Evaluation of seminal vesicle volume variability in patients receiving radiotherapy to the prostate

Abstract

Introduction:Prostate positional variability has been widely explored with seminal vesicle (SV) variability, coming into the forefront only in recent years. While planning target volume (PTV) margins and preparation protocols ameliorate the effects of bladder and rectum volume changes on prostate, studies on SV variation have looked at only position, not volume variability.Aim:The aim of this study was to investigate whether the inter-fraction volume variability of the VSs can exist in patients receiving radiotherapy to the prostate.Method:SV variability was investigated by comparing four on-treatment cone beam computer tomography scans to a planning computer tomography (CT) image for two patients receiving prostate radiotherapy. For each case, variation in volumes (cm3) was compared with intra-observer variation.Results:SV volume variability was seen in both patients, with the largest change in volume being 78·38%. This variance was considerably (between 2 and 10 times) larger than the measured intra-observer variance.Conclusion:This study identified the potential for daily SV volume variability in patients receiving prostate radiotherapy. Future large-scale studies are warranted to identify the extent of this motion and potential clinical impact. Evidence-informed PTV margins and possible SV volume control protocols may need to be adopted.

Seminal vesicle inter- and intra-fraction motion during radiotherapy for prostate cancer: A review

“…In addition, volume changes of the SV can lead to additional treatment uncertainties and may need to be accounted for during treatment. Bairstow et al [26] analysed 10 patients with at least 4 CBCTs. Two outliers showed considerable volume changes with a mean variance for patient 1 of 0.29 cc ± 0.45 / 0.53 cc ± 0.72 depending on the delineator.…”

“…The publications reporting on the magnitude of volume changes show different results, which can be, partially, explained by the different experimental methods. Where Miralbell et al [41] used the planning scan as reference, Bairstow et al [26]. used the mean SV volume as a reference.…”

“…In contrast, Frank et al [31] found no significant volume changes in 15 patients with repeated CT-on-rails images. As these varying results suggest, no consensus regarding the extent of these volume changes has been reached and further research is needed to clarify the geometrical and clinical effect of these volume changes [26].…”