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

Abstract

Background Dose 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 Methods For 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. Results We 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). Conclusion We 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.

Proton or Carbon Ion Therapy for Skull Base Chordoma: Rationale and First Analysis of a Mono-Institutional Experience

“…The dose constraint for the brainstem was D0.1cc at less than 40 Gy (RBE) [ 35 ]. Due to the different RBE model used (mMKM vs. LEM), these doses would correspond in our center to a prescription of 68.8 Gy (RBE) and a constraint for the brainstem of 46 Gy (RBE) [ 36 ].…”

Dose–volume constraints for head‐and‐neck cancer in carbon ion radiotherapy: A literature review

“…The LEM is used at European and Chinese institutions. The models are different with regard to their physical and mathematical assumptions and consider different endpoints 11 . Recent articles have already reported LEM‐based dose–volume constraints that are currently being used at European facilities 11,16 .…”

“…10 This implies that the same constraints as X-ray intensity-modulated radiotherapy (IMRT) can be used for proton therapy. 11 In CIRT, the RBE models are more complex compared with the constant scaling factor used in proton therapy. Currently, three RBE models are used in clinical practice: the mixed-beam model, the modified microdosimetric kinetic model (MKM), which is an update of the mixedbeam model, and the local effect model (LEM).…”

“…11 Recent articles have already reported LEM-based dose-volume constraints that are currently being used at European facilities. 11,16 One study also reported constraints based on the Japanese RBE models; however, the complications considered were very few. 11 Previous studies have associated various constraints with OAR complications related to the HN cancer CIRT.…”

“…11,16 One study also reported constraints based on the Japanese RBE models; however, the complications considered were very few. 11 Previous studies have associated various constraints with OAR complications related to the HN cancer CIRT. 2,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] This review provides an extensive list of constraints for HN cancer CIRT based on the Japanese RBE models.…”