Quality indicators and technique for analyzing permanent I-125 prostate seed implants: Seven years postimplant dosimetry evaluation
ABSTRACT The roles of postimplant dosimetry (PID) after permanent I-125 implant are to identify and rectify inadequate implants, assess the dosimetric quality indicators, and evaluate dose to the organs at risk. The aim of the current work was to assess the progress of prostate implant quality via postimplant dosimetry over seven years.
The following factors were investigated to assess the PID results obtained over seven years: the improvement in implant technique, the computed tomography (CT) delineation-based PID versus ultrasound-CT (US-CT) fusion-based PID, and the evolution of parameters such as D90 and NDR (natural dose ratio). The correlation between dosimetric parameters and clinical outcomes were also evaluated.
The seven years PID learning curve shows clear changes in dosimetric trend for the 265 patients studied. Manual target contouring on CT was shown to overestimate the prostate volume when compared to ultrasound data, translating to CT-based D90 values being lower than US-CT D90. It was found that NDR does not contribute with additional dosimetric information to postimplant dosimetry evaluation. Patient follow-up data show that 4.7% patients have relapsed, and urinary retention was reported in 2.7% of the patients.
CT-based PID was found less reliable than US-CT fusion-based PID due to target volume overestimation. This result shows the biased interpretation of low D90 values based on CT-based targeting, providing unreliable correlations between D90 and relapse probability. The low urinary retention statistics are in accordance with the PID data for the organ, as only 5.2% of patients had their PID D10 > 218 Gy, i.e., above the recommended GEC-ESTRO guidelines. Besides the "learning" component, the PID D90 curve is influenced by the PID technique.
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ABSTRACT: BACKGROUND: Low risk prostate cancers are commonly treated with low dose rate (LDR) brachytherapy involving I-125 seeds. The implementation of a 'live-planning' technique at the Royal Adelaide Hospital (RAH) in 2007 enabled the completion of the whole procedure (i.e. scanning, planning and implant) in one sitting. 'Live-planning' has the advantage of a more reliable delivery of the planned treatment compared to the 'traditional pre-plan' technique (where patient is scanned and planned in the weeks prior to implant). During live planning, the actual implanted needle positions are updated real-time on the treatment planning system and the dosimetry is automatically recalculated. The aim of this investigation was to assess the differences and clinical relevance between the planned dosimetry and the updated real-time implant dosimetry. METHODS: A number of 162 patients were included in this dosimetric study. A paired t-test was performed on the D90, V100, V150 and V200 target parameters and the differences between the planned and implanted dose distributions were analysed. Similarly, dosimetric differences for the organs at risk (OAR) were also evaluated. RESULTS: Small differences between the primary dosimetric parameters for the target were found. Still, the incidence of hotspots was increased with approximately 20% for V200. Statistically significant increases were observed in the doses delivered to the OAR between the planned and implanted data; however, these increases were consistently below 3% thus probably without clinical consequences. CONCLUSIONS: The current study assessed the accuracy of prostate implants with I-125 seeds when compared to initial plans. The results confirmed the precision of the implant technique which RAH has in place. Nevertheless, geographical misses, anatomical restrictions and needle displacements during implant can have repercussions for centres without live-planning option if dosimetric changes are not taken into consideration.Radiation Oncology 11/2012; 7(1):196. DOI:10.1186/1748-717X-7-196 · 2.36 Impact Factor
- The British journal of radiology 03/2013; 86(1026). DOI:10.1259/bjr.20130058 · 1.53 Impact Factor
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ABSTRACT: Low dose rate prostate brachytherapy treatments began at the Royal Adelaide Hospital (RAH), Australia, in September 2004. This paper will focus on the evolution of treatment technique since then showing how procedural improvements have enabled timely diagnosis of under-dose and scheduling of top-up treatments for sub-optimum implants, and how significant time savings have been achieved for staff and patients. In addition, implant dosimetry trends over this period have been investigated and results are presented. Iodine-125 seeds (Oncura model 6711) have been used since LDR prostate treatments began, with an aim to deliver a prostate dose of 145 Gy. Three key changes in implant technique took place during the period Sept 2004 to Sept 2011. The live implant dosimetry trends of the prostate D90, urethra V150, and rectum D0.1cc and D2.0cc, were assessed to see if the change in technique had an impact on the treatment planning and seed deployment. The switch from manual loading of seeds to pre-loaded needles and the change from a two-step pre-planning procedure to live planning have realized the greatest time savings with approximately 1.0 FTE physicist day saved per 2 patient implant day and 2 patient visits saved per treatment. Dosimetric parameters also improved with mean implant D90s rising from 166 Gy to 180 Gy. The average Urethra D10 also increased over the study group, rising from 186 Gy to 199 Gy while the rectum dose remained unchanged. Both rectum and urethra dose remained below GEC-ESTRO guidelines despite the observed rise in urethral dose.Physica Medica 09/2012; DOI:10.1016/j.ejmp.2012.07.004 · 1.85 Impact Factor