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An Analysis of Patient-Specific Radiotherapy Plan Quality Process Control for Intra-Cranial Benign Tumors

J Lamb

J Lamb*, C Chevillard , P Chow , K Sheng , S Tenn , D Low , T Kaprealian , N Agazaryan , UCLA School of Medicine, Los Angeles, AA


MO-RPM-GePD-T-1 (Monday, July 31, 2017) 3:45 PM - 4:15 PM Room: Therapy ePoster Lounge

Purpose: Radiotherapy plan quality, defined as the distance of the plan to the Pareto front, or surface of optimal tradeoffs between target dose and organ at risk (OAR) sparing, is difficult to assess on an individual plan basis because the space of achievable plans depends on patient anatomy. Knowledge-based plan-quality metrics based on anatomic similarity to and/or an analytic function extracted from a library of previously treated cases have been demonstrated in prostate, head and neck, and other cancers. This work investigates a heuristic plan quality estimation model in a large sample of radiotherapy plans for benign intracranial tumors.

Methods: OAR dose-volume histogram (DVH) endpoints achieved in a database of 187 clinical intensity-modulated meningioma and acoustic neuroma radiotherapy (IMRT) plans were parameterized in terms of closest distance to the planning target volume (PTV). Clinical plans were optimized using BrainLAB iPlan v. 4.1.2 or 4.5.3. Cases were re-planned based on a criterion that a different plan in the database had both a smaller distance between an OAR and the PTV and also a lower dose to that OAR. A metric, deemed η, was developed for the purpose of predicting the expected gain from re-planning. The η metric was computed as the sum over all database elements of a function of OAR dose and OAR-PTV distance.

Results: For most OARs studied, increasing OAR-PTV distance led to predictable OAR dose decrease. Lens dose did not decrease in aggregate as a function of distance. Applying re-planning criteria led to re-plan of 47 cases, of which 20 resulted in decreased OAR dose without sacrificing other dosimetric endpoints. The η metric was mildly predictive of re-plan dosimetric gain for some OARs.

Conclusion: The η metric shows promise as a clinical tool to evaluate the expected benefit from re-planning on a case-by-case basis but needs further development.

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