Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology
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To use radiobiological modelling to estimate the number of initial days of treatment imaging required to gain most of the benefit from off-line correction of systematic errors in the conformal radiation therapy of prostate cancer. ⋯ Daily variations of target position markedly reduced the TCP if small margins were used. Off-line correction of systematic errors can only partly compensate for these TCP reductions. The adequate number of treatment imaging days required for systematic error correction depends on the magnitude of the random component compared with the systematic component, and on the size of PTV margin used. For random components equal to or smaller than the systematic component, 3 consecutive treatment imaging days are estimated to be sufficient to gain most of the benefit from correction for current clinically used margins (6-10 mm); otherwise more days are required.
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To evaluate treatment errors from set-up and inter-fraction prostatic motion with port films and implanted prostate fiducial markers during conformal radiotherapy for localized prostate cancer. ⋯ Systematic set-up errors were small using real-time isocentre placement corrections. Patient instruction to help control variation in bladder and rectal distension during therapy may explain the observed small SD for prostate motion in this group of patients. Inter-fraction prostate motion remained the largest source of treatment error, and observed motion was greatest at the gland base. In the absence of real-time pre-treatment imaging of prostate position, sequential portal films of implanted prostatic markers should improve quality assurance by confirming organ position within the treatment field over the course of therapy.