Clinical quality assurance for endovascular brachytherapy devices

Endovascular brachytherapy is still an important therapy modality with a high number of treated patients per year. Quality assurance of devices used has been addressed already in several publications (AAPM, DGMP, ESTRO, NCS). However, there are no clear recommendations given on test procedures and related equipment. Our experience with four different devices containing beta- ((32)P, (90)Sr/Y) and gamma-sources ((192)Ir), which were used in clinical routine during the last 3 years is described.

The incoming check includes leakage radiation, missing catheter interlock, positioning test, timer check, interrupt button check, power-off test and verification of the manual retraction facility. Dose profiles are measured using GafChromic film. Source strength verification is performed using well type chambers or air-kerma measurements. In addition, the proposed reference absorbed dose rate at 2 mm distance from the source centre is measured with a dedicated film dosimetry technique where two additional films are exposed to two known doses in a (60)Co field for calibration.

Dosimetrical parameters (dose profiles, source strength) are found to be within +/-10% of the manufacturers specifications. The reference dose rate measured with film is on average +3.1% for 13 (90)Sr seed trains, +8.1% for three (32)P wire sources and -3.7% for one (192)Ir seed ribbon compared to the source certificate. The activity of 30 individual (32)P wire sources measured by using a calibrated well type chamber showed a deviation of mean -0.3%, the activity of 16 (192)Ir seed ribbons determined with air kerma measurements a deviation of mean 2.8%.

The QA programme introduced in our department provides methods to verify all relevant parameters proposed by international recommendations. Film dosimetry can be used as independent verification of the reference dose rate within a 10% limit.