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.

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.

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.; 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

Medical Physics, aBelvoir Park Hospital bRoyal Victoria Hospital, Belfast, UK Abstracts of the 34th Annual Meeting of the British Nuclear Medicine Society Manchester International Conference Centre, UK, 27–29 March 2006

The potential role of positron emission tomography (PET) in radiotherapy still requires careful evaluation as it becomes increasingly integrated into the radiotherapy planning process. Diagnosis and subsequent radiotherapy planning based solely upon X-ray CT are known to be less sensitive and specific for disease than PET imaging in non-small cell lung cancer. The CT images may not demonstrate the true extent of intrathoracic disease. To overcome this limitation, the direct use of combined PET/CT image data in the treatment planning process has been investigated. A small pilot study of five patients was carried out at the Royal Victoria Hospital, Belfast, following the installation of a GE Discovery LS PET/CT scanner. The initial aims were to investigate the system and to make preliminary clinical evaluations. The key issues that were addressed included: verification of PET/CT alignment, patient position and reproducibility for imaging and treatment; verification of CT numbers on the PET/CT systems for dose calculation, integrity of data transfer; radiation protection of staff, protocols for target volume delineation, and the implications for physiologically-gated PET and CT acquisitions. This paper reviews our practical experience, and technical problems are described.