부산대학교 도서관

Objective:Bladder motion necessitates large target expansions for organ-preserving treatment of muscle-invasive bladder cancer. These volumes prevent radiation dose escalation and exacerbate treatment-associated morbidity. The use of gold seed markers (GSMs) for improved tracking of the tumor bed during radiotherapy was therefore investigated.Methods:Nine consecutive patients with muscle-invasive bladder cancer undergoing bladder preservation therapy from August 2012 through October 2013 underwent maximal transurethral resection of bladder tumor, cystoscopic placement of tumor bed GSMs, and chemoradiation. Continuous orthogonal X-ray imaging for robotic-assisted intensity-modulated radiotherapy (IMRT), daily megavoltage imaging, or both were used to localize GSMs.Results:Less than 5 % of intra-fraction GSM and tumor centroid movements were >4 mm across 481 orthogonal images obtained during robotic-assisted IMRT. Patients receiving linear accelerator- and helical tomotherapy-based radiation underwent a total of 246 daily megavoltage imaging sessions, during which <5 % of inter-fraction GSM and tumor centroid movements were >10 mm. A cumulative dose-population algorithm accounting for both systematic and random errors corroborated these findings. Both intra- and inter-fraction displacements were approximately twofold greater for GSMs in the superior half of the bladder (p = 0.03) and in patients with average bladder volume >100 mL (p < 0.0001).Conclusions:This is the first case series of intra-fraction GSM tracking for organ-preserving treatment of muscle-invasive bladder cancer. The data suggest that GSM tracking during radiotherapy for bladder cancer is feasible and associated with minimal intra- and inter-fraction displacement. With prospective investigation, this technique may be used to minimize target volumes and reduce radiation-associated toxicity.