Displacement patterns of stranded I-125 seeds after permanent brachytherapy of the prostate: Dosimetry in the operating room put into perspective.

BACKGROUND AND PURPOSE: The reliability of post-implant dosimetry in the OR depends on the geometrical variability of implant and anatomy after the procedure. The purpose was to gain detailed information on seed displacement patterns in different sectors of the prostate. MATERIALS AND METHODS: Of 33 patients with stranded seed implants the seed geometry and the dose distribution were compared between the situation in the OR just after the procedure, based on ultrasound images, and the situation after 1month, based on registered CT and MR images. RESULTS: There was a substantial displacement of ventral seeds of 3.8±2.5mm in caudal direction (p<0.001). Of these ventral seeds cranially located seeds moved more than caudally located seeds, 4.5±2.7mm and 2.9±2.6mm, respectively (p<0.001). The D90 in the dorsal-caudal and ventral-caudal sectors increased with respectively 44±20Gy and 29±28Gy (p<0.001) and decreased with 17±31Gy in the ventral-cranial sector (p=0.008). CONCLUSIONS: There were substantial changes in dose distribution 1month after the procedure, mainly due to implant and prostate shrinkage and displacement of ventral seed strands in caudal direction. When performing dynamic dosimetry or dosimetry at the end of the procedure the effect of these phenomena has to be taken into account when using stranded seeds.

Re-distribution of brachytherapy dose using a differential dose prescription adapted to risk of local failure in low-risk prostate cancer patients.

BACKGROUND AND PURPOSE: We investigated the application of a differential target- and dose prescription concept for low-dose-rate prostate brachytherapy (LDR-BT), involving a re-distribution of dose according to risk of local failure and treatment-related morbidity. MATERIAL AND METHODS: Our study included 15 patients. Multi-parametric MRI was acquired prior to LDR-BT for gross tumor volume (GTV) delineation. Trans-rectal ultrasound (US) images were acquired during LDR-BT for prostate gland- (CTV(Prostate)) and organs at risk delineation. The GTV contour was transferred to US images after US/MRI registration. An intermediate-risk target volume (CTV(Prostate)) and a high-risk target volume (CTV(HR)=GTV+5 mm margin) were defined. Two virtual dose plans were made: Plan(risk-adapt) consisted of a de-escalated dose of minimum 125 Gy to the CTV(Prostate) and an escalated dose to 145-250 Gy to the CTV(HR); Plan(ref) included the standard clinical dose of minimum 145 Gy to the CTV(Prostate). Dose-volume-histogram (DVH) parameters were expressed in equivalent 2 Gy fractionation doses. RESULTS: The median D(90%) to the GTV and CTV(HR) significantly increased by 44 Gy and 17 Gy, respectively when comparing Plan(risk-adapt) to Plan(ref). The median D(10%) and D(30%) to the urethra significantly decreased by 9 Gy and 11 Gy, respectively and for bladder neck by 18 Gy and 15 Gy, respectively. The median rectal D(2.0cm(3)) had a significant decrease of 4 Gy, while the median rectal D(0.1cm(3)) showed an increase of 1 Gy. CONCLUSIONS: Our risk adaptive target- and dose prescription concept of prescribing a lower dose to the whole gland and an escalated dose to the GTV using LDR-BT seed planning was technically feasible and resulted in a significant dose-reduction to urethra and bladder neck.

Is there a relation between the radiation dose to the different sub-segments of the lower urinary tract and urinary morbidity after brachytherapy of the prostate with I-125 seeds?

BACKGROUND AND PURPOSE: To investigate possible relationships between the dose to the sub-segments of the lower urinary tract and lower urinary tract symptoms (LUTS) after brachytherapy of the prostate. MATERIALS AND METHODS: This study involved 225 patients treated for prostate cancer with I-125 seeds. Post-implant dose-volume histograms of the prostate, urethra, bladder wall, bladder neck and external sphincter were determined. Endpoints were the mean and the maximum International Prostate Symptom Score (IPSS) during the first 3months after the treatment. For binary analysis the patients were stratified in a group with enhanced LUTS and a group with non-enhanced LUTS. RESULTS: The dose to 0.5cm(3) of the bladder neck 'D0.5cc-blne' (p=0.002 and p=0.005), the prostate volume prior to treatment 'Vpr-0' (p=0.005 and p=0.024) and the pre-treatment IPSS (both p<0.001) were independently correlated with mean and maximum IPSS, respectively. Of the patients with a D0.5cc-blne⩾175Gy and a Vpr-0⩾42cm(3), 68% suffered from enhanced LUTS, against just 30% of the other patients (p<0.0001). CONCLUSIONS: Pre-treatment IPSS, prostate volume and dose to the bladder neck are correlated with post-implant IPSS. A combination of a large prostate and a high dose to the bladder neck is highly predictive for enhanced early LUTS.

