PO41 Presentation Time: 4:45 PM: Initial Experience with the New Commercial Aarhus MR Compatible Hybrid Interstitial Brachytherapy Applicator in Indian Setting

Abstract

<h3>Purpose -</h3> We have been using CT based intracavitary applicator in our clinic for cervical cancer. The advent of new hybrid applicator and short sequence cube MRI sequence opened up opportunity to do advanced MRI based brachytherapy in our clinic. We present the initial clinical experience of Aarhus ring and tandem MR compatible hybrid interstitial applicator with both straight and oblique needles and no ring channel (Varian may need to add TM) which was recently approved for use in a patient with bulky cervical cancer. <h3>Material and methods -</h3> A 45 years old lady, with initial diagnosis of carcinoma cervix, stage 1B3, completed External beam radiotherapy to a total dose of 45Gy in 25 Fractions, with a good clinical response, was taken up for further treatment with brachytherapy to a total dose of 28 Gy in 4 fractions. Brachytherapy was split into two applications one week apart and two treatment fractions delivered with each application, with 8 hours gap between each fraction.We used 60 degree Aarhus applicator set with Intrauterine tandem of 40 mm length and outer ring diameter of 32 mm. The Ring includes 19 guide holes for plastic interstitial needles arranged in 2 circles, 9 in inner circle for oblique needles and 10 in outer circle for straight needles.After external radiation patient underwent MRI pelvis with only T2 weighted axial and Cube sequences, which showed residual disease limited to cervix on the right side. The depth of needle insertion into the cervix was measured on MRI to be 3cms. Procedure performed under short general anaesthesia and 4 straight plastic needles through the ring were inserted with two on either side along with 4 cm central Tandem. CT and MR performed for both applications and fused. GTV-primary and HR CTV delineated on MRI, while OARs were delineated on CT. A dose of 7 Gy per fraction prescribed to HR CTV. An optimised plan was generated on eclipse treatment planning system with repeat CT planning for remaining fractions. <h3>Results -</h3> Treatment delivery went uneventful with very minimal blood loss. Average Dose per fraction received by 90 % of volume (D90) of HR CTV was 7.617 Gy and D98 of GTV primary was 10.35 Gy, delivering a total EQD2 of 89 Gy to HR CTV and at the same time delivering 115 Gy to the GTVp. OAR doses were well constrained with Bladder 2cc receiving 79.25 Gy, Rectum 2cc constrained to 53.48 Gy, sigmoid 2cc to 58.99 Gy and small bowel to 51.98 Gy. <h3>Conclusions -</h3> We successfully implemented MRI based planning with new Aarhus applicator in our clinic. Procedure was uneventful with excellent dosimetry. We will continue to use it in our clinic for patients with locally advanced cancer.