Preliminary clinical study on brass compensator-based intensity-modulated radiation therapy.

Objective: The objective of this study is to preliminarily evaluate the feasibility of brass compensator-based intensity-modulated radiation therapy (CB-IMRT).

Materials And Methods: Ten patients (three cases of nasopharyngeal cancer, four of esophageal cancer, and three of rectal cancer) who underwent an IMRT treatment planning were selected for this study. The transmission coefficient of brass plates with different thicknesses was measured under a 6 MV photon beam used in the treatment planning system, and the equation for thickness computation was fitted out. The plan file RTPLAN file of each patient was exported from the planning system and transformed to a compensator thickness matrix; therefore, it was input into a numerical control machine for the manufacturing and cutting of the compensators. The CB-IMRT plans obtained were verified on a homogeneous phantom with commercial software. Planar doses were measured by films, and the computed ones were compared using gamma evaluation with 3-mm distance to agreement and 3% dose difference criteria adopting a pass rate of Pγ >90%. The monitor units (MUs) of the multileaf collimator IMRT plan (MLC-IMRT) and the CB-IMRT plans were compared. Depth of cut was computed through the equation fitted from real measurements. The planned RTPLAN files were used to transform the cutting files needed by the numerical control machine.

Results: Plan validations show that the minimum and maximum of gamma pass rate among the 10 patients are 90.2% and 98.2%, respectively, which both satisfy the requirements of clinical planning. The MUs of CB-IMRT are significantly smaller compared with MLC-IMRT.

Conclusion: CB-IMRT satisfies the requirements of clinical therapy and can be used in a radiotherapy routine.