Biological Target Volume Research Articles

A Phase I/II Clinical Trial of Dose Escalation on Biological Target Volume With Intensity Modulated Radiation Therapy: The Long-term Results

A Phase I/II Clinical Trial of Dose Escalation on Biological Target Volume With Intensity Modulated Radiation Therapy: The Long-term Results

PET Tumor Volume Segmentation: A Comparison of Automated Versus Oncologist Drawn Volumes

Segmentation of biological target volumes on positron emission tomography (PET) images is affected by spatial resolution, partial volume effects and the window and level settings. Many automated segmentation methods have been investigated to overcome these issues, each with different strengths and weaknesses. In this study five independent tumor segmentation methods were combined using a previously validated majority vote (MJV) method. We investigated the level of agreement between the individual and combined automated volumes and those defined by experienced radiation oncologists.

Comparaison de différentes méthodes de segmentation en TEP/TDM pour le ciblage en radiothérapie des carcinomes épidermoïdes des VADS

IntroductionTo assess interobserver variability for biological target volume (BTV) delineation and to compare the reproductibility of different semiautomatic segmentation methods in pretreatment 18-fluorodeoxyglucose positron emission tomography (PET/CT) of head and neck squamous cell carcinoma (HNSCC). Patients and methodsPatients with histologically proved HNSCC referred to the nuclear medicine service in Brest for pretreatment PET/CT were prospectively included from February 2009 to June 2010. Three nuclear medicine physicians (two specialized in oncology) delineated manually and independently BTV on each primary tumor. Four semiautomatic segmentation methods have been studied; three using a fixed threshold and one applying an adaptive threshold based on the signal-to-background ratio (Daisne). The variability between κ observers and/or methods has been assessed. The concordance between the various BTV intersections and unions has been also assessed. ResultsThirty patients (29M; 1F) were included. The primary site location was oropharynx in six patients, oral cavity in 10 patients, hypopharynx in five patients and larynx in nine patients. A statistically significant global interobserver variability (P=0.01) was showed, but without statistically difference between the two experienced oncologists (P=0.15). The maximal concordance of the two experienced observers with the semiautomatic methods was found for the Daisne method (CI=61.5%; κ=0.68), expressing a good agreement according to the Landis and Koch criteria, better than with the segmentation method using a fixed threshold with 40% of maximal signal intensity (CI=52.1%; κ=0.53). ConclusionOur results suggest the feasibility of achieving HNSCC BTV delineation by PET/CT using semiautomatic methods, in particular those which apply an adaptative threshold but under the supervision of an experienced operator.

FDG-PET based dose escalated adjuvant tomotherapy (image-guided intensity-modulated radiotherapy) utilizing 4D-CT planning for high-risk adrenocortical carcinoma (ACC): A case study.

e13522 Background: ACC is a rare endocrine malignancy with an annual incidence of 0.5-2/million/year. Surgery is the mainstay of treatment but relapse rate is high and the prognosis is dismal (20-50% 5 year survival). Adjuvant Radiotherapy improves local control in cases with high risk of local failure and dose escalation may achieve better results. Dose Escalation with 3-Dimensional computed tomography (CT) based radiotherapy is difficult for ACC due to unacceptable toxicity to several adjacent organs at risk (OARs) e.g., the kidneys, stomach bowel, liver, spinal cord. FDG-PET helps delineation of areas of higher metabolic activity and density of clonogenic cells within the target (Biological Target Volume or BTV) where focal dose escalation could be directed safely for improving local control as in other solid tumours. Tomotherapy (IMRT with daily image guidance) delivers precision radiotherapy with integrated boost to the BTV, lower dose to OARs, improved coverage of the targets, and better dose delivery across the targets which are essential for tumour control. 4-Dimensional CT for planning allows adequate Clinical Target Volume(CTV) coverage despite respiratory movements. Methods: A 63 year old lady had left adrenalectomy for an adrenocortical carcinoma measuring 29 x 18 x 25mm (TNM pT1NXMX) thought to be microscopically incompletely excised (R1) with a proliferation index ( Ki-67) of 40% for which adjuvant radiotherapy was advised. PET-CT, 4D-CT and Tomotherapy were used for planning. A total dose of 50.4Gy to PTV with a simultaneous integrated boost to BTV taking it up to 59.40Gy (1.98Gy/ fraction) in 30 daily fractions was prescribed. Results: Target dose and coverage were very satisfactory. The doses to OARs were well within tolerance despite dose escalation; she completed treatment with only grade- fatigue. She had metastatic disease at 11 months follow-up without local relapse. Conclusions: To our knowledge this is the first report of using FDG –PET based dose escalation, 4D CT and Tomotherapy in high risk ACC to improve local control and needs further study.

