Variability of target volume delineation in cervical esophageal cancer

Purpose: Three-dimensional (3D) conformal radiation therapy (CRT) assumes and requires the precise delineation of the target volume. To assess the consistency of target volume delineation by radiation oncologists, who treat esophageal cancers, we have performed a transCanada survey.Materials and Methods: One of three case presentations, including CT scan images, of different stages of cervical esophageal cancer was randomly chosen and sent by mail. Respondents were asked to fill in questionnaires regarding treatment techniques and to outline boost target volumes for the primary tumor on CT scans, using ICRU-50 definitions.Results: Of 58 radiation oncologists who agreed to participate, 48 (83%) responded. The external beam techniques used were mostly anterior-posterior fields, followed by a multifield boost technique. Brachytherapy was employed by 21% of the oncologists, and concurrent chemotherapy by 88%. For a given case, and the three volumes defined by ICRU-50 (i.e., gross tumor volume [GTV], clinical target volume [CTV], and planning target volume [PTV]) we determined: 1. The total length in the cranio-caudal dimension; 2. the mean diameter in the transverse slice that was located in a CT slice that was common to all participants; 3. the total volume for each ICRU volume; and 4. the (5, 95) percentiles for each parameter. The PTV showed a mean length of 14.4 (9.6, 18.0) cm for Case A, 9.4 (5.0, 15.0) cm for Case B, 11.8 (6.0, 16.0) cm for Case C, a mean diameter of 6.4 (5.0, 9.4) cm for Case A, 4.4 (0.0, 7.3) cm for Case B, 5.2 (3.9, 7.3) cm for Case C, and a mean volume of 320 (167, 840) cm³ for Case A and 176 (60, 362) cm³ for Case C. The results indicate variability factors (95 percentile divided by 5 percentile values) in target diameters of 1.5 to 2.6, and in target lengths of 1.9 to 5.0.Conclusion: There was a substantial inconsistency in defining the planning target volume, both transversely and longitudinally, among radiation oncologists. The potential benefits of 3D treatment planning with high-precision dose delivery could be offset by this inconsistency in target-volume delineation by radiation oncologists. This may be particularly important for multicenter clinical trials, for which quality assurance of this step will be essential to the interpretation of results.     

Impact of integrated PET/CT on variability of target volume delineation in rectal cancer

Several studies have demonstrated substantial variability among individual radiation oncologists in defining target volumes using computed tomography (CT). The objective of this study was to determine the impact of combined positron emission tomography and computed tomography (PET/CT) on inter-observer variability of target volume delineation in rectal cancer. We also compared the relative concordance of two PET imaging tracers, 18F-fluorodeoxyglucose (FDG) and 18F-fluorodeoxythymidine (FLT), against conventional computed tomography (CT). Six consecutive patients with locally advanced rectal cancer were enrolled onto an institutional protocol involving preoperative chemoradiotherapy and correlative studies including FDG- and FLT-PET scans acquired in the treatment position. Using these image data sets, four radiation oncologists independently delineated primary and nodal gross tumor volumes (GTVp and GTVn) for a hypothetical boost treatment. Contours were first defined based on CT alone with observers blinded to the PET images, then based on combined PET/CT. An inter-observer similarity index (SI), ranging from a value of 0 for complete disagreement to 1 for complete agreement of contoured voxels, was calculated for each set of volumes. For primary gross tumor volume (GTVp), the difference in estimated SI between CT and FDG was modest (CT SI = 0.77 vs. FDG SI = 0.81), but statistically significant (p = 0.013). The SI difference between CT and FLT for GTVp was also slight (FLT SI = 0.80) and marginally non-significant (p < 0.082). For nodal gross tumor volume, (GTVn), SI was significantly lower for CT based volumes with an estimated SI of 0.22 compared to an estimated SI of 0.70 for FDG-PET/CT (p < 0.0001) and an estimated SI of 0.70 for FLT-PET/CT (p < 0.0001). Boost target volumes in rectal cancer based on combined PET/CT results in lower inter-observer variability compared with CT alone, particularly for nodal disease. The use of FDG and FLT did not appear to be different from this perspective.     

