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Optimized 4π Radiotherapy Planning for Cochlear Dose Reduction in Acoustic Neuroma Treatment
K Woods*, T Kaprealian, P Lee, K Sheng, UCLA School of Medicine, Los Angeles, CA
Presentations
SU-I-GPD-T-331 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: There are 2-3,000 new cases of benign acoustic neuroma in the U.S. annually, and ~25% are treated with radiotherapy. Following treatment, many patients experience complications such as tinnitus and sensorineural hearing loss (SNHL), and there is some evidence that these are associated with cochlear dose. This study investigates whether 4π radiotherapy can spare the cochleae and consequently reduce complications in acoustic neuroma patients.
Methods: Clinical radiotherapy plans for 30 acoustic neuroma patients were included (14 SRS, 6 SRT, 10 IMRT). 4π plans were created for each patient with 20 optimal beams selected using a greedy column generation approach, with the dose then recalculated in Eclipse for comparison. 4π plans were normalized to match clinical PTV coverage (95-100%, 12-54 Gy prescriptions). OAR doses, homogeneity index (HI), van’t Riet conformity number (CN), and tumor control probability (TCP) were compared. Normal tissue complication probability (NTCP) was calculated for tinnitus and SNHL. The dose for each plan was escalated to achieve 95% TCP, and the resulting NTCP values were compared.
Results: 4π significantly reduced the mean dose to both cochleae (by 1.7 Gy for SRS, 9.3 Gy for IMRT) and the mean/maximum brainstem dose. Mean dose to other OARs was reduced by 20-54% on average. 4π plans had the same average HI (0.93), CN (0.72), and TCP (77.6%), with significantly lower average NTCP for tinnitus (21.5% vs 12.5%) and SNHL (1.4% vs 0.3%). Average dose escalation of 116% of the prescription dose achieved 95% TCP for all plans and resulted in 37.3% (clinical) and 21.9% (4π) NTCP for tinnitus and 7.6% (clinical) and 1.8% (4π) for SNHL.
Conclusion: Compared to conventional planning methods, 4π radiotherapy enables significantly better sparing of the cochleae. This could reduce the risk of complications such as tinnitus and sensorineural hearing loss in benign acoustic neuroma treatment.
Funding Support, Disclosures, and Conflict of Interest: DOE DE-SC0017057, NIH R44CA183390, NIH R01CA188300, NIH R43CA183390, NIH U19AI067769
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