Aims: High local control rates are achieved in stage I lung cancer using stereotactic ablative radiotherapy. Target delineation is commonly based on four-dimensional computed tomography (CT) scans. Target volumes defined by positron emission tomography/computed tomography (PET/CT) are compared with those defined by four-dimensional CT and conventional ('three-dimensional') F-18-fluorodeoxyglucose (F-18-FDG) PET/CT.Materials and methods: For 16 stage I non-small cell lung cancer tumours, six approaches for deriving PET target volumes were evaluated: manual contouring, standardised uptake value (SUV) absolute threshold of 2.5, 35% of maximum SUV (35% SUVMAX), 41% of SUVMAX (41% SUVMAX) and two different source to background ratio techniques (SBR-1 and SBR-2). PET-derived target volumes were compared with the internal target volume (ITV) from the modified maximum intensity projection (MIPMOD ITV). Volumetric and positional correlation was assessed using the Dice similarity coefficient (DSC).Results: PET-based target volumes did not correspond to four-dimensional CT-based target volumes. The mean DSC relative to MIPMOD ITV were: PET manual = 0.64, SUV2.5 = 0.64, 35% SUVMAX = 0.63, 41% SUVMAX = 0.57. SBR-1 = 0.52, SBR-2 = 0.49. PET-based target volumes were smaller than corresponding MIP ITVs.Conclusions: Conventional three-dimensional F-18-FDG PET-derived target volumes for lung stereotactic ablative radiotherapy did not correspond well with those derived from four-dimensional CT, including those in routine clinical use (MIPMOD ITV). Caution is required in using three-dimensional PET for motion encompassing target volume delineation. (C) 2012 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

OBJECTIVEPositron emission tomography (PET)/CT scans can improve target definition in radiotherapy for non-small cell lung cancer (NSCLC). As staging PET/CT scans are increasingly available, we evaluated different methods for co-registration of staging PET/CT data to radiotherapy simulation (RTP) scans.METHODS10 patients underwent staging PET/CT followed by RTP PET/CT. On both scans, gross tumour volumes (GTVs) were delineated using CT (GTV(CT)) and PET display settings. Four PET-based contours (manual delineation, two threshold methods and a source-to-background ratio method) were delineated. The CT component of the staging scan was co-registered using both rigid and deformable techniques to the CT component of RTP PET/CT. Subsequently rigid registration and deformation warps were used to transfer PET and CT contours from the staging scan to the RTP scan. Dice's similarity coefficient (DSC) was used to assess the registration accuracy of staging-based GTVs following both registration methods with the GTVs delineated on the RTP PET/CT scan.RESULTSWhen the GTV(CT) delineated on the staging scan after both rigid registration and deformation was compared with the GTV(CT)on the RTP scan, a significant improvement in overlap (registration) using deformation was observed (mean DSC 0.66 for rigid registration and 0.82 for deformable registration, p = 0.008). A similar comparison for PET contours revealed no significant improvement in overlap with the use of deformable registration.CONCLUSIONSNo consistent improvements in similarity measures were observed when deformable registration was used for transferring PET-based contours from a staging PET/CT. This suggests that currently the use of rigid registration remains the most appropriate method for RTP in NSCLC.

Radioterapia wiązkami zewnętrznymi odgrywa kluczową rolę w leczeniu wielu typów nowotworów. Istnieje duże zainteresowanie wykorzystaniem obrazów pozytonowej tomografii emisyjnej (PET) z wykorzystaniem 18F-Fluorodeoxyglukozy (FDG) w planowaniu leczenia napromienianiem (RTP), o czym świadczy wciąż rosnąca liczba publikacji na ten temat. Ponadto w ostatnich latach opublikowano wytyczne dotyczące zastosowania i standaryzacji tej techniki. Celem niniejszej pracy jest podsumowanie aktualnej wiedzy i omówienie zagadnień związanych z wykorzystaniem 18F-FDG PET-CT w planowaniu leczenia napromienianiem.

