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Study of dose escalation protocols in prostate cancer radiation therapy with patient realignment by using internal fiducial markers Zhang, Miao


Use of internal fiducial markers and electronic portal imaging (EPID) to realign patients has been shown to significantly reduce positioning uncertainties in prostate radiation treatment. This creates the possibility of improving the treatment by decreasing the planning target volume (PTV) margin added on the clinical target volume (CTV), which in turn may allow dose escalation. As a first step we do test on 3 patients. Conformal treatment plans for 3 prostate cancer patients were evaluated by using different PTV margins with dose prescription of 70Gy/35fr initially. Two beam arrangements, 4-Field-Box (4FB) and 4-Field-Oblique (4FO), were used. Then, two dose escalation schemes, 74Gy and 78Gy, with tighter prescribed PTV margins chosen from the first simulation were tested. A Monte Carlo model was developed to simulate the daily organ motion and calculate the dose to organs. After the whole treatment, dose-volume histograms were produced and tumour control probability (TCP), equivalent uniform dose (EUD) and the effective dose to critical organs (Deff) were calculated. By comparing the biological factors, optimized dose escalation schemes were found. The results show that using internal fiducial markers and EPID, the prescription dose can be escalated to 78Gy/37fr with a 4mm PTV margin. Based on the available dose-response data for intermediate ' risk prostate patients this is estimated to result in a 20% increase of TCP and significantly reduced rectal complications. From these results, another test on 20 patients was performed to test the general validity of the dose escalation, which counts the second step of this project. We compared the outcome of two plans: one is 70Gy/35fr, 10mm PTV margin and without patient realignment (Reference Plan) and another is 78Gy/39fr, 5mm PTV margin with patient realignment (Escalated Plan). Four-field-oblique (gantry angles 35°, 90°, 270°, 325°) beam arrangement was used. Using the same method described before. Results show that for intermediate risk prostate patients by using dose escalation to 78Gy/39fr with a 5mm PTV margin will provide a 20% increase of local control and significantly reduced rectal complications.

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