Clinical variability of target volume description in conformal radiotherapy planning

Purpose: The pivotal step in radiation planning is delineation of the target volume and production of a treatment plan to encompass this. This study assesses the variation of physicians in creation of these volumes.Methods and Materials: Three radiologists and eight radiation oncologists outlined the gross tumour volume (GTV) on the planning CT scans of four cases with T3 bladder cancer. In addition, the radiation oncologists (RO) created a planning target volume according to a set protocol for all cases. Volumes were produced and comparison of these volumes and the position of the isocenters were analysed. In addition, the margins allowed were measured and compared.Results: There was a maximum variation ratio (largest to smallest volume outlined) of the GTV in the four cases of 1.74 among radiologists and 3.74 among oncologists. There was a significant difference (p = 0.01) in mean GTV between RO and the radiologists. The mean GTV of the RO exceeded the radiologists by a factor of 1.29 with a mean difference of 13.4 cm³. The variation ratio in PTV among oncologists ranged from 1.25 to 3.33. There was no significant difference in mean PTV values between the two groups of ROs divided by specialization in uro-oncology. The mean variation in location of the isocenter from the centroid of the radiologists’ volume in the four cases was from 2.6 to 5.7 mm. There was, however, a wide range of values from 1.4 mm to 24.1 mm. Median margin per case ranged from 14.7 to 18.7 mm. Minimum margins allowed in each case varied from minus 7 mm to 9 mm.Conclusion: This study demonstrates significant interphysician variability in producing target volumes and radiation plans for conformal radiotherapy. The scale of this difference is clearly of significance, with up to 3-fold variation in volumes delineated by clinicians. The factors leading to these differences will be further addressed. The existence of such variability, however, clearly needs to be accepted as a factor in the overall uncertainty analysis in conformal radiotherapy planning.     

Variability of gross tumor volume delineation in head-and-neck cancer using CT and PET/CT fusion

PURPOSE: To assess the need for gross tumor volume (GTV) delineation protocols in head-and-neck cancer (HNC) treatment planning by use of positron emission tomography (PET)/computed tomography (CT) fusion imaging. Assessment will consist of interobserver and intermodality variation analysis. METHODS AND MATERIALS: Sixteen HNC patients were accrued for the study. Four physicians (2 neuroradiologists and 2 radiation oncologists) contoured GTV on 16 patients. Physicians were asked to contour GTV on the basis of the CT alone, and then on PET/CT fusion. Statistical analysis included analysis of variance for interobserver variability and Student's paired sample t test for intermodality and interdisciplinary variability. A Boolean pairwise analysis was included to measure degree of overlap. RESULTS: Near-significant variation occurred across physicians' CT volumes (p = 0.09) and significant variation occurred across physicians' PET/CT volumes (p = 0.0002). The Boolean comparison correlates with statistical findings. One radiation oncologist's PET/CT fusion volumes were significantly larger than his CT volumes (p < 0.01). Conversely, the other radiation oncologist's CT volumes tended to be larger than his fusion volumes (p = 0.06). No significant interdisciplinary variation was seen. Significant disagreement occurred between radiation oncologists. CONCLUSION: Significant differences in GTV delineation were found between multiple observers contouring on PET/CT fusion. The need for delineation protocol has been confirmed.     

Radiothérapie préopératoire des cancers du rectum : volumes cibles

Preoperative radiochemotherapy followed by total mesorectal excision is the standard of care for T3-T4-N0 or TxN1 rectal cancer. Defining target volumes relies on the patterns of nodal and locoregional failures. The lower limit of the clinical target volume depends also on the type of surgery. Conformational radiotherapy with or without intensity-modulated radiotherapy implies an accurate definition of volumes and inherent margins in the context of mobile organs such as the upper rectum. Tumoral staging recently improved with newer imaging techniques such as MRI with or without USPIO and FDG-PET-CT. The role of PET-CT remains unclear despite encouraging results and MRI is a helpful tool for a reliable delineation of the gross tumour volume. Co-registration of such modalities with the planning CT may particularly guide radiation oncologists through the gross tumour volume delineation. Acute digestive toxicity can be reduced with intensity modulation radiation therapy. Different guidelines and CT-based atlas regarding the target volumes in rectal cancer give the radiation oncologist a lot of ground for reproducible contours.     

