title: Dynamic delivery of IMRT using an independent collimator: a model study.
abstract: This study aims to develop intensity-modulated beam delivery using an independent collimator in dynamic mode (dIC). A model was built to solve the problem of optimizing the dIC jaw trajectories for a desired beam intensity map with the adaptive simulated annealing technique. Like a leaf trajectory for a dynamic multileaf collimator (dMLC), a dIC jaw trajectory is composed of a series of control points. When delivering a beam in dynamic mode, all four jaws move continuously and independently while the beam is on. The performance of the proposed model is evaluated by comparing the delivery time of dIC with that of dMLC for 56 intensity maps of eight prostate cases and 72 maps of eight nasopharynx cases. The premises for the comparison are that (1) all MLC leaves have a width of 1 cm; (2) MLC leaf trajectories are generated with the algorithm of Spirou and Chui (1994 Generation of arbitrary intensity profiles by dynamic jaws or multileaf collimators Med. Phys. 21 1031), and (3) dIC delivers the desired intensity maps with equivalent or better accuracy as that of dMLC. We found that the dIC delivery time was 2.00 +/- 0.83 times that of dMLC delivery for 56 intensity maps of prostate cases, and 2.90 +/- 1.39 times that of dMLC delivery for 72 intensity maps of nasopharynx cases. The estimated mean treatment delivery time is 5.8 min for prostate cases, and 12.2 min for nasopharynx cases. Considering the advantages of dIC such as two-dimensional continuous spatial resolution, sharp penumbra, minimal leakage and no tongue-and-groove effects, dIC has the potential for high-resolution IMRT treatments of certain lesions.
authors.affiliation: Department of Radiation Oncology, Cancer Institute (Hospital), Chinese Academy of Medical Sciences, PO Box 2258, Beijing 100021, People's Republic of China.
authors.forename: Yongqian
authors.initials: Y
authors.lastname: Zhang
authors.forename: Yimin
authors.initials: Y
authors.lastname: Hu
authors.forename: Lijun
authors.initials: L
authors.lastname: Ma
authors.forename: Jianrong
authors.initials: J
authors.lastname: Dai