MRI-based contouring of functional sub-structures of the lower urinary tract in gynaecological radiotherapy

• Published in: Radiotherapy and oncology 2020-04, Vol.145, p.117-124
• Main Authors: Spampinato, Sofia, Tanderup, Kari, Marinovskij, Edvard, Axelsen, Susanne, Pedersen, Erik M., Pötter, Richard, Lindegaard, Jacob C., Fokdal, Lars
• Format: Article
• Language: English
• Subjects: Bladder sub-structures; Brachytherapy; Cervix cancer; Female; Gynecological radiotherapy; Humans; Magnetic Resonance Imaging; Radiotherapy Dosage; Radiotherapy, Image-Guided; Urinary Bladder - diagnostic imaging; Urinary morbidity; Urinary Tract - diagnostic imaging; Uterine Cervical Neoplasms - diagnostic imaging; Uterine Cervical Neoplasms - radiotherapy
• ISSN: 0167-8140; 1879-0887
• DOI: 10.1016/j.radonc.2019.12.011

•There are no common guidelines for lower urinary tract contouring in pelvic radiotherapy.•The main bladder substructures involved in morbidity are: bladder wall, trigone, bladder neck and urethra.•Comparison between MRIs for brachytherapy and EBRT showed that the trigone remains stable during treatment.•The length of the urethra is influenced by different treatment conditions.•New dose points and reference dimensions are suggested for gynecological radiotherapy. Research in radiation-induced urinary morbidity is limited by lack of guidelines for contouring and dose assessment of the lower urinary tract. Based on literature regarding anatomy, physiology and imaging of the lower urinary tract, this study aimed to provide advice on contouring of relevant sub-structures, reference points and reference dimensions for gynaecological radiotherapy. 210 MRIs for Image-Guided Adaptive Brachytherapy (IGABT) were analysed in 105 locally advanced cervical cancer patients treated with radio(chemo)therapy. Sub-structures (trigone, bladder neck and urethra) were contoured and trigone height (TH) and width (TW) were measured. Internal urethral ostium (IUO) and Posterior inferior border of pubic symphysis-urethra (PIBS-U) points were used to identify proximal and middle/low urethra, respectively. Urethra reference length (URL) was defined as IUO and PIBS-U distance. TH, TW and URL were also quantified on 54 MRIs acquired for External Beam Radiotherapy (EBRT). Median absolute differences in volumes and dimensions between first and second IGABT fraction were 0.7 cm3, 4.3 cm3, 0.2 cm, 0.3 cm and 0.2 cm for trigone, bladder neck, TH, TW and URL, respectively. Mean(±SD) TH and TW were 2.7(±0.4)cm and 4.4(±0.4)cm, respectively, with no significant difference (p = 0.15 and p = 0.06, respectively) between IGABT and EBRT. URL was significantly shorter in EBRT than in IGABT MRIs (p