Room: Exhibit Hall | Forum 7
Purpose: To evaluate a new design concept tandem applicator using dynamic shielding for delivering HDR brachytherapy of cervical cancer with 169-Yb source
Methods: A static-direction modulated brachytherapy(S-DMBT) tandem applicator designed for IGABT, compatible with MRI, for cervical cancer. The design has 6 peripheral holes of 1.3-mm width, grooved along a 5.4-mm diameter nonmagnetic tungsten alloy rod, capable of generating directional dose profiles through inverse planning for each patient anatomy. A dynamic DMBTconcept applicator is proposed in this study. The new design has a single central hole with a small window that acts to collimate a highly directional beam. This shield is then assumed to dynamically rotate to deliver an arc therapy while modulating intensity at each angular dwell position to generate customized dose distribution. The S-DMBT and six angular windows of D-DMBT designs (i.e.,20,33,53,60,90,and 120-degrees) in combination with the HDR 169Yb source are MC simulated and imported into a developed inverse planning code to generate treatment plans for a single representative patient case, along with a conventional tandem-and-ring (T&R) â€œreferenceâ€? plan. All plans were normalized to the same CTVHR D90. The D2cm3 for organs at risk (OAR) such as bladder, rectum, and sigmoid, and D98 and D10 were compared to the reference T&R plan.
Results: As expected, the directionality of the beam (i.e., angular narrowness) increased as the window angle decreased. For S-DMBT and at all angles of D-DMBT, generated plans were of higher quality than that of the reference plans. The bladder D2cm3 decreased by 3.3%,4.3%,5.7%,6.3%,8.7%,9.6%, and 9.3% for the 20,33,53,60,90,120 degrees of D-DMBT and S-DMBT tandem-and-ring, respectively. The corresponding values for the rectum(sigmoid) were reduced by 2.3%(0.6%), 1.3%(2.4%), 1.2%(2.8%), 3.6%(7.1%), 4.6%(8.0%), 5.7%(8.4%), and 6.1%(7.1%), respectively.
Conclusion: A concept tandem that can generate highly conformal dose distributions tailored for patient-specific anatomy is proposed, to be used with IGABT.