M. Antoine

Use of FDG-PET to guide dose prescription heterogeneity in stereotactic body radiation therapy for lung cancers with volumetric modulated arc therapy: a feasibility study

BackgroundThe aim of this study was to assess if FDG-PET could guide dose prescription heterogeneity and decrease arbitrary location of hotspots in SBRT.MethodsFor three patients with stage I lung cancer, a CT-simulation and a FDG-PET were registered to define respectively the PTVCT and the biological target volume (BTV). Two plans involving volumetric modulated arc therapy (VMAT) and simultaneous integrated boost (SIB) were calculated. The first plan delivered 4 × 12 Gy within the PTVCT and the second plan, with SIB, 4 × 12 Gy and 13.8 Gy (115% of the prescribed dose) within the PTVCT and the BTV respectively. The Dmax-PTVCT had to be inferior to 60 Gy (125% of the prescribed dose). Plans were evaluated through the D95%, D99% and Dmax-PTVCT, the D2 cm, the R50% and R100% and the dice similarity coefficient (DSC) between the isodose 115% and BTV. DSC allows verifying the location of the 115% isodose (ideal value = 1).ResultsThe mean PTVCT and BTV were 36.7 (±12.5) and 6.5 (±2.2) cm3 respectively. Both plans led to similar target coverage, same doses to the OARs and equivalent fall-off of the dose outside the PTVCT. On the other hand, the location of hotspots, evaluated through the DSC, was improved for the SIB plans with a mean DSC of 0.31 and 0.45 for the first and the second plans respectively.ConclusionsUse of PET to decrease arbitrary location of hotspots is feasible with VMAT and SIB for lung cancer.

Doses aux organes à risque en radiothérapie conformationnelle et en radiothérapie stéréotaxique : les poumons

Radiation-induced lung disease (RILD) is common after radiation therapy and represents cornerstone toxicities after treatment of thoracic malignancies. From a review of literature, the objective of this article was to summarize clinical and non-clinical parameters associated with the risk of RILD in the settings of normo-fractionated radiotherapy and stereotactic body radiation therapy (SBRT). For the treatment of lung cancers with a normo-fractionated treatment, the mean lung dose (MLD) should be below 15-20Gy. For a thoracic SBRT, V20Gy<10% and MLD<6Gy are recommended. One should pay attention to central tumors and respect specific dose constraints to the bronchial tree. The recent technological improvements may represent an encouraging way to decrease lung toxicities. Finally, our team developed a calculator in order to predict the risk of radiation pneumonitis.

EP-1398: Acute gastro-intestinal toxicities after pre-operative tomotherapy for retroperitoneal liposarcoma

Material and Methods: From April 2009 to September 2013, 48 patients were included in a prospective multicenter study. Feasibility of tomotherapy, acute toxicities and local control at 3 years were the principal and secondary objectives. Inclusion criteria were operable, biopsy-proven, retroperitoneal liposarcoma. Patients with non-operable tumors validated after multi-disciplinary team evaluation, other histology or metastatic disease were excluded.Clinical Target Volume (CTV) and mains organs at risk (contralateral kidney, duodenum, bowel bag) were systematically delineated with the surgeon. Dose constraints to the bowel bag were defined as V45 Gy<33% and V30 Gy<50%. Surgery was planned 4 to 8 weeks after RT. Clinical visits were performed weekly during RT, before surgery, and 2 and 6 months after surgery. Toxicity was recorded according to CTCAE V4.0 scale.