6 Modern Imaging in Brachytherapy

146 Modern Imaging

6 Image Assisted Quality Control of Dose Delivery In certain situations it seems to be advantageous to control and verify the applicator position related to the target and to organs at risk during or after brachytherapy. This can be done in principle by any imaging method available, as far as the patient with the applicator or the radioactive sources can be examined and taken to the respective imaging device (in contrast to external beam therapy). Usually, the imaging method chosen is the one used for definitive treatment planning.

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Fig 5.16: Prostate Cancer: Image assisted quality control of dose distribution in a patient after iodine seed implantation (compare Fig 5.5 and 13: identical patient): pelvic X-ray (A) and transverse MRI (B) with delineation of the PTV, the urethra and rectum on the MRI and isodose lines based on 3D dose calculation. The post planning DVH (C) indicates that 93% of the PTV is enclosed by the prescribed dose (140 Gy) (“V100”) (a), about 5% of the delineated rectal wall (< 1cm 3 ) receive more than 110 Gy (b), and less than 5% of the prostatic urethra receive more than 250 Gy. Compared to the DVH taken from the on line definitive treatment planning based on ultrasound, there is a slight decrease in PTV coverage (“V100”), a similar dose volume relation for the rectum, and a slight increase in the volume of the urethra that receives 250 Gy. (level 2/3) (compare 5.13B).