Impact of oedema on implant geometry and dosimetry for temporary high dose rate brachytherapy of the prostate

Abstract

The optimal timing of dosimetry for permanent seed prostatic implants remains contentious given the half life of post-implant oedema resolution. The aim of this study was to establish whether prostatic oedematous change over the duration of a temporary high dose rate (HDR) interstitial brachytherapy (BR) boost would result in significant needle displacement, and whether this change in geometry would influence dosimetry. Two CT scans, one for dosimetric purposes on the day of the implant and the second just prior to implant removal, were obtained for four patients receiving transperineal interstitial prostate brachytherapy. The relative changes in cross-sectional dimensions of the implants were calculated by establishing the change in mean radial distance (MRD) of the needle positions from the geometric centre of the implant for each patient's pair of CT studies. The treatment plan, as calculated from the first CT scan, was used in the second set of CT images to allow a comparison of dose distribution. The percentage change in MRD over the duration of the temporary implants ranged from -1.91% to 1.95%. The maximum change in estimated volume was 3.94%. Dosimetric changes were negligible. In the four cases studied, the degree of oedematous change and consequent displacement of flexiguide needle positions was negligible and did not impact on the dosimetry. The rate and direction of oedematous change can be extremely variable but on the basis of the four cases studied and the results of a larger recent study, it might not be necessary to re-image patients for dosimetric purposes over the duration of a fractionated HDR BT boost to the prostate where flexiguide needles are utilized. Nevertheless, further investigation with larger patient numbers is required.

The impact of prostate volume changes during external-beam irradiation in consequence of HDR brachytherapy in prostate cancer treatment

“…In the combined-treatment setting, various fractionation and implant timing schedules of HDR therapy have been described [7,9,11,24,27,28]. Numerous articles have been published regarding the influence of edema on postimplant dosimetry in permanent brachytherapy [5,31,33,36] and several studies have investigated not only the impact of edema on HDR dosimetry but also needle and template displacement during fractions in temporary HDR brachytherapy [4,6,14,19,22,25,26,31,38]. The purpose of the current prospective evaluation was to quantitatively assess the impact of prostate volume changes on the treatment volumes during external-beam irradiation in consequence of HDR brachytherapy in prostate cancer treatment.…”

Edema worsens target coverage in high-dose-rate interstitial brachytherapy of mobile tongue cancer: a report of two cases

“…However, the dosimetry will change if there is any change in the geometry between the applicator positions and the clinical target volume (CTV) following treatment planning. In prostate brachytherapy, both edema and applicator displacement are considered as causes of underdosage or overdosage to the CTV and organs at risk (OAR) [11, 12, 13, 14]. In case of prostate implants, the end of the applicator tip is inside the body and is not in a fixed position.…”

Preliminary results in prostate cancer patients treated with high-dose-rate brachytherapy and intensity modulated radiation therapy (IMRT) vs. IMRT alone

“…The prostate gland constituted the clinical target volume (CTV) for the brachytherapy. We planned cases using a computed tomography scan of the prostate implant (15) and the SIMUPLAN treatment planning system (Advanced Brachytherapy Solutions, Madrid, Spain). The brachytherapy dose was prescribed to the 100% isodose line that encompassed the planning target volume (PTV).…”

“…With high-dose-rate (HDR) brachytherapy, which is also sometimes referred to as a temporary seed implant (14,15), intrafraction prostate motion does not have to be accounted for as it does with IMRT (9, 10) because the radioactive source moves with the prostate. As a result, by using HDR brachytherapy, one can safely escalate radiation doses, for example, in patients with high-risk disease (7,8,11,12,16).…”