3794 - A Dosimetric Feasibility of UPFRONT Single-Fraction Brachy-like MR-Guided SBRT Followed By Chemoradiation and Brachytherapy as a Radical Re-Sequencing Therapy to Boost Radio-Immunopotentiation In Cervical Cancer
Presenter(s)
T. Prasartseree1,2, E. Y. Han3, J. Duan3, P. Wongtrakool2, N. Thumyongkit2, B. Lee1, C. Owens3, S. Suwandee2, S. Suwanprateep2, T. Jaikuna2, P. Nakkrasae2, W. Sittiwong2, S. Pojai2, C. Spicer1, J. Yang3, Z. Yu3, A. H. Klopp4, Y. Kim3, and P. Dankulchai2; 1Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 2Division of Radiation Oncology, Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand, 3Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 4Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX
Purpose/Objective(s):
Re-sequencing heterogeneous radiation including brachytherapy to the initial tumor may generate more neoantigen and immunomodulation compared to after large nodal field radiation. This study was aimed to evaluate a novel induction "Brachy-like" SBRT technique delivering aimed to enhance tumor reduction and immunopotentiation before definitive chemoradiation and brachytherapy. Dose summation with VMAT 40Gy/20F and IGABT was explored with conventional summationMaterials/Methods:
Ten cervical-cancer patients were retrospectively re-optimized on the same initial planning CT. “Brachy-like” SBRT was planned on Monaco TPS for online adaptive treatment on 1.5T MR-linac. A 2-cm diameter “Virtual-tandem core PTV (VTC-PTV)” was generated along the central core of HR-CTV (cervical tumor gross volume and whole cervix) using an automated central spline function. A single-fraction simultaneous integrated boost was prescribed: 8Gy to the VTC-PTV, aiming Dmax of 10-12Gy and 3Gy to 90% of HR-CTV (D90). Stringent limits for the bladder (D2cc<3Gy) and rectal/sigmoid (D2cc<2.2Gy) were constrolled with higher priority. 12-beam gantry angles were arranged with isocenter at the center of the HR-CTV. All plans underwent patient-specific quality assurance using an ArcCheck phantom and 3%/2mm gamma analysis. The VMAT was planned on to deliver 40 Gy in 20 fractions with SIB to 53/55Gy to gross lymph nodes. Organs* was generated as the intercepted volume of OOI and 2-cm isotropic expansion of HR-CTV achieve more accurate potential EBRT-Brachy-overlapped dose measurement. Summation of the EQD2 from the original brachytherapy plans was performed. Mutual small volume (D2cc) was directly combined to assume worst-case scenario.Results:
Ten patients harbored a median initial tumor volume of 77 cc (range 6-161 cc). All were dosimetrically feasible and clinically acceptable. Median D90%/D50%/Dmax VTC-PTV were 8/9/11 Gy and D90% HR-CTV was 3.2 Gy, respectively. Sparing of organs at risk was successful, with median D2cc of Bladder at 2.65 Gy and Rectum at 1.8 Gy, respectively. Plans demonstrated efficient delivery characteristics with a median of the second optimization time and an estimated delivery time of 2.1 (range 1.7-2.8) and 11.8 (range 9.7-15) minutes. Plans achieved a median gamma passing rate of 98.2% (range 96.9-99.8%). For summative dose, median D90% HR-CTV of 89.6 Gy10, D2cc Bladder of 77.4 Gy3 and Rectum of 60.7Gy3 were acceptable per international protocols.Conclusion: UPFRONT Brachy-like SBRT followed by VMAT 40Gy/20F with SIB 53/55Gy and standard image guided brachytherapy achieves favorable HR-CTV coverage while adhere to international organs at risk criteria for further clinical investigation.
| Median (Min-Max) | Gy | UPFRONT single fraction | Cumulative EQD2 UPFRONT+20F VMAT+Brachy |
| VTC PTV | D90 | 8 (6.6-8.7) | na |
| D50 | 9.3 (8-10.3) | na | |
| Dmax | 11.4 (9.6-12.4) | na | |
| HR-CTV | D90 | 3.2 (2.9-3.5) | 89.6 (84.5-90.4) |
| Bladder | D2cc | 2.65 (2.6-2.7) | 77.4 (66.4-85.3) |
| Rectum | D2cc | 1.8 (1.4-2.1) | 60.7 (55.9-69.6) |