Amplitude-based gated phase-controlled rescanning in carbon-ion scanning beam treatment planning under irregular breathing conditions using lung and liver 4DCTs

Abstract

Amplitude-based gating aids treatment planning in scanned particle therapy because it gives better control of uncertainty with the gate window. We have installed an X-ray fluoroscopic imaging system in our treatment room for clinical use with an amplitude-based gating strategy. We evaluated the effects of this gating under realistic organ motion conditions using 4DCT data of lung and liver tumors. 4DCT imaging was done for 24 lung and liver patients using the area-detector CT. We calculated the field-specific target volume (FTV) for the gating window, which was defined for a single respiratory cycle. Prescribed doses of 48 Gy relative biological effectiveness (RBE)/fraction/four fields and 45 Gy RBE/two fractions/two fields were delivered to the FTVs for lung and liver treatments, respectively. Dose distributions were calculated for the repeated first respiratory cycle (= planning dose) and the whole respiratory data (= treatment dose). We applied eight phase-controlled rescannings with the amplitude-based gating. For the lung cases, D95 of the treatment dose (= 96.0 ± 1.0%) was almost the same as that of the planning dose (= 96.6 ± 0.9%). Dmax/Dmin of the treatment dose (= 104.5 ± 2.2%/89.4 ± 2.6%) was slightly increased over that of the planning dose (= 102.1 ± 1.0%/89.8 ± 2.5%) due to hot spots. For the liver cases, D95 of the treatment dose (= 97.6 ± 0.5%) was decreased by ∼ 1% when compared with the planning dose (= 98.5 ± 0.4%). Dmax/Dmin of the treatment dose was degraded by 3.0%/0.4% compared with the planning dose. Average treatment times were extended by 46.5 s and 65.9 s from those of the planning dose for lung and liver cases, respectively. As with regular respiratory patterns, amplitude-based gated multiple phase-controlled rescanning preserves target coverage to a moving target under irregular respiratory patterns.

Reducing Dose Uncertainty for Spot-Scanning Proton Beam Therapy of Moving Tumors by Optimizing the Spot Delivery Sequence

“…Similarly to rescanning, delivery sequence optimization requires only postprocessing of the treatment plan and does not alter the work flow of treatment delivery. This is different from some other motion mitigation techniques, such as beam tracking (9), breath sampling (7), and phase-controlled rescanning (25, 26). …”

Comparison of particle beam therapy and stereotactic body radiotherapy for early stage non-small cell lung cancer: A systematic review and hypothesis-generating meta-analysis

“…Irregularities in respiratory pattern and inconsistencies between the external marker position and the internal target motion remain challenges with gating [128,129]. These issues may be mitigated through the adaptation of amplitude-based gating and internal positional tracking with or without fiducial markers [125,130,131]. Alternative to gating, 4D planning may improve dose conformity and homogeneity, which warrants further clinical exploration [132].…”

Particle therapy of moving targets—the strategies for tumour motion monitoring and moving targets irradiation

“…38,55 In general, 4DCT examinations are carried out under free-breathing conditions using multislice CT scanners, collaborating with external respiratory-sensing systems. 26,57 Although the best available 4DCT detector is based on 320-multislice CT, which enables acquiring a 13-cm scan range in a single rotation, most treatment centres have less technically advanced scanners with longer acquisition times. 26 Therefore, the planning respiratory cycle is reconstructed by averaging data from multiple breathing periods.…”

“…37 One should remember that CT imaging increases the radiation dose delivered to the body. 57 Novel radiographic techniques At the leading hadron therapy centres, such as HIT Center, work is going on to develop novel devices that use particle beams for planar or volumetric imaging. Heavy charged particles slow down in the patient body because of energy loss in the Coulomb inelastic interaction with the electrons.…”