Commissioning a newly developed treatment planning system, VQA Plan, for fast-raster scanning of carbon-ion beams

Abstract

In this study, we report our experience in commissioning a commercial treatment planning system (TPS) for fast-raster scanning of carbon-ion beams. This TPS uses an analytical dose calculation algorithm, a pencil-beam model with a triple Gaussian form for the lateral-dose distribution, and a beam splitting algorithm to consider lateral heterogeneity in a medium. We adopted the mixed beam model as the relative biological effectiveness (RBE) model for calculating the RBE values of the scanned carbon-ion beam. To validate the modeled physical dose, we compared the calculations with measurements of various relevant quantities as functions of the field size, range and width of the spread-out Bragg peak (SOBP), and depth–dose and lateral-dose profiles for a 6-mm SOBP in water. To model the biological dose, we compared the RBE calculated with the newly developed TPS to the RBE calculated with a previously validated TPS that is in clinical use and uses the same RBE model concept. We also performed patient-specific measurements to validate the dose model in clinical situations. The physical beam model reproduces the measured absolute dose at the center of the SOBP as a function of field size, range, and SOBP width and reproduces the dose profiles for a 6-mm SOBP in water. However, the profiles calculated for a heterogeneous phantom have some limitations in predicting the carbon-ion-beam dose, although the biological doses agreed well with the values calculated by the validated TPS. Using this dose model for fast-raster scanning, we successfully treated more than 900 patients from October 2018 to October 2020, with an acceptable agreement between the TPS-calculated and measured dose distributions. We conclude that the newly developed TPS can be used clinically with the understanding that it has limited accuracies for heterogeneous media.

Technical note: Delivery benefit and dosimetric implication of synchrotron‐based proton pencil beam scanning using continuous scanning mode

“…Therefore, BDT and dose delivery accuracy must be balanced to achieve an acceptable dose deviation with a BDT as short as possible. Although not directly comparable, our results with a stop ratio constraint of 1 agree with the finding of Yagi et al., 17 who reported accepted patient‐specific quality assurance (QA) results with DDCS delivery where stop ratio constraint of 1 was used.…”

Beam delivery characteristics of the Hitachi carbon ion scanning system at Osaka Heavy Ion Medical Accelerator in Kansai (HIMAK)

“…Thousands of treatments have been performed at Osaka HIMAK, and the quality of the beams used for treatment has met the standards. 10 This also indicates that the accelerator controls not only the spot dose but also the dose during beam movement in a stable manner,and that unintended doses which may occur in beam on/off control by BPs, are rarely observed. In actual treatment planning, however, the spot dose is quite large relative to the move dose, so the move dose cannot be detected from normal measurement.…”

“…[7][8][9] Line scanning and DDCS are characterized by the fact that the beam is irradiated to the spot in the irradiation field placed to administer the dose to the target without turning off the beam when the spot is moved, which is expected to shorten irradiation time. 7,10 The main difference between DDCS and line scanning compared to spot scanning is that there is a move dose between spots. Not only Osaka Heavy Ion Medical Accelerator in Kansai (Osaka HIMAK, HyBeat Heavy-ion Therapy System, Hitachi, Ltd., Tokyo, Japan), but also other carbon ion therapy facilities around the world using scanning irradiation methods employ DDCS as a method to irradiate tumors in three dimensions.…”

“…The limits on the move dose at HIMAK are a move dose upper limit of 3.29 mMU and a stop dose ratio of 1 or less (i.e.,a move-stop ratio of 1:1). 10 If the beam is within those constraints, the next spot can be irradiated without turning off the beam within the same energy layer. On the other hand, if the spot irradiation condition exceeds the constraints, the beam is turned off, moved to the next spot, and irradiation is resumed.…”

Ultra-high Dose-rate Carbon-ion Scanning Beam With a Compact Medical Synchrotron Contributing to Further Development of FLASH Irradiation

“…We also noted that the contribution of the time needed for scanning the beam over the irradiation field was small (<14 ms, 0.025 ms for moving between spots) compared to the overall time of the irradiation field, which was completely dominated by the extraction process. The beam current was measured with a digital oscilloscope (TBS2000, Tektronix, Beaverton, OR, USA) connected to HyBeat Heavy-ion Therapy System (Hitachi, Ltd., Tokyo, Japan) (15).…”