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MO_10_2712 - Daily Tracking with MRI-Guided Radiation Therapy of Glioblastoma Resection Cavity and Cerebral Edema Volumes

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Daily Tracking with MRI-Guided Radiation Therapy of Glioblastoma Resection Cavity and Cerebral Edema Volumes
S. Mehta1, S. Gajjar2, K. R. Padgett2, D. Asher2, R. Stoyanova3, and J. C. Ford2; 1University of Miami, School of Medicine, Miami, FL, 2Department of Radiation Oncology, University of Miami, Sylvester Comprehensive Cancer Center, Miami, FL, 3University of Miami, Miami, FL

Purpose/Objective(s): Radiation therapy (RT) plays a critical role in the treatment of glioblastoma. Studies of brain imaging during RT for glioblastoma have demonstrated changes in the brain during RT. However, feasibility has limited frequent or daily utilization of standalone MRI scans during RT. The recent release of the Tri-Cobalt-60 MRI-Guided RT (MR-IGRT) device allows for daily brain MRI for RT setup. Findings from daily brain MRIs during RT have not been previously reported.

Materials/Methods: Under an IRB approved protocol, resection cavities, edema, and visible tumor were measured from daily MRI of three post-operative patients undergoing RT (60 Gy) and temozolomide for glioblastoma over a six week course. Simulation and daily MRIs were obtained by the MR-IGRT system. Scans were performed with the balanced steady state free precession sequence included with the scanner, which has significant T2-weighting (128 sec acquisition, 0.15 x 0.15 x 0.15 cm resolution, 40 x 43 x 40 cm field of view). The volumes and dimensions of the cavity, edema, and visible tumor were generated from manual contours.

Results: Changes to the cavity and edema could be visualized on a daily basis. A general trend of daily decreases in cavity measurements was observed in all patients. Table 1 displays the measurements taken at fraction 1, fraction 15 and fraction 30. For the patient with edema, the edema volume increased until fraction 13 and then began to decrease, though the patient never required steroids during RT. Two other patients had no or minimal edema even on diagnostic scans. The measurements of a second, unresected tumor seen in one patient did not change during RT.
Fraction 1 Fraction 15 Fraction 30
Patient Structure Volume (cc) Size (cm) Volume (cc) Size (cm) Volume (cc) Size (cm) Total Days
1 Cavity 2.3 3.0x0.8x1.1 0.8 2.6x0.6x0.7 0.6 1.7x0.4x0.5 45
2 Cavity 82.6 7.2x3.3x8.0 77.6 7.1x3.1x7.6 72.0 6.9x3.0x7.5 39
3 Cavity 3.6 2.4x1.0x2.7 2.3 2.7x0.6x1.6 1.9 2.3x0.6x1.3 41
3 Secondary Tumor 0.8 1.2x0.6x1.1 0.7 1.3x0.7x1.1 0.7 1.3x0.7x1.2 41
3 Edema 55.2 5.7x3.6x7.4 68.1 6.2x3.6x6.8 51.4 5.8x2.8x5.8 41

Conclusion: In this preliminary analysis of daily MR-IGRT of glioblastoma, we observed and quantified changes in tumor cavities, edema, and visible tumor in three patients. This suggests that daily MRI could be used for onboard re-simulation and adaptive radiotherapy for future fluctuations in sizes of tumors, cavities, or cystic components. This would ensure proper targeting and reduced RT of healthy brain tissue. Additional MRI pulse sequences could provide further information about the tumor microenvironment for adaptation of therapy during the course of RT.

Author Disclosure: S. Mehta: None. S. Gajjar: None. K.R. Padgett: None.

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