Author:
Seiri Mahnaz,Jaberi Ramin,Solgi Razieh,Shakeri Mahsa,Ghadiri Hossein
Abstract
Abstract
Brachytherapy (BT) is subjected to uncertainties from
imaging, treatment planning, and anatomical variations. It is
necessary to identify the uncertainties, their magnitude, and their
impact on the overall uncertainty of dose delivery. The aim of the
present phantom-based study is to investigate the deformation of the
uterus anatomy induced by BT applicator insertion and the
relationship between dose and location of the inserted applicator. A
novel flexible phantom was designed based on female pelvic anatomy
by the 3D printing process to simulate the deformation and movement
of the uterine during the BT process. The applicator was inserted
into the uterus and in order to simulate the uterus motion, the
phantom was moved in four directions, right, left, down, and up. The
CT and ultrasound images were obtained. A two-stage registration
algorithm was designed to register the ultrasound and CT images in
order to calculate the applicator displacements map. This map was
used to calculate delivered dose error to uterus and rectum and to
correct the planned dose values in treatment planning procedure. The
results showed that in a planned D90 (dose) of 9.4 Gy for the
uterus and maximum dose of 1.8 Gy to the rectum, movement of
applicator leads to a big deviation in final delivered doses. After
the applicator moved to the right and left directions, the D90
delivered to the uterus was 6.2 Gy and 5.6 Gy, respectively.
Moreover, by moving downwards and upwards, the uterus received 0.4
and 1.2 Gy lower than 9.4 Gy. Similarly, the maximum dose to the
rectum in right, left, down, and up directions after applicator
movement were 3.4 Gy, 3.3 Gy, 3.7 Gy and 3.2 Gy, respectively
which highlighted the higher delivered dose to the rectum. The
results of the study demonstrate that applicator displacement can
lead to uterine underdosing and also increase the risk of rectum
irradiation. Ultimately, image-guided brachytherapy and using image
registration can increase the accuracy of treatment and reduce the
errors of delivered dose to target volume and organs at risk,
especially in uterus cancer.
Subject
Mathematical Physics,Instrumentation