Conformal radiotherapy planning of cervix carcinoma: differences in the delineation of the clinical target volume. A comparison between gynaecologic and radiation oncologists.

PURPOSE: To assess uncertainties in the definition of the clinical target volume (CTV) for patients scheduled for primary radiotherapy of cervix carcinoma. METHODS AND MATERIALS: Seven physicians (five radiation oncologists and two gynaecologists) independently contoured the CTVs for three patients. All observers were provided with the same clinical information. CTVs were entered directly in the treatment planning system. Differences were analysed qualitatively and quantitatively. RESULTS: The qualitative analysis revealed a good agreement by all observers on anatomical structures identified to be at risk for tumour spread. Quantitatively, however, a large interobserver variability was found. The ratio between largest and smallest volumes ranged between 3.6 and 4.9 for all observers (3.6-4.9 for the radiation oncologists, 1.3-2.8 for the gynaecologists). The median three-dimensional difference in gravity centres ranged between 10.9 and 26.3mm for the respective patients. The ratio of common volumes to encompassing volumes ranged between 0.11 and 0.13 for the radiation oncologists, and between 0.30 and 0.57 for the gynaecologists. CONCLUSIONS: Although there was a good consistency in outlined anatomical structures, for the radiation therapy of carcinomas of the uterine cervix a large interobserver variability in CTV delineation concerning the magnitude and relative location of volumes was observed. Compared to other factors, e.g. set-up and organ motion, interobserver variability in CTV definition seems to have the highest impact on the geometrical accuracy in the radiotherapy of this tumour entity.     

Reduction of observer variation using matched CT-PET for lung cancer delineation: a three-dimensional analysis

PURPOSE: Target delineation using only CT information introduces large geometric uncertainties in radiotherapy for lung cancer. Therefore, a reduction of the delineation variability is needed. The impact of including a matched CT scan with 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) and adaptation of the delineation protocol and software on target delineation in lung cancer was evaluated in an extensive multi-institutional setting and compared with the delineations using CT only. METHODS AND MATERIALS: The study was separated into two phases. For the first phase, 11 radiation oncologists (observers) delineated the gross tumor volume (GTV), including the pathologic lymph nodes of 22 lung cancer patients (Stages I-IIIB) on CT only. For the second phase (1 year later), the same radiation oncologists delineated the GTV of the same 22 patients on a matched CT-FDG-PET scan using an adapted delineation protocol and software (according to the results of the first phase). All delineated volumes were analyzed in detail. The observer variation was computed in three dimensions by measuring the distance between the median GTV surface and each individual GTV. The variation in distance of all radiation oncologists was expressed as a standard deviation. The observer variation was evaluated for anatomic regions (lung, mediastinum, chest wall, atelectasis, and lymph nodes) and interpretation regions (agreement and disagreement; i.e., >80% vs. <80% of the radiation oncologists delineated the same structure, respectively). All radiation oncologist-computer interactions were recorded and analyzed with a tool called "Big Brother." RESULTS: The overall three-dimensional observer variation was reduced from 1.0 cm (SD) for the first phase (CT only) to 0.4 cm (SD) for the second phase (matched CT-FDG-PET). The largest reduction in the observer variation was seen in the atelectasis region (SD 1.9 cm reduced to 0.5 cm). The mean ratio between the common and encompassing volume was 0.17 and 0.29 for the first and second phases, respectively. For the first phase, the common volume was 0 in 4 patients (i.e., no common point for all GTVs). In the second phase, the common volume was always >0. For all anatomic regions, the interpretation differences among the radiation oncologists were reduced. The amount of disagreement was 45% and 18% for the first and second phase, respectively. Furthermore, the mean delineation time (12 vs. 16 min, p<0.001) and mean number of corrections (25 vs. 39, p<0.001) were reduced in the second phase compared with the first phase. CONCLUSION: For high-precision radiotherapy, the delineation of lung target volumes using only CT introduces too great a variability among radiation oncologists. Implementing matched CT-FDG-PET and adapted delineation protocol and software reduced observer variation in lung cancer delineation significantly with respect to CT only. However, the remaining observer variation was still large compared with other geometric uncertainties (setup variation and organ motion).     

