Session Item

It has been shown that high dose intraluminal high dose rate brachytherapy (BT) is superior to stent alone in terms of stent occlusion and mean survival in the palliative treatment of malignant bile duct obstruction [1, 2]. The most common complication associated with BT treatment has been duodenal ulceration, which could, in addition to high doses delivered, result from highly non-uniform dose distributions of BT treatments [2]. In this study, we evaluated the feasibility of CyberKnife (CK) radiosurgery system to deliver a single high dose to the stented area, allowing more flexibility in achieving high dose coverage and delivering accurate dose distribution in various treatment anatomies.

3D printed phantoms along with dynamic motion CIRS phantom capable of resembling breathing motion were used for irradiating treatment plans created with Multiplan TPS and Oncentra Brachy TPS. Three different treatment geometries were simulated: A) straight, B) curved and C) branched stent (Fig 1). Four fiducial markers were attached around the metallic stents and the stents were inserted inside the phantoms. EBT3 radiochromic films were inserted in the middle of the split stents to measure the delivered 2D dose distributions. A 15 Gy single fraction dose irradiations were performed in static and moving conditions with the CK system and with the aid of Synchrony Respiratory Tracking System. With BT treatments, only a static phantom was used. All the irradiations were repeated twice and two films were irradiated simultaneously, thus four films in total for each scenario were irradiated and analysed.

The global gamma index (±3mm / ±3%) was used to compare the agreement between measured and calculated 2D-dose distributions. The results are presented in Table 1. Overall, the agreement with CK irradiations was around 95%, with the exception of branched stationary phantom (84.3%). With BT the gamma agreement was also close to 95% with straight and branched geometries, but with the curved geometry the agreement was only 68.4%. This might be due the snaking effect of the source wire or catheter positioning inside the stent.

Figure 1: Three different stent geometries: A) straight, B), curved and C) branched stent.

Table 1: Global gamma index (±3mm / ±3%) of the three geometries for the calculated and measured CyberKnife and Brachytherapy treatments.

The CK system was able to track and treat the moving 3D phantoms resembling bile duct obstruction after stent placement using fiducial markers. CK was able to produce accurate dose distributions in the moving phantom and could be an option for the palliative treatment of bile duct obstruction. The dose delivery accuracy was also comparable to BT.