Evaluation of dose calculation accuracy of ISOgray treatment planning system in prediction of dose fluctuation levels during radiotherapy of breast cancer at ۶-۱۵ MV beam energies

Objective: In radiation therapy, ensuring the accuracy of the calculated and delivered dose to the patient may not be easily achieved, because many computational and dosimetrical errors can exist between the dose calculations of the treatment planning system (TPS) and the amount of delivered dose using the treatment machine. The question of the current research is whether there is an acceptable agreement between the calculated dose distribution performed by the point kernel algorithm of ISOgray TPS in virtual wedge fields (in the heterogeneous thorax phantom) with the experimental dose distribution in Breast radiotherapy?Methods: An anthropomorphic thorax phantom similar to the human body was designed and manufactured using materials equivalent to the body. After CT imaging, the treatment area and vital tissues such as heart and thorax were contoured by the oncologist. The treatment plan was done by the radiotherapy physicist on the phantom with suitable fields. ۳D dose distribution was calculated by CCS algorithm. Irradiation to the phantom was performed according to the treatment plan using a Siemens ARTISTE linear accelerator. Two-dimensional film dose distributions were acquired in a specific slice in the phantom. Finally, using VeriSoft software (MEPHYSTO PTW, Freiburg, Germany) and ۲D gamma analysis, the behaviour of the calculated isodose curves and the measured dose distributions at standard virtual wedge angles at ۶ and ۱۵ energies were investigated.Results: Evaluation of two-dimensional dose distribution obtained from TPS calculations and film measurements showed that the value of gamma acceptance rate (۳%–۳ mm gamma criteria, local mode) was in the range of ۷۸.۰ ± ۰.۸% to ۸۸.۸ ± ۰.۶% at low energy and between ۸۸.۳ ± ۰.۵% to ۹۲.۰ ± ۰.۳% at high energy. In addition, we found that there is no significant difference in the change of the virtual wedge angles in different energies. But the results of our study state that this algorithm overestimated the dose of the soft tissue. Also, the ISOgray underestimated the dose in lung regions at both energies.Conclusion: Our findings demonstrate that the dose calculation accuracy of ISOgray TPS in Breast radiotherapy was good agreements with practical dose distributions at ۶-۱۵ MV photon energies.

Keywords:

ISOgray TPS , Breast radiotherapy , Thorax phantom , Virtual Wedge Filter , Siemens ARTISTE linac