Optic nerve constraints for carbon ion RT at CNAO - Reporting and relating outcome to European and Japanese RBE

Jon Espen Dale; Silvia Molinelli; Viviana Vitolo; Barbara Vischioni; Maria Bonora; Giuseppe Magro; Helge Egil Seime Pettersen; Andrea Mairani; Azusa Hasegawa; Olav Dahl; Francesca Valvo; Piero Fossati

doi:10.1016/j.radonc.2019.06.028

Optic nerve constraints for carbon ion RT at CNAO - Reporting and relating outcome to European and Japanese RBE

Radiother Oncol. 2019 Nov:140:175-181. doi: 10.1016/j.radonc.2019.06.028. Epub 2019 Jul 13.

Affiliations

¹ Department of Oncology and Medical Physics, Haukeland University Hospital, Bergen, Norway; Department of Clinical Science, Faculty of Medicine, University of Bergen, Norway. Electronic address: jon.espen.dale@helse-bergen.no.
² National Center of Oncological Hadrontherapy, Pavia, Italy.
³ Department of Oncology and Medical Physics, Haukeland University Hospital, Bergen, Norway.
⁴ National Center of Oncological Hadrontherapy, Pavia, Italy; Heidelberg Ion-Beam Therapy Center, Heidelberg, Germany.
⁵ National Center of Oncological Hadrontherapy, Pavia, Italy; Osaka Heavy Ion Therapy Center, Osaka, Japan.
⁶ Department of Oncology and Medical Physics, Haukeland University Hospital, Bergen, Norway; Department of Clinical Science, Faculty of Medicine, University of Bergen, Norway.
⁷ National Center of Oncological Hadrontherapy, Pavia, Italy; MedAustron Ion Therapy Center, Wiener Neustadt, Austria.

PMID: 31310888
DOI: 10.1016/j.radonc.2019.06.028

Abstract

Background and purpose: Until now, carbon ion RT (CIRT) dose constraints for the optic nerve (ON) have only been validated and reported in the NIRS RBE-weighted dose (D_NIRS). The aim of this work is to improve CNAO's RBE-weighted dose (D_LEM) constraints by analyzing institutional toxicity data and by relating it to D_NIRS.

Material and methods: A total of 65 ONs from 38 patients treated with CIRT to the head and neck region in the period 2013-14 were analyzed. The absorbed dose (D_Abs) of the treatment plans was reproduced and subsequently both D_LEM and D_NIRS were applied, thus relating CNAO clinical toxicity to D_NIRS.

Results: Median FU was 47 (26-67) months. Visual acuity was preserved for the 56 ONs in which the old constraints were respected. Three ONs developed visual decline at D_LEM|1% ≥71 Gy(RBE)/D_LEM|20% ≥68 Gy(RBE), corresponding to D_NIRS|1% ≥68 Gy(RBE)/D_NIRS|20% ≥62 Gy(RBE). Dose recalculation revealed that NIRS constraints of D_NIRS|1% ≤40 Gy(RBE)/D_NIRS|20% ≤28 Gy(RBE) corresponded to D_LEM|1% ≤50 Gy(RBE)/D_LEM|20% ≤40 Gy(RBE). Reoptimization of treatment plans with these new D_LEM constraints showed that the dose distribution still complied with NIRS constraints when evaluated in D_NIRS. However, due to uncertainties in the method, and to comply with the EQD2-based constraints used at GSI/HIT, a more moderate constraint relaxation to D_LEM|1% ≤45 Gy(RBE)/D_LEM|20% ≤37 Gy(RBE) has been implemented in CNAO clinical routine since October 2018.

Conclusion: New D_LEM constraints for the ON were derived by analyzing CNAO toxicity data and by linking our results to the experience of NIRS and GSI/HIT. This work demonstrates the value of recalculating and reporting results in both D_LEM and D_NIRS.

Keywords: Carbon ion radiotherapy; Long term adverse effects; Optic nerve; Organs at risk; Relative biological effectiveness; Vision disorders.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adolescent
Adult
Aged
Aged, 80 and over
Female
Heavy Ion Radiotherapy / adverse effects*
Humans
Male
Middle Aged
Optic Nerve / radiation effects*
Radiotherapy Dosage
Relative Biological Effectiveness*
Young Adult