In the treatment of NSCLC with radiotherapy (RT) 18F-FDG PET/CT has been shown to reduce target volumes and normal tissue dose estimates when used in the radiotherapy treatment planning (RTP) process. This is particularly evident in those patients with atelectasis. However, this may be due to improved baseline tumor staging as distinct from the impact that PET/CT may have at RTP simulation. The impact of PET/CT simulation on PTV volumes and normal lung tissue dose estimates in a cohort of patients already PET/CT staged is reported. RTP PET/CT scans were performed on 28 already PET/CT staged NSCLC patients (stage IA to IIIB; 14 received induction chemotherapy). In place of a RTP CT scan, patients were scanned on a PET/CT scanner. In a virtual planning study, 4 radiation oncologists independently delineated the GTV on the CT alone and then on PET/CT. PTV were obtained using standardized expansion margins with no respiratory compensation. Dosimetry plans were generated following standard department procedures. The mean percentage volume change (MPVC) from the CT PTV (PTVCT) to the PET/CT PTV (PTVPET/CT) for each case was calculated for all patients and for those with atelectasis alone. Interobserver variation was assessed using the concordance index (CI) and normal lung tissue dose estimates were calculated using the percentage volume of normal lung receiving 20 Gy (V20). The Wilcoxon signed ranks test (WSRT) was used for paired samples comparison and the Mann-Whitney U (WHU) in independent samples comparison. For all patients the median of the MPVC from PTVCT to PTVPET/CT was -2.3%. The MPVC from PTVCT to PTVPET/CT was -5.0% in those with atelectasis (n = 10) and was 4.3% with no atelectasis (WHU p = 0.084). Assessing the impact on interobserver variation, for all patients the mean PTVCT CI was 0.74 and this improved to 0.78 comparing PTVPET/CT but this difference failed to reach significance (WSRT p = 0.08). However in the subgroup of those with atelectasis the mean PTVCT was 0.68 and was significantly improved to 0.78 when comparing PTVPET/CT (WSRT p = 0.005). In all patients there was a significant reduction from the median V20 based on the PTVCT (V20 = 19.3) to the V20 using the PTVPET/CT plan (V20 = 16.2, p < 0.001). In those with atelectasis, a similar improvement was seen (PTVCT based V20 = 22.1, PTVPET/CT based V20 = 19.7, p = 0.005). TV delineation based on PET/CT simulation reduces mean lung dose estimates and reduces PTV interobserver variation in patients with atelectasis. The potential reduction in lung dose estimates may permit RT dose escalation in future clinical investigations. In addition to PET/CT staging, PET/CT RTP simulation should be considered in all patients but especially in those patients with atelectasis.

High local control rates are achieved in stage I lung cancer using stereotactic radiotherapy (SRT). Target volume (TV) definitions are commonly based on four-dimensional (4D) CT scans. A commonly reported approach is to use a maximum intensity projection (MIP) CT dataset, with subsequent modification of the MIP contours after reviewing the tumor position in different respiratory phases. The resulting approach is a so-called 'MIP Modified TV' (MIPMOD-ITV) and is used to define the internal target volume (ITV), which encompasses all motion. Some centers have reported the use of positron emission tomography (PET) for the definition of the ITV in SRT lung treatments. We compare the TVs defined by both these techniques. Conventional (3D) PET/CT scan and 4DCT scan images were acquired of a motion phantom equipped with a 3cm 18F-FDG-filled sphere, during the same periodic motion (4 seconds, 1.5cm peak-to-peak motion amplitude). In 15 patients with 16 stage I NSCLC lesions, 6 approaches for deriving PET-TVs were evaluated, including manual PET contouring (PET Manual), standardized uptake value (SUV) absolute threshold of 2.5 (SUV2.5), 35% of maximum SUV (35%SUVMAX), 41% of SUVMAX (41%SUVMAX) and two different source to background ratio techniques (SBR1 and SBR2). Following deformable registration, the PET based contours were compared to a 4DCT-based gross tumor volume (GTV) and the MIPMOD-ITV. Volumetric and positional correlation was assessed using the dice similarity coefficient (DSC). Phantom study: PET volumes did not correspond in size or shape to MIPMOD-ITV regardless of threshold used or to the dimensions of the phantom. Clinical study: PET-based TVs did not correspond to 4DCT-based TVs. The mean DSCs with respect to 4DCT-based GTVs were: PET Manual = 0.66, SUV2.5 = 0.64, 35%SUVMAX = 0.66, 41%SUVMAX = 0.64. SBR1 = 0.56, SBR2 = 0.58. The mean DSCs relative to MIPMOD-ITVs were: PET Manual = 0.64, SUV2.5 = 0.64, 35%SUVMAX = 0.63, 41%SUVMAX = 0.57. SBR1 = 0.52, SBR2 = 0.49. PET-based TVs were smaller than corresponding MIPMOD-ITVs. The mean percentage volume reduction from MIPMOD-ITVs to the PET based contours was: PET Manual = 14.4%, SUV2.5 = 15.4%, 35%SUVMAX = 20.6%, 41%SUVMAX = 40.8%. SBR1 = 54%, SBR2 = 36.4%. As conventional PET based TVs do not correspond to 4DCT-based TVs commonly used in SRT, PET should not be relied upon for GTV edge definition or motion compensation.

