Differences in the definition of internal target volumes using slow CT alone or in combination with thin-slice CT under breath-holding conditions during the planning of stereotactic radiotherapy for lung cancer

PurposeTo investigate how the delineations of the internal target volume (ITV) made from ‘slow’ CT alter with reference to ‘thin-slice’ CT.Materials and methodsThin-slice CT images taken under breath-holding conditions and slow CT images taken under shallow-breathing conditions (8 s/image) of 11 lung cancers were used for this study. Five radiation oncologists delineated ITV of the 11 lesions using slow CT images (ITV1), and then redefined them with reference to thin-slice CT images (ITV2). SD-images (standard deviation image) were created for all patients from ITV images in order to visualize the regional variation of the ITVs.ResultsThe mean value of ITV2 was smaller than that initially defined by ITV1. There was no significant change in ITV1 and ITV2 between operators with regard to standard deviation in volume. There was a significant difference in the distribution of the ratio of ITV1 to ITV2 obtained on thin-slice CTs between cases with and without ground glass opacity. In cases without ground glass opacity there was a tendency for ITV2 to have a smaller volume than ITV1.ConclusionsCombined use of slow CT and thin-slice CT in delineation of ITV contours appeared to be useful in making adjustments for obscured tumor images caused by respiratory movement.     

Dynamics of tumor hypoxia assessed by 18F-FAZA PET/CT in head and neck and lung cancer patients during chemoradiation: Possible implications for radiotherapy treatment planning strategies

IntroductionTo define the optimal time point for the integration of hypoxia ¹⁸F-FAZA-PET/CT information into radiotherapy treatment planning to benefit from hypoxia modification or dose escalation treatment. Therefore, we performed a prospective cohort study, using serial hypoxic imaging (¹⁸F-FAZA-PET/CT) prior to and at several time-points during (chemo)radiotherapy (CHRT) in six head and neck squamous cell (HNSCC) and six non-small cell lung cancer (NSCLC) patients.MethodsThe spatio-temporal dynamics of tumor hypoxia and fractional hypoxic volumes (FHV) were evaluated using a voxel-by-voxel analysis based on a ¹⁸F-FAZA-T/B ratio of 1.4 at four time points in HNSCC patients, at baseline (FAZA-BL), at week one (FAZA-W1), two (FAZA-W2), and four (FAZA-W4) during CHRT and at three time points in NSCLC patients (baseline; W2, W4).ResultsTen out of twelve patients showed a substantial pre-treatment tumor hypoxia representing a FHV ⩾ 1.4 assessed by ¹⁸F-FAZA-PET/CT. The median FHV was 38% (FAZA-BL), 15% (FAZA-W1), 17% (FAZA-W2) and 1.5% (FAZA-W4) in HNSCC patients, and 34% (FAZA-BL), 26% (FAZA-W2) and 26% (FAZA-W4) in NSCLC patients, respectively. Stable tumor hypoxia was observed in three HNSCC patients and two NSCLC patients at FAZA-W2. In three HNSCC patients and two NSCLC patients FHVs declined to non-detectable hypoxia levels at FAZA-W4 during CHRT, while two NSCLC patients, showed increasing FHVs.ConclusionOur results indicate that, instead of using the FAZA-BL scan as the basis for the dose escalation, FAZA-W2 of CHRT is most suitable and might provide a more reliable basis for the integration of ¹⁸F-FAZA-PET/CT information into radiotherapy treatment planning for hypoxia-directed dose escalation strategies.