Robustness of IPSA optimized high-dose-rate prostate brachytherapy treatment plans to catheter displacements

Abstract

PurposeInverse planning simulated annealing (IPSA) optimized brachytherapy treatment plans are characterized with large isolated dwell times at the first or last dwell position of each catheter. The potential of catheter shifts relative to the target and organs at risk in these plans may lead to a more significant change in delivered dose to the volumes of interest relative to plans with more uniform dwell times.Material and methodsThis study aims to determine if the Nucletron Oncentra dwell time deviation constraint (DTDC) parameter can be optimized to improve the robustness of high-dose-rate (HDR) prostate brachytherapy plans to catheter displacements. A set of 10 clinically acceptable prostate plans were re-optimized with a DTDC parameter of 0 and 0.4. For each plan, catheter displacements of 3, 7, and 14 mm were retrospectively applied and the change in dose volume histogram (DVH) indices and conformity indices analyzed.ResultsThe robustness of clinically acceptable prostate plans to catheter displacements in the caudal direction was found to be dependent on the DTDC parameter. A DTDC value of 0 improves the robustness of planning target volume (PTV) coverage to catheter displacements, whereas a DTDC value of 0.4 improves the robustness of the plans to changes in hotspots.ConclusionsThe results indicate that if used in conjunction with a pre-treatment catheter displacement correction protocol and a tolerance of 3 mm, a DTDC value of 0.4 may produce clinically superior plans. However, the effect of the DTDC parameter in plan robustness was not observed to be as strong as initially suspected.

Comparison of the IPSA and HIPO algorithms for interstitial tongue high-dose-rate brachytherapy

“…This option allows smoother source movements and more smooth distributions of the dwell time per dwell position in the catheter. However, the value of the DTGR was set as 0 (i.e., this dwell time gradient objective was ignored during optimization) since the DTGR is not a key factor to improve plan quality [ 18 ].…”

“…IPSA is a CT-based inverse planning method that can produce an optimized plan within 1 minute [ 18 ]. IPSA has been widely used for clinical purposes and has been demonstrated to have clinical efficiency.…”

“…The clinical superiority of anatomy-based inverse treatment plan optimizations (i.e., IPSA and HIPO) for HDR brachytherapy of prostate and cervical cancers has been demonstrated by several groups [ 18 , 19 , 21 , 25 – 27 ]. However, although a role of HDR brachytherapy has been demonstrated in tongue cancer treatment, the clinical effectiveness of inverse planning has not been evaluated for tongue cancer.…”

Influence of dwell time homogeneity error weight parameter on treatment plan quality in inverse optimized HDR cervix brachytherapy using SagiPlan

“…In case of changes in applicator/anatomy relative positions from the planned geometry, a further problem may arise, in which cold spots in the target volume may occur due to short dwell times. Therefore, fulfilling plan objectives with less dwell time fluctuations is desirable [5].…”

A Monte Carlo study on the feasibility of real-time in vivo source tracking during ultrasound based HDR prostate brachytherapy treatments

“…The major drawback of this technique is that it necessitates movement of the patient off the operating table and out of the dorsal lithotomy position. Multiple studies have reported that movement of the patient in this manor may increase the risk of catheter displacement in the inferior direction, relative to the prostate, in the time between CT scanning and treatment [6,7]. The use of transrectal ultrasound (TRUS) for treatment planning [8] has been shown to reduce the magnitude of these shifts, as well as improve visibility of the prostate and organs at risk (OARs) [9].…”