused by progressive disease and required replanning to achieve adequate coverage. For the other patients, the minimum dose to the primary tumor did not significantly deviate from the planned dose: -0.2 ± 1.7% (p = 0.71) and -0.1 ± 1.7% (p = 0.85) for the bony anatomy setup and the primary tumor setup, respectively. For patients (n = 31) with nodal involvement, 10% showed a decrease in minimum dose larger than 5% for the bony anatomy setup and 13% for the primary tumor setup. The mean lung dose exceeded the maximum allowed 20 Gy in 21% of the patients for the bony anatomy setup and in 13% for the primary tumor setup, whereas for the spinal cord this occurred in 10% and 13% of the patients, respectively.

CONCLUSIONS

In 10% and 13% of patients with nodal involvement, setup based on bony anatomy or primary tumor, respectively, led to important dose deviations in nodal target volumes. Overdosage of critical structures occurred in 10-20% of the patients. In cases of progressive disease, repeated imaging revealed underdosage of the primary tumor. Development of practical ways for setup procedures based on repeated high-quality imaging of all tumor sites during radiotherapy should therefore be an important research focus.

Optimizing principal component models for representing interfraction variation in lung cancer radiotherapy

PURPOSE

To optimize modeling of interfractional anatomical variation during active breath-hold radiotherapy in lung cancer using principal component analysis (PCA).

METHODS

In 12 patients analyzed, weekly CT sessions consisting of three repeat intrafraction scans were acquired with active breathing control at the end of normal inspiration. The gross tumor volume (GTV) and lungs were delineated and reviewed on the first week image by physicians and propagated to all other images using deformable image registration. PCA was used to model the target and lung variability during treatment. Four PCA models were generated for each specific patient: (1) Individual models for the GTV and each lung from one image per week (week to week, W2W); (2) a W2W composite model of all structures; (3) individual models using all images (weekly plus repeat intrafraction images, allscans); and (4) composite model with all images. Models were reconstructed retrospectively (using all available images acquired) and prospectively (using only data acquired up to a time point during treatment). Dominant modes representing at least 95% of the total variability were used to reconstruct the observed anatomy. Residual reconstruction error between the model-reconstructed and observed anatomy was calculated to compare the accuracy of the models.

RESULTS

An average of 3.4 and 4.9 modes was required for the allscans models, for the GTV and composite models, respectively. The W2W model required one less mode in 40% of the patients. For the retrospective composite W2W model, the average reconstruction error was 0.7 +/- 0.2 mm, which increased to 1.1 +/- 0.5 mm when the allscans model was used. Individual and composite models did not have significantly different errors (p = 0.15, paired t-test). The average reconstruction error for the prospective models of the GTV stabilized after four measurements at 1.2 +/- 0.5 mm and for the composite model after five measurements at 0.8 +/- 0.4 mm.

CONCLUSIONS

Retrospective PCA models were capable of reconstructing original GTV and lung shapes and positions within several millimeters with three to four dominant modes, on average. Prospective models achieved similar accuracy after four to five measurements.

Interfraction and intrafraction changes in amplitude of breathing motion in stereotactic liver radiotherapy

PURPOSE

Interfraction and intrafraction changes in amplitude of liver motion were assessed in patients with liver cancer treated with kV cone beam computed tomography (CBCT)-guided stereotactic body radiation therapy (SBRT).

METHODS AND MATERIALS

A total of 314 CBCTs obtained with the patient in the treatment position immediately before and after each fraction, and 29 planning 4DCTs were evaluated in 29 patients undergoing six-fraction SBRT for unresectable liver cancer, with (n = 15) and without (n = 14) abdominal compression. Offline, the CBCTs were sorted into 10 bins, based on phase of respiration. Liver motion amplitude was measured using liver-to-liver alignment from the end-exhale and end-inhale CBCT and four-dimensional CT reconstructions. Inter- and intrafraction amplitude changes were measured from the difference between the pre-SBRT CBCTs relative to the planning four-dimensional CT, and from the pre-SBRT and post-SBRT CBCTs, respectively.

