ESTRO 2022 - Abstract Book

S499

Abstract book

ESTRO 2022

Results The treatment planning goal for D90 is to deliver a minimum of 90% of the prescribed dose. Majority of treatment plans for synchronous catheter shift simulations show PTV dose coverage meeting this clinical constraint in the range of − 3 to 6 . Increase in D30 of the urethra is seen as the catheters are shifted inferiorly; bladder V70 increases as the catheters shift superiorly; and as the catheters shift inferiorly, more of the rectal V70 accumulates. For selective catheter shift simulation, a significant dose increase to the PTV was detected at 3 superiorly upon shifting the catheters in the middle segment for all patient groups. For urethral D30, a distinct dose increase is observed in the results for the ‘anterior segment’ and ‘posterior segment’ catheter shift as the shifts increase inferiorly. However, simulating the inferior shifts for the ‘middle segment’ catheters resulted in a random dose fall-off to the urethra. There is an increase in V70 for the bladder as the catheters shift superiorly, and for the rectum, dose increase is observed when catheters in the posterior segment shift inferiorly. To estimate the needle shift tolerance, the normalised dose coverage drop to the PTV is plotted using the data from the selective catheter shift simulation, see Figure 2.

Conclusion Approximately 90% of all treatment plans experience a dose decrease of less than and equal to 5% when the catheters were displaced by 3 . To ensure PTV dose coverage is maintained at an optimum level and to reduce organ toxicity, the needle shift tolerance has been concluded to be 3 . PD-0570 Axially rigid active steerable needle for high-dose-rate prostate brachytherapy 1 Delft University of Technology, Biomechanical Engineering, Delft, The Netherlands; 2 University of Twente + University of Groningen and University Medical Center Groningen, Biomechanical Engineering, Enschede + Groningen, The Netherlands Purpose or Objective High-dose-rate (HDR) brachytherapy (BT) implant needles are rigid and restricted to linear insertion paths. Steerable instruments allow for precise access to deeply-seated targets while sparing sensitive tissues and avoiding anatomical structures. In addition, steerable instruments can enlarge the potential patient group eligible for HDR prostate BT, as generally patients with a prostate volume > 50-60 cm 3 are excluded from this treatment modality due to pubic arch interference (PAI). In this study, we present and evaluate a novel omnidirectional steerable needle for HDR BT of the prostate. M. Vries 1 , J. Sikorski 2 , S. Misra 2 , J. van den Dobbelsteen 1