X. Geets

Evolution of [18F]fluorodeoxyglucose and [18F]fluoroazomycin arabinoside PET uptake distributions in lung tumours during radiation therapy

Abstract Background: Dose painting (DP) aims to improve radiation therapy (RT) outcome by targeting radioresistant tumour regions identified through functional imaging, e.g., positron emission tomography (PET). Importantly, the expected benefit of DP relies on the ability of PET imaging to identify tumour areas which could be consistently targeted throughout the treatment. In this study, we analysed the spatial stability of two potential DP targets in lung cancer patients undergoing RT: the tumour burden surrogate [18F]fluorodeoxyglucose (FDG) and the hypoxia surrogate [18F]fluoroazomycin arabinoside (FAZA). Materials and methods: Thirteen patients with unresectable lung tumours underwent FDG and FAZA 4D-PET/CT before (pre), and during the second (w2) and third (w3) weeks of RT. All PET/CT were reconstructed in their time-averaged midposition (MidP) for further analysis. The metabolic tumour volume (MTV: FDG standardised uptake value (SUV) > 50% SUVmax) and the hypoxic volume (HV: FAZA SUV >1.4) were delineated within the gross tumour volume (GTVCT). The stability of FDG and FAZA PET uptake distributions during RT was subsequently assessed through volume-overlap analysis and voxel-based correlation analysis. Results: The volume-overlap analysis yielded median overlapping fraction (OF) of 0.86 between MTVpre and MTVw2 and 0.82 between MTVpre and MTVw3. In patients with a detectable HV, median OF was 0.82 between HVpre and HVw2 and 0.90 between HVpre and HVw3. The voxel-based correlation analysis yielded median Spearman’s correlation coefficient (rS) of 0.87 between FDGpre and FDGw2 and 0.83 between FDGpre and FDGw3. Median rS was 0.78 between FAZApre and FAZAw2 and 0.79 between FAZApre and FAZAw3. Conclusions: FDG and FAZA PET uptake distributions were spatially stable during the 3 first weeks of RT in patients with unresectable lung cancer, both based on volume- and voxel-based indicators. This might allow for a consistent targeting of high FDG or FAZA PET uptake regions as part of a DP strategy.

Metabolic imaging in non-small-cell lung cancer radiotherapy

Metabolic imaging by positrons emission tomography (PET) offers new perspectives in the field of non-small-cell lung cancer radiation therapy. First, it can be used to refine the way nodal and primary tumour target volumes are selected and delineated, in better agreement with the underlying tumour reality. In addition, the non-invasive spatiotemporal mapping of the tumour biology and the organs at risk function might be further used to steer radiation dose distribution. Delivering higher dose to low responsive tumour area, in a way that better preserves the normal tissue function, should thus reconcile the tumour radiobiological imperatives (maximising tumour local control) with dose related to the treatment safety (minimising late toxicity). By predicting response early in the course of radiation therapy, PET may also participate to better select patients who are believed to benefit most from treatment intensification. Altogether, these technological advances open avenues to in-depth modify the way the treatment plan is designed and the dose is delivered, in better accordance with the radiobiology of individual solid cancers and normal tissues.

Correlation analysis of [18F]fluorodeoxyglucose and [18F]fluoroazomycin arabinoside uptake distributions in lung tumours during radiation therapy

Abstract Background: PET-guided dose painting (DP) aims to target radioresistant tumour regions in order to improve radiotherapy (RT) outcome. Besides the well-known [18F]fluorodeoxyglucose (FDG), the hypoxia positron emission tomography (PET) tracer [18F]fluoroazomycin arabinoside (FAZA) could provide further useful information to guide the radiation dose prescription. In this study, we compare the spatial distributions of FDG and FAZA PET uptakes in lung tumours. Material and methods: Fourteen patients with unresectable lung cancer underwent FDG and FAZA 4D-PET/CT on consecutive days at three time-points: prior to RT (pre), and during the second (w2), and the third (w3) weeks of RT. All PET/CT were reconstructed in their time-averaged midposition (MidP). The metabolic tumour volume (MTV: FDG standardised uptake value (SUV) > 50% SUVmax), and the hypoxic volume (HV: FAZA SUV > 1.4) were delineated within the gross tumour volume (GTVCT). FDG and FAZA intratumoral PET uptake distributions were subsequently pairwise compared, using both volume-, and voxel-based analyses. Results: Volume-based analysis showed large overlap between MTV and HV: median overlapping fraction was 0.90, 0.94 and 0.94, at the pre, w2 and w3 time-points, respectively. Voxel-wise analysis between FDG and FAZA intratumoral PET uptake distributions showed high correlation: median Spearman’s rank correlation coefficient was 0.76, 0.77 and 0.76, at the pre, w2 and w3 time-points, respectively. Interestingly, tumours with high FAZA uptake tended to show more similarity between FDG and FAZA intratumoral uptake distributions than those with low FAZA uptake. Conclusions: In unresectable lung carcinomas, FDG and FAZA PET uptake distributions displayed unexpectedly strong similarity, despite the distinct pathways targeted by these tracers. Hypoxia PET with FAZA brought very little added value over FDG from the perspective of DP in this population.

PO-0787: CT-based geometric dose escalation as an alternative to PET-based dose painting by numbers

PO-0786 Can we derive the radiation target volume for moving lesions from 3D-PET? E.G.C. Troost, L. Kuder, M. Mix, C. Doll, V. Duncker-Rohr, F. Momm, A.L. Grosu, U. Nestle MAASTRO Clinic, Radiation Oncology, Maastricht, The Netherlands University Hospital Freiburg, Radiation Oncology, Freiburg, Germany University Hospital Freiburg, Nuclear Medicine, Freiburg, Germany Ortenau Klinikum Offenburg, Radiation Oncology, Offenburg, Germany

La moderna radioterapia: verso la radioterapia adattativa guidata da immagini biologiche

Il fine ultimo della radioterapia (RT) e l’eradicazione della totalita delle cellule tumorali clonogeniche (cellule staminali), con contenimento del danno ai tessuti irradiati entro livelli accettabili. A tale scopo le recenti innovazioni nell’ambito delle tecniche di radioterapia si sono tradotte in un miglioramento nella selezione e nel contornamento dei volumi di interesse e nella messa a punto di piani di trattamento per l’ottimizzazione del calcolo delle dosi. Inoltre, si e aggiunta la disponibilita di nuovi macchinari dotati di congegni per l’acquisizione di immagini e controllati da computer molto veloci, che consentono una maggiore precisione nell’erogazione delle dosi. I trattamenti convenzionali sono stati sostituiti da tecniche di radioterapia altamente conformazionale, quali la radioterapia a intensita modulata (IMRT) e la terapia ad arco con modulazione d’intensita (IMAT), che consentono di individualizzare la distribuzione della dose rispetto all’esatta morfologia del tumore, con un migliore risparmio dei tessuti sani e degli organi a rischio circostanti.