Assessment of radiation treatment chain for cervical cancer with combined external and brachy radiation therapy

ABSTRACT

Performing radiotherapy of cervical cancer by combined external radiotherapy and brachytherapy includes several stages. Inaccuracy of each stage may cause insufficient dose delivery and produce complications in neighboring radiosensitive organs. In this study a technique was developed in order to assure the quality of treatment delivery. A solid pelvic phantom was designed and fabricated for simulation of the entire radiotherapy procedure of the cervical cancer. Treatment planning for external radiotherapy was accomplished using computed tomography images and for intracavitary brachytherapy using orthogonal radiographs. Dose measurements were performed with an intracavitary ionization chamber. External radiotherapy was done using linear accelerator. The Nucletron Selectron low dose rate [LDR] machine was used for brachytherapy. For both modalities, the software calculated dose values were compared to the values measured in the pelvic phantom. The calculated data obtained from the treatment planning system was consistent with the measured data. The comparison between measurements and calculations showed a maximum variation of +/- 2 % for external radiation therapy and +/- 3.6 % for brachytherapy. The phantom and the procedure developed in this study successfully provided a tool for comprehensive evaluation of each step in the chain of radiation therapy under the same conditions found in actual treatment. This method can be used to verify the accuracy and reproducibility of this treatment in any department and also during commissioning of the treatment planning systems