Quality correction factors of composite IMRT beam deliveries: Theoretical considerations

摘要: Purpose: In the scope of intensity modulated radiation therapy (IMRT) dosimetry using ionization chambers, quality correction factors plan-class-specific reference (PCSR) fields are theoretically investigated. The symmetry problem is studied to provide recommendable criteria for composite beam deliveries where minimal and also establish a theoretical limit PCSR delivery k{sub Q} factors. Methods: concept virtual symmetric collapsed (VSC) beam, being associated given delivery, defined in this investigation. Under symmetrical measurement conditions, any has property having factor identical its VSC beam. Using VSC, fundamental IMRT demonstrated form theorem. sensitivity conditions required by theorem thoroughly examined. Results: states that if produces uniform dose distribution volume V{sub cyl} which with cylindrical all beams fulfills two cyl}: (1) modulation function unchanged along axis, (2) gradient direction constant givenmore » lateral position; then no cyl}, matter what or gantry angles used. examination lead following results. effect depth-dose not perfectly depth on found negligible. degraded be only related scatter hardening, as holds diverging beams. Conclusions: use present paper leads valuable showing close unity under specific conditions. Q{sub p{sub c{sub s{sub r,Q{sub m{sub r}{sup f{sub p}{sub c}{sub s}{sub r},f{sub m}{sub r}}}}}}}}}=1 determined based target volume. approach explains recent experimental observations proposes ideal dosimetry. result study could potentially serve basis routine assurance.« less