A preliminary study of a new high-resolution detector matrix applied to three-dimensional dose verification in intensity-modulated radiotherapy

Objective

To test the basic dosimetry characteristics of a new high-resolution matrix and to perform a preliminary study on the three-dimensional (3D) dose verification of intensity-modulated treatment (IMRT).

Methods

The dosimetry characteristics of the new matrix were investigated, including repeatability, dose-rate response, and dose linearity. Twenty cases of nasopharyngeal carcinoma (NPC) and 20 cases with lung cancer were randomly selected for IMRT plans, and the novel matrix was employed for 3D dose verification. The measured results were evaluated using the gamma passing rate (GPR) and dose volume histogram (DVH). The action limit (AL) and tolerance limit (TL) of the target volume and each organ at risk (OAR) were calculated with reference to the American Association of Physicists in Medicine (AAPM) TG218 report.

Results

The matrix performed well for all dosimetry characteristic tests, with a deviation of <1%. The average GPRs of the body were (99.32 ​± ​0.32)%, (98.36 ​± ​0.59)%, and (96.27 ​± ​1.20)% for NPC, and (99.17 ​± ​0.74)%, (98.09 ​± ​1.33)%, and (95.83 ​± ​2.22)% for lung cancer at the gamma standards of 3%/3 ​mm, 3%/2 ​mm, and 2%/2 ​mm. The average GPRs difference between the head-neck and thorax-abdomen plans were <1% for the same gamma standard. For both the target volumes and OARs, the average GPRs were >90% under the relatively strict standard of 2%/2 ​mm. The DVH showed that the measurement results of D₉₈ and D₉₅ for the target volumes were slightly lower and D₂ were higher than those of treatment planning system (TPS) (P ​< ​0.01). In addition, with the same standard, there may be significant differences in the values of AL and TL between different structures for target volumes and OARs, especially small-volume OARs such as the chiasma and optic nerve-L.

Conclusions

The new matrix showed good dosimetry characteristics and can be effectively applied to the treatment planning dose verification of the head-neck and lung cancer. Further research is needed to establish how to analyze the GPR and DVH of the target volume and OARs, and to determine more precise dose verification standards combined with the parameters of AL and TL to better guide 3D dose verification in clinic.