A new methodological approach for PET implementation in radiotherapy treatment planning

In this paper, a new methodological approach to using PET information in radiotherapy treatment planning has been discussed. Computed tomography (CT) represents the primary modality to plan personalized radiation treatment, because it provides the basic electron density map for correct dose calculation. If PET scanning is also performed it is typically coregistered with the CT study. This operation can be executed automatically by a hybrid PET/CT scanner or, if the PET and CT imaging sets have been acquired through different equipment, by a dedicated module of the radiotherapy treatment planning system. Both approaches have some disadvantages: in the first case, the bore of a PET/CT system generally used in clinical practice often does not allow the use of certain bulky devices for patient immobilization in radiotherapy, whereas in the second case the result could be affected by limitations in window/level visualization of two different image modalities, and the displayed PET volumes can appear not to be related to the actual uptake into the patient. To overcome these problems, at our centre a specific procedure has been studied and tested in 30 patients, allowing good results of precision in the target contouring to be obtained. The process consists of segmentation of the biological target volume by a dedicated PET/CT console and its export to a dedicated radiotherapy system, where an image registration between the CT images acquired by the PET/CT scanner and a large-bore CT is performed. The planning target volume is contoured only on the large-bore CT and is used for virtual simulation, to individuate permanent skin markers on the patient.

Role of PET/CT functional imaging on constructing a tumor radiotherapeutic biological target volume

In studies on intensity modulated radiotherapy with conventional fractionation,different radiosensitivity areas require different irradiation doses.In tumor radiotherapy areas CR,boosts in radiotherapy doses should be determined according to whether there are survived tumor cells or not.To those survived cells,CT imaging has become the key tool to delineate the radiotherapy target.Thus,the study on the construction of biological target volume with PET/CT functional imaging,which could reflect either radiosensitivity or cell proliferation-related cell metabolism,anoxia and DNA number of various cell cycle phases,is an important research area. Key words: Neoplasms ; Radiotherapy; Biological target; Tomography, emission-computed ; Tomography, X-ray computed

A free database of radionuclide voxel S values for the dosimetry of nonuniform activity distributions

The increasing availability of SPECT/CT devices with advanced technology offers the opportunity for the accurate assessment of the radiation dose to the biological target volume during radionuclide therapy. Voxel dosimetry can be performed employing direct Monte Carlo radiation transport simulations, based on both morphological and functional images of the patient. On the other hand, for voxel dosimetry calculations the voxel S value method can be considered an easier approach than patient-specific Monte Carlo simulations, ensuring a good dosimetric accuracy at least for anatomic regions which are characterized by uniform density tissue. However, this approach has been limited because of the lack of tabulated S values for different voxel dimensions and radionuclides. The aim of this work is to provide a free dataset of values which can be used for voxel dosimetry in targeted radionuclide studies. Seven different radionuclides (89Sr, 90Y, 131I, 153Sm, 177Lu, 186Re, 188Re), and 13 different voxel sizes (2.21, 2.33, 2.4, 3, 3.59, 3.9, 4, 4.42, 4.8, 5, 6, 6.8 and 9.28 mm) are considered. Voxel S values are calculated performing simulations of monochromatic photon and electron sources in two different homogeneous tissues (soft tissue and bone) with DOSXYZnrc code, and weighting the contributions on the basis of the radionuclide emission spectra. The outcomes are validated by comparison with Monte Carlo simulations obtained with other codes (PENELOPE and MCNP4c) performing direct simulation of the radionuclide emission spectra. The differences among the different Monte Carlo codes are of the order of a few per cent when considering the source voxel and the bremsstrahlung tail, whereas the highest differences are observed at a distance close to the maximum continuous slowing down approximation range of electrons. These discrepancies would negligibly affect dosimetric assessments. The dataset of voxel S values can be freely downloaded from the website www.medphys.it.

