The delivery of IMRT with a single physical modulator for multiple fields: a feasibility study for paranasal sinus...

This study describes a new intensity-modulated radiation therapy (IMRT) delivery method that utilizes a single modulator to deliver multiple fields ("multifield modulator"). This technique reduces the treatment time and manufacturing costs typically associated with modulator-IMRT. Technical feasibility was evaluated for treating paranasal sinus cancers.

Technical feasibility was measured by three criteria: The dose distributions of the multifield modulator-IMRT plans should offer improvements over those produced by 3D conformal plans and be equivalent to those of step-and-shoot multileaf collimator (MLC) IMRT plans, the manufactured modulators should meet quality assurance specifications, and the effort required to use this technology should not substantially exceed the effort required for current IMRT practice. Seven paranasal cancer cases were examined. The Wilcoxon signed rank test was used for statistical analysis.

Multifield modulator-IMRT plans can improve target coverage while reducing critical structure doses compared to 3D conformal plans. Multifield modulator-IMRT plans are at least equivalent to the corresponding step-and-shoot MLC-IMRT plans. Multifield modulators can be constructed to meet design specifications in quality assurance tests. The time required for manufacturing, quality assurance, and treatment delivery using multifield modulators was measured and found to be only slightly greater than that for current IMRT treatment methods.

IMRT treatments using multifield modulators for paranasal sinus tumors are feasible. Clinics may find it worthwhile to commit the minimal extra time for quality assurance and treatment to benefit from the improved dose distribution and lack of interplay between MLC leaf motion and internal target motion.