GSOR07  Presentation Time: 12:30 PM: Combining Novel Direction Modulated Brachytherapy Tandem-and-Ovoids Applicators for Treatment Planning of Multi-Institutional Cervical Cancer Cases: Removing Needles in Intracavitary-Interstitial Techniques

• Published in: Brachytherapy Vol. 22; no. 5; pp. S62 - S63
• Main Authors: Alam, Sharmin, Richeson, Dylan, Manandhar, Binod, Gholami, Somayeh, Gautam, Suman, Scanderbeg, Daniel, Yashar, Catheryn M., Prisciandaro, Joann, Jolly, Shruti, Fields, Emma, Song, William Y.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.09.2023
• ISSN: 1538-4721; 1873-1449
• DOI: 10.1016/j.brachy.2023.06.096

There are no standard guidelines for optimal needle insertion/placement during high-dose-rate (HDR) intracavitary-interstitial (IC-IS) brachytherapy of the cervix. Therefore, sophisticated technical skillset must be acquired through repeated practice of inserting IS needles next to IC applicators to enhance dosimetry of improving target coverage while limiting dose to organs at risk (OARs). This study sought to evaluate potential of two direction modulated brachytherapy (DMBT) tandem applicators combined with one DMBT ovoids of unique designs to effectively removing the need for IS needles in a range of IC-IS cases found in multi-institutional clinics via achieving equivalent or better dosimetry. A cohort of 32 retrospective clinical HDR brachytherapy plans, from three institutions, were re-planned with Varian's BrachyVision® (v16.1) treatment planning system (BV-TPS), using the latest VEGO® inverse optimization algorithm, with dose heterogeneity accounted for through the AcurosBV® model-based dose calculation algorithm. All plans consisted of IC-IS cases, with a range of 2-4 freehand-loaded needles, with an average prescription dose of 709±53 cGy. The average high-risk clinical target volume (HRCTV) was 36.7±17.1 [range 9.8-69.6] cm3. Two unique DMBT tandem models of 5.4- and 8.0-mm thicknesses along with a novel DMBT ovoids design, introduced for the first time here, with 9 equi-angled grooves and 10-mm-diameter width (30 mm length) were integrated for the first time into the BV-TPS. During re-planning, the conventional tandems, ovoids/rings (20 ovoids & 12 rings cases), and all of the needles were replaced by one of the two DMBT tandem models and the one-and-only DMBT ovoids model. A two-step inverse optimization process was performed such that the lowest possible OAR D2cc doses could be achieved while 1) keeping equivalent target coverage (ΔHRCTV-D90 to within ±0.5%) and, at the same time, 2) maintaining the general pear-shape dose distribution of the original plans. For all plans, this process was repeated using each of the two DMBT tandem-ovoids combinations for a total re-planning of (32×2=) 64 cases. Average ΔHRCTV-D90 was +4.3±2.9 cGy. Significant improvements in plan quality were achieved by combining the DMBT tandem-and-ovoids despite not using the IS needles (Figure 1A). On average, -47.15±29.61 (-40.40±34.90) cGy, -42.98±26.58 (-41.70±27.40) cGy, and -40.47±25.05 (-32.55±25.30) cGy reductions in D2cc across bladder, rectum, and sigmoid, respectively, were achieved for the 8-mm (5.4-mm) DMBT tandem-and-ovoids combinations while maintaining equivalent D90 target coverage as the original IC-IS plans. Additionally, D2cc reductions in terms of EQD2 [Gy] were calculated assuming each re-plan was delivered throughout the course of treatment (Figure 1C), which includes the external beam radiotherapy dose of 45 Gy, and showed significant reductions of -4.05±2.47 (-3.37±2.83) Gy, -2.71±1.79 (-2.59±1.74) Gy, and -3.27±1.96 (-2.65±2.06) Gy for bladder, rectum, and sigmoid, respectively. These reductions were achieved with an average net increase in total dwell times of 241.0±87.6 seconds (i.e., 4-5 minutes) at the luxury of avoiding IS needles to insert. We have successfully incorporated two DMBT tandems and one ovoids models into a commercial TPS and re-planned 32 cases, to a total of 64 plans. According to the results, it is clinically feasible to replace the conventional IC-IS cases, with 2-4 freehand-loaded needles, with the DMBT tandem-and-ovoids technology, effectively avoiding the need for IS needles.