FDG-PET,a Complementary Modality to Computed Tomography in Radiotherapy Target Volume Delineation for Head and Neck Cancer

The objective of the current review was to use published data to assess the role of [18F] fluorodeoxyglucose-positron emission tomography (FDG-PET) as a complementary modality to computed-tomography (CT) in radiotherapy target volume delineation for head and neck cancer (HNC). Studies were identified by searching PubMed electronic databases. Both prospective and retrospective studies were included. Information regarding the role of FDG-PET for radiotherapy target volume delineation for HNC was analyzed. FDG-PET is a promising tool for improving radiotherapy target volume delineation by defining a metabolically active biological target volume (BTV). The use of novel PET tracers representing properties such as hypoxia, protein synthesis and proliferation remain to be better characterized. The role of FDG-PET for radiotherapy target volume delineation for patients with HNC is expanding and should be further evaluated in clinical trials.

PET/CT in Radiotherapy Planning for Head and Neck Cancer

The use of PET/CT as an adjunct in radiotherapy planning is an attractive option in head and neck cancer (HNC) for several reasons. First, with potentially better identification of the disease extent, i.e., staging, the risk of geographical miss of radiation delivery to the gross tumor volume is reduced. Second, in characterizing the biological behavior of the disease for example, areas of hypoxia, rich or poor vascularity, or high cell proliferation, PET/CT can identify biological target volumes either for escalation of radiation dose or to predict the requirement for the addition of a radiosensitizer or alternative treatment strategies. 18F-FDG is the most common tracer used in oncology studies, but many other tracers have been investigated with several entering clinical practice, although these remain predominantly in the research domain in HNC.

11C-CHO PET in optimization of target volume delineation and treatment regimens in postoperative radiotherapy for brain gliomas

We explored the clinical values of (11)C-choline ((11)C-CHO) PET in optimization of target volume delineation and treatment regimens in postoperative radiotherapy for brain gliomas. Sixteen patients with the pathological confirmation of the diagnosis of gliomas prior to receiving radiotherapy (postoperative) were included, and on whom both MRI and CHO PET scans were performed at the same position for comparison of residual tumors with the two techniques. (11)C-CHO was used as the tracer in the PET scan. A plain T1-weighted, T2-weighted and contrast-enhanced T1-weighted imaging scans were performed in the MRI scan sequence. The gliomas' residual tumor volume was defined as the area with CHO-PET high-affinity uptake and metabolism (V(CHO)) and one with MRI T1-weighted imaging high signal intensity (V(Gd)), and was determined by a group of experienced professionals and clinicians. (1) In CHO-PET images, the tumor target volume, i.e., the highly metabolic area with a high concentration of isotopes (SUV 1.016-4.21) and the corresponding contralateral normal brain tissues (SUV0.1-0.62), was well contrasted, and the boundary between lesions and surrounding normal brain tissues was better defined compared with MRI and (18)F-FDG PET images. (2) For patients with brain gliomas of WHO Grade II, the SUV was 1.016-2.5; for those with WHO Grades III and IV, SUVs were >26-4.2. (3) Both CHO PET and MRI were positive for 10 patients and negative for 2 patients. The residual tumor consistency between these two studies was 75%. Four of the 10 CHO-PET-positive patients were negative on MRI scans. The maximum distance between V(Gd) and V(CHO) margins was 1.8 cm. (4) The gross tumor volumes (GTVs) and the ensuing treatment regimens were changed for 31.3% (5/16) of patients based on the CHO-PET high-affinity uptake and metabolism, in which the change rate was 80% (4/5), 14.3 % (1/7) and 0% (0/4) for patients with WHO Grade II III, and IV gliomas, respectively. Our data demonstrate that difference exists between CHO PET and MRI by which to judge and identify residual tumor for patients with brain gliomas. CHO PET is considered to be a supplementary diagnostic approach for MRI. Biological tumor target volume (BTV) displayed in the CHO PET images is useful in determining or delineating the radiotherapy target volume and making decisions in selecting treatment regimens. Tumor target volume may be defined more accurately and rationally when the CHO PET is combined with MRI.

