ESTRO 2021 Abstract Book

S9

ESTRO 2021

- J. R. Pérez-Sánchez et al. Neurologia 2020 GK – 13 pts (6-PD, 4 ET [essential tremor], 3 PD+ET) – 130 Gy, Unified Parkinson's disease rating scale (UDPRS) improvement after 1 year 71.3% and 60.3% at the end of FU - S.S. Raju et al. Stereotact Funct Neurosurg 2017 GK – 33 pts (PD) – 130-150 Gy, 93.9% of improvement (70% complete or nearly complete relief). In the last FU – 96.8% of responders. 6% of toxicity - C. Ohye et al. 2012 GK – 72 pts (59 PD, 13 ET) – 130 Gy, in 2 years of FU (53 pts) – 81.1% of improvement - A. Franzini et al. Acta Neurochir 2011 CK – 2 pts with unilateral DBS and contralateral SRS – both with tremor control Our results Material: 23 patients irradiated (3 F, 20 M). Duration of the disease before SRS - 60 to 192 months (med. 96). In 16 cases right and in 7 left side was dominant. 91% used levodopa (300-1800 mg/24 h, med. 700), 83% benserazide and 39% carbidopa. Beck’s Depression Inventory (BDI) before treatment varied from 3 to 39 points (med. 16) and UDPRS from 1 to 4 (mean 2.5). FU was 3 – 72.2 months (med. 27.9). Method: Every three patients were irradiated using CK with increasing dose (step 5 Gy) starting from 70 Gy to 105 Gy (only 2 pts were irradiated with 105 Gy – study was interrupted because of severe adverse event of one patient). The maximal dose for an internal capsule was 8-34 Gy (mean 23 Gy). Results: In the time of last control 73.3% of patients reported decrease, 13.3% stagnation and 13.3% increase of tremor. In responders group relief varied from 10 to 100% (med. 60). 35.7% reported subjective improvement, 21.4% stagnation and 42.9% worsening. In group with good answer an improvement was 10-60% (med. 30). In 39% of patients we noted new symptoms which could be related to treatment toxicity. During the last control 87% used levodopa, 47% benserazide and 47% carbidopa. BDI after 1 year ranged from 4 to 31 (med. 14.5) and UDPRS from 1to 3 (med. 2). There were no significant difference between UDRS and BDI scores before SRS and one year later. Conclusions: Published and our own data permit us to conclude that SRS for trigeminal neuralgia is safe and effective treatment modality. Indirect comparison of own result to published ones shows worse results after CK SRS of PD, what could be influenced by suboptimal treatment modality (?), lower dose or patients’ selection (mixed material in other publications and homogenous our PD group (ET patients respond better for SRS).

SP-0026 Primary and repeat radiosurgery for functioning and nonfunctioning pituitary adenoma G. Minniti Italy

Abstract not available

SP-0027 Can we treat epilepsy and obsessive-compulsive disorder with radiation? S. Sheth USA

Abstract not available

Symposium: Clinical implementation of in vivo dosimetry

SP-0028 Large scale clinical implementation of in vivo dosimetry - What value does it bring? E. Bossuyt 1 1 Iridium Netwerk, Medical Physics, Antwerp, Belgium Abstract Text In vivo dosimetry is recommended in radiotherapy to avoid major treatment errors and to improve accuracy. Large scale clinical implementation however is not always easy. Recently, commercially automated systems have made it feasible to perform transit dosimetric quality assurance on a very large scale. We started using such a system for all our machines and all our patients in 2018 using transit EPID images. We analyzed results in both 2019 and 2020 for more than 7000 patients in total, including causes and actions for failed fractions. Ten different sets of parameters for gamma analysis, depending on treatment site, were empirically determined, balancing the rate between detection of clinically relevant problems and the number of false positive results. The choice of tolerance levels was based on an AMARA-principle: the goal of detecting errors and deviations, but only As Many As Reasonably Achievable, taking into account economic and societal factors. In-vivo analysis in 2019 showed 16% of fractions failed, of which 6% were false positives and 10% were caused by patient related issues. The number of false positives depended on machine type. Causes for failed in-vivo analysis included deviations in patient positioning (4,9%) and anatomy change (4,3%). In addition, errors in planning, imaging, treatment delivery, simulation, breath hold and positioning devices were detected. Actions for failed fractions were mostly to repeat the measurement while taking extra care in positioning and to intensify imaging procedures. Four percent of failed fractions initiated plan adjustments, showing the potential of the system as a trigger for adaptive planning. Based on these in vivo results, some permanent actions were taken for improving quality, e.g. extra imaging for boost breast, extra education to the RTT’s and extra help from dietitians. When analyzing results in 2020, it was seen these actions had resulted in a reduction of failed fractions from 16% to 13%, including a drop from 4,9% to 3,0% in patient positioning deviations and a drop from 4,3% to 3,3% in anatomy changes. In conclusion, large scale clinical implementation of EPID-based in-vivo transit dosimetry using a commercially available automated system is feasible and it efficiently reveals a wide variety of deviations. Evaluating