Dosimetric evaluation of alternative techniques to brachytherapy in advanced-stage cervical cancer radiotherapy

Objective: To investigate whether a high treatment dose can be achieved with external beam radiotherapy (ERT) in patients for whom Brachytherapy (BRT) cannot be applied. The aim was to dosimetrically compare the Volumetric Modulated Arc Therapy (VMAT) and Helical Tomotherapy (HT) treatment planning techniques prepared with the Simultaneous Integrated Boost (SIB) method, which will be used instead of brachytherapy in advanced cervical cancer radiotherapy. Method: Target volumes and critical organ contours are performed using computer tomography (CT) images of ten retrospective patients diagnosed with advanced cervical cancer. External Radiotherapy (ERT) to be used instead of brachytherapy. ERT-SIB is a technique that allows two different planned target volumes (PTV) to receive different doses of radiation simultaneously. Since the SIB plan will be performed, dose limitations are calculated from the equivalent dose formula. In VMAT and HT plans, the dose per fraction was set to 3.1 Gy, and a total dose of 77.50 Gy was applied in 25 fractions. Two different planning techniques were statistically evaluated according to PTV77.5 and PTV45 dose coverage, conformity and homogeneity index values, tolerance doses for critical organ doses, and treatment times. Results: When evaluated in terms of PTV77.5, VMAT and HT gave similar results regarding dose coverage. The HI value for PTV77.5 was similar for both techniques, and when the CI value was compared, HT technique was superior to VMAT technique. When evaluated in terms of PTV45, HT technique gave better dose coverage results than VMAT. Overall, the HT technique gave better results than VMAT from a dosimetric perspective. Critical organ doses were lower in HT technique compared to VMAT. When both techniques were compared in terms of treatment times, VMAT technique was observed to have a shorter treatment time than HT technique. Conclusion: For the VMAT and HT plans prepared with the SIB method used in patients who could not undergo brachytherapy, the HT technique gave better results in terms of CI value in PTV77.5, dose coverage in PTV45 and critical organ doses, and a clear superiority of the VMAT technique to HT in terms of treatment duration was observed.