Consistency in seroma contouring for partial breast radiotherapy: impact of guidelines

PURPOSE: Inconsistencies in contouring target structures can undermine the precision of conformal radiation therapy (RT) planning and compromise the validity of clinical trial results. This study evaluated the impact of guidelines on consistency in target volume contouring for partial breast RT planning. METHODS AND MATERIALS: Guidelines for target volume definition for partial breast radiation therapy (PBRT) planning were developed by members of the steering committee for a pilot trial of PBRT using conformal external beam planning. In phase 1, delineation of the breast seroma in 5 early-stage breast cancer patients was independently performed by a "trained" cohort of four radiation oncologists who were provided with these guidelines and an "untrained" cohort of four radiation oncologists who contoured without guidelines. Using automated planning software, the seroma target volume (STV) was expanded into a clinical target volume (CTV) and planning target volume (PTV) for each oncologist. Means and standard deviations were calculated, and two-tailed t tests were used to assess differences between the "trained" and "untrained" cohorts. In phase 2, all eight radiation oncologists were provided with the same contouring guidelines, and were asked to delineate the seroma in five new cases. Data were again analyzed to evaluate consistency between the two cohorts. RESULTS: The "untrained" cohort contoured larger seroma volumes and had larger CTVs and PTVs compared with the "trained" cohort in three of five cases. When seroma contouring was performed after review of contouring guidelines, the differences in the STVs, CTVs, and PTVs were no longer statistically significant. CONCLUSION: Guidelines can improve consistency among radiation oncologists performing target volume delineation for PBRT planning.     

Intraobserver and interobserver variability in GTV delineation on FDG-PET-CT images of head and neck cancers

PURPOSE: To determine if the addition of fluorodeoxyglucose positron emission tomography (FDG-PET) data changes primary site gross tumor volumes (GTVs) in head and neck cancers. METHODS AND MATERIALS: Computed tomography (CT), contrast-enhanced CT, and FDG-PET-CT scans were obtained in 10 patients with head and neck cancers. Eight experienced observers (6 head and neck oncologists and 2 neuro-radiologists) with access to clinical and radiologic reports outlined primary site GTVs on each modality. Three cases were recontoured twice to assess intraobserver variability. The magnitudes of the GTVs were compared. Intra- and interobserver variability was assessed by a two-way repeated measures analysis of variance. Inter- and intraobserver reliability were calculated. RESULTS: There were no significant differences in the GTVs across the image modalities when compared as ensemble averages; the Wilcoxon matched-pairs signed-rank test showed that CT volumes were larger than PET-CT. Observers demonstrated the greatest consistency and were most interchangeable on contrast-enhanced CT; they performed less reliably on PET-CT. CONCLUSIONS: The addition of PET-CT to primary site GTV delineation of head and neck cancers does not change the volume of the GTV defined by this group of expert observers in this patient sample. An FDG-PET may demonstrate differences in neck node delineation and in other disease sites.     

An evaluation of the variability of tumor-shape definition derived by experienced observers from CT images of supraglottic carcinomas (ACRIN protocol 6658)

PURPOSE: Accurate target definition is considered essential for sophisticated, image-guided radiation therapy; however, relatively little information has been reported that measures our ability to identify the precise shape of targets accurately. We decided to assess the manner in which eight "experts" interpreted the size and shape of tumors based on "real-life" contrast-enhanced computed tomographic (CT) scans. METHODS AND MATERIALS: Four neuroradiologists and four radiation oncologists (the authors) with considerable experience and presumed expertise in treating head-and-neck tumors independently contoured, slice-by-slice, his/her interpretation of the precise gross tumor volume (GTV) on each of 20 sets of CT scans taken from 20 patients who previously were enrolled in Radiation Therapy Oncology Group protocol 91-11. RESULTS: The average proportion of overlap (i.e., the degree of agreement) was 0.532 (95% confidence interval 0.457 to 0.606). There was a slight tendency for the proportion of overlap to increase with increasing average GTV. CONCLUSIONS: Our work suggests that estimation of tumor shape currently is imprecise, even for experienced physicians. In consequence, there appears to be a practical limit to the current trend of smaller fields and tighter margins.     