Impact of [18F]FDG PET imaging parameters on automatic tumour delineation: need for improved tumour delineation methodology

PurposeDelineation of tumour boundaries is important for quantification of [18F]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) studies and for definition of biological target volumes in radiotherapy. Several (semi-)automatic tumour delineation methods have been proposed, but these methods differ substantially in estimating tumour volume and their performance may be affected by imaging parameters. The main purpose of this study was to explore the performance dependence of various (semi-)automatic tumour delineation methods on different imaging parameters, i.e. reconstruction parameters, noise levels and tumour characteristics, and thereby the need for standardization or inter-institute calibration.MethodsSix different types of delineation methods were evaluated by assessing accuracy and precision in estimating tumour volume from simulations and phantom experiments. The evaluated conditions were various tumour sizes, iterative reconstruction algorithm settings and image filtering, tumour to background ratios (TBR), noise levels and region growing initializations.ResultsThe accuracy of all automatic delineation methods was influenced when imaging parameters were varied. The performance of all tumour delineation methods depends on variation of TBR, image resolution and image noise level, and to a lesser extent on number of iterations during image reconstruction or the initialization method of the region generation. For sphere sizes larger than 20 mm diameter a contrast-oriented method provided the most accurate results, on average, over all simulated conditions. For threshold-based methods the accuracy of tumour delineation improved after image denoising/filtering.ConclusionThe accuracy and precision of all studied tumour delineation methods was affected by physiological and imaging parameters. The latter illustrates the need for optimizing imaging parameters and/or for careful calibration and optimization of delineation methods.Electronic supplementary materialThe online version of this article (doi:10.1007/s00259-011-1899-5) contains supplementary material, which is available to authorized users.

Effects of Image Characteristics on Performance of Tumor Delineation Methods: A Test–Retest Assessment

PET can be used to monitor response during chemotherapy and assess biologic target volumes for radiotherapy. Previous simulation studies have shown that the performance of various automatic or semiautomatic tumor delineation methods depends on image characteristics. The purpose of this study was to assess test-retest variability of tumor delineation methods, with emphasis on the effects of several image characteristics (e.g., resolution and contrast). Baseline test-retest data from 19 non-small cell lung cancer patients were obtained using (18)F-FDG (n = 10) and 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) (n = 9). Images were reconstructed with varying spatial resolution and contrast. Six different types of tumor delineation methods, based on various thresholds or on a gradient, were applied to all datasets. Test-retest variability of metabolic volume and standardized uptake value (SUV) was determined. For both tracers, size of metabolic volume and test-retest variability of both metabolic volume and SUV were affected by the image characteristics and tumor delineation method used. The median volume test-retest variability ranged from 8.3% to 23% and from 7.4% to 29% for (18)F-FDG and (18)F-FLT, respectively. For all image characteristics studied, larger differences (≤10-fold higher) were seen in test-retest variability of metabolic volume than in SUV. Test-retest variability of both metabolic volume and SUV varied with tumor delineation method, radiotracer, and image characteristics. The results indicate that a careful optimization of imaging and delineation method parameters is needed when metabolic volume is used, for example, as a response assessment parameter.

TU‐G‐211‐01: Uptake Volume Histograms: A Novel Avenue towards Delineation of Biological Target Volumes (BTV) in Radiotherapy