RESULTS

Mean liver motion amplitude for all patients (range) was 1.8 (0.1-7.0), 8.0 (0.1-18.8), and 4.3 (0.1-12.1) mm in the mediolateral (ML), craniocaudal (CC), and anteroposterior (AP) directions, respectively. Mean absolute inter- and intrafraction liver motion amplitude changes were 1.0 (ML), 1.7 (CC), and 1.6 (AP) mm and 1.3 (ML), 1.6 (CC), and 1.9 (AP) mm, respectively. No significant correlations were found between intrafraction amplitude change and intrafraction time (range, 4:56-25:37 min:sec), and between inter- and intrafraction amplitude changes and liver motion amplitude. Intraobserver reproducibility (sigma, n = 29 fractions) was 1.3 (ML), 1.4 (CC), and 1.4 (AP) mm.

CONCLUSIONS

For the majority of liver SBRT patients, the change in liver motion amplitude was minimal over the treatment course and showed no apparent relationships with the magnitude of liver motion and intrafraction time.

4D imaging for target definition in stereotactic radiotherapy for lung cancer

Stereotactic radiotherapy of Stage I lung tumors has been reported to result in high local control rates that are far superior to those obtained with conventional radiotherapy techniques, and which approach those achieved with primary surgery. Breathing-induced motion of tumor and target tissues is an important issue in this technique and careful attention should be paid to the contouring and the generation of individualized margins. We describe our experience with the use of 4DCT scanning for this group of patients, the use of post-processing tools and the potential benefits of respiratory gating.

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

INTRODUCTION

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Volumetric image-guidance: does routine usage prompt adaptive re-planning? An institutional review

PURPOSE

To investigate how the use of volumetric image-guidance using an on-board cone-beam computed tomography (CBCT) system impacts on the frequency of adaptive re-planning.

MATERIAL AND METHODS

Treatment courses of 146 patients who have undergone a course of external beam radiation therapy (EBRT) using volumetric CBCT image-guidance were analyzed. Target locations included the brain, head and neck, chest, abdomen, as well as prostate and non-prostate pelvis. The majority of patients (57.5%) were treated with hypo-fractionated treatment regimens (three to 15 fraction courses). The frequency of image-guidance ranged from daily (87.7%) to weekly or twice weekly. The underlying medical necessity for adaptive re-planning as well as frequency and consequences of plan adaptation to dose-volume parameters was assessed.

RESULTS

Radiation plans of 34 patients (23.3%) were adapted at least once (up to six time) during their course of EBRT as a result of image-guidance CBCT review. Most common causes for adaptive planning were: tumor change (mostly shrinkage: 10 patients; four patients more than one re-plan), change in abdominal girth (systematic change in hollow organ filling; n=7, two patients more than one re-plan), weight loss (n=5), and systematic target setup deviation from simulation (n=5). Adaptive re-plan was required mostly for conventionally fractionated courses; only 5 patient plans undergoing hypo-fractionated treatment were adjusted. In over 91% of adapted plans, the dose-volume parameters did deviate from the prescribed plan parameters by more than 5% for at least 10% of the target volume, or organs-at-risk in close proximity to the target volume.

DISCUSSION

Routine use of volumetric image-guidance has in our practice increased the demand for adaptive re-planning. Volumetric CBCT image-guidance provides sufficient imaging information to reliably predict the need for dose adjustment. In the vast majority of cases evaluated, the initial and adapted dose-volume parameters differed to a degree that was considered clinically significant.

Respiration correlated cone-beam computed tomography and 4DCT for evaluating target motion in Stereotactic Lung Radiation Therapy

An image-guidance process for using cone-beam computed tomography (CBCT) for stereotactic body radiation therapy (SBRT) of peripheral lung lesions is presented. Respiration correlated CBCT on the treatment unit and four dimensional computed tomography (4DCT) from planning are evaluated for assessing respiration-induced target motion during planning and treatment fractions. Image-guided SBRT was performed for 12 patients (13 lesions) with inoperable early stage non-small cell lung carcinoma. Kilovoltage (kV) projections were acquired over a 360 degree gantry rotation and sorted based on the pixel value of an image-based aperture located at the air-tissue interface of the diaphragm. The sorted projections were reconstructed to provide volumetric respiration correlated CBCT image datasets at different phases of the respiratory cycle. The 4D volumetric datasets were directly compared with 4DCT datasets acquired at the time of planning. For ten of 12 patients treated, the lung tumour motion, as measured by respiration correlated CBCT on the treatment unit, was consistent with the tumour motion measured by 4DCT at the time of planning. However, in two patients, maximum discrepancies observed were 6 and 10 mm in the anterior-posterior and superior-inferior directions, respectively. Respiration correlated CBCT acquired on the treatment unit allows target motion to be assessed for each treatment fraction, allows target localization based on different phases on the breathing cycle, and provides the facility for adaptive margin design in radiation therapy of lung malignancies. The current study has shown that the relative motion and position of the tumour at the time of treatment may not match that of the planning 4DCT scan. Therefore, application of breathing motion data acquired at simulation for tracking or gating radiation therapy may not be suitable for all patients - even those receiving short course treatment techniques such as SBRT.

