Room: AAPM ePoster Library
Purpose: some pelvic tumors, due to the complex shape of the target and the surrounding nerve, blood vessels and other OARs , it is difficult to obtain a better dose distribution by manual implantation. Therefore, this study proposes a mathematical modeling method which can individually improve the accuracy of implantation and the dose distribution in brachytherapy treatment planning.
Methods: patient with recurrent rectal cancer whose lesions were located in posterior vagina wall and left posterior wall of the cervix was selected. The vaginal mucosa was extended with a cylindrical applicator and thin CT scanning was performed at the bladder lithotomy position. Structures were imported from TPS into MATLAB to establish the mathematical model. According to relative anatomical position of organs, the model can be iteratively analysed by combing geometric segmentation algorithm and dose optimization algorithm together. With some restrictions rules (needle distance, angel, depth), optimal needle arrangements are reversely calculated, and preoperative distribution (plan1) can be obtained. Channels were difined as the part of needle paths lengthened 5mm beyong the marked vulvar skin in reserve direction.By using 3D printing technology, the template with novel channels and marked skin was exactly Boolean summed and printed. Then CT scanning and dose calculation (plan2) was performed.
Results: CT images showed that the needles guided by template can reach expected position. Compared plan1 with plan2, D90 of the CTV were 750cGy vs. 745cGy, D2cc of the bladder were 295cGy vs. 303cGy, HI were 3.18 vs. 3.23, CI were 0.75 vs. 0.70. Dosimetry parameters and dwell points weight were similiar
Conclusion: Compared with the conventional methods, the template guided surgery can not only reduce damage risk and improve the accuracy of implantation, but also potentially improve treatment quality. Moreover, further mathematical and dosimetry algorithms need to be discussed to optimize better needle channels.