ABSTRACT
Objective To investigate the dosimetric differences between Utrecht applicator and ring applicator in three-dimensional (3D) conformal brachytherapy for locally advanced cervical cancer.Methods Twenty-five patients with locally advanced cervical cancer were treated with magnetic resonance imaging-guided 3D conformal brachytherapy.Utrecht applicator and ring applicator were used interchangeably for 96 cycles.Patients were divided into two groups according to the type of applicator.Each group received 48 cycles of treatment, in which ring applicator was first applied for 26 cycles and Utrecht applicator was first applied for 22 cycles.High-risk clinical target volume ( HR-CTV) , width, thickness, and D90 at the point A level, D2 cm3 of organs at risk (OARs), V7 Gy , W7 Gy,A, V7 Gy ,A, and W/T7 Gy were evaluated and analyzed using paired t-test.Results There were no significant differences in HR-CTV and the width, thickness, and D90 at the point A level between the Utrecht group and the ring group ( P=0.487;P=0.340;P=0.857;P=0.921);there were no significant differences in D2 cm3 values of bladder, rectum, sigmoid, and bowel between the two groups ( P=0.136;P=0.802;P=0.985;P=0.458);there were no significant differences in V7 Gy and T7 Gy,A between the two groups ( P=0.076;P=0.435) .The Utrecht group had a significantly larger W/T7 Gy,A than the ring group ( P=0.002 ) .Conclusions Utrecht applicator is appropriate for patients with relatively large width and width/thickness ratio of HR-CTV at the point A level.
ABSTRACT
Objective To explore the correlation between the dose measured in the rectum and reference dose in three?dimensional brachytherapy ( 3DBT ) for cervical cancer, and to evaluate the significance of the dose measured in the rectum. Methods Fifty patients receiving radiotherapy for cervical cancer were selected, and 3DBT was performed after pelvic external beam radiotherapy. According to the rectal monitoring method recommended in the report ICRU38, in vivo monitoring was applied to obtain the dose measured in the rectum, reference point dose ( DICRU ) , and D2 cm3 , and the planned dose was obtained from the planning system. The differences in these values were determined by the paired t?test and correlation analysis was performed with Pearson test. Results The dose measured in the rectum was higher than the planned dose (3. 48 vs. 3. 25,P=0. 000), and lower than DICRU(3. 48 vs. 3. 71,P=0. 000) and D2 cm3(3. 48 vs. 3. 87,P=0. 002). A linear relationship existed between the dose measured in the rectum and the planned dose, with a deviation percentage of-20% to 40% and an average deviation of 8. 16%;63%of the patients with cervical cancer had a deviation of<± 10%;the maximum deviation was 60%. The dose measured in the rectum had a strong correlation with DICRU(r=0. 722), but a weak correlation with D2 cm3 ( r=0. 284) . Conclusions During 3DBT for cervical cancer, the dose measured in the rectum has certain deviations, but has a linear correlation with the planned dose. Both the dose measured and the planned dose underestimate the dose at the reference point in the rectum, and in vivo rectal monitoring may be an effective method for quality control.