http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:2876 INTRODUCTION: To achieve high precision prostate radiotherapy requires accurate delineation of the prostate combined with accurate targeting of treatment with image-guided techniques. MRI scans have been shown to have lower inter-observer variability in prostate contouring than CT scans. If dose planning could also be performed on MRI scans then uncertainties due to registration to a CT scan would be reduced, as well as the resources required to use two imaging modalities. The feasibility of dose planning directly on MRI scans is investigated in this study. METHODS: Ten patients treated at the Newcastle Mater Hospital had three 0.9 × 7 mm gold markers implanted by a urologist under trans-rectal guidance. Each patient then underwent a planning CT with urethral contrast. The prostate was delineated on the CT for field definition as per our normal protocol. Patients were treated with daily on-line corrections using electronic portal images of the implanted markers. The patients also received a MRI scan in the treatment position following their planning CT. Several MRI sequences were utilized; a T2 whole pelvis scan, a T2 small field-of-view scan to visualise prostate borders, and a T2* gradient echo scan to visualise implanted markers. All scans were transferred to the Pinnacle treatment planning system. The CT and MRI scans were registered using bony anatomy. Dose plans were produced on both sets of scans. For the CT scans, plans were produced with full electron density information, a bulk uniform density of 1, and bulk density plus a density of 1.3 assigned to the bone regions. For the MRI plans, uniform and uniform+bone densities were assigned to the scans and dose plans using the same beam arrangements produced. The doses to the ICRU point for the dose plans were then compared. RESULTS: Dose plans for two patients have been analyzed to date. Assigning a bulk uniform density to the CT scan was found to give average dose errors of 2.7% to the ICRU point compared to the full density plan. When the bulk density of bony anatomy was added, this was reduced to within 1%. Bulk density MRI plans gave average dose errors of 3.7%, which was reduced to 2.3% with bulk density of bone added. [Figure 1. Example of bulk density CT and MRI dose plans.] DISCUSSION & CONCLUSIONS: The CT results suggest that scans with bulk densities assigned produce reasonably accurate dose plans for prostate. By optimizing the densities used, further improvements may be achieved. However the errors when bulk densities were assigned to MRI scans were greater. This is due to differences in patient contour due to both MRI spatial uniformity and patient positioning differences. Futher work is required to quantify the errors due to spatial unformity differences with a rigid phantom. 2013-03-01T05:00:06.459Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:5608 The aim of the study was to determine prostate set-up accuracy and set-up margins with off-line bony anatomy-based imaging protocols, compared with online implanted fiducial marker-based imaging with daily corrections. Eleven patients were treated with implanted prostate fiducial markers and online set-up corrections. Pretreatment orthogonal electronic portal images were acquired to determine couch shifts and verification images were acquired during treatment to measure residual set-up error. The prostate set-up errors that would result from skin marker set-up, off-line bony anatomy-based protocols and online fiducial marker-based corrections were determined. Set-up margins were calculated for each set-up technique using the percentage of encompassed isocentres and a margin recipe. The prostate systematic set-up errors in the medial–lateral, superior–inferior and anterior–posterior directions for skin marker set-up were 2.2, 3.6 and 4.5 mm (1 standard deviation). For our bony anatomy-based off-line protocol the prostate systematic set-up errors were 1.6, 2.5 and 4.4 mm. For the online fiducial based set-up the results were 0.5, 1.4 and 1.4 mm. A prostate systematic error of 10.2 mm was uncorrected by the off-line bone protocol in one patient. Set-up margins calculated to encompass 98% of prostate set-up shifts were 11–14 mm with bone off-line set-up and 4–7 mm with online fiducial markers. Margins from the van Herk margin recipe were generally 1–2 mm smaller. Bony anatomy-based set-up protocols improve the group prostate set-up error compared with skin marks; however, large prostate systematic errors can remain undetected or systematic errors increased for individual patients. The margin required for set-up errors was found to be 10–15 mm unless implanted fiducial markers are available for treatment guidance. 2012-01-30T04:06:48.536Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:5391 The aims of this study were to investigate whether intrafraction prostate motion can affect the accuracy of online prostate positioning using implanted fiducial markers and to determine the effect of prostate rotations on the accuracy of the software-predicted set-up correction shifts. Eleven patients were treated with implanted prostate fiducial markers and online set-up corrections. Orthogonal electronic portal images were acquired to determine couch shifts before treatment. Verification images were also acquired during treatment to assess whether intrafraction motion had occurred. A limitation of the online image registration software is that it does not allow for in-plane prostate rotations (evident on lateral portal images) when aligning marker positions. The accuracy of couch shifts was assessed by repeating the registration measurements with separate software that incorporates full in-plane prostate rotations. Additional treatment time required for online positioning was also measured. For the patient group, the overall postalignment systematic prostate errors were less than 1.5 mm (1 standard deviation) in all directions (range 0.2–3.9 mm). The random prostate errors ranged from 0.8 to 3.3 mm (1 standard deviation). One patient exhibited intrafraction prostate motion, resulting in a postalignment prostate set-up error of more than 10 mm for one fraction. In 14 of 35 fractions, the postalignment prostate set-up error was greater than 5 mm in the anterior–posterior direction for this patient. Maximum prostate rotations measured from the lateral images varied from 2° to 20° for the patients. The differences between set-up shifts determined by the online software without in-plane rotations to align markers, and with rotations applied, was less than 1 mm (root mean square), with a maximum difference of 4.1 mm. Intrafraction prostate motion was found to reduce the effectiveness of the online set-up for one of the patients. A larger study is required to determine the magnitude of this problem for the patient population. The inability in the current software to incorporate in-plane prostate rotations is a limitation that should not introduce large errors, provided that the treatment isocentre is positioned near the centre of the prostate. 2012-01-30T04:06:23.898Z ]]>