One Minute Poster Pitches Archive

UK & Ireland Prostate Brachytherapy Conference 2024

Abstract number 4 

The impact of needle reconstruction uncertainties on TRUS prostate plan parameters

Jennifer Wilson Royal Devon University Healthcare NHS Foundation Trust 

Purpose: This study aimed to explore the impact of uncertainties in needle reconstruction on trans-rectal ultrasound prostate planning. While an independent plan check, inclusive of needle reconstruction, is standard practice, accurate reconstruction proves challenging due to needle visualisation limitations caused by ultrasound image distortion from the stainless-steel needles, and subtle discrepancies among planners can occur. 

Methods: Systematic shifts were applied between needles and contours in 5 previous plans, simulating a worst-case scenario. Shift magnitudes were determined by visual needle position uncertainty assessments, resulting in lateral and ant/post shifts of 1.5mm each, and a 3mm shift in the sup/inf direction. The plans were then recalculated based on these shifted positions and compared with the original treatment plans using clinically relevant parameters. 

Results: Lateral needle positioning uncertainties of 1.5mm had least impact on PTV coverage, with a mean reduction in D90 of 1.3±0.7%. The most significant impact on PTV D90 (-1.9±0.7%) resulted from the 3mm shifts in the sup/inf direction. Errors in rectal doses were pronounced when needles were erroneously reconstructed higher than their actual positions, leading to a potential 13% increase in rectal D2cc with a 1.5mm shift in this direction. Urethral doses were less affected, with mean differences in D10 and D30 <1.5% for all shifts, although V150>0 was introduced in some cases. 

Conclusion: An independent plan check with a focus on needle reconstruction is essential for gross error detection. Minor uncertainties in lateral and sup/inf needle positioning may not significantly affect PTV coverage or OAR doses, although particular attention should be paid when needles are close to OARs. Incorrectly positioning needles anteriorly may elevate rectal doses and should be a focus for checking. During planning, leaving space between isodoses and critical structures can mitigate overlap risks stemming from reconstruction uncertainty.