Effects of different bladder filling volumes on target areas and organs at risk during three-dimensional image-guided adaptive brachytherapy for locally advanced cervical cancer

Objective To investigate the effects of different bladder filling volumes on target areas and organs at risk during three-dimensional image-guided adaptive brachytherapy (3D-IGABT) for locally advanced cervical cancer.

Methods A prospective study was conducted involving 153 non-surgical locally advanced cervical cancer patients treated at the Affiliated Cancer Hospital of Guizhou Medical University from November 2020 to March 2022, with a mean age of (55.4±4.3) years. All patients collectively underwent a total of 526 sessions (hereafter denoted as n) of 3D-IGABT. Using random number table method, all patients were divided into two groups in accordance with the volume of saline containing contrast agent instilled into the bladder (bladder filling volumes): 50–70 ml group (n=266) and 80–100 ml group (n=260). Then, using a median volume of 35.85 cm³ for the high-risk clinical target volume (HR-CTV) as the cut-off value, patients with HR-CTV≥35.85 cm³ were divided into 50–70 ml group (n=123) and 80–100 ml group (n=140); patients with HR-CTV<35.85 cm³ were divided into 50–70 ml group (n=143) and 80–100 ml group (n=120). In reference to the International Commission on Radiation Units and Measurements No.89 report, residual gross tumor volume (GTV_res); HR-CTV; and organs at risk, such as bladder, rectum, sigmoid colon, and small intestine, were delineated. Treatment plans were developed using the Oncentra MasterPlan 3.2 treatment planning system. The volumes and doses of GTV_res and HR-CTV, the dose received by 1 cm³ volume of organs at risk near the applicator in high-dose region (\rmD_1\;\rmc\rmm^3 ), and the dose received by 2 cm³ volume near the applicator in high-dose region (\rmD_2\;\rmc\rmm^3 ) were recorded. Intergroup comparisons were performed using independent sample t-test or nonparametric rank-sum test.

Results Comparison between the 50–70 ml group (n=266, 123, 143) and the 80–100 ml group (n=260, 140, 120) showed no statistically significant difference in the volume or dose of GTV_res and HR-CTV (Z=−1.96 to −0.02, all P>0.05). Comparison between the 50–70 ml group (n=266) and the 80–100 ml group (n=260), 50–70 ml group (n=266) revealed a significant reduction in bladder \rmD_2\;\rmc\rmm^3 and \rmD_1\;\rmc\rmm^3 , with statistically significant differences ((280.40 (259.53, 303.41) cGy vs. 297.88 (272.10, 320.87) cGy, 304.65 (281.61, 330.33) cGy vs. 319.49 (295.19, 348.97) cGy, Z=−5.40, −4.83, both P<0.001); 50–70 ml group (n=266) sigmoid colon \rmD_2\;\rmc\rmm^3 and \rmD_1\;\rmc\rmm^3 were significant increases, and the differences were statistically significant ((204.36 (165.19, 240.71) cGy vs. 188.89 (152.56, 229.53) cGy, 245.33 (186.42, 260.81) cGy vs. 210.31 (174.02, 250.12) cGy, Z=−2.24, −1.67, both P<0.05). Comparison between the 50–70 ml group (n=123) and the 80–100 ml group (n=140), showed that the bladder \rmD_2\;\rmc\rmm^3 and \rmD_1\;\rmc\rmm^3 of the 50–70 ml group (n=123) were significantly reduced, and the differences were statistically significant ((282.10±31.27) cGy vs. (297.22±29.05) cGy, (304.57±34.98) cGy vs. (320.58±31.45) cGy, t=−4.04, −3.88, both P<0.001). Comparison between the 50–70 ml group (n=143) and the 80–100 ml group (n=120) showed that the 50–70 ml group (n=143) had significantly reduced bladder \rmD_2\;\rmc\rmm^3 and \rmD_1\;\rmc\rmm^3 , with statistically significant differences ((279.93±33.70) cGy vs. (296.45±34.15) cGy, (306.14±38.27) cGy vs. (322.15±37.79) cGy, t=−3.93, −3.40, both P<0.05). Meanwhile, the 80–100 ml group (n=120) demonstrated a significant reduction in sigmoid colon \rmD_2\;\rmc\rmm^3 and \rmD_1\;\rmc\rmm^3 , and the differences were statistically significant ( (173.93±53.16) cGy vs. (191.81±59.53) cGy, (202.44±54.67) cGy vs. (220.01±61.38) cGy, t=−2.83, −1.21, both P<0.05).

Conclusions Among patients with locally advanced cervical cancer receiving 3D-IGABT, when HR-CTV≥35.85 cm³, bladder filling volume of 50–70 ml is recommended. This plan ensures the doses of GTV_res and HR-CTV and helps reduce the radiation dose to the bladder. When HR-CTV<35.85 cm³, bladder filling volumes of 50–70 and 80–100 ml are preferable to protect the bladder and the sigmoid colon, respectively.