Context: Little accurate information is available regarding the risk of hypopituitarism after irradiation of skull base meningiomas.Design: Retrospective study in a single centre.Patients: 48 patients with a skull base meningioma and normal pituitary function at diagnosis, treated with radiotherapy (RXT) between 1998 and 2017 (median followup of 90 months). Measurements:The GH, TSH, LH/FSH and ACTH hormonal axes were evaluated yearly for the entire follow-up period. Mean doses delivered to the pituitary gland (PitD) and the hypothalamus (HypoD) were calculated, as well as the doses responsible for the development of deficits in 50% of patients after 5 years (TD50).Results: At least one hormone deficit was observed in 38% of irradiated patients and complete hypopituitarism in 13%. The GH (35%), TSH (32%) and LH/FSH axes (28%) were the most frequently affected, while ACTH secretion axis was less altered (13%).The risk of hypopituitarism was independently related to planning target volume (PTV) and to the PitD (threshold dose 45 Gy; TD50 between 50 and 54 Gy). In this series, the risk was less influenced by the HypoD, increasing steadily between doses of 15 and 70 Gy with no clear-cut dose threshold.Conclusions: Over a median follow-up period of 7.5 years, hypopituitarism occurred in more than one third of patients irradiated for a skull base meningioma, and this prevalence was time-and dose-dependent. In this setting, the risk of developing hypopituitarism was mainly determined by the irradiated target volume and by the dose delivered to the pituitary gland.

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Background and Purpose: There are several alternatives to the widespread ITV strategy in order to account for breathing-induced motion in PTV margins. The most sophisticated one includes the generation of a motion-compensated CT scan with the CTV placed in its average position -the midposition approach (MidP). In such configuration, PTV margins integrate breathing as another random error. Despite overall irradiated volume reduction, such approach is barely used in clinical practice because of its dependence to deformable registration and its unavailability in commercial treatment planning systems. As an alternative, the mid-ventilation approach (MidV) selects the phase in the 4D-CT scan that is the closest to the MidP, with a residual error accounted for in the PTV margin. We propose a treatment planning system-integrated strategy, aiming at better approximating the MidP approach without its drawbacks: Hybrid MidV-MidP approach, i.e. the delineation on the MidV-CT and translation at the mid-position coordinates using treatment planning system built-in capabilities.Material and Methods: Forty-five lung lesions treated with stereotactic radiotherapy were selected. PTV was defined using MidP, MidV, Hybrid MidV-MidP and ITV strategies. Margin definitions were adapted and resulting PTVs were compared.Results: Hybrid MidV-MidP showed similar target volume and location than the MidP and confirmed that margin-incorporated tumor motion strategies lead to significantly smaller PTVs than the ITV with mean reduction of 26±7%. Conclusion:We report on the successful implementation of a pseudo-MidP solution without its inherent drawbacks. It answers the need for TPS-embedded tumor motion range identification and related margin's component calculation.

Kilovoltage intrafraction monitoring (KIM) is a method allowing to precisely infer the tumour trajectory based on cone beam computed tomography (CBCT) 2D-projections. However, its accuracy is deteriorated in the case of highly mobile tumours involving hysteresis. A first adaptation of KIM consisting of a prior amplitude based binning step has been developed in order to minimize the errors of the original model (phase-KIM). In this work, we propose enhanced methods (KIMsub-arc optim and phase-KIMsub-arc optim) to improve the accuracy of KIM and phase-KIM which relies on the selection of the optimal starting CBCT gantry angle. Aiming at demonstrating the interest of our approach, we carried out a simulation study and an experimental study: we compared the accuracy of the conventional versus sub-arc optim methods on simulated realistic tumour motions with amplitudes ranging from 5 to 30 mm in 1 mm increments. The same approach was performed using a lung dynamic phantom generating a 30 mm amplitude sinusoidal motion. The results show that for in-silico simulated motions of 10, 20 and 30 mm amplitude, the three-dimensional root mean square error (3D-RMSE) can be reduced by 0.67 mm, 0.91 mm, 0.94 mm and 0.18 mm, 0.25 mm, 0.28 mm using KIMsub-arc optim and phase-KIMsub-arc optim respectively. Considering all in-silico simulated trajectories, the percentage of errors larger than 1 mm decreases from 21.9% down to 1.6% for KIM (p < 0.001) and from 6.6% down to 1.2% for phase-KIM (p < 0.001). Experimentally, the 3D-RMSE is lowered by 0.5732 mm for KIM and by 0.1 mm for phase-KIM. The percentage of errors larger than 1 mm falls from 39.7% down to 18.5% for KIM and from 23.2% down to 11.1% for phase-KIM. In conclusion, our method efficiently anticipates CBCT gantry angles associated with a significantly better accuracy by using KIM and phase-KIM.