Carbon Ion Dose Constraints in the Head and Neck and Skull Base: Review of MedAustron Institutional Protocols.

Piero Fossati,Ana Perpar,Eugen B. Hug,Markus Stock,Petra Georg,Antonio Carlino,Joanna Gora,Giovanna Martino

doi:10.14338/ijpt-20-00093.1

Abstract

BackgroundDose constraints are of paramount importance for the outcome of any radiotherapy treatment. In this article, we report dose-volume constraints as well as currently used fractionation schedules for carbon ion radiotherapy as applied in MedAustron (Wiener Neustadt, Austria).Materials and MethodsFor fractionation schedules, both German and Japanese regimes were used. From the clinical experience of National Institute of Radiological Sciences (Chiba, Japan) and Heidelberg Ion Therapy (Heidelberg, Germany; formerly GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany) and the work by colleagues in Centro Nazionale Adroterapia Oncologica (Pavia, Italy) recalculating the dose from the microdosimetric kinetic model to the local effect model, we have set the dose constraints for critical organs of the head and neck area. Where no clinical data was available, an educated guess was made, based on data available from photon and proton series.ResultsWe report the constraints for the optic nerve and chiasm, brainstem, spinal cord, cochlea, brain parenchyma, salivary gland, eye and adnexa, and mandibular/maxillary bone; constraints are grouped based on a fractionation scheme (German versus Japanese) and the risk of toxicity (safe, low to middle, and middle to high).ConclusionWe think validation of dose constraints should present a relevant part of the activity of any carbon ion radiotherapy facility, and we anticipate future multicentric, joint evaluations.

Highlights

Dose constraints to the organs at risk (OARs) are of paramount importance for the outcome of any radiotherapy (RT) treatment
The group from GSI/Heidelberg Ion Therapy (HIT) in Germany has reported on 59 patients treated for skull base chordoma and chondrosarcoma with Carbon ion RT (CIRT) with a dose per fraction between 3 and 3.5 Gy Gy relative biological effectiveness (RBE) (LEM) [44]
Future developments should depend on 3 main activities: (1) extending and validating institutional dose constraints by formally analyzing observed clinical toxicity, (2) pooling multi-institutional data to increase statistical power and further validating the RBE conversion method, and (3) interacting with the QUANTEC community to discuss the possibility of a carbon-ion subsection in the planned QUANTEC revision

Summary

Introduction

Dose constraints to the organs at risk (OARs) are of paramount importance for the outcome of any radiotherapy (RT) treatment. At MedAustron, we use dose constraints that are derived from clinical practice and extrapolation from low-LET data (Table 5) Those constraints are more conservative than the constraints reported by colleagues from HIT in the ICRU report [9], but in our experience, they are relatively easy to fulfill, at least on one side, without compromising target coverage. The group from GSI/HIT in Germany has reported on 59 patients treated for skull base chordoma and chondrosarcoma with CIRT with a dose per fraction between 3 and 3.5 Gy RBE (LEM) [44]. Patients receiving high-dose CIRT for head and neck cancer had a high risk of developing radiologic findings consistent with necrosis. We extrapolated the MKM/LEM conversion from analogous cases and used more-conservative values for the teeth-bearing portion of the bone (Table 9)

Findings

Discussion

Conclusion