RBE-weighted dose in carbon ion therapy for ACC patients: Impact of the RBE model translation on treatment outcomes

Silvia Molinelli; Maria Bonora; Giuseppe Magro; Silvia Casale; Jon Espen Dale; Piero Fossati; Azusa Hasegawa; Alfredo Mirandola; Sara Ronchi; Stefania Russo; Lorenzo Preda; Francesca Valvo; Roberto Orecchia; Mario Ciocca; Barbara Vischioni

doi:10.1016/j.radonc.2019.08.022

RBE-weighted dose in carbon ion therapy for ACC patients: Impact of the RBE model translation on treatment outcomes

Radiother Oncol. 2019 Dec:141:227-233. doi: 10.1016/j.radonc.2019.08.022. Epub 2019 Sep 12.

Authors

Affiliations

¹ Clinical Department, National Center for Oncological Hadrontherapy (CNAO), Pavia, Italy. Electronic address: molinelli@cnao.it.
² Clinical Department, National Center for Oncological Hadrontherapy (CNAO), Pavia, Italy.
³ Department of Diagnostic Medicine, Institute of Radiology, IRCCS San Matteo University Hospital Foundation, Pavia, Italy.
⁴ Department of Oncology and Medical Physics, Haukeland University Hospital, Bergen, Norway.
⁵ MedAustron Ion Therapy Center, Wiener Neustadt, Austria.
⁶ Osaka Heavy Ion Therapy Center, Osaka, Japan.
⁷ Clinical Department, National Center for Oncological Hadrontherapy (CNAO), Pavia, Italy; Department of Clinical-Surgical, Diagnostic and Paediatric Sciences, University of Pavia, Italy.
⁸ Clinical Department, National Center for Oncological Hadrontherapy (CNAO), Pavia, Italy; European Institute of Oncology, Milan, Italy.

PMID: 31522881
DOI: 10.1016/j.radonc.2019.08.022

Abstract

Purpose/objective: The purpose of this study is to assess the impact of the conversion scheme for relative biological effectiveness (RBE)-weighted dose (D_RBE), implemented at our center, on treatment outcomes of adenoid cystic carcinoma (ACC) patients.

Material/methods: Treatment plans of 78 ACC patients, optimized with the Local Effect Model (LEM), were recalculated with the modified Microdosimetric Kinetic Model (mMKM). D_RBE to 95%, 50% and 2% (D_V%) of the clinical target volume (CTV), were selected as relevant parameters to compare LEM and mMKM D_RBE. The pattern of failure of ACC treatments was analyzed in relation to uncertainties involved in the D_RBE translation methodology.

Results: mMKM recalculations of LEM plans, optimized to a prescription dose of 68.8 Gy(RBE), showed a D_50% 8% higher, on average, than the expected value (60.8 Gy(RBE)), closer to the most frequently used mMKM prescription D_RBE (64 Gy(RBE)). D_95% and D_2% deviations, with respect to the optimization goals in the two RBE systems, increased of 0.5% and 14.2%, respectively, due to the steeper mMKM RBE variation along the beam path. Local recurrences were mainly (63%) reported in areas where CTV coverage was not satisfactory in the original LEM plan and the mMKM analysis showed that OARs constraints were too conservative.

Conclusion: No case of local recurrence could be explained by inadequate mMKM target coverage that was not already present in the LEM plan. New constraints have been defined for optic pathways and brainstem to improve target coverage with no expected increase in tissue complications.

Keywords: Adenoid cystic carcinoma; Carbon ion therapy; Relative biological effectiveness modeling.

MeSH terms

Carcinoma, Adenoid Cystic / radiotherapy*
Heavy Ion Radiotherapy / methods*
Humans
Neoplasm Recurrence, Local
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods*
Relative Biological Effectiveness*
Treatment Outcome