ESTABLISHING RADIATION RISKS FOR VIDEOCYSTOURETHROGRAPHY
M. RANTELL1, I. PALMER 2, A. PASCOAL 3, D. ROBINSON 4, L. CARDOZO 4;
1Urogynaecology, King's Coll. Hosp., London, United Kingdom, 2medical physics, King's Coll. Hosp., London, United Kingdom, 3radiation protection service, King's Coll. Hosp., London, United Kingdom, 4King's Coll. Hosp., London, United Kingdom.
Introduction: Videocystourethrography (VCU) is a diagnostic technique utilising X-ray fluoroscopy to assess lower urinary tract dysfunction, and add anatomical detail to urodynamic data including cystometry and pressure flow studies. The legal requirement under The Ionising Radiation (Medical Exposure) Regulations 2000 is that employers undertake regular patient dose audits and establish local diagnostic reference levels (DRLs) for X-ray examinations. DRLs are defined for typical examinations for groups of standard-size patients. For many examinations, the local DRL can be compared to national DRLs published by Public Health England using data gathered from the National Patient Dose Database . There is currently no national DRL set for VCU exposure due to the wide range of protocols used by different centres. A local DRL must therefore be established by interrogating patient data.
Objective: The aim of this study was to review current VCU exposures in women and establish a local DRL.
Methods: This was a retrospective study of consecutive VCU procedures performed over a period of approximately 11 months following referral from primary care or tertiary referral. Procedures that were not fully completed, or with missing data, were excluded from the study. Indications for VCU include women with lower urinary tract symptoms or those with incontinence or prolapse prior to and after surgery. Dose-area product (DAP), fluoroscopy time (FT) and patient weight were collected manually for each VCU procedure. Through consultation with clinical staff, a typical examination time was defined. Patient weight range was established by considering the mean weight of the patients in the data set. The average DAP was calculated for a sample meeting these inclusion criteria. PCXMC (version 2.0, STUK), a MonteCarlo based patient dose calculator was used to calculate organ doses and effective dose associated with the VCU procedure.
In total, 333 VCU procedures were analysed. Of these, 39 cases met the inclusion criteria described above (fluoroscopy time 60±10s; patient weight 76±10kg). A wide range of DAP (mean 114±50), fluoroscopy time and weights were observed (see Table 1).
Individual organ doses were calculated using PCXMC for the organs lying within the field during a VCU examination (see Table 2). The geometric parameters and exposure settings used for the simulation were estimated based on observation of a number of VCU procedures: field size 18x20cm2, focus to skin distance 80cm, and x-ray tube potential 100kV. The calculated effective dose was 0.26mSv, which for an adult female leads to an estimate radiation risk of cancer induction of ≅1 in 60000 which is categorised as very low .
Women undergoing a VCU procedure are exposed to a small amount of ionising radiation, which results in a very low increased risk of lifetime cancer. The local DRL for VCU procedures was set at 114cGy.cm2. Based on this finding, a dose investigation level (DIL) was set at the 95th percentile of the DAP distribution (194cGy.cm2) to trigger investigation of clinical procedures where individual patient dose differs significantly from the DRL.
A UK national DRL of 700cGy.cm2 has been set for micturating cystourethrography (MCU) examinations  which are also aimed at examination of the urinary tract. However, MCU examinations tend to require several periods of imaging in acquisition mode, whereas VCU at this centre solely uses fluoroscopy mode, so the DRL established in this study is significantly lower than the national DRL for MCU examinations.
Conclusions: From the data collected in this study, women who undergo VCU are exposed to minimal ionising radiation, which results in a very low increased risk of lifetime cancer.
References:  Public Health England (2016) Diagnostic radiology: national diagnostic reference levels (NDRLs).  Int Urogynecol J (2013) 24:1547-1551  Public Health England, HPA-CRCE-028
calculated organ doses for organs lying with the radiation field during a VCU examination
Organ Dose (mGy)
the range and mean of the examination parameters recorded for 333 VCU examinations
fluoroscopy time (S)
Patient weight (KG)