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01.12.2017 | Research | Ausgabe 1/2017 Open Access

Radiation Oncology 1/2017

A novel CBCT-based method for derivation of CTV-PTV margins for prostate and pelvic lymph nodes treated with stereotactic ablative radiotherapy

Radiation Oncology > Ausgabe 1/2017
Ciara A. Lyons, Raymond B. King, Sarah O.S. Osman, Stephen J. McMahon, Joe M. O’Sullivan, Alan R. Hounsell, Suneil Jain, Conor K. McGarry
Wichtige Hinweise

Electronic supplementary material

The online version of this article (doi:10.​1186/​s13014-017-0859-z) contains supplementary material, which is available to authorized users.
Ciara A. Lyons and Raymond B. King are joint first authors.
Suneil Jain and Conor K. McGarry are joint senior authors.



Traditional CTV-PTV margin recipes are not generally applicable in the situation of stereotactic ablative radiotherapy (SABR) treatments of multiple target volumes with a single isocentre. In this work, we present a novel geometric method of margin derivation based on CBCT-derived anatomical data.


Twenty patients with high-risk localized prostate cancer were selected for retrospective review. Individual volumes of interest (prostate, prostate and seminal vesicles and pelvic lymph nodes) were delineated on five representative CBCTs and registered to the planning CT using two registration protocols: bone match or prostate-based soft tissue match. Margins were incrementally expanded around composite CTV structures until 95% overlap was achieved.


CTV-PTV margins of 5.2, 6.5 and 7.6 mm were required for prostate, prostate and seminal vesicles and pelvic lymph nodes respectively using a prostate matching protocol. For the prostate and seminal vesicle structures, margins calculated using our method displayed good agreement with a conventional margin recipe (within ±1.0 mm).


We have presented an alternative method of CTV-PTV margin derivation that is applicable to SABR treatments with more than one isocentric target. These results have informed an institutional trial of prostate and pelvic nodal SABR in men with high-risk localized prostate cancer.
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