ESTRO 38performed.Table 1 summarizes the results obtained in terms of: number of CBCT acquired (#CBCT), number of CBCT/TPCT registrations (#REG) and threshold below which the agreement between the observers was 90% and 95% (Threshold_mm95% and Threshold_mm90%).The prostate patient had the largest threshold values, but always inferior to the planning target (PTV) margin and only 4% of the 713 differences evaluated were above the 5 mm or 7mm PTV margins used in the clinical routine for the respective VMAT treatment paradigms.

Background and purpose: With the advent of automatic treatment planning options like Pinnacle's Autoplanning (PAP), the challenge arises how to assess the quality of a plan that no dosimetrist did work on. The aim of this study was to assess plan quality consistency of PAP prostate cancer patients in clinical practice. Materials and methods: 100 prostate cancer patients were included from NKI and 129 from RadboudUMC (RUMC). Per institute a previously developed [1] treatment planning QA model, based on overlap volume histograms, was trained on PAP plans to predict achievable dose metrics which were then compared to the clinical PAP plans. A threshold of 3 Gy (DVH dose parameters)/3% (DVH volume parameters) was used to detect outliers. For the outlier plans, the PAP technique was adjusted with the aim of meeting the threshold. Results: The average difference between the prediction and the clinically achieved value was < 0.5 Gy (mean dose parameters) and < 1.2% (volume parameters), with standard deviation of 1.9 Gy/1.5% respectively. We found 8% (NKI)/25% (RUMC) of patients to exceed the 3 Gy/3% threshold, with deviations up to 6.7 Gy (mean dose rectum) and 6% (rectal wall V64Gy). In all cases the plans could be improved to fall within the thresholds, without compromising the other dose metrics. Conclusion: Independent treatment planning QA was used successfully to assess the quality of clinical PAP in a multi-institutional setting. Respectively 8% and 25% suboptimal clinical PAP plans were detected that all could be improved with replanning. Therefore we recommend the use of independent treatment plan QA in combination with PAP for prostate cancer patients. (C) 2018 Elsevier B.V. All rights reserved.

________________________________________________________________________________plan into two stages was performed for radiobiological reasons.Planning goals were D98>95% and Dmax<110% for the PTVs with maximum OAR sparing.The plans were analyzed for planning time efficiency (hands-on time of the planner and total planning time) and the sum of stage 1 and stage 2 was tested against our clinical DVH constraints for OARs.

Purpose or Objective: To evaluate the dosimetric effect of placing the isocenter away from the planning target volume on intensity-modulated radiosurgery (IMRS) plans to treat brain lesions.Material and Methods: Fifteen patients, who received cranial IMRS at our institution, were randomly selected.Each patient

_____________________________________________________________________________________________________equally spaced beams with total of 35 segments.Step-andshoot IMRT with minimum segment area of 5x5 cm and minimum of 10 monitor units per segment was used in each plan.Dvh and Energy plans were normalized such that 95% of the propagated PTV for each phase received the prescription dose.Once prescription was achieved, the doses to OARs, such as spinal cord, heart, esophagus, and healthy lungs were iteratively lowered until standard deviation of the dose across the PTV in each plan became less than 4%.After generating Dvh and Energy plans for each breathing phase, deformable dose accumulation to the reference breading phase for each optimization scheme was performed.The resulting 4D Dvh and Energy plans were compared on the basis of dose indices (DIs), such as DPTV95% (dose to 95% of the PTV), DCord1%, Desophagus50%, Dheart33%, Dlungs20%, Dlungs30%, and volume indices (VIs) such as Vlungs2000 cGy, and Vlungs3000 cGy.The differences among the DIs and the VIs were subjected to a two-tailed paired t-test to determine the statistically significant dose differences (p < 0.05).In addition, total deposited energy in the irradiated volume was assessed. Results:The table summarizes statistically significant differences over all quantities.On average the DIs and the VIs from the 4D Energy optimization are lower than the indices obtained with the 4D Dvh optimization.The total energy deposited in the entire irradiated volume outside of the target was lower for all Energy optimized 4D plans with statistically significant difference of 13% as compared to the 4D Dvh plans. Conclusion:In this work time-resolved treatment planning optimization schemes in NSCLC were investigated.The results reveal that 4D Energy based optimization outperforms 4D Dvh based optimization in terms of OAR sparing.For comparable target coverage 4D Energy based plans resulted in statistically significant lower OAR doses ranging from 14% to almost 50%.