Analysis of daily setup variation with tomotherapy megavoltage computed tomography

The purpose of this study was to evaluate different setup uncertainties for various anatomic sites with TomoTherapy pretreatment megavoltage computed tomography (MVCT) and to provide optimal margin guidelines for these anatomic sites. Ninety-two patients with tumors in head and neck (HN), brain, lung, abdominal, or prostate regions were included in the study. MVCT was used to verify patient position and tumor target localization before each treatment. With the anatomy registration tool, MVCT provided real-time tumor shift coordinates relative to the positions where the simulation CT was performed. Thermoplastic facemasks were used for HN and brain treatments. Vac-Lok cushions were used to immobilize the lower extremities up to the thighs for prostate patients. No respiration suppression was administered for lung and abdomen patients. The interfractional setup variations were recorded and corrected before treatment. The mean interfractional setup error was the smallest for HN among the 5 sites analyzed. The average 3D displacement in lateral, longitudinal, and vertical directions for the 5 sites ranged from 2.2-7.7 mm for HN and lung, respectively. The largest movement in the lung was 2.0 cm in the longitudinal direction, with a mean error of 6.0 mm and standard deviation of 4.8 mm. The mean interfractional rotation variation was small and ranged from 0.2-0.5 degrees, with the standard deviation ranging from 0.7-0.9 degrees. Internal organ displacement was also investigated with a posttreatment MVCT scan for HN, lung, abdomen, and prostate patients. The maximum 3D intrafractional displacement across all sites was less than 4.5 mm. The interfractional systematic errors and random errors were analyzed and the suggested margins for HN, brain, prostate, abdomen, and lung in the lateral, longitudinal, and vertical directions were between 4.2 and 8.2 mm, 5.0 mm and 12.0 mm, and 1.5 mm and 6.8 mm, respectively. We suggest that TomoTherapy pretreatment MVCT can be used to improve the accuracy of patient positioning and reduce tumor margin.

Quantification of tumor volume changes during radiotherapy for non-small-cell lung cancer

PURPOSE

Dose escalation for lung cancer is limited by normal tissue toxicity. We evaluated sequential computed tomography (CT) scans to assess the possibility of adaptively reducing treatment volumes by quantifying the tumor volume reduction occurring during a course of radiotherapy (RT).

METHODS AND MATERIALS

A total of 22 patients underwent RT for Stage I-III non-small-cell lung cancer with conventional fractionation; 15 received concurrent chemotherapy. Two repeat CT scans were performed at a nominal dose of 30 Gy and 50 Gy. Respiration-correlated four-dimensional CT scans were used for evaluation of respiratory effects in 17 patients. The gross tumor volume (GTV) was delineated on simulation and all individual phases of the repeat CT scans. Parenchymal tumor was evaluated unless the nodal volume was larger or was the primary. Subsequent image sets were spatially co-registered with the simulation data for evaluation.

RESULTS

The median GTV reduction was 24.7% (range, -0.3% to 61.7%; p < 0.001, two-tailed t test) at the first repeat scan and 44.3% (range, 0.2-81.6%, p < 0.001) at the second repeat scan. The volume reduction was not significantly different between patients receiving chemoradiotherapy vs. RT alone, a GTV >100 cm(3) vs. <100 cm(3), and hilar and/or mediastinal involvement vs. purely parenchymal or pleural lesions. A tendency toward a greater volume reduction with increasing dose was seen, although this did not reach statistical significance.

CONCLUSION

The results of this study have demonstrated significant alterations in the GTV seen on repeat CT scans during RT. These observations raise the possibility of using an adaptive approach toward RT of non-small-cell lung cancer to minimize the dose to normal structures and more safely increase the dose directed at the target tissues.

Four-dimensional computed tomography-based interfractional reproducibility study of lung tumor intrafractional motion

PURPOSE

To evaluate the interfractional reproducibility of respiration-induced lung tumors motion, defined by their centroids and the intrafractional target motion range.