18F-FDG PET-CT has benefits in target volume (TV) definition in radiotherapy treatment planning (RTP) for NSCLC, however an optimal protocol for TV delineation has not been determined. Doubt exists as to the precise definition of PET based TVs, with the suggestion that PET based TVs may represent an internal target volume rather than gross tumor volume (GTV). Furthermore it has been shown in previous CT based work that Diagnostic Radiologists outline smaller TVs than Oncologists. We investigate variations in PET-CT TVs between 3 Radiation Oncologists and a PET Radiologist. RTP PET-CT scans were performed on 28 NSCLC patients (Stage IA to IIIB; 14 induction chemotherapy(IC)). In place of a RTP CT scan, patients were scanned on a PET-CT scanner. In a virtual planning study, 3 Oncologists and a PET Radiologist in conjunction with a fourth Oncologist, independently delineated the GTV on the CT alone, and then on PET-CT. The mean percentage volume change (MPVC) from the CT GTV (GTVCT) to the PET-CT GTV (GTVPET-CT) for the 3 oncologists for each given case was compared to the same volume change for the joint outlining TV, using the Wilcoxon signed ranks test (WSRT). A significant difference in MPVC from GTVCT to GTVPET-CT exists between the Oncologists (5.9%), and the Radiologist (-0.4%, p = 0.001) for the group as a whole. The MPVC for the radiotherapy alone subset was 25.4% for the Oncologists and 3.0% for the Radiologist (p = 0.002) and for the IC group the MPVCs were -1.6% and -6.1%, respectively (p=0.272). Volume changes from GTVCT to GTVPET-CT, were lower for the Radiologist than for the Oncologists. Oncologists outlining on PET-CT may include elements of respiratory motion, not included by the Radiologist. Guidelines are needed to standardize the use of PET-CT for TV delineation in RTP. It is important that TV delineation utilizes the expertise of a PET Radiologist.

The acquisition of radiotherapy planning scans on positron emission tomography (PET)-CT scanners requires the involvement of radiotherapy radiographers. This study assessed the radiation dose received by these radiographers during this process. Radiotherapy planning (18)F-fluorodeoxyglucose ((18)F-FDG) PET-CT scans were acquired for 28 non-small cell lung cancer patients. In order to minimise the radiation dose received, a two-stage process was used in which the most time-consuming part of the set-up was performed before the patient received their (18)F-FDG injection. Throughout this process, the radiographers wore electronic personal dosemeters and recorded the doses received at different stages of the process. The mean total radiation dose received by a radiotherapy radiographer was 5.1+/-2.6 microSv per patient. The use of the two-stage process reduced the time spent in close proximity to the patient by approximately a factor of four. The two-stage process was effective in keeping radiation dose to a minimum. The use of a pre-injection set-up session reduces the radiation dose to the radiotherapy radiographers because of their involvement in PET-CT radiotherapy treatment planning scans by approximately a factor of three.

