title: A serial 4DCT study to quantify range variations in charged particle radiotherapy of thoracic cancers.
abstract: Weekly serial 4DCT scans were acquired under free breathing conditions to assess water-equivalent path length (WEL) variations due to both intrafractional and interfractional changes in tissue thickness and density and to calculate proton dose distributions resulting from anatomical variations observed in serial 4DCT. A template of region of interests (ROIs) was defined on the anterior-posterior (AP) beam's eye view, and WEL measurements were made over these ROIs to quantify chest wall thickness variations. Interfractional proton dose distributions were calculated to assess changes in the expected dose distributions caused by range variations. Mean intrafractional chest wall WEL changes during respiration varied by: -4.1 mm (<-10.2 mm), -3.6 mm (<-7.1 mm), -3.2 mm (<-5.6 mm) and -2.5 mm (<-5.1 mm) during respiration in the ITV, upper, middle and lower lung regions, respectively. The mean interfractional chest wall WEL variation at Week 6 decreased by -4.0 mm (<-8.6 mm), -9.1 mm (<-17.9 mm), -9.4 mm (<-25.3 mm) and -4.5 mm (<-15.6 mm) in the ITV, upper, middle and lower lung regions, respectively. The variations were decomposed into anterior and posterior chest wall thickness changes. Dose overshoot beyond the target was observed when the initial boli was applied throughout the treatment course. This overshoot is due to chest wall thickness variations and target positional variations. The radiological path length can vary significantly during respiration as well as over the course of several weeks of charged particle therapy. Intrafractional/interfractional chest wall thickness changes can be a significant source of range variation in treatment of lung tumors with charged particle beams, resulting in dose distribution perturbations from the initial plan. Consideration of these range variations should be made in choosing the therapeutic charged particle beam range.
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1, Anagawa, Inage-ku, Chiba, Japan.
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Mori
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
authors.forename: George
authors.initials: G
authors.lastname: Starkschall
authors.forename: Radhe
authors.initials: R
authors.lastname: Mohan
authors.forename: George T Y
authors.initials: GT
authors.lastname: Chen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D061766:Proton Therapy; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D013902:Radiography, Thoracic / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011882:Radiotherapy, High-Energy / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013899:Thoracic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D016896:Treatment Outcome; D011522:Protons
chemical_list: D011522:Protons
keywords: charged particle radiotherapy; dose distribution perturbation; interfractional range variation; intrafractional range variation