Impact of FDG-PET on lung cancer delineation for radiotherapy

Purpose: The purpose of this study is to assess the impact of fused diagnostic F‐18 2‐fluoro‐2‐deoxy‐D‐glucose (FDG) positron emission tomography (PET)/computed tomography (CT) and planning FDG‐PET/CT scans on voluming of lung cancer for radiotherapy. Methods: Five radiation oncologists (ROs), five radiation oncology trainees and a radiologist contoured five cases of non‐small cell lung cancer. The CT alone, the diagnostic FDG‐PET/CT and planning FDG‐PET/CT each registered to the CT, were used to contour three volumes. The concordance index (CI) was used to compare each volume with a reference RO. Results: Although there was considerable inter‐observer variability in CT contouring, there was no significant difference between mean volumes of the gross tumour volume for the RO and radiation oncology trainees using any technique. There was no increase in CI with the addition of PET/CT, either diagnostic or planning, for the RO. However, the volumes of the radiation oncology trainees showed a significant increase in CI from 65.8% with CT alone to 68.0% and 72.3% with diagnostic PET/CT and planning PET/CT, respectively (P = 0.028). Mean variation at the tumour/mediastinum interface was significantly reduced with addition of registered PET/CT. Conclusions: The concordance of RO with the reference RO did not significantly increase with use of integrated FDG PET/CT images. However, the contouring of radiation oncology trainees' became more concordant with the reference.     

CT Scanning for Definitive Radiotherapy Planning of Prostate Cancer: Necessity or Nicety? Results from survey of radiation oncologists working at different institutions in Australasia

Interactive computerised tomographic (CT) planning techniques offer the prospect of better anatomical localisation, more consistent tumour coverage, and limiting normal tissue dose. However, its value in the management of prostate cancer remains undefined. The present study addresses the impact of planning CT on the designated target volumes for localised carcinoma of the prostate at a multi-institution national level. Nine radiation oncologists from different centres in Australia and New Zealand were asked to designate a target volume on five sample patients with different disease stages (A2-C2) using both conventional cystogram films and planning CT scans. Target volumes estimated by CT means in this study differed by more than 10% from those estimated by conventional means in 75.6% of instances, being smaller in 55.6%. Volumes varied widely between individual radiation oncologists, both using conventional planning and CT information. These variations were found to exceed any differences in the volume caused by the planning technique itself. Results from this survey suggest that volumes appear to change more according to the individual radiation oncologist rather than to any other factor. In most or all of the sample cases six of nine radiation oncologists defined the borders of their CT volumes to be either consistently smaller (5 out of 9) or greater (1 out of 9) than their conventionally defined borders. The results of this survey are potentially important and warrant repetition with larger sample numbers in other countries where interactive CT planning facilities exist, both with and without diagnostic radiological input, to exclude similar variation and to define causes for any variations that do become apparent.     

Brain tumor target volume determination for radiation treatment planning through automated MRI segmentation