Despite the recent technological improvements in the delivery of radiotherapy (RT) in Non-small cell lung cancer (NSCLC), local recurrence rates and survival remains poor. Geographic miss may be one explanation for these poor outcomes. Positron Emission Tomography (PET) has been shown to improve to be superior and complementary to computerized tomography (CT) in the staging of NSCLC. When used to inform RT planning volumes it has also been shown to have a significant effect, though this is mainly through up or down staging. The impact of using PET-CT data in the RT planning process for fully PET staged patients has yet to be widely evaluated. We seek to investigate the effect of using PET-CT information in patients already PET-CT staged. From March 2005 to June 2007, 28 patients with pathologically confirmed NSCLC were enrolled in a PET-CT treatment planning study. All patients had a staging PET-CT scan prior to consent to ensure they were suitable for radical radiotherapy. 14 patients received induction chemotherapy. In place of a planning radiotherapy CT scan, patients went on to be scanned on a GE Discovery LS PET-CT scanner. All patients were treated based on their CT scan volumes. In a virtual planning study, 4 radiation oncologists independently delineated the GTV on the CT images alone, and then on the Fused PET-CT images. The oncologists had access to a complete set of diagnostic and clinical information for each patient including the staging PET-CT images. In-house software was used to compare the GTVs outlined. The 112 sets of GTVs created on the fused dataset where compared with CT GTVs and assessed using concordance index (CI) as measure of correlation of volume. 58% of cases had CIs comparing CT-GTV and FUSED-GTV of less than 0.75, indicating a sizeable alteration in volume with use of the PET data in RT planning. 46% of all 112 treatment plans had CIs of less than 0.60. The mean CI was 0.63 (SD 0.17) for all sets. 45% of the RT alone group and 48% of the induction chemotherapy group had CIs for the CT to FUSED comparison of less than 0.60. There was no difference for the size of the effect in either the RT alone group (mean CI = 0.62, n = 56) or the induction chemotherapy group (mean CI = 0.63, n = 56) with a 2 tailed T-Test demonstrating no significant difference in the means of 2 groups (p = 0.682). The degree of modification of RT GTVs by use of a planning PET-CT scan in an already PET staged patient population is surprising and suggests that PET-CT aids the RT planning process in addition to its role in baseline staging. The optimal use of PET-CT in RT planning for NSCLC and its precise role remain unclear and further investigation is required before its use in routine clinical practice.

A method is proposed to synchronize positron emission tomography (PET) list-mode data with an externally recorded respiratory signal in the absence of a master clock. When the respiratory signal reaches a user-defined threshold, a trigger mark is stored in the list-mode file. After the acquisition, synchronization is achieved when the stored trigger marks are superimposed on the respiratory curve to form a horizontal line over time at the user-defined threshold. Synchronization was possible and unequivocal for ten out of ten clinical studies. The list-mode acquisition actually started approximately 40 and 4 s after acquisition initiation at the user interface of the Philips Gemini and the GE DLS PET-CT systems, respectively.

1Medical Physics, Northern Ireland Cancer Centre, Belfast City Hospital 2Medical Physics, Royal Victoria Hospital, Belfast, UK British Nuclear Medicine Society Oral and Poster Abstracts 2007

Carson, K.J.1; Fleming, L.2; Cosgrove, V.P.3; Jarritt, P.H.1; Hounsell, A.R.3 Author Information

Carson, K.J.; Cosgrove, V.P.; Zatari, A.; Eakin, R.; Clarke, J.C.; Stewart, D.P.; McAleese, J.; Fleming, L.; Hounsell, A.R.; Jarritt, P.H. Author Information

The introduction of functional data into the radiotherapy treatment planning process is currently the focus of significant commercial, technical, scientific and clinical development. The potential of such data from positron emission tomography (PET) was recognized at an early stage and was integrated into the radiotherapy treatment planning process through the use of image fusion software. The combination of PET and CT in a single system (PET/CT) to form an inherently fused anatomical and functional dataset has provided an imaging modality which could be used as the prime tool in the delineation of tumour volumes and the preparation of patient treatment plans, especially when integrated with virtual simulation. PET imaging typically using 18F-Fluorodeoxyglucose (18F-FDG) can provide data on metabolically active tumour volumes. These functional data have the potential to modify treatment volumes and to guide treatment delivery to cells with particular metabolic characteristics. This paper reviews the current status of the integration of PET and PET/CT data into the radiotherapy treatment process. Consideration is given to the requirements of PET/CT data acquisition with reference to patient positioning aids and the limitations imposed by the PET/CT system. It also reviews the approaches being taken to the definition of functional/tumour volumes and the mechanisms available to measure and include physiological motion into the imaging process. The use of PET data must be based upon a clear understanding of the interpretation and limitations of the functional signal. Protocols for the implementation of this development remain to be defined, and outcomes data based upon clinical trials are still awaited.