METHODS AND MATERIALS

Twentythree pairs of four-dimensional/computed tomography scans were acquired for 22 patients. Gross tumor volumes were contoured, Clinical target volumes (CTVs) were generated. Geometric data for CTVs and lung volumes were extracted. The motion tracks of CTV centroids, and CTV edges along the cranio-caudal, anterior-posterior, and lateral directions were evaluated. The Pearson correlation coefficient for motion tracks along the cranio-caudal direction was determined for the entire respiratory cycle and for five phases about the end of expiration.

RESULTS

The largest motion extent was along the cranio-caudal direction. The intrafractional motion extent for five CTVs was <0.5 cm, the largest motion range was 3.59 cm. Three CTVs with respiration-induced displacement >0.5 cm did not exhibit the similarity of motion, and for 16 CTVs with motion >0.5 cm the correlation coefficient was >0.8. The lung volumes in corresponding phases for cases that demonstrated CTVs motion similarity were reproducible. No correlation between tumor size and mobility was found.

CONCLUSION

Target motion reproducibility seems to be present in 87% of cases in our dataset. Three cases with dissimilar motion indicate that it is advisable to verify target motion during treatment. The adaptive adjustment to compensate the possible interfractional shifts in a target position should be incorporated as a routine policy for lung cancer radiotherapy.

Adaptive radiotherapy planning on decreasing gross tumor volumes as seen on megavoltage computed tomography images

PURPOSE

To evaluate gross tumor volume (GTV) changes for patients with non-small-cell lung cancer by using daily megavoltage (MV) computed tomography (CT) studies acquired before each treatment fraction on helical tomotherapy and to relate the potential benefit of adaptive image-guided radiotherapy to changes in GTV.

METHODS AND MATERIALS

Seventeen patients were prescribed 30 fractions of radiotherapy on helical tomotherapy for non-small-cell lung cancer at London Regional Cancer Program from Dec 2005 to March 2007. The GTV was contoured on the daily MVCT studies of each patient. Adapted plans were created using merged MVCT-kilovoltage CT image sets to investigate the advantages of replanning for patients with differing GTV regression characteristics.

RESULTS

Average GTV change observed over 30 fractions was -38%, ranging from -12 to -87%. No significant correlation was observed between GTV change and patient's physical or tumor features. Patterns of GTV changes in the 17 patients could be divided broadly into three groups with distinctive potential for benefit from adaptive planning.

CONCLUSIONS

Changes in GTV are difficult to predict quantitatively based on patient or tumor characteristics. If changes occur, there are points in time during the treatment course when it may be appropriate to adapt the plan to improve sparing of normal tissues. If GTV decreases by greater than 30% at any point in the first 20 fractions of treatment, adaptive planning is appropriate to further improve the therapeutic ratio.

Assessment of Gross Tumor Volume Regression and Motion Changes During Radiotherapy for Non–Small-Cell Lung Cancer as Measured by Four-Dimensional Computed Tomography

PURPOSE

To investigate the magnitudes of the changes in mobility and volume of locally advanced non-small-cell lung cancer (NSCLC) tumors during radiotherapy, using four-dimensional computed tomography (4DCT).

METHODS AND MATERIALS

Five to ten 4DCT data sets were acquired weekly for each of 8 patients throughout treatment. Gross tumor volumes (GTVs) were outlined on each data set. Volumes and coordinates of the GTV centroids were calculated at the 0 (end-inspiration) and 50% (end-expiration) respiration phases. Trends in magnitudes of intrafraction and interfraction positional variations were assessed for the GTV and internal target volume (ITV) during treatment.

RESULTS

Tumor volume reduction ranged from 20% to 71% (end-inspiration) and from 15% to 70% (end-expiration). Increased tumor mobility was observed in the superior-inferior and anterior-posterior directions. However, no trends in tumor motion were observed. Motion along the superior-inferior direction was significantly greater (p < 0.001), with mean +/- SD values of 0.86 +/- 0.19 cm, as compared with 0.39 +/- 0.08 cm and 0.19 +/- 0.05 cm in the anterior-posterior and right-left directions, respectively. A marginally significant (p = 0.049) increase in total GTV positional variation was observed with increasing treatment weeks, and similar results were seen for the interfractional ITV mobility.

CONCLUSIONS

Because of changes in tumor size and mobility, an explicit initial determination of the ITV may not be sufficient, especially where small setup margins are used. Repeat 4DCT scans might be warranted for highly mobile tumors to reduce the potential for missing the tumor.

