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Abstract
BackgroundThe use of intraprostatic gold fiducial markers (FMs) ensures highly accurate and precise image-guided radiation therapy for patients diagnosed with prostate cancer thanks to the ease of localising FMs on photon-based imaging, like Computed Tomography (CT) images. Recently, Magnetic Resonance (MR)-only radiotherapy has been proposed to simplify the workflow and reduce possible systematic uncertainties. A critical, determining factor in the accuracy of such an MR-only simulation will be accurate FM localisation using solely MR images.PurposeThe aim of this study is to evaluate the performances of manual MR-based FM localisation within a clinical environment.MethodsWe designed a study in which 5 clinically involved radiation therapy technicians (RTTs) independently localised the gold FMs implanted in 16 prostate cancer patients in two scenarios: employing a single MR sequence or a combination of sequences. Inter-observer precision and accuracy were assessed for the two scenarios for localisation in terms of 95% limit of agreement on single FMs (LoA)/ centre of mass (LoA CM) and inter-marker distances (IDs), respectively.ResultsThe number of precisely located FMs (LoA <2 mm) increased from 38/48 to 45/48 FMs when localisation was performed using multiple sequences instead of single one. When performing localisation on multiple sequences, imprecise localisation of the FMs (3/48 FMs) occurred for 1/3 implanted FMs in three different patients. In terms of precision, we obtained LoA CM within 0.25 mm in all directions over the precisely located FMs. In terms of accuracy, IDs difference of manual MR-based localisation versus CT-based localisation was on average (±1 STD) 0.6 ±0.6 mm.ConclusionsFor both the investigated scenarios, the results indicate that when FM classification was correct, the precision and accuracy are high and comparable to CT-based FM localisation. We found that use of multiple sequences led to better localisation performances compared with the use of single sequence. However, we observed that, due to the presence of calcification and motion, the risk of mislocated patient positioning is still too high to allow the sole use of manual FM localisation. Finally, strategies to possibly overcome the current challenges were proposed.
Highlights
The use of intraprostatic gold fiducial markers (FMs) ensures highly accurate and precise image-guided radiation therapy for patients diagnosed with prostate cancer thanks to the ease of localising Fiducial marker (FM) on photon-based imaging, like Computed Tomography (CT) images
Inter-observer precision and accuracy were assessed for the two scenarios for localisation in terms of 95% limit of agreement on single FMs (LoA)/ centre of mass (LoACM) and inter-marker distances (IDs), respectively
IDs difference of manual Magnetic Resonance (MR)-based localisation versus CT-based localisation was on average (±1 standard deviation (STD)) 0.6±0.6 mm
Summary
The use of intraprostatic gold fiducial markers (FMs) ensures highly accurate and precise image-guided radiation therapy for patients diagnosed with prostate cancer thanks to the ease of localising FMs on photon-based imaging, like Computed Tomography (CT) images. The use of intraprostatic fiducial markers (FMs) ensures highly accurate and precise image-guided radiation therapy (IGRT) for patients diagnosed with prostate cancer [1]. Gold FMs are generally employed and their use allows accurate prostate localisation [7] on photon-based images thanks to their high density, which increases radio opacity [8]. To ensure geometrically accurate IGRT treatments, FMs are localised on computed tomography (CT) during treatment simulation and they are localised on kV/MV imaging before patient irradiation to verify and eventually match the pre-treatment patient position with the planned position [9, 10]. The distinctness of the contrast ensures that false classification of FMs, e.g. due the presence of calcifications, is unlikely
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