Central Nervous System

PV QA 2 - Poster Viewing Q&A 2

MO_6_2616 - Treatment of Multiple Brain Metastases Using Single Isocentric Technique with Forward Planned Dynamic Arcs

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

Treatment of Multiple Brain Metastases Using Single Isocentric Technique with Forward Planned Dynamic Arcs
D. Jiang1, N. Cnossen2, J. Rahimian1, and M. R. Girvigian1; 1Kaiser Permanente Los Angeles Medical Center, Los Angeles, CA, 2Southern California Permanente Medical Group, Los Angeles, CA

Purpose/Objective(s): Image guided radiosurgery (IGRS) delivered with a single isocenter using forward planned dynamic arcs, without intensity modulation, is an attractive option for multiple brain metastases. We recently commissioned a new system at our institution designed to treat up to 15 lesions with optimized forward planned dynamic conformal arcs. We examined the safety and efficacy of patients treated with this new planning system.

Materials/Methods: Forty patients underwent IGRS with the single isocenter planning system at our institution from 05/2017 to 12/2017. Treatment plans were made and optimized using either 5 or 6 couch positions with up to 12 dynamic conformal arcs. Treatment plans using 6X and 6x flattening filter free mode were compared for each patient and the better dosimetric plan was used for treatment. IGRS was delivered using a 6D robotic couch with stereoscopic imaging to position the patient. Corrections were made at each couch position using 0.5 mm and 0.5 degrees correction tolerances.

Results: A total of 283 lesions were treated in 40 patients, in 46 individual treatment sessions (6 patients with retreatments). Median age was 57 (24 to 87) years. A median number of 5 lesions (2 to 15) were treated per session, with a median total treated volume of 3.049 cm3 (range 0.038 cm3 to 105.809 cm3). Median integral whole brain dose was 135.5cGy and median hippocampal dose was 153cGy. Median treatment time was 21 minutes. Follow up imaging at time of analysis was available for 65% (30) of treatment plans. At a median follow up time of 2.2 months, 85% (34) of patients showed control of disease in the treated lesions. Six patients (15%) showed radiographic enlargement of treated lesions, of these 4 were asymptomatic. At time of analysis, 70% (28) of patients were alive. Of the 12 deaths, 50% (6) were due to neurological causes. Death was only significantly associated with the number of lesions treated (p=0.004). No cases of radiation necrosis were reported. Three patients developed seizures more than 10 days after IGRS date. Three patients developed transient fatigue and confusion (grade 2-3). Two patients developed weakness (grade 2) that improved with steroids. On univariate analyses toxicity was significantly associated with the total treated volume (p=0.010) but not the number of treated lesions (p=0.370). Toxicities were greater for patients with treatment volume >5 cm3 (p=0.032).

Conclusion: For patients with multiple brain metastases, utilizing IGRS with single isocentric technique using forward planned dynamic arcs reduced the planning and on-table treatment time. Lower monitor units allow for a lower integral whole brain dose than would be expected with a similar volumetric arc radiotherapy (VMAT) plan. At analysis, there was an acceptable level of lesion control. Toxicity noted was transient, and possibly not related to IGRS treatment in all cases. There were no instances of radiation necrosis to date.

Author Disclosure: D. Jiang: None. N. Cnossen: None. J. Rahimian: None. M.R. Girvigian: None.

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