Dose-effect relationships for individual pelvic floor muscles and anorectal complaints after prostate radiotherapy.
SourceInternational Journal of Radiation Oncology, Biology, Physics, 83, 2, (2012), pp. 636-644
Article / Letter to editor
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International Journal of Radiation Oncology, Biology, Physics
SubjectIGMD 2: Molecular gastro-enterology and hepatology; ONCOL 3: Translational research; ONCOL 4: Quality of Care
PURPOSE: To delineate the individual pelvic floor muscles considered to be involved in anorectal toxicity and to investigate dose-effect relationships for fecal incontinence-related complaints after prostate radiotherapy (RT). METHODS AND MATERIALS: In 48 patients treated for localized prostate cancer, the internal anal sphincter (IAS) muscle, the external anal sphincter (EAS) muscle, the puborectalis muscle (PRM), and the levator ani muscles (LAM) in addition to the anal wall (Awall) and rectal wall (Rwall) were retrospectively delineated on planning computed tomography scans. Dose parameters were obtained and compared between patients with and without fecal urgency, incontinence, and frequency. Dose-effect curves were constructed. Finally, the effect of an endorectal balloon, which was applied in 28 patients, was investigated. RESULTS: The total volume of the pelvic floor muscles together was about three times that of the Awall. The PRM was exposed to the highest RT dose, whereas the EAS received the lowest dose. Several anal and rectal dose parameters, as well as doses to all separate pelvic floor muscles, were associated with urgency, while incontinence was associated mainly with doses to the EAS and PRM. Based on the dose-effect curves, the following constraints regarding mean doses could be deduced to reduce the risk of urgency: </= 30 Gy to the IAS; </= 10 Gy to the EAS; </= 50 Gy to the PRM; and </= 40 Gy to the LAM. No dose-effect relationships for frequency were observed. Patients treated with an endorectal balloon reported significantly less urgency and incontinence, while their treatment plans showed significantly lower doses to the Awall, Rwall, and all pelvic floor muscles. CONCLUSIONS: Incontinence-related complaints show specific dose-effect relationships to individual pelvic floor muscles. Dose constraints for each muscle can be identified for RT planning. When only the Awall is delineated, substantial components of the continence apparatus are excluded.
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