Prostate Bed Motion during Intensity Modulated Radiotherapy Treatment

Abstract

Purpose/Objective(s)-Conformal radiation therapy in the post-prostatectomy setting requires accurate setup and localization of the prostatic fossa. In this series, we report prostate bed localization and motion characteristics using data collected from implanted radiofrequency transponders.Materials and Methods-The Calypso 4D Localization System uses three implanted radiofrequency transponders for daily target localization and real-time tracking throughout a course of radiation therapy. We reviewed the localization and tracking reports of 20 patients who received ultrasound-guided placement of Calypso transponders within the prostate bed prior to a course of intensity modulated radiation therapy at Fox Chase Cancer Center.Results-At localization, prostate bed displacement relative to bony anatomy exceeded 5 mm in 9% of fractions in the Anterior-Posterior (A-P) direction, and 21% of fractions in the SuperiorInferior (S-I) direction. The three-dimensional vector length from skin marks to Calypso alignment exceeded 1 cm in 24% of all 652 fractions with available setup data. During treatment, the target exceeded the 5 mm tracking limit for at least 30 seconds in 11% of all fractions, generally in the A-P or S-I directions. In the A-P direction, target motion was twice as likely to move posteriorly, towards the rectum, than anteriorly. 15% of all treatments were interrupted for repositioning, and 70% of patients were repositioned at least once during their treatment course.Conclusion-Set-up errors and motion of the prostatic fossa during radiotherapy are nontrivial, leading to potential undertreatment of target and excess normal tissue toxicity if not taken into account during treatment planning. Localization and real-time tracking of the prostate bed via implanted Calypso transponders can be used to improve the accuracy of plan delivery.

Gold seed fiducials in analysis of linear and rotational displacement of the prostate bed

“…We did not measure the intrafraction PBM but Klayton et al [15] used Calypso and radiofrequency transponders to investigate the PBM during IMRT. They found out that PBM during the treatment fraction was likely to be the consequence of rectum and bladder filling like in a case of intact prostate motion which has been studied earlier [20][21][22][23].…”

“…Prostate bed motion (PBM) has been examined thoroughly by ultrasound-based technologies [10,11], by CBCT in combination of rectal wall or surgical clips localization [6,[12][13][14], by electronic portal imaging device (EPID) and gold seed fiducials localization [4], and by orthogonal kV images together with radiofrequency beacons or surgical clips localization [5,15]. In this study we investigate the prostate bed localization difference between soft tissue registration and gold seed fiducial localization.…”

Role of fiducial markers in the assessment of prostate bed motion in post-prostatectomy patients treated with volumetric modulated arc therapy

“…Wider margins may be necessary to account for intrafraction motion and prostate bed deformation which were not addressed in the present study. 17,24 Moreover, strict bladder and rectal filling protocols may prove beneficial in minimising prostate bed motion and deformation.…”

“…11 Various image-guided radiation therapy (IGRT) methods have been used to assess prostate bed motion such as ultrasound, cone beam CT (CBCT), electronic portal imaging, kilovoltage (KV) orthogonal imaging, surgical clips and gold seed fiducial markers. [12][13][14][15][16][17][18][19][20][21][22] The use of fiducials specifically in post-prostatectomy patients has been uncommon due to the lack of an intact organ where they can be implanted. 23 The present study was undertaken to determine the feasibility of using gold seed fiducial markers for prostate bed localisation, determine the magnitude of prostate bed motion and provide recommendations regarding appropriate planning target volume (PTV) margins in post-prostatectomy radiation therapy.…”

Effects on the photon beam from an electromagnetic array used for patient localization and tumor tracking

“…Patient radiation target localization with Calypso system was demonstrated to agree well with a linear accelerator on‐board imaging system (7–9,11) . The Calypso system has been used to study the inter‐ and intrafraction tumor motion in various treatment sites including prostate, (12,13) pancreas, (14) and lung (15) . The motion data assessed from Calypso system were used for motion management and margin reduction to improve the target coverage and organ sparing in prostate radiotherapy (16–19) .…”