Abstract
PurposeProton therapy (PT) can be a good option to achieve tumor control while reducing the probability of radiation induced toxicities compared to X-ray-based radiotherapy. However, there are still uncertainties about the effects of PT on the organs in direct contact with the irradiated volume. The aim of this prospective series was to report 6-month follow-up of clinical and functional optic neuropathy rates of patients treated by proton therapy using a standardized comprehensive optic examination.Methods and MaterialsStandardized ophthalmological examinations were performed to analyze subclinical anomalies in a systematic way before treatment and 6 months after the end of proton therapy with: Automatic visual field, Visual evoked potential (VEP) and optic coherence of tomography (OCT).ResultsFrom October 2018 to July 2020 we analyzed 81 eyes. No significant differences were found in the analysis of the clinical examination of visual functions by the radiation oncologist. However, considering VEP, the impairment was statistically significant for both fibers explored at 30’angle (p:0.007) and 60’angle (p <0.001). In patients with toxicity, the distance of the target volume from the optical pathways was more important with a p-value for 30’VEP at 0.035 and for 60’VEP at 0.039.ConclusionsThese results confirm uncertainties concerning relative biological effectiveness of proton therapy, linear energy transfer appears to be more inhomogeneous especially in areas close to the target volumes. The follow-up of patients after proton therapy is not an easy process to set up but it is necessary to improve our knowledges about the biological effects of proton therapy in real life. Our study which will continue during the coming years, suggests that follow-up with in-depth examinations such as VEP as a biomarker could improve the detection of early abnormalities.
Highlights
The treatment of skull base tumors often relies on surgery and radiotherapy [1, 2]
An information letter is sent to each patient informing them that data from patients treated with proton therapy in Caen were related to clinical research
Patients were referred from multiple institutions but all were treated at the Normandy proton therapy center (Caen, France) and underwent optic examinations at the University hospital of Caen
Summary
The treatment of skull base tumors often relies on surgery and radiotherapy [1, 2]. The delivery of a high dose to the tumor nearby organs at risk (OAR) such as optic nerves and chiasma can be challenging. The advantageous dose distribution of proton may be used to spare OARs located close to the tumor [11,12,13] and to spare healthy brain In such cases, the aim of proton therapy (PT) is to achieve tumor control while reducing the probability of radiation induced toxicities compared to modern X-ray-based radiotherapy (RT), such as intensity modulated radiation therapy (IMRT) or stereotactic radiation therapy (SRT). Proton therapy series report a 7% risk to develop severe optic neuropathy [15] These rates may be underestimated because data are generally based on patient’s spontaneous reporting instead of systematic and standardized collection. These optic toxicities do not appear to follow the previously established dose volume effects for optic neuropathy, based on photons irradiation (X-rays). At the populational scale could be to contribute to improve biomathematical modelling for outcome predictions, and treatment planning optimization, for safer treatments
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