title: Extended phase-correlated rescanning irradiation to improve dose homogeneity in carbon-ion beam liver treatment.
abstract: We previously reported that an adequate number of simple layered phase-correlated rescanning (PCR) irradiations improve dose conformation to a moving target. However, if PCR is not completed within a single gating window due to the particular irradiation specifications selected in advance and/or layer size, the iso-energy layer is completed using next gating window, and the effect of rescanning is effectively nullified. To solve this problem, we developed extended PCR irradiation. Extended PCR is conceptually based on simple PCR. It differs in that the dose rate is adjusted to irradiate the number of rescans within multiple gating windows when simple PCR is not finished within a single gating window. This process is repeated until the total prescribed dose is given. Here, 4DCT imaging was performed under free-breathing conditions in 10 patients with hepatocellular carcinoma. 4D dose distributions for a single field approach were performed with simple PCR and extended PCR using 4DCT. A total dose of 11.25 Gy(RBE) was administered to the field-specific target volume. The number of rescans was changed from 1 to 10. Respiratory gating of a 30% duty cycle around exhalation was applied. Dose assessment metrics (CTV-D95, CTV-Dmin, CTV-Dmax) with PCR improved with an increasing number of rescans, and largely plateaued at five or more rescans. Minimum D95 and Dmin values, and maximum Dmax and HI values fluctuated at odd and even numbers of rescans. Extended PCR improved all dose assessment metrics whereas PCR did not. Values with extended PCR were mostly constant with three or more rescans, or in other words independent of the number of rescans. Extended PCR improved dose conformation to a moving target with greater efficacy than simple PCR when more than two gating windows were necessary. Extended PCR can be applied to irradiation machines having a low maximum dose rate.
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences.
authors.forename: Risa
authors.initials: R
authors.lastname: Ogata
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Mori
authors.forename: Shigeo
authors.initials: S
authors.lastname: Yasuda
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002244:Carbon / Q000627:therapeutic use; D005260:Female; D006801:Humans; D008113:Liver Neoplasms / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*
chemical_list: D002244:Carbon