PURPOSE: To assess the effectiveness of two automated magnetic resonance imaging (MRI) segmentation methods in determining the gross tumor volume (GTV) of brain tumors for use in radiation therapy treatment planning. METHODS AND MATERIALS: Two automated MRI tumor segmentation methods (supervised k-nearest neighbors [kNN] and automatic knowledge-guided [KG]) were evaluated for their potential as "cyber colleagues." This required an initial determination of the accuracy and variability of radiation oncologists engaged in the manual definition of the GTV in MRI registered with computed tomography images for 11 glioma patients. Three sets of contours were defined for each of these patients by three radiation oncologists. These outlines were compared directly to establish inter- and intraoperator variability among the radiation oncologists. A novel, probabilistic measurement of accuracy was introduced to compare the level of agreement among the automated MRI segmentations. The accuracy was determined by comparing the volumes obtained by the automated segmentation methods with the weighted average volumes prepared by the radiation oncologists. RESULTS: Intra- and inter-operator variability in outlining was found to be an average of 20% +/- 15% and 28% +/- 12%, respectively. Lowest intraoperator variability was found for the physician who spent the most time producing the contours. The average accuracy of the kNN segmentation method was 56% +/- 6% for all 11 cases, whereas that of the KG method was 52% +/- 7% for 7 of the 11 cases when compared with the physician contours. For the areas of the contours where the oncologists were in substantial agreement (i.e., the center of the tumor volume), the accuracy of kNN and KG was 75% and 72%, respectively. The automated segmentation methods were found to be least accurate in outlining at the edges of the tumor volume. CONCLUSIONS: The kNN method was able to segment all cases, whereas the KG method was limited to enhancing tumors and gliomas with clear enhancing edges and no cystic formation. Both methods undersegment the tumor volume when compared with the radiation oncologists and performed within the variability of the contouring performed by experienced radiation oncologists based on the same data.     

Measurement of lung tumor volumes using three-dimensional computer planning software

PURPOSE: To examine the interclinician variation in the definition of gross tumor volume (GTV) in patients undergoing radiotherapy for non-small-cell lung cancer (NSCLC), develop methods to minimize this variation, and test these methods. METHODS AND MATERIALS: The radiotherapy planning computed tomography (CT) scans of 6 consecutive patients with NSCLC in which the radiologist was able to define and outline the GTV were used. Six oncologists independently contoured the tumors with the radiologist's markings as a guide using a three-dimensional treatment planning system. Separate contours were prepared using only mediastinal window settings and using both mediastinal and lung window settings. The volumes were calculated using the planning system software (series 1). Factors that resulted in interclinician variation were determined, and, after a 3-year interval, 5 of the 6 clinicians redefined the GTVs using a revised protocol aimed at minimizing variation (series 2). RESULTS: For series 1, the interclinician variation in the measurement of volumes ranged from 5%, in the most tightly measured tumor, to 42%, in the most variable, but was, on average, 20%. Statistically significant differences were noted among the clinicians (p = 0.002), that is, some clinicians tended to record relatively small and some relatively large volumes. The reasons for the variation among the oncologists included a tendency to include regions with a low probability of containing tumor, as if the oncologist were contouring a target volume; inclusion of adjacent atelectasis (ignoring the radiologist's outline); and variable treatment of spicules. When the exercise was repeated using the revised protocol (series 2), the degree of interclinician variation was reduced, with a range of 7-22% (average 13%). In series 2, the differences among the clinicians were not statistically significant (p = 0.25). CONCLUSION: Despite major radiologic input, significant variation occurred in the delineation of the three-dimensional GTVs of NSCLC among oncologists. Standardization of the approach with guidelines resulted in a reduction in this variation.     

Inter‐observer variability of clinical target volume delineation for bladder cancer using CT and cone beam CT

To compare the image quality of cone beam CT (CBCT) with that of planning CT (pCT) scan, and quantify inter‐observer differences in therapeutic indices based on these scans prior to the introduction of an adaptive radiation therapy protocol for bladder cancer. Four consecutive patients were selected with muscle invasive bladder cancer receiving radical dose radiation therapy. Four radiation oncologists specializing in genitourinary malignancies contoured the clinical target volume (CTV) and rectum on both a pCT and a randomly chosen CBCT of the same patient. A conformity index (CI) for CTV and the rectum was determined for both pCT and CBCT. The maximal lateral, anterior, posterior, cranial and caudal extensions of the CTV for both CT and CBCT were determined for each observer. Variation in volumes of both the CTV and rectum for both pCT and were also compared using Varian Eclipse planning software (Varian Medical Systems, Palo Alto, CA, USA). Using pCT the mean CI for the CTV was 0.79; using CBCT the mean CI for the CTV was 0.75. For the rectum, the mean CI for using CT was 0.80 and for CBCT was 0.74. Greatest variation on CBCT CTV contours was seen in the supero‐inferior direction with variation up to 2.1 cm between different radiation oncologists. With the variation in CI for pCT and CBCT of the CTV and rectum (0.04 and 0.06 respectively), CBCT is not significantly inferior to the pCT in terms of inter‐observer contouring variability.     

