SU‐E‐T‐222: Contribution Of In Vivo Dose Measurement To The Intensity Modulated Radiotherapy Technique In The Treatment Of Prostate Cancer

Abstract

Purpose: The contribution of in‐vivo dose measurement of organs at risk by TLD and semiconductor detectors during Intensity‐modulated radiotherapy technique in treatment of prostate cancer was studied. Methods: Appropriate prostate cancer patients target and organs at risk contours that managed for IMRT planning were fusion on CT images of Rando phantom. For PTV1 and 2 the equally angel nine fields (within 200°− 160°)IMRT plans were designed using 6MV photon energy with 180cGy per fraction to total dose of 45 and 72Gy respectively. The point dose and two‐dimensional dose measurements for the quality control evaluation of IMRT plans were done and found in appropriate limits. The 3 sub‐slab of Rando phantom were re‐made from paraffin and rectum cavity was created in accordance with the probe for measuring rectal dose. Based on dosimetric method each dosimeter was selected and located on measurement region. Prostate IMRT plans were applied to the phantom. In‐vivo dose measurements were repeated several times by TLD and diode, obtained dose values for rectum and bladder compared with TPS. Results: Both semiconductor and TLD dose measurement values for bladder and rectum is generally in agreement with the TPS. The rectum dose measurement values were differing from TPS up to 30% in intense dose gradient regions. This is because when the coordinates of the reference points are in intense dose gradient regions, +/− 1 mm changes in position create +/− 3–10% difference between the calculated and measured doses. Conclusion: The intracavitary rectum and bladder probes used for brachytherapy dosimetry applications could be applicable in external radiation treatments. In‐vivo dosimetry has an important role in the quality assurance of radiotherapy, especially to preventing errors which may occur in every stage of treatment. In this context,for more complex treatment techniques like IMRT the traditional in‐vivo dosimetric methods using TLD and semiconductor diodes was found to be reliable.