Intra- and interfraction breathing variations during curative radiotherapy for lung cancer

BACKGROUND AND PURPOSE

This study aimed at quantifying the breathing variations among lung cancer patients over full courses of fractionated radiotherapy. The intention was to relate these variations to the margins assigned to lung tumours, to account for respiratory motion, in fractionated radiotherapy.

MATERIALS AND METHODS

Eleven lung cancer patients were included in the study. The patients' chest wall motions were monitored as a surrogate measure for breathing motion during each fraction of radiotherapy by use of an external optical marker. The exhale level variations were evaluated with respect to exhale points and fraction-baseline, defined for intra- and interfraction variations respectively. The breathing amplitude was evaluated as breathing cycle amplitudes and fraction-max-amplitudes defined for intra- and interfraction breathing, respectively.

RESULTS

The breathing variations over a full treatment course, including both intra- and interfraction variations, were 15.2mm (median over the patient population), range 5.5-26.7mm, with the variations in exhale level as the major contributing factor. The median interfraction span in exhale level was 14.8mm, whereas the median fraction-max-amplitude was 6.1mm (median of patient individual SD 1.4). The median intrafraction span in exhale level was 1.6mm, and the median breathing cycle amplitude was 4.0mm (median of patient individual SD 1.4).

CONCLUSIONS

The variations in externally measured exhale levels are larger than variations in breathing amplitude. The interfraction variations in exhale level are in general are up to 10 times larger than intrafraction variations. Margins to account for respiratory motion cannot safely be based on one planning session, especially not if relying on measuring external marker motion. Margins for lung tumours should include interfraction variations in breathing.

Four-dimensional measurement of lung tumor displacement using 256-multi-slice CT-scanner

The concept of internal target volume is of marked importance for radiotherapy to lung tumors as respiration-induced motion is important. Individualized assessment of motion is required as tumor site may not predict the extent or pattern of tumor motion. We performed volumetric cine scanning using the 256-multi-slice CT (256MSCT) to study tumor motion during free breathing in 14 inpatients who were treated with carbon-ion radiotherapy. Motion assessment in 16 respiratory phases of the cine CT revealed most tumors to show hysteresis-like behavior. Isocenter displacement between peak exhalation and inhalation for the average of the right and left lungs were 7 mm, 7 mm and 15 mm for the upper, middle and lower lobes, respectively. Cine CT with the 256MSCT improved the evaluation of tumor displacement and overcomes some of the limitations associated with current CT methods. Volumetric cine CT data provides useful data on motion for planning in all radiation approaches for lung tumors.

Is Adaptive Treatment Planning Required for Stereotactic Radiotherapy of Stage I Non–Small-Cell Lung Cancer?

PURPOSE

Changes in position or size of target volumes have been observed during radiotherapy for lung cancer. The need for adaptive treatment planning during stereotactic radiotherapy of Stage I tumors was retrospectively analyzed using repeat four-dimensional computed tomography (4DCT) scans.

METHODS AND MATERIALS

A planning study was performed for 60 tumors in 59 patients using 4DCT scans repeated after two or more treatment fractions. Planning target volumes (PTV) encompassed all tumor mobility, and dose distributions from the initial plan were projected onto PTVs derived from the repeat 4DCT. A dosimetric and volumetric analysis was performed.

RESULTS

The repeat 4DCT scans were performed at a mean of 6.6 days (range, 2-12 days) after the first fraction of stereotactic radiotherapy. In 25% of cases the repeat PTV was larger, but the difference exceeded 1 mL in 5 patients only. The mean 3D displacement between the center of mass of both PTVs was 2.0 mm. The initial 80% prescription isodose ensured a mean coverage of 98% of repeat PTVs, and this isodose fully encompassed the repeat internal target volumes in all but 1 tumor. "Inadequate" coverage in the latter was caused by a new area of atelectasis adjacent to the tumor on the repeat 4DCT.

CONCLUSIONS

Limited "time trends" were observed in PTVs generated by repeated uncoached 4DCT scans, and the dosimetric consequences proved to be minimal. Treatment based only on the initial PTV would not have resulted in major tumor underdosage, indicating that adaptive treatment planning is of limited value for fractionated stereotactic radiotherapy.