Purpose: To investigate the feasibility of decomposition of differential uptake volume histograms (UVH) derived from FDG‐PET and CT data for uncovering tumor sub‐volumes as a novel approach for defining biological target volumes (BTV) for use in radiotherapy treatment planning. Methods: For a cohort of 27 histopathologically proven non‐small cell lung carcinoma (NSCLC) patients, background uptake values were sampled within contra‐lateral healthy lung over PET slices containing tumor and then scaled by the ratio of tissue densities between healthy lung and tumor derived from CT data. Signal‐to‐background uptake values within volumes of interest encompassing the tumor were scored from which differential uptake volume histograms were constructed. These were subsequently decomposed into the minimum number of analytical functions that yielded acceptable net fits, as assessed by chî2 values. Results: Based on the assumption that each function used to decompose the UVH may correspond to a single sub‐volume comprising the volume of interest sampled, at least four sub‐volumes consistently evolved for our patient population. Furthermore, if crossing points between adjacent functions are interpreted as threshold values that differentiate sub‐volumes, average threshold values between the four sub‐volumes were found to be 0.80±0.21, 1.56±0.48, and 2.96±1.04 for adenocarcinomas, 0.89±0.48, 1.60±0.40, and 2.85±0.75 for large cell carcinomas, and 0.84±0.31, 1.70±0.58, and 3.72±1.68 for squamous cell carcinomas. Conclusions: Our study suggests that FDG‐based PET data could be used to identify biological sub‐volumes within tumor in NSCLC patients. Significant fluctuations in threshold values throughout the patient cohort can be explained as a consequence of large variability in physiological status of the tumor volume for each patient at the time of the PET/CT scan. This further suggests that BTV threshold values may be rather patient‐specific, and could be determined by creation and curve fitting of differential uptake volume histograms on a patient‐specific basis.

WE‐G‐214‐03: Investigating the Repeatability of Quantitative PET Imaging of Heterogeneous Tumors

Purpose: High precision within quantitative imaging studies is required to define biological targets for dose painting, and to evaluate responses to therapy. However, within PET imaging systems there are position‐dependent systematic fluctuations in contrast‐recovery. The objective of this study was to determine the impact of patient set‐up on PET‐based quantification of heterogeneous tumors. Methods: Ten dogs with sinonasal tumors received six repeated [18F]FDG‐PET scans. Between each PET acquisition, known set‐up errors were produced by varying patient position in precisely controlled 1.0±0.5 mm steps. Image noise was investigated by retrospectively varying acquisition time of a stationary scan. Resulting changes in SUVmax and PET‐based target volumes were evaluated. Correlation between corresponding voxels of co‐registered images determined repeatability of spatial distributions. A theoretical upper limit of repeatability was estimated from simulated PET images using empirical models of position‐dependent contrast‐recovery. Results: From the simulated PET images, a theoretical upper limit of 0.90 was estimated for the repeatability of spatial distributions when set‐up errors are present. When only image noise was varied between [18F]FDG‐PET scans, repeatability of spatial distributions was measured at 0.95. However, set‐up errors lead to significant decreases (p < 0.01) in voxel correlations. Introducing set‐up errors between [18F]FDG‐PET acquisitions reduced the repeatability of spatial distributions to 0.80, and caused changes of 5% in SUVmax and 10% in volumes of PET‐based targets. Conclusions: Set‐up errors as small as a few millimeters (< 3mm) reduced the reproducibility of quantitative PET imaging of heterogeneous tumors. PET‐based quantitative values generally varied within 10%, but target volumes within some tumors changed by 30%. Errors during PET acquisition will lead to uncertainty in quantifying changes in tumor function, and to limited accuracy and precision of PET‐based biological target volumes. Therefore, tumor delineation must be independent of SUV thresholds and uncertainty margins are required for PET‐based response quantification.

48 speaker IMAGE REGISTRATION IN RADIOTHERAPY

Image registration is widely recognized as an important tool in Radiotherapy (RT) to better configure RT plans and to evaluate RT efficacy. Image registration is more and more used to integrate multimodal information derived from different imaging modalities, in order to better define structural and functional characteristics of the tumor and consequently to enhance delineation of Planning and Biological Target Volumes; furthermore registration of CT images acquired before and during RT is employed to estimate patient anatomical changes during time, thus allowing the study of deformation of organs induced by RT as well as the introduction of Adaptive RT. However, the good behavior of an image registration technique is strictly related to the specific clinical application and often to the specific image acquisition protocol: each registration approach presents relative merits and limitations that should be known in order to really exploit the value of registration in RT. In this context an important point is the availability of tools able to quantitatively assess the spatial accuracy of registration. The lesson introduces the principal registration techniques from the theoretical point of view. Specifically, the models of spatial transformations (rigid and non rigid) as well as the main categories of registrations (feature-based, voxel-based) are comparatively discussed. The main proposed approaches for non rigid deformation are reviewed. Finally, the methodological framework to evaluate the performance of image registration in RT applications is presented and the main indices to quantitatively assess registration accuracy are introduced.

