S382
Clinical - CNS
ESTRO 2026
Conclusion: Routine screening for radiotherapy-induced
hypopituitarism appears unnecessary in adult brain tumour survivors who received low pituitary radiation doses (<30 Gy) and are not candidates for growth hormone replacement. Keywords: Glioma, radiotherapy, hypopituitarism Digital Poster 3637 SRS for Vestibular Schwannoma: Impact of Treatment Time Differences on the Biologically Effective Dose - Gamma Knife, Cyberknife and Truebeam Compared Matt Skinner 1 , Lauren Weinstein 1 , Ian Paddick 2 1 Radiation Oncology, Kaiser Permanente, South San Francisco, USA. 2 Queen Square Radiosurgery Centre, National Hospital for Neurology and Neurosurgery, London, United Kingdom
Results: The prevalence of GH deficiency was low dose 35%, middle dose 30% and high dose 78%. Gonadotropin, adrenocorticotrophic hormone (ACTH) and thyroid stimulating hormone (TSH) deficiency did not arise in the low dose group. Gonadotropin deficiency were 3% of middle dose group and 18% of high dose group. ACTH deficiency occurred in 16% of the middle dose group and 15% of the high dose group. TSH deficiencies were 3% of the middle dose group and 14% of the high dose group. A composite of gonadotropin, ACTH and TSH deficiency occurred in 0, 17 and 23% in the low, middle and high dose groups, respectively. Panhypopituitarism was only observed in the high dose group (n=3/40, 8%). Pituitary radiation dose thresholds (lowest dose at which specific hormone deficits occurred) were GH axis >12.2Gy, gonadotropin axis >37.1Gy, ACTH axis >36.9 Gy and thyroid axis >43.4Gy.
Purpose/Objective: Many Gamma Knife (GK) studies suggest that
biological effective dose (BED) better predicts clinical outcomes than physical dose1,2. BED increases with faster treatment times as sub-lethal damage repair, ignored by the linear-quadratic (LQ) model, is reduced. However, little data exists that compares BED in stereotactic radiosurgery (SRS) between GK, where
many SRS doses originate, and faster linear accelerators. We illustrate the importance of
considering treatment duration when prescribing SRS for vestibular schwannoma (VS) and demonstrate how reduction of BED can be achieved through physical dose and PTV margin modification Material/Methods: 1031 VS patients were treated between 2001 and 2025 with GK Model B (219), Perfexion (344), Cyberknife VSI (193), or Truebeam (VMAT 169, DCA 106) with one- (813) or multiple- (218) fraction regimens of 11/1, 12/1, 12.5/1, 13/1, 14/1Gy, 18/3, 25/5, or 27.5/5Gy. Truebeam used GTV-to-PTV margins of 0(206), 0.5(45) or 1mm(35). GK and CK didn’t use margins. Total treatment and beam-on times for each patient were collected to calculate BEDs with Jones’ A9 formalism3. Radiobiological parameters used were α / β =2.47Gy and
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