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Real-Time Motion Management Will Increase the Patient Population Eligible for Lung SBRT

R Berbeco

R Berbeco1*, A Chen1, P Keall2, D Kozono1, R Mak1, J Lewis1, (1) Brigham and Women's Hospital, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA (2) University of Sydney, Sydney, Australia

SU-E-J-139 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Lung toxicities encountered during the early lung SBRT clinical trials have been largely abated by adhering to strict planning limits on lung dose and PTV size. This restricts the maximum safely treatable GTV size in the presence of respiratory motion. We hypothesize that real-time motion management (e.g. tracking) will enable the maximum GTV size to increase, thereby making more patients eