Radiation and Cancer Physics

PD 06 - Physics 2 - Poster Discussion - Treatment Delivery

1046 - Stereotactic MR-guided Online Adaptive Radiation Therapy With High Dose Rate (SMART-HDR) Brachytherapy

Monday, October 22
10:51 AM - 10:57 AM
Location: Room 217 C/D

Stereotactic MR-guided Online Adaptive Radiation Therapy With High Dose Rate (SMART-HDR) Brachytherapy
K. E. Mittauer, J. Miller, K. A. Bradley, and J. Bayouth; Department of Human Oncology, University of Wisconsin School of Medicine and Public Health, Carbone Cancer Center, Madison, WI

Purpose/Objective(s): Despite overall good cure rates for cervical cancer with chemoradiation, the relapse rates for FIGO stages IIB–IVA ranges from 25-75%, with the rates of pelvic failures increasing with stage. We describe a proof of concept of integrating stereotactic MR-guided online adaptive radiotherapy to supplement high dose rate (SMART-HDR) brachytherapy (BT) for gynecological (GYN) cancer. We hypothesize that SMART HDR can improve dosimetric target coverage to HR-CTV without significantly violating OAR constraints for stage II-III GYN cancers, compared to conventional brachytherapy (C-BT).

Materials/Methods: The feasibility and indication of incorporating MR-guided online adaptive external beam (EB) with MR-guided HDR BT treatments was evaluated in 16 patients. SMART-HDR workflow for a single treatment session would include applicator implant; MR simulation; contouring, catheter reconstruction, dose calculation and optimization on a single MR dataset; MR-guided radiotherapy (MRgRT), followed by HDR BT in the MRI vault. A MR-compatible motor for use in a MR-compatible afterloader was developed and characterized to allow for BT delivery in MRI vault, minimizing motion between imaging and treatment. Patients received 45-50.4 Gy EB followed by 27.5-30 Gy C-BT in 4-5 fractions for stage II-III GYN cancers of cervix or cuff. Post-applicator implant, patients received a simulation scan on a commercial MRgRT system for C-BT planning, followed by C-BT delivery. Indication of SMART-HDR was studied through retrospectively re-planning C-BT cases for SMART-HDR. Dosimetric differences were evaluated using GEC-ESTRO criteria.

Results: Motor accuracy was ±0.1 mm in 0.35 T. Dosimetric results are in Table I. HR-CTV coverage significantly improved for SMART-HDR compared to C-BT p<0.001 for D90, D95, and V100, with similar OAR sparing (3.7%±20% or 0.1±0.4 Gy mean difference to C-BT, N=55). MRgRT delivery time was 3.3±2.3 min (N=16). Multi-modality radiotherapy planning on one dataset minimized contouring time and dose accumulation uncertainty. For tandem and ovoid cases, a correlation (R2=0.8) was found between HR-CTV volume (cm3) and increase in coverage (∆D95) on SMART-HDR with respect to C-BT.

Conclusion: Compared to C-BT, combining adaptive MRgRT to BT is feasible and improved HR-CTV coverage (p<0.001), while maintaining similar dose to adjacent OARs (0.1±0.4 Gy mean difference), for patients not a candidate for interstitial needles or for unfavorable tumor geometry. Further investigation of feasibility of clinical implementation of SMART-HDR is underway.
HR-CTV coverage (16 patients)
D90 D95 V100
C-BT 94% ±8% 85% ±9% 86% ±5%
SMART-HDR 109% ±3% 103% ±2% 97% ±1%
p-value 4E-07 3E-07 2E-07
Fractional D2cc OAR toxicity (16 patients)
Bladder Bowel Sigmoid Rectum
C-BT 3.7 ±1.5 Gy 1.5 ±1.3 Gy 2.3 ±1.1 Gy 2.8 ±1.3 Gy
SMART-HDR 4.0 ±1.6 Gy 1.6 ±1.4 Gy 2.5 ±1.2 Gy 2.9 ±1.4 Gy
p-value 0.08 0.06 0.002 5E-06

Author Disclosure: K.E. Mittauer: Honoraria; ViewRay. J. Miller: None. K.A. Bradley: writer of educational material on gynecologic cancers for UpToDate, for which I receive royalties; UpToDate. J. Bayouth: None.

Kathryn Mittauer, PhD

University of Wisconsin: Researcher/Staff Medical Physicist: Employee

ViewRay: Honoraria


Send Email for Kathryn Mittauer


1046 - Stereotactic MR-guided Online Adaptive Radiation Therapy With High Dose Rate (SMART-HDR) Brachytherapy

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