J Patel, P Myers*, K Andrews, N Toups, I Corona, N Papanikolaou, N Kirby, N Newman University of Texas HSC SA, San Antonio, TX

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  P Myers

PO-GePV-T-210 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: Reduction in dose to bone marrow has the potential to reduce hematologic toxicities and is associated with better clinical outcomes. The dosimetric impact of sparing bone marrow has previously been explored for pelvic radiotherapy. The goal of this study is to assess the feasibility of thoracic bone marrow sparring in esophageal and lung radiotherapy plans.

Methods: This study was reviewed by our Institutional Review Board. The initial goal for bone marrow sparing is to reduce the thoracic vertebral volume receiving 10, 20, and 30 Gy to below 190, 150, and 100 cm3, respectively. A total of 20 previously treated plans were analyzed relative to these goals (10 esophagus and 10 lung). The esophagus patients had a prescription of 50.4 Gy in 28 fractions. The lung patients were treated in 2 Gy fractions to either 60 or 66 Gy.

Results: The mean volumes above 10, 20, and 30 Gy were 321, 284, and 187 cm3, respectively, for the esophageal patients. For the lung patients, the respective volumes were 210, 165, and 113 cm3. Only 3 out of 20 of the treated patient plans met the vertebral objectives (1 esophagus and 2 lung). Though many of the patients are not far from meeting the constraints, the more challenging ones were tested in this project. As an example, one tested had 348, 321, and 173 cm3, respectively. These could be reduced to 300, 238, and 147 cm3, respectively, while maintaining a conformal plan with reasonable doses to other structures; however, the resulting plan became highly non-conformal beyond this..

Conclusion: Dose to the vertebral bone marrow can be optimized and reduced while still maintain a conformal plan and appropriate constraints to the other OARs. A further investigation will be performed into the best way to quantify the achievable dose reductions.

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