Intrafraction displacement of prone versus supine prostate positioning monitored by real‐time electromagnetic tracking

Abstract

Implanted radiofrequency transponders were used for real‐time monitoring of the intrafraction prostate displacement between patients in the prone position and the same patients in the supine position. Thirteen patients had three transponders implanted transperineally and were treated prone with a custom‐fitted thermoplastic immobilization device. After collecting data from the last fraction, patients were realigned in the supine position and the displacements of the transponders were monitored for 5–7 minutes. Fourier transforms were applied to the data from each patient to determine periodicity and its amplitude. To remove auto correlation from the stream of displacement data, the distribution of short‐term and long‐term velocity components were calculated from Poincaré plots of paired sequential vector displacements. The mean absolute displacement was significantly greater prone than supine in the superior–inferior (SI) plane (1.2±0.6mm vs. 0.6±0.4mm, p=0.015), but not for the lateral or anterior–posterior (AP) planes. Displacements were least in the lateral direction. Fourier analyses showed the amplitude of respiratory oscillations was much greater for the SI and AP planes in the prone versus the supine position. Analysis of Poincaré plots confirmed greater short‐term variance in the prone position, but no difference in the long‐term variance. The centroid of the implanted transponders was offset from the treatment isocenter by > 5 mm for 1.9% of the time versus 0.8% of the time for supine. These results confirmed significantly greater net intrafraction prostate displacement of patients in the prone position than in the supine position, but most of the difference was due to respiration‐induced motion that was most pronounced in the SI and AP directions. Because the respiratory motion remained within the action threshold and also within our 5 mm treatment planning margins, there is no compelling reason to choose one treatment position over the other.PACS number: 87.50.st

Reduction of intra-fraction prostate motion – Determining optimal bladder volume and filling for prostate radiotherapy using daily 4D TPUS and CBCT

“…A full bladder has been shown to reduce inter-fraction setup error when compared to an empty bladder [10], although difficulty maintaining a consistent bladder volume has been reported in the literature. Nakamura et al [11] and O'Doherty et al [12] both observed inconsistent bladder volume during the course of radiotherapy when using a full bladder protocol, whilst irregular prostate motion has been attributed to both bladder filling and patient movement [13]. Previous studies have also investigated the impact of rectal diameter on prostate motion [14][15][16].…”

Effect of metal hip prosthesis on the accuracy of electromagnetic localization tracking

“…4,11 Our previous work has shown that obese patients are tracked just as accurately as nonobese men, 12 and that patients may be monitored in either the prone or supine position. 13 Currently, the manufacturer does not recommend implantation of transponders in patients with a hip prosthesis due to concerns that metallic hip material may interfere with electromagnetic tracking of the transponders. To our knowledge this has not been validated in the setting of a peer-reviewed study but is instead argued on a theoretical basis.…”

Image-guided radiotherapy reduces the risk of under-dosing high-risk prostate cancer extra-capsular disease and improves biochemical control

“…An additional limitation of our study is that 3D–translations of the prostate gland were simulated, which may or may not reflect the motion experienced by the whole gland and the vesicles [ 25 ]. Further, we have disregarded intra-fraction motion, which may vary (marginally) for supine and prone positioning [ 26 ]. In addition, potential rotations or deformations were not included in the simulation model.…”