Three-Dimensional Dosimetry of the Full and Empty Bladder in High Dose Rate Vaginal Cuff Brachytherapy

ObjectivesThe objectives of the study were to assess the bladder doses during vaginal cuff brachytherapy and to examine the effect of bladder filling on normal tissue dosimetry by means of computed tomography.Materials and MethodsA total number of 45 women were enrolled in a prospective clinical trial. Patients were treated with the application of a single-line source vaginal cylinder. All the patients were asked to consume 400 mL of water 40 minutes before computed tomography scans were taken. For each patient, 2 treatment plans were performed—one with full bladder and the other one when the bladder was emptied. A dose-volume histogram and the equivalent of 2-Gy dose for full and empty bladder were calculated. Doses to the bowels in 2 states of the bladder were estimated.ResultsThirty-five patients received a lower dose to the empty bladder than to the filled organ. The average dose difference was 0.5 Gy. Ten patients received a lower dose to the full bladder than to the empty one. However, in this case, the difference amounted only to 0.2 Gy on average. Dose parameters (the maximal dose received by 0.1 cm3 of tissue and the maximal dose received by 2 cm3 of tissue) were lower in the empty state, but the volumetric parameters (the percent of bladder volume receiving ≥50% of the prescribed dose and the percent of bladder volume receiving ≥80% of the prescribed dose) were higher in the empty state of the bladder. Doses to the bowels seemed to be higher in the empty bladder. However, none of the doses exceeded the limitations.ConclusionsThe results have shown that in most cases, the dose to the empty bladder is lower than when the bladder is full. Simultaneously, the doses to the bowels increase proportionally in the empty state of the bladder comparing to the full organ. Protection of the bowels, which are more radiosensitive, suggests treating the patients in the full state of the bladder. Early and late bowel toxicity should be investigated to establish clear standards of treatment.