Effect of endorectal balloon positioning errors on target deformation and dosimetric quality during prostate SBRT

Abstract

An inflatable endorectal balloon (ERB) is often used during stereotactic body radiation therapy (SBRT) for treatment of prostate cancer in order to reduce both intrafraction motion of the target and risk of rectal toxicity. However, the ERB can exert significant force on the prostate, and this work assessed the impact of ERB position errors on deformation of the prostate and treatment dose metrics. Seventy-one cone-beam computed tomography (CBCT) image datasets of nine patients with clinical stage T1cN0M0 prostate cancer were studied. An ERB (Flexi-Cuff, EZ-EM, Westbury, NY) inflated with 60 cm(3) of air was used during simulation and treatment, and daily kilovoltage (kV) CBCT imaging was performed to localize the prostate. The shape of the ERB in each CBCT was analyzed to determine errors in position, size, and shape. A deformable registration algorithm was used to track the dose received by (and deformation of) the prostate, and dosimetric values such as D95, PTV coverage, and Dice coefficient for the prostate were calculated. The average balloon position error was 0.5 cm in the inferior direction, with errors ranging from 2 cm inferiorly to 1 cm superiorly. The prostate was deformed primarily in the AP direction, and tilted primarily in the anterior-posterior/superior-inferior plane. A significant correlation was seen between errors in depth of ERB insertion (DOI) and mean voxel-wise deformation, prostate tilt, Dice coefficient, and planning-to-treatment prostate inter-surface distance (p < 0.001). Dosimetrically, DOI is negatively correlated with prostate D95 and PTV coverage (p < 0.001). For the model of ERB studied, error in ERB position can cause deformations in the prostate that negatively affect treatment, and this additional aspect of setup error should be considered when ERBs are used for prostate SBRT. Before treatment, the ERB position should be verified, and the ERB should be adjusted if the error is observed to exceed tolerable values.

Changes in prostate orientation due to removal of a Foley catheter

“…[13][14][15] Other studies have measured inter-and intrafraction prostate rotations [16][17][18] and the dosimetric impact of rotations. 19 Many strategies have been investigated to manage prostate rotations through appropriate PTV margins, [20][21][22] motion management devices, 23 rotation compensations with the table, collimator or gantry, 24,25 and adaptive replanning. 21,26,27 Given the risks of catheter placement, including urinary tract infections and discomfort, we utilized data from a multiinstitutional prostate SBRT study conducted from 2011 to 2013 to better determine the impact and benefit of the Foley catheter placement.…”

Adaptive radiotherapy and the dosimetric impact of inter- and intrafractional motion on the planning target volume for prostate cancer patients

“…The ERB contributes to rectal wall dose sparing by keeping the posterior wall distant from the high dose region, which is one reason for choosing ERB for our clinical workflow and it is widely applied in the literature [6,15,33]. In the present research, the interfractional ERB discrepancy showed the largest magnitude for systematic and random errors in SI direction (2.28 mm and 3.19 mm, respectively), which is an indication of daily placements depth variation [16,34].…”

“…The importance of intrafractional target motion for external beam radiation treatments (EBRT) increases as treatment margins are reduced due to IGRT [6,7]. Therefore, at the University Hospital Erlangen, patients treated for PCa receive planning computed tomography (CT) and radiotherapy treatment based on a filled bladder and endorectal balloon (ERB) protocol in order to minimize target motion and spare dose to organs at risk (OAR) [8][9][10][11][12][13][14][15][16][17]. Prior to treatment, PCa patients are first localized with kV/kV-orthogonal image pairs (OIP) based on the position of fiducial markers (FM).…”

Application of rectal retractor for postprostatectomy salvage radiotherapy of prostate cancer: A case report and literature review

“…Contrast to ERB, the use of the RR did not result in increasing dose to the anterior rectal wall, as shown in Figure D. Moreover, the ERB position is not reproducible between treatment sessions that can cause deformations in the prostate . As reported by studies, the implantation of prostate‐rectum spacers can lead to rectal ulceration, and perforation, perineal abscess, etc .…”