Reformulation of a clinical-dose system for carbon-ion radiotherapy treatment planning at the National Institute of Radiological Sciences, Japan

Abstract

At the National Institute of Radiological Sciences (NIRS), more than 8,000 patients have been treated for various tumors with carbon-ion (C-ion) radiotherapy in the past 20 years based on a radiobiologically defined clinical-dose system. Through clinical experience, including extensive dose escalation studies, optimum dose-fractionation protocols have been established for respective tumors, which may be considered as the standards in C-ion radiotherapy. Although the therapeutic appropriateness of the clinical-dose system has been widely demonstrated by clinical results, the system incorporates several oversimplifications such as dose-independent relative biological effectiveness (RBE), empirical nuclear fragmentation model, and use of dose-averaged linear energy transfer to represent the spectrum of particles. We took the opportunity to update the clinical-dose system at the time we started clinical treatment with pencil beam scanning, a new beam delivery method, in 2011. The requirements for the updated system were to correct the oversimplifications made in the original system, while harmonizing with the original system to maintain the established dose-fractionation protocols. In the updated system, the radiation quality of the therapeutic C-ion beam was derived with Monte Carlo simulations, and its biological effectiveness was predicted with a theoretical model. We selected the most used C-ion beam with αr = 0.764 Gy(-1) and β = 0.0615 Gy(-2) as reference radiation for RBE. The C-equivalent biological dose distribution is designed to allow the prescribed survival of tumor cells of the human salivary gland (HSG) in entire spread-out Bragg peak (SOBP) region, with consideration to the dose dependence of the RBE. This C-equivalent biological dose distribution is scaled to a clinical dose distribution to harmonize with our clinical experiences with C-ion radiotherapy. Treatment plans were made with the original and the updated clinical-dose systems, and both physical and clinical dose distributions were compared with regard to the prescribed dose level, beam energy, and SOBP width. Both systems provided uniform clinical dose distributions within the targets consistent with the prescriptions. The mean physical doses delivered to targets by the updated system agreed with the doses by the original system within ± 1.5% for all tested conditions. The updated system reflects the physical and biological characteristics of the therapeutic C-ion beam more accurately than the original system, while at the same time allowing the continued use of the dose-fractionation protocols established with the original system at NIRS.

Respiration-gated fast-rescanning carbon-ion radiotherapy

“…Dose was expressed in photon-equivalent doses (Gy(RBE)), derived by multiplication of physical dose by the RBE of carbon ions (16). Carbon-ion beams generated by the Heavy-Ion Medical Accelerator in Chiba (HIMAC) were used to deliver external CIRT using the hybrid-depth scanning technique with markerless amplitude-based respiratory gating, as previously described (15).…”

Single-energy metal artefact reduction with CT for carbon-ion radiation therapy treatment planning

“…It was designed reflecting the physical and biological characteristics of carbon-ion beam to provide accurate relative biological effectiveness (RBE). [24][25][26][27] Carbon-ion irradiation was performed by delivering the dose in beam spots. The beam range was changed using a hybrid depth scanning technique, which consists of the combination of a synchrotron with 11 distinct energies for steps of 30 mm and a range shifter for WEPL steps of 3 mm.…”

No Deterioration in Clinical Outcomes of Carbon Ion Radiotherapy for Sarcopenia Patients with Hepatocellular Carcinoma

“…The planning target volume (PTV) was defined as a summation of CTV, IM, and setup margin (8). Radiation dose measurements for the target volume and surrounding normal structures were expressed in Gy (relative biologic effectiveness [RBE]), which was defined as the physical dose multiplied by the RBE of carbon ions (10). XiO-N (version 4.47; collaborated product of Elekta AB, Stockholm, Sweden and Mitsubishi Electric, Tokyo, Japan) was used for treatment planning.…”