Lymphangiogram-assisted lymph node target delineation for patients with gynecologic malignancies

PURPOSE: Intensity-modulated radiotherapy for gynecologic malignancies requires proper knowledge of the volumes to be irradiated and accurate delineation of these volumes on a three-dimensional projection. In this study, assisted by lymphangiography (LAG), we derived guidelines for delineating nodal target volumes on CT. METHODS AND MATERIALS: Sixteen patients with cervical cancer who underwent radiotherapy between 1995 and 1999 at the Mallinckrodt Institute of Radiology were enrolled in the study. The initial 6 patients underwent bipedal LAG as part of the staging workup. Cross-sectional CT images were acquired and analyzed, and lymph node locations were described relative to the aorta, vena cava, common iliac, external iliac, and femoral vessels. The greatest distance from lymph node to vessel wall and pelvic sidewall was determined for each nodal group. This served as a guideline from which the clinical target volume (CTV) definitions were developed. This proposed CTV was then applied to CT scans of 10 patients to determine the amounts of normal tissues encompassed. RESULTS: Nodal CTV guidelines were derived to cover 100% of LAG-avid lymph nodes. This CTV definition encompassed an average of 58.1 +/- 22.8 cm(3) (6.8% +/- 2.8% of total volume) small bowel, 28.4 +/- 19.2 cm(3) (4.2% +/- 3.2%) large bowel, 8.6 +/- 8.6 cm(3) (3.2% +/- 2.6%) bladder, and 1.6 +/- 3.1 cm(3) (1.0% +/- 1.7%) rectum. The absolute volume and fraction of normal tissues encompassed by CTV plus 1- or 2-cm margins were calculated. CONCLUSION: This study presents the first time that three-dimensional lymph node mapping with the aid of LAG has been used to generate a nodal CTV guideline. This information may assist radiation oncologists in properly determining nodal target volumes and selecting a margin around the CTV for intensity-modulated radiotherapy.     

Automated functional image-guided radiation treatment planning for rectal cancer

PURPOSE: Computer tomography-based (CT-based) tumor-volume definition is time consuming and is subject to clinical interpretation. CT is not accessible for standardized algorithms for the purpose of treatment-volume planning. We have evaluated the accuracy of target-volume definition based on the positron emission tomography (PET) data from an integrated PET/CT system with 2-[(18)F]fluoro-2-deoxy-D-glucose (FDG) for standardized target-volume delineation. MATERIALS AND METHODS: Eleven patients with rectal cancer who were undergoing preoperative radiation therapy (RT) were studied. A standardized region-growing algorithm was tested to replace the CT-derived gross tumor volume by the PET-derived gross tumor volume (PET-GTV) or the biologic target volume (BTV). A software tool was developed to automatically delineate the appropriate tumor volume as defined by the FDG signal, the PET-GTV, and the planning target volume (PTV). The PET-derived volumes were compared with the target volumes from CT. RESULTS: The BTV defined for appropriate GTV assessment was set at a single peak threshold of 40% of the signal of interest. Immediate treatment volume definition based on the choice of a single-tumor volume-derived PET-voxel resulted in a tumor volume that strongly correlated with the CT-derived GTV (r(2) = 0.84; p < 0.01) and the volume as assessed on subsequent anatomic-pathologic analysis (r(2) = 0.77; p < 0.01). In providing sufficient extension margins from the CT-derived GTV and the PET-derived GTV, to PTV, respectively, the correlation of the CT-derived and PET-derived PTV was sufficiently accurate for PTV definition for external-beam therapy (r(2) = 0.96; p < 0.01). CONCLUSION: Automated segmentation of the PET signal from rectal cancer may allow immediate and sufficiently accurate definition of a preliminary working PTV for preoperative RT. If required, correction for anatomic precision and geometric resolution may be applied in a second step. Computed PET-based target-volume definition could be useful for the definition of standardized simultaneous internal-boost volumes for intensity-modulated radiation therapy (IMRT) based on biologic target volumes.     

