Development of in-house software to calculate dose for intensity-modulated radiation therapy based on lung CT-patient data

Background: In external radiotherapy, the delivered dose is calculated from the treatment planning system. Various types of software have been used to verify the patient dose distribution.

Objective: Develop the in-house software (ISOFT) to calculate dose in intensity-modulated radiotherapy (IMRT) based on lung CT-patient data by combining the modified Clarkson integration with 3D-beam subtraction method.

Materials and methods: An ISOFT was developed for 6MV X-rays Varian Clinac21EX linear accelerator and the CT-based patient data. The multileaf collimators (MLCs) file from the Varian Eclipse treatment planning was transferred to the ISOFT. The ISOFT was used to calculate the dose distribution with correction of tissue inhomogeneity. To test the accuracy of the ISOFT, the normal MLC-shaped fields and IMRT plans were measured in a water phantom and in a thorax phantom, respectively. Then, these measurements were compared with the doses calculated from the ISOFT and the Varian Eclipse treatment planning system.

Results: The deviation between the measurements and calculations by the ISOFT for MLC-shaped fields in the water phantom fell within 0.5%. There were mostly higher calculated doses in lung compared with the measured result in the thorax phantom. The overestimated doses due to loss of scattering in the low-density materials were considered less in all methods of calculation. The measured lung dose difference from the ISOFT was within 5% criterion of acceptability.

Conclusion: The ISOFT can be used conveniently to verify dose calculation in heterogeneous media.