A model for predicting lung cancer response to therapy

PURPOSE

Volumetric computed tomography (CT) images acquired by image-guided radiation therapy (IGRT) systems can be used to measure tumor response over the course of treatment. Predictive adaptive therapy is a novel treatment technique that uses volumetric IGRT data to actively predict the future tumor response to therapy during the first few weeks of IGRT treatment. The goal of this study was to develop and test a model for predicting lung tumor response during IGRT treatment using serial megavoltage CT (MVCT).

METHODS AND MATERIALS

Tumor responses were measured for 20 lung cancer lesions in 17 patients that were imaged and treated with helical tomotherapy with doses ranging from 2.0 to 2.5 Gy per fraction. Five patients were treated with concurrent chemotherapy, and 1 patient was treated with neoadjuvant chemotherapy. Tumor response to treatment was retrospectively measured by contouring 480 serial MVCT images acquired before treatment. A nonparametric, memory-based locally weight regression (LWR) model was developed for predicting tumor response using the retrospective tumor response data. This model predicts future tumor volumes and the associated confidence intervals based on limited observations during the first 2 weeks of treatment. The predictive accuracy of the model was tested using a leave-one-out cross-validation technique with the measured tumor responses.

RESULTS

The predictive algorithm was used to compare predicted verse-measured tumor volume response for all 20 lesions. The average error for the predictions of the final tumor volume was 12%, with the true volumes always bounded by the 95% confidence interval. The greatest model uncertainty occurred near the middle of the course of treatment, in which the tumor response relationships were more complex, the model has less information, and the predictors were more varied. The optimal days for measuring the tumor response on the MVCT images were on elapsed Days 1, 2, 5, 9, 11, 12, 17, and 18 during treatment.

CONCLUSIONS

The LWR model accurately predicted final tumor volume for all 20 lung cancer lesions. These predictions were made using only 8 days' worth of observations from early in the treatment. Because the predictions are accurate with quantified uncertainty, they could eventually be used to optimize treatment.

Tomotherapy as a tool in image-guided radiation therapy (IGRT): current clinical experience and outcomes

Modern radiotherapy is characterised by a better target definition through medical imaging accompanied by significantly improved radiation delivery methods, most notably Intensity-Modulate Radiation Therapy (IMRT). However, the treatment can only be as accurate as the positioning of patients for their daily radiotherapy fraction. It is in this context that a number of imaging modalities - ranging from ultrasound to on-board kilovoltage imaging and computed tomography (CT) - have found their way into the treatment room where they verify accurate patient positioning prior to or even during delivery of radiation. Helical tomotherapy (HT) combines IMRT delivery with in-built image guidance using megavoltage CT scanning. This paper discusses the initial experience of different centres with IGRT using HT illustrated by a number of clinical examples from the installation in London in Ontario, Canada, one of the world’s first HT sites. We found that HT allows the delivery of highly conformal radiation dose distributions combined with adequate daily image acquisition. An important feature of this unit is its seamless integration, which also includes a customised inverse treatment planning system and a quality assurance module for individual patients.

Intra-patient variability of tumor volume and tumor motion during conventionally fractionated radiotherapy for locally advanced non-small-cell lung cancer: a prospective clinical study

PURPOSE

The aim of this study was to investigate the change in tumor volume, motion, and breathing frequency during a course of radiotherapy, for locally advanced non-small-cell lung cancer.

METHODS AND MATERIALS

A total of 23 patients underwent computed tomography-positron emission tomography (CT-PET) and respiration correlated CT scans before treatment, which was repeated in the first and second weeks after the start of radiotherapy. Patients were treated with an accelerated fractionation schedule, 1.8 Gy twice a day, with a total tumor dose depending on preset dose constraints for the lungs and spinal cord.

RESULTS

A striking heterogeneity of tumor volume changes was observed at all time points. In some patients the volume decreased >30% (3/23), whereas in others the volume increased >30% (4/24); but for the majority of patients (16/23), the tumor volume changed only slightly (<30%). No significant changes in average tumor motion or breathing frequencies were observed during treatment. Although a number of changes in individual tumor motion were seen, only in 1 patient would this have led to an increase of the internal margin >1 mm in 1 direction, 1 week after the start of treatment, and in 3 patients for 1 direction, 2 weeks after the start of the treatment.

CONCLUSION

In this patients in this study, a large variability in changes in tumor volume was observed. This underscores the need for repeated imaging during the course of radiotherapy. However, the changes in tumor motion are small, which indicates that repeated respiration correlated CT does not appear to be necessary.

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.