Quantitative imaging in medicine and surgery · 2025
Dosimetric impact of bladder volume variation on online adaptive radiotherapy for cervical cancer based on cone-beam computed tomography and clinical management strategies.
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Qi Yingnan, Chen Xuemei, Chi Feng, Chen Zhanlin, Luo Yu, Xu Senkui, Wang Yilin, Shang Lintao, Wang Tong, Mai Xiuying, Lin Yaoyao, Zheng Weizheng, Feng Yunfei, Chen Foping, Jiang Xiaobo
Аннотация
BACKGROUND: During cervical cancer radiotherapy, unstable bladder volume can compromise target accuracy and increase radiation exposure to organs at risk (OARs). Although online adaptive radiotherapy (ART) can correct for interfractional variations, intrafractional bladder filling may still lead to dose deviations. This study aimed to evaluate the dosimetric optimization of ART for interfractional bladder fluctuations, analyze the impact of intrafractional dynamics, and evaluate the clinical benefits of personalized bladder management.
METHODS: Fourteen patients with cervical cancer receiving radical radiotherapy with a prescription dose of 45-50 Gy/25 fractions from December 2023 to July 2024 were analyzed. Online ART for cervical cancer was applied in 350 external beam radiotherapy fractions. Two bladder preparation protocols were compared: personalized prefilling (2 hours before treatment) and natural filling. The personalized protocol involved weight-adjusted water intake: consumed within 20 minutes for patients ≤50 years, or within 30 minutes with fractionated intake for those >50 years. Two cone-beam computed tomography (CBCT) scans were acquired per fraction: initial (CBCT1) and pretreatment (CBCT2). ART plans were optimized based on CBCT1, while nonoptimized ART end plans were calculated by transferring doses to CBCT2. Image-guided radiotherapy (IGRT) plans were derived by mapping original planning parameters onto CBCT1. Dosimetric comparisons were performed between ART and IGRT plans, and intrafractional bladder volume changes and their dosimetric impact were analyzed.
RESULTS: Interfractional bladder volume inversely correlated with bladder volume percentage receiving ≥30 Gy (V30, r=-0.50) and small bowel absolute volume receiving ≥45 Gy (V45; r=-0.49), and small bowel V40 (r=-0.51) (all P<0.01). A bladder volume below 265 cm3 indicates an increased risk of small-bowel radiation overdose and signals the need for initiating ART clinical intervention. Stratified studies showed that compared with IGRT, ART for cervical cancer significantly reduced the dose received by OARs both above and below the bladder volume threshold (bladder V30 reduced from 80.32% to 62.82%; P<0.01), increased the target volume coverage from 1.3% to 2.2% (P<0.01), thereby systematically verifying the dosimetric advantage of ART. Personalized bladder filling reduced intrafractional volume variation (from 190.66±69.97 to 88.23±27.79 cm3; P<0.01), stabilizing when the initial volume exceeds 400 cm3. Intrafractional bladder dynamics induced three dose effects: (I) OAR protection (bladder V30 decreased from 62.82% to 58.65%, with P=0.01; small-bowel V40 decreased from 108.61 to 96.94 cm3, with P<0.01), (II) target risk (planning target volume V100% decreased by 1.5% when bladder expansion >100 cm3; P<0.01), and (III) organ stability (no significant rectal or femoral head dose changes).
CONCLUSIONS: ART for cervical cancer mitigates interfractional bladder-related dosimetric variations, while personalized bladder management enhances intrafractional stability. Combining ART with personalized bladder protocols for cervical cancer ensures target coverage while simultaneously enhancing protection of OARs.
METHODS: Fourteen patients with cervical cancer receiving radical radiotherapy with a prescription dose of 45-50 Gy/25 fractions from December 2023 to July 2024 were analyzed. Online ART for cervical cancer was applied in 350 external beam radiotherapy fractions. Two bladder preparation protocols were compared: personalized prefilling (2 hours before treatment) and natural filling. The personalized protocol involved weight-adjusted water intake: consumed within 20 minutes for patients ≤50 years, or within 30 minutes with fractionated intake for those >50 years. Two cone-beam computed tomography (CBCT) scans were acquired per fraction: initial (CBCT1) and pretreatment (CBCT2). ART plans were optimized based on CBCT1, while nonoptimized ART end plans were calculated by transferring doses to CBCT2. Image-guided radiotherapy (IGRT) plans were derived by mapping original planning parameters onto CBCT1. Dosimetric comparisons were performed between ART and IGRT plans, and intrafractional bladder volume changes and their dosimetric impact were analyzed.
RESULTS: Interfractional bladder volume inversely correlated with bladder volume percentage receiving ≥30 Gy (V30, r=-0.50) and small bowel absolute volume receiving ≥45 Gy (V45; r=-0.49), and small bowel V40 (r=-0.51) (all P<0.01). A bladder volume below 265 cm3 indicates an increased risk of small-bowel radiation overdose and signals the need for initiating ART clinical intervention. Stratified studies showed that compared with IGRT, ART for cervical cancer significantly reduced the dose received by OARs both above and below the bladder volume threshold (bladder V30 reduced from 80.32% to 62.82%; P<0.01), increased the target volume coverage from 1.3% to 2.2% (P<0.01), thereby systematically verifying the dosimetric advantage of ART. Personalized bladder filling reduced intrafractional volume variation (from 190.66±69.97 to 88.23±27.79 cm3; P<0.01), stabilizing when the initial volume exceeds 400 cm3. Intrafractional bladder dynamics induced three dose effects: (I) OAR protection (bladder V30 decreased from 62.82% to 58.65%, with P=0.01; small-bowel V40 decreased from 108.61 to 96.94 cm3, with P<0.01), (II) target risk (planning target volume V100% decreased by 1.5% when bladder expansion >100 cm3; P<0.01), and (III) organ stability (no significant rectal or femoral head dose changes).
CONCLUSIONS: ART for cervical cancer mitigates interfractional bladder-related dosimetric variations, while personalized bladder management enhances intrafractional stability. Combining ART with personalized bladder protocols for cervical cancer ensures target coverage while simultaneously enhancing protection of OARs.