Minimizing the number of implantation needles for prostate (125)I brachytherapy: an investigation of possibilities and implications.

PURPOSE: Reduction of the number of implantation needles for prostate brachytherapy will shorten the duration of implantation procedures and possibly reduce trauma-related morbidity. The purpose of this study was to investigate possibilities for the minimization of the number of needles and to investigate the consequences for the dose distribution. METHODS AND MATERIALS: A planning study for six different prostate volumes was performed. The number of needles was minimized by changing fixed 1cm interseed spacing to free interseed spacing within the needles and by increasing the seed activity. Dose-volume parameters of prostate and organs at risk (OAR) bladder, rectum, and urethra were determined. For plans with different needle and seed configurations, the sensitivity for random seed placement inaccuracies was tested. Dose distributions of realized implants based on fixed (n=21) and free interseed spacing (n=21) were compared. RESULTS: The average number of needles (±1 standard deviation) could be reduced from 18.8±3.6 to 12.7±2.9 (-33%) when changing from fixed interseed spacing to free interseed spacing and subsequently to 7.3±1.0 (-42%) by increasing the seed strength from 0.57U to 1.14U. These needle reductions resulted in increased dose inhomogeneity within the prostate and increased sensitivity of dose-volume parameters of the OAR for random geometrical inaccuracies. Introduction of free interseed spacing in our clinic resulted in very satisfactory dose coverage of the prostate (D(90)=172±17Gy), while the average number of needles was reduced by 30%. CONCLUSIONS: Substantial reduction of the number of implantation needles is possible without compromising adequate dose coverage of the prostate. However, the chance of an unpredicted high dose to the OAR increases as fewer needles are used.

An analysis of the relation between physical characteristics of prostate I-125 seed implants and lower urinary tract symptoms: bladder hotspot dose and prostate size are significant predictors.

PURPOSE: Lower urinary tract symptoms are frequently observed after I-125 seed implantation of the prostate. More knowledge about causes and predictors is necessary to be able to develop less toxic implantation techniques. The aim of this study was to identify implantation related factors that contribute to post-implant urinary morbidity. MATERIALS AND METHODS: Analysed was a group of 72 patients that filled in a symptom score questionnaire before, 3 months and 6 months after implantation as well as a group of 15 patients that suffered from acute urinary retention. Several dose-volume parameters of prostate, urethra and bladder wall were determined based on a post-implant TRUS-CT scan. RESULTS: The dose to a 1cm(3) hotspot in the bladder wall (D1cc-bl) as well as the prostate volume were independently correlated with urinary morbidity symptom scores at 3 months (p=0.006 and p=0.005, respectively) and at 6 months (p=0.001 and p=0.015, respectively) after implantation. The number of implanted seeds and the D1cc-bl were significant discriminators (p<0.001 and p=0.015, respectively) for either mild or severe early urinary morbidity. CONCLUSION: Bladder hotspot dose appears to be an important dosimetric predictor for urinary morbidity both at 3 months and at 6 months after implantation. Other predictors are prostate volume, or equivalently, the number of implanted seeds.

The influence of geometrical changes on the dose distribution after I-125 seed implantation of the prostate.

PURPOSE: After prostate implantation, dose calculation is usually based on a single imaging session, assuming no geometrical changes occur during the months of dose accumulation. In this study, the effect of changes in anatomy and implant geometry on the dose distribution was investigated. MATERIALS AND METHODS: One day, 1 month and 312 months after seed implantation, a combined TRUS-CT scan was made of 13 patients. Based on these scans changes in dose rate distribution were determined in prostate, urethra and bladder and a 'geometry corrected' dose distribution was estimated. RESULTS: When based on the day-1 scan, parameters representing high dose volumes in prostate and urethra were largely underestimated: V150 of the prostate 18+/-10% and V120 of the urethra 47+/-32%. The dose to a 2cm(3) hotspot in the bladder wall (D2cc), however, was overestimated by 31+/-35%. Parameters based on scans 1 month post-implant or later were all within +/-5% of geometry corrected values. CONCLUSION: Values meant to indicate the adequacy of dose coverage of the prostate, V100 and D90, were not influenced by geometrical changes and were independent of the post-implant scan date. Other parameters representing high dose volumes changed strongly within the first month after implantation.