Effect of bladder distension on dosimetry of organs at risk in computer tomography based planning of high-dose-rate intracavitary brachytherapy for cervical cancer

Abstract

PurposeDistension and shape of urinary bladder may vary during intracavitary brachytherapy (ICBT) for cervical cancer, significantly affecting doses to bladder, rectum, sigmoid colon and small intestine and consequently late radiation toxicities. This study is to evaluate the effects of different fixed volume bladder distention on dosimetry, assessed by three dimensional image based planning, in different organs at risk during the treatment of cervical cancer with ICBT.Material and methodsForty seven cervical cancer patients (stage IB to IVA) were qualified for ICBT following external beam radiotherapy. Urinary bladder was distended with different volumes of normal saline instilled by a Foley's catheter. Planning CT scans were performed after insertion of applicators and three dimensional treatment planning was done on Brachyvision® treatment planning system (Varian Medical Systems, Palo Alto, CA). Dose volume histograms were analyzed. Bladder, rectum, sigmoid colon and small intestine doses were collected for individual plans and compared, based on the amount of bladder filling.ResultsMean dose to the bladder significantly decreased with increased bladder filling. However, doses to the small volumes (0.1 cc, 1 cc, 2 cc) which are relevant for brachytherapy, did not change significantly with bladder filling for bladder, rectum or sigmoid colon. Nevertheless, all dose values of small intestine are decreased significantly with bladder filling.ConclusionsBladder distension has no significant effect on doses received during brachytherapy by relevant volumes of bladder, rectum and sigmoid colon except intestine where values are decreased with bladder distension. A larger study with clinical correlation of late toxicities is essential for proper evaluation of this strategy.

A comparison of organs at risk doses in GYN intracavitary brachytherapy for different tandem lengths and bladder volumes

“…In some other studies bladder distension was found to have no significant influence on bladder, rectum, and sigmoid doses 6 , 17 . This was contrary to what we observed in our study.…”

“…The reason behind this might be methodological, as we compared the full bladder volume of a specific patient to her own empty bladder volume. In previous studies however, various bladder volumes of different patients were calculated and compared to one another; as such, additional patient specific features, such as OARs' wall elasticity or their relative distances, could potentially contribute to producing somewhat different results 6 , 17 …”

“…In the literature it is suggested that the bladder should be kept full in all treatment fractions as it then pushes the intestine upwards and preserves the small bowel 6 , 16 . In clinical practice, some practitioners would deliberately employ a full bladder to displace the small bowel when it falls anterior to the uterus.…”

“…The anatomy and topography of bladder has a substantial influence on bladder dose values in cervical cancer brachytherapy 3 , 4 , 5 , 6 , 7 , 8 . In order to reduce the dose to small intestine in gynecological (GYN) brachytherapy, treating the patient with a refilled bladder is often practiced (2) .…”

“…We also follow a protocol in our center (explained further in the text) in which the patient's bladder is refilled before the treatment. In the literature, the effect of bladder volume on dose to OARs has been studied 3 , 4 , 5 , 6 . We chose to investigate how keeping the bladder full during our treatments affects the dose to the bladder and other OARs, namely rectum and sigmoid.…”