49 speaker ADVANCES IN REFERENCE DOSIMETRY – WHERE DO WE GO NEXT?

Image registration is widely recognized as an important tool in Radiotherapy (RT) to better configure RT plans and to evaluate RT efficacy. Image registration is more and more used to integrate multimodal information derived from different imaging modalities, in order to better define structural and functional characteristics of the tumor and consequently to enhance delineation of Planning and Biological Target Volumes; furthermore registration of CT images acquired before and during RT is employed to estimate patient anatomical changes during time, thus allowing the study of deformation of organs induced by RT as well as the introduction of Adaptive RT. However, the good behavior of an image registration technique is strictly related to the specific clinical application and often to the specific image acquisition protocol: each registration approach presents relative merits and limitations that should be known in order to really exploit the value of registration in RT. In this context an important point is the availability of tools able to quantitatively assess the spatial accuracy of registration. The lesson introduces the principal registration techniques from the theoretical point of view. Specifically, the models of spatial transformations (rigid and non rigid) as well as the main categories of registrations (feature-based, voxel-based) are comparatively discussed. The main proposed approaches for non rigid deformation are reviewed. Finally, the methodological framework to evaluate the performance of image registration in RT applications is presented and the main indices to quantitatively assess registration accuracy are introduced.

Ten-Year Outcomes: The Clinical Utility of Single Photon Emission Computed Tomography/Computed Tomography Capromab Pendetide (Prostascint) in a Cohort Diagnosed With Localized Prostate Cancer

To evaluate the clinical utility of capromab pendetide imaging with single photon emission computed tomography coregistration with computed tomography (SPECT/CT) in primary prostate cancer (CaP) for pretreatment prognostic staging and localization of biologic target volumes (BTV) for individualized image-guided radiotherapy dose escalation (IGRT-DE). Patients consecutively presenting for primary radiotherapy (February 1997 to December 2002), having a clinical diagnosis of localized CaP, were evaluated for tumor stage using conventional staging and SPECT/CT (N=239). Distant metastatic uptake (mets) were identified by SPECT/CT in 22 (9.2%). None of the suspected mets could be clinically confirmed. Thus, all subjects were followed without alteration in disease management. The SPECT/CT pelvic images defined BTV for IGRT-DE (+150% brachytherapy dose) without (n=150) or with (n=89) external radiation of 45 Gy. The National Comprehensive Cancer Network criteria defined risk groups (RG). The median survivor follow-up was 7 years. Biochemical disease-free survival (bDFS) was reported by clinical nadir +2 ng/mL (CN+2) criteria. Statistical analyses included Kaplan-Meier, multivariate analysis, and Concordance-index models. At 10-year analyses, overall survival was 84.8% and bDFS was 84.6%. With stratification by RG, CN+2 bDFS was 93.5% for the low-RG (n=116), 78.7% for the intermediate-RG (n=94), and 68.8% for the high-RG (n=29), p=0.0002. With stratification by pretreatment SPECT/CT findings, bDFS was 65.5% in patients with suspected mets (n=22) vs. 86.6% in patients with only localized uptake (n=217), p=0.0014. CaP disease-specific survival (DSS) was 97.7% for the cohort. With stratification by SPECT/CT findings, DSS was 86.4% (with suspected mets) vs. 99.0% (localized only), p=0.0001. Using multivariate analysis, the DSS hazard ratio for SPECT/CT findings (mets vs. localized) was 3.58 (p=0.0026). Concordance-index tests, based on all data, by CN+2 bDFS criteria were 0.710 for RG alone and 0.773 for SPECT/CT + RG. Through long-term outcomes we demonstrate statistically significant bDFS and DSS predictive value for pretreatment capromab pendetide SPECT/CT imaging in primary CaP. Dual clinical utility is demonstrated, using SPECT/CT to define BTV for individualized IGRT-DE.

