How long is enough? Defining the treatment length in endovascular brachytherapy

The International Commission on Radiation Units and Measurement (IRCU) 50 has clearly defined treatment volumes in radiation therapy in the management of neoplasms. These concepts are applied to the field of endovascular brachytherapy (EVBT) for the prevention of postangioplasty restenosis. The following definitions are proposed: gross target length (GTL) is defined as the narrowed segment of the artery that requires intervention. Clinical target length (CTL) is defined as the intervened or injured length, which could be due to angioplasty, stent strut injury, stent deployment, or debulking procedures. Planning target length (PTL) is the CTL plus a margin to account for heart/catheter movement and uncertainty in target localization. The final treatment length (TL) is the PTL plus the effect of penumbra. The accurate specification of treatment length serves several important purposes. Based on an understanding of the different factors constituting the treatment length, adequate margins can be provided beyond the GTL; this will avoid geographic misses and minimize edge failures. These definitions of target length ensure treatment consistency and provide a standard terminology for communication among practitioners of EVBT, something of critical importance in the conduct of multi-institutional trials in this new and multidisciplinary therapy. Finally, since the efficacy of EVBT is critically dependent on the precision of radiation delivery, these guidelines ensure that the benefits of EVBT seen in prospective randomized trials can be translated into daily clinical practice at the community level.