title: Accuracy of inhomogeneity correction algorithm in intensity-modulated radiotherapy of head-and-neck tumors.
abstract: We examined the degree of calculated-to-measured dose difference for nasopharyngeal target volume in intensity-modulated radiotherapy (IMRT) based on the observed/expected ratio using patient anatomy with humanoid head-and-neck phantom. The plans were designed with a clinical treatment planning system that uses a measurement-based pencil beam dose-calculation algorithm. Two kinds of IMRT plans, which give a direct indication of the error introduced in routine treatment planning, were categorized and evaluated. The experimental results show that when the beams pass through the oral cavity in anthropomorphic head-and-neck phantom, the average dose difference becomes significant, revealing about 10% dose difference to prescribed dose at isocenter. To investigate both the physical reasons of the dose discrepancy and the inhomogeneity effect, we performed the 10 cases of IMRT quality assurance (QA) with plastic and humanoid phantoms. Our result suggests that the transient electronic disequilibrium with the increased lateral electron range may cause the inaccuracy of dose calculation algorithm, and the effectiveness of the inhomogeneity corrections used in IMRT plans should be evaluated to ensure meaningful quality assurance and delivery.
authors.affiliation: Research Institute and Hospital, National Cancer Center, Ilsan-gu, Goyang, Korea.
authors.forename: Myonggeun
authors.initials: M
authors.lastname: Yoon
authors.forename: Doo-Hyun
authors.initials: DH
authors.lastname: Lee
authors.forename: Dongho
authors.initials: D
authors.lastname: Shin
authors.forename: Se Byeong
authors.initials: SB
authors.lastname: Lee
authors.forename: Sung Yong
authors.initials: SY
authors.lastname: Park
authors.forename: Kwan Ho
authors.initials: KH
authors.lastname: Cho
mesh_terms: D000465:Algorithms; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods*