Electronic portal imaging by rose wekesa

Electronic portal imaging by rose wekesa

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  ELECTRONIC PORTAL IMAGING:Achieving accuracy and precision for external beam radiation therapy Rose Wekesa : Cancer Care Kenya, Nairobi
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  Image Comparison DigitallyReconstructed Radiograph Portal Image
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  Radiotherapy goal •The inherent goal of radiation therapy is to eradicate all the cancer cells or palliate symptoms by delivering enough doses to the tumour, while minimizing injury to normal tissues • This is normally described in terms of tumour control probability (TCP) and normal tissue complication probability (NTCP). • Imaging for treatment planning and for verification of treatment among other factors makes it possible to achieve the radiotherapy goal. • This presentation focuses on treatment verification by portal imaging.
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  TCP and NTCPCurves SuntharalingamN, Podgorsak EB & Hendry JH 2005. Basic radiobiology. IAEA. Vienna
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  Introduction Radiation therapyis one of the safest and most effective ways to treat cancer. Errors do occur, but they are extremely rare, with a very small fraction of treatments involving an incident that puts a patient at risk of harm. These errors can be avoided if we put certain measures in our daily practice.
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  Sequential process ofplanning and delivering radiotherapy.
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  Purpose • Toevaluate patient set-up variations for oesophageal cancers treated with External Beam Radiation Therapy • Six anatomical landmarks were selected for comparison and recorded; the X (Left-Right, L-R), Y(Superior-Inferior, S-I) and Z (Anterior-Posterior, A-P) directions • Data was used to set acceptable tolerance limits for portal imaging of the oesophagus.
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  Methods and Materials • Fifty seven patients with locally advanced disease treated with chemoradiation were randomly selected for this study over a period of two years. • Patients were positioned using body tattoos. • EPI's were performed prior to treatment and registered to the digitally reconstructed radiographs (DRR). • DRRs were used to adjust patient setups before treatment delivery. A total of 163 EPI pairs were analyzed and errors calculated • Orthogonal pair images were acquired, which were used to give displacement • If a patient had a single field or two opposing fields, the accuracy of field placement was assessed in two dimensions only.
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  Treatment verification Process PRE-TREATMENT: Acquire reference images TREATMENT 1 Fraction 1 Acquire portal images 2 Fraction 1 3 Fraction 1 Acquire portal images Acquire portal images Online review of images against reference Gross error? Action level? No Yes Continue with current set up STOP: Revise set up, re-image Calculate the mean displacement (MD) in all 3 axes No Yes MD Action level? Continue with current set up Revise set up, re-image X2 #s Fraction 4 Fraction 5 No imaging No imaging Portal Imaging Portal Imaging Calculate the mean displacement (MD) in all 3 axes MD No Action level? Yes Continue with current set up STOP: Investigate further Weekly Portal Imaging
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  Portal imaging byanatomical matching • Isocenter variation in X and in Y directions were measured on anterior (AP) portal images, whereas, in Z and Y direction were measured on lateral portal images. • After the anatomical matching was performed on the treatment fields for an individual patient, variations were recorded into a Microsoft Excel spreadsheet. • The reported X, Y and Z displacement of isocenter between simulation and treatment was applied into the appropriate shifts along each body axis.
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  Radiotherapy Targeting! •For treatment, same position as of simulation is set • Lasers, immobilization & tattoo's are used to verify the correct position.
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  during Radiation therapy  Two questions always emerge. 1. Are they hitting the right spot? 2. Am I getting the right dose?
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  Anatomical match structuresused
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  RESULTS Displacement Noof Patients Portal image pairs (Total=163) Total Mean (Mpop) mean (%) Left-Right (L-R) 57 57 2.05 3.6 Supero- Inferior (S-I) 57 57 2.79 4.9 Antero-posterior (A-P) 57 49 3.09 6.3
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  DISCUSSION: • Thesystematic and random errors for EPI’s were; 2.05mm in L-R, 2.79mm in S-I and 3.09mm in A-P directions. • The population-based mean variation is less than 5 mm, thus the set-up provides sufficient targeting for all of the patients. • Consistent with recommendations by the RCR, Institute of Physics & Engineering in Medicine & Royal college of radiographers (in line with ICRU Reports 50 & 62) • Variations were more significant during the first sessions in treatment than the weekly portals. • This could be attributed to patient relaxing in the course of the treatment and getting over the anxiety.
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  CONCLUSION • Radiotherapyverification is a process that helps us ascertain that we are treating tumor volume as planned. • EPI results in different position correction for verification of radiotherapy in all malignancies. •When protocols are formulated & used at specified intervals, patients can benefit in terms of treatment accuracy since most of the set up errors if not all can be corrected. • Portal imaging is therefore a must in every radiation treatment.
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