Impact of FDG-PET on radiation therapy volume delineation in non-small-cell lung cancer

PURPOSE: Locoregional failure remains a significant problem for patients receiving definitive radiation therapy alone or combined with chemotherapy for non-small-cell lung cancer (NSCLC). Positron emission tomography (PET) with [(18)F]fluoro-2-deoxy-d-glucose (FDG) has proven to be a valuable diagnostic and staging tool for NSCLC. This prospective study was performed to determine the impact of treatment simulation with FDG-PET and CT on radiation therapy target volume definition and toxicity profiles by comparison to simulation with computed tomography (CT) scanning alone. METHODS: Twenty-six patients with Stages I-III NSCLC were studied. Each patient underwent sequential CT and FDG-PET simulation on the same day. Immobilization devices used for both simulations included an alpha cradle, a flat tabletop, 6 external fiducial markers, and a laser positioning system. A radiation therapist participated in both simulations to reproduce the treatment setup. Both the CT and fused PET/CT image data sets were transferred to the radiation treatment planning workstation for contouring. Each FDG-PET study was reviewed with the interpreting nuclear radiologist before tumor volumes were contoured. The fused PET/CT images were used to develop the three-dimensional conformal radiation therapy (3DCRT) plan. A second physician, blinded to the results of PET, contoured the gross tumor volumes (GTV) and planning target volumes (PTV) from the CT data sets, and these volumes were used to generate mock 3DCRT plans. The PTV was defined by a 10-mm margin around the GTV. The two 3DCRT plans for each patient were compared with respect to the GTV, PTV, mean lung dose, volume of normal lung receiving > or =20 Gy (V20), and mean esophageal dose. RESULTS: The FDG-PET findings altered the AJCC TNM stage in 8 of 26 (31%) patients; 2 patients were diagnosed with metastatic disease based on FDG-PET and received palliative radiation therapy. Of the 24 patients who were planned with 3DCRT, PET clearly altered the radiation therapy volume in 14 (58%), as follows. PET helped to distinguish tumor from atelectasis in all 3 patients with atelectasis. Unsuspected nodal disease was detected by PET in 10 patients, and 1 patient had a separate tumor focus detected within the same lobe of the lung. Increases in the target volumes led to increases in the mean lung dose, V20, and mean esophageal dose. Decreases in the target volumes in the patients with atelectasis led to decreases in these normal-tissue toxicity parameters. CONCLUSIONS: Radiation targeting with fused FDG-PET and CT images resulted in alterations in radiation therapy planning in over 50% of patients by comparison with CT targeting. The increasing availability of integrated PET/CT units will facilitate the use of this technology for radiation treatment planning. A confirmatory multicenter, cooperative group trial is planned within the Radiation Therapy Oncology Group.     

Observer variation in contouring gross tumor volume in patients with poorly defined non-small-cell lung tumors on CT: the impact of 18FDG-hybrid PET fusion.

PURPOSE: To quantify interobserver variation in gross tumor volume (GTV) localization using CT images for patients with non-small-cell lung carcinoma and poorly defined tumors on CT and to determine whether variability would be reduced if coregistered 2-[18F]fluoro-2-deoxy-d-glucose (FDG)-hybrid positron emission tomography (PET) with CT images were used. METHODS AND MATERIALS: Prospectively, 30 patients with non-small-cell lung carcinoma had CT and FDG-hybrid PET examinations in radiation treatment position on the same day. Images were coregistered using eight fiducial markers. Guidelines were established for contouring GTVs. Three radiation oncologists performed localization independently. The coefficient of variation was used to assess interobserver variability. RESULTS: The size of the GTV defined showed great variation among observers. The mean ratios of largest to smallest GTV were 2.31 and 1.56 for CT only and for CT/FDG coregistered data, respectively. The addition of PET reduced this ratio in 23 of 30 cases and increased it in 7. The mean coefficient of variation for GTV based on the combined modalities was significantly smaller (p < 0.01) than that for CT data only. CONCLUSIONS: High observer variability in CT-based definition of the GTV can occur. A more consistent definition of the GTV can often be obtained if coregistered FDG-hybrid PET images are used.