A feasibility study on adaptive 18F-FDG-PET-guided radiotherapy for recurrent and second primary head and neck cancer in the previously irradiated territory.

PURPOSE: To evaluate feasibility, disease control, survival, and toxicity after adaptive 18F-fluorodeoxyglucose (FDG) positron emisson tomography (PET) guided radiotherapy in patients with recurrent and second primary head and neck squamous cell carcinoma. METHODS: A prospective trial investigated the feasibility of adaptive intensity modulated radiotherapy (IMRT) ± concomitant cetuximab in 10 patients. The primary endpoint was achieving a 2-year survival free of grade >3 toxicity in ≥30% of patients. Three treatment plans based on 3 PET/CT scans were consecutively delivered in 6 weeks. The range of dose painting was 66.0-85.0 Gy in the dose-painted tumoral volumes in 30 fractions. RESULTS: Two-year locoregional and distant control rates were 38 and 76%, respectively. Overall and disease-free survival at 2 years was 20%. No grade 4 or 5 acute toxicity was observed in any of the patients, except for arterial mucosal hemorrhage in 1 patient. Three months after radiotherapy, grade 4 dysphagia and mucosal wound healing problems were observed in 1/7 and 1/6 of patients, respectively. Grade 5 toxicity (fatal bleeding) was seen in 2 patients, at 3.8 and 4.1 months of follow-up. Data on 2­year toxicity could only be assessed in 1 of the 2 surviving patients, in whom grade 4 mucosal wound healing problems were observed; no other grade >3 toxicity was observed. In this respect, a 30% 2­year survival free of grade >3 toxicity will not be achieved. CONCLUSIONS: Adaptive PET-guided reirradiation is feasible. However, due to slow accrual and treatment results that seemed inconsistent with achieving the primary endpoint, the trial was stopped early.

Evaluation of uncertainty-based stopping criteria for monte carlo calculations of intensity-modulated radiotherapy and arc therapy patient dose distributions.

PURPOSE: To formulate uncertainty-based stopping criteria for Monte Carlo (MC) calculations of intensity-modulated radiotherapy and intensity-modulated arc therapy patient dose distributions and evaluate their influence on MC simulation times and dose characteristics. METHODS AND MATERIALS: For each structure of interest, stopping criteria were formulated as follows: sigma(rel) or=95% of the voxels, where sigma(rel) represents the relative statistical uncertainty on the estimated dose, D. The tolerated uncertainty (sigma(rel,tol)) was 2%. The dose limit (D(lim)) equaled the planning target volume (PTV) prescription dose or a dose value related to the organ at risk (OAR) planning constraints. An intensity-modulated radiotherapy-lung, intensity-modulated radiotherapy-ethmoid sinus, and intensity-modulated arc therapy-rectum patient case were studied. The PTV-stopping criteria-based calculations were compared with the PTV+OAR-stopping criteria-based calculations. RESULTS: The MC dose distributions complied with the PTV-stopping criteria after 14% (lung), 21% (ethmoid), and 12% (rectum) of the simulation times of a 100 million histories reference calculation, and increased to 29%, 44%, and 51%, respectively, by the addition of the OAR-stopping criteria. Dose-volume histograms corresponding to the PTV-stopping criteria, PTV+OAR-stopping criteria, and reference dose calculations were indiscernible. The median local dose differences between the PTV-stopping criteria and the reference calculations amounted to 1.4% (lung), 2.1% (ethmoid), and 2.5% (rectum). CONCLUSIONS: For the patient cases studied, the MC calculations using PTV-stopping criteria only allowed accurate treatment plan evaluation. The proposed stopping criteria provided a flexible tool to assist MC patient dose calculations. The structures of interest and appropriate values of sigma(rel,tol) and D(lim) should be selected for each patient individually according to the clinical treatment planning goals.