Gastrointestinal Cancer

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SU_6_2057 - Assessing Radiation Induced Liver Damage Following MR-Guided Stereotactic Body Radiation Therapy (SBRT): Challenging Current Dose Constraints

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

Assessing Radiation Induced Liver Damage Following MR-Guided Stereotactic Body Radiation Therapy (SBRT): Challenging Current Dose Constraints
A. Kuczmarska-Haas1, P. Yadav1, H. B. Musunuru1, J. S. Witt1, D. M. Francis1, S. A. Rosenberg1, H. C. Ko1, Q. Khan2, K. A. Matkowskyj3, D. A. Deming4, A. M. Baschnagel5, J. Bayouth5, P. M. Harari5, and M. F. Bassetti1; 1Department of Human Oncology, University of Wisconsin Hospital and Clinics, Madison, WI, 2University of Wisconsin School of Medicine and Public Health, Madison, WI, 3Department of Pathology and Laboratory Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI, 4University of Wisconsin, Carbone Cancer Centre, Madison, WI, 5Department of Human Oncology, University of Wisconsin School of Medicine and Public Health, Carbone Cancer Center, Madison, WI

Purpose/Objective(s): Long term disease free survival (DFS) is possible in oligometastatic cancer with aggressive treatment such as SBRT. Hepatic failure after SBRT for liver metastases is rare, but life threatening. Treatment plans commonly constrain a “critical volume” of functional liver below a threshold dose (e.g. > 700 cc of liver to < 15 Gy, Rusthoven, et al. 2009). We sought to correlate liver damage with radiation dose using Gadotexate MR contrast to demarcate non-functional liver after SBRT. To determine the threshold dose, we examined isodose lines (IDLs) of inhale breath hold MR-guided SBRT treatment plans using a 60Co source. 60Co plans have a lower dose gradient index and thus, greater separation of moderate dose IDLs than traditional linear accelerator plans, potentially allowing more accurate correlation.

Materials/Methods: Patients who underwent 5-fraction breath-hold cobalt60 MR-guided liver SBRT for metastases were screened for a post-treatment gadoxetic acid enhanced MR. An experienced radiation oncologist contoured radiation-induced liver damage (RILD), defined as new areas of hypointensity on the follow-up 20 minute post-contrast T1 MRI. Treatment IDLs were aligned to the follow-up scan with rigid registration of the centroid of the IDLs with the centroid of the RILD contour. Sørensen–Dice coefficients (DC) were calculated using the computer algorithm and the IDL with the highest DC was considered to be relevant.

Results: Of 17 patients treated with MR-guided SBRT for metastatic liver lesions, 8 had post-treatment gadoxetate contrast enhanced MR available for evaluation. Three patients were previously treated with microwave ablation. SBRT dosing ranged from 50 Gy to 60 Gy over 5-fractions. Follow-up MRI was acquired at a median time of 4.0 months (range 1.6-6.6 months). On scans acquired 2-5 months following treatment, the highest DC (0.75-0.9) was observed at a median dose of 33 Gy in 5-fractions (range 27 Gy-36 Gy, N=5 patients). Of the remaining 3 patients, higher DC values were observed at higher IDLs (60 Gy-71 Gy). These scans were acquired following treatment either early (prior to full radiographic damage), or late (resulting in liver fibrosis and contraction of the RILD area). The optimal IDLs enveloping RILD in one patient were observed to be 36 Gy, 47 Gy and 59 Gy on MR scans acquired at 3.8 months, 7.3 months and 11.5 months, respectively; once again demonstrating contraction of the treated liver tissue with increasing time lag between treatment and FU.

Conclusion: Breath hold MR-guided liver SBRT induces a sharply demarcated hypointense area of RILD on the early follow-up MRI scans (2-5 months). This area of RILD correlated with a dose level ranging from 27 Gy-36 Gy in 5-fractions, higher than commonly used threshold dose constraints. Liberating liver dose constraints may be safe, and allow greater patient access to liver SBRT.

Author Disclosure: A. Kuczmarska-Haas: None. P. Yadav: None. H.B. Musunuru: None. J.S. Witt: None. D.M. Francis: None. S.A. Rosenberg: None. H.C. Ko: None. K.A. Matkowskyj: None. D.A. Deming: None. J. Bayouth: None. P.M. Harari: Member; ASTRO Board of Directors. M.F. Bassetti: Independent Contractor; ThirdBridge. Travel Expenses; Viewray. Stock; Seattle genetics.

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SU_6_2057 - Assessing Radiation Induced Liver Damage Following MR-Guided Stereotactic Body Radiation Therapy (SBRT): Challenging Current Dose Constraints



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