18F-FDG PET/CT-based gross tumor volume definition for radiotherapy in head and neck Cancer: a correlation study between suitable uptake value threshold and tumor parameters

BackgroundTo define a suitable threshold setting for gross tumor volume (GTV) when using 18Fluoro-deoxyglucose positron emission tomography and computed tomogram (PET/CT) for radiotherapy planning in head and neck cancer (HNC).MethodsFifteen HNC patients prospectively received PET/CT simulation for their radiation treatment planning. Biological target volume (BTV) was derived from PET/CT-based GTV of the primary tumor. The BTVs were defined as the isodensity volumes when adjusting different percentage of the maximal standardized uptake value (SUVmax), excluding any artifact from surrounding normal tissues. CT-based primary GTV (C-pGTV) that had been previously defined by radiation oncologists was compared with the BTV. Suitable threshold level (sTL) could be determined when BTV value and its morphology using a certain threshold level was observed to be the best fitness of the C-pGTV. Suitable standardized uptake value (sSUV) was calculated as the sTL multiplied by the SUVmax.ResultsOur result demonstrated no single sTL or sSUV method could achieve an optimized volumetric match with the C-pGTV. The sTL was 13% to 27% (mean, 19%), whereas the sSUV was 1.64 to 3.98 (mean, 2.46). The sTL was inversely correlated with the SUVmax [sTL = -0.1004 Ln (SUVmax) + 0.4464; R2 = 0.81]. The sSUV showed a linear correlation with the SUVmax (sSUV = 0.0842 SUVmax + 1.248; R2 = 0.89). The sTL was not associated with the value of C-pGTVs.ConclusionIn PET/CT-based BTV for HNC, a suitable threshold or SUV level can be established by correlating with SUVmax rather than using a fixed threshold.

« Dose-painting » : mythe ou réalité ?

“Dose-painting” radiotherapy allows for a heterogeneous delivery of radiation within the tumour volume by targeting radioresistant areas defined by functional imaging. Within gross tumour volume, it is possible to define one or more target volumes based on biology (biological target volume [BTV]) and to apply a strategy of intensity modulated radiation therapy (IMRT) that will deliver a higher dose to these regions. In this review of the literature, we will highlight the biological elements responsible for radioresistance, and how to image them, then we will detail the radiotherapy techniques necessary for this approach, before presenting clinical results in various situations (head and neck tumours, prostate, brain tumours, etc.). Despite many difficulties that make dose-painting IMRT unusable in routine nowadays, biology-guided radiation therapy represents one of the major pathways of development of radiotherapy in the coming years.

Coregistration of Prechemotherapy PET-CT for Planning Pediatric Hodgkin's Disease Radiotherapy Significantly Diminishes Interobserver Variability of Clinical Target Volume Definition

To assess the interobserver variability in clinical target volume (CTV) definitions when using registered (18)F-labeled deoxyglucose positron emission tomography (FDG-PET-CT) versus side-by-side image sets in pediatric Hodgkin's disease (HD). Prechemotherapy FDG-PET-CT scans performed in the treatment position were acquired from 20 children (median age, 14 years old) with HD (stages 2A to 4B) and registered with postchemotherapy planning CT scans. The patients had a median age of 14 years and stages of disease ranging between 2A and 4B. Image sets were coregistered using a semiautomatic coregistration system. The biological target volume was defined on all the coregistered images as a guide to defining the initial site of involvement and to avoid false-positive or negative results. Five radiation oncologists independently defined the CTV for all 20 patients: once using separate FDG-PET-CT images as a guide (not registered) to define CTVa and once using the registered FDG-PET-CT data to define CTVb. The total volumes were compared, as well as their coefficients of variation (COV). To assess the interobserver variability, the percentages of intersection between contours drawn by all observers for each patient were calculated for CTVa and for CTVb. The registration of a prechemotherapy FDG-PET-CT scan caused a change in the CTV for all patients. Comparing CTVa with CTVb showed that the mean CTVb increased in 14 patients (range, 0.61%-101.96%) and decreased in 6 patients (range, 2.97%-37.26%). The COV for CTVb significantly decreased for each patient; the mean COVs for CTVa and CTVb were 45% (21%-65%) and 32% (13%-57%), respectively (p = 0.0004). The percentage of intersection among all CTVbs for the five observers increased significantly by 89.77% (1.99%-256.41%) compared to that of CTVa (p = 0.0001). High observer variability can occur during CT-based definition of CTVs for children diagnosed with HD. Registration of FDG-PET and planning CT images resulted in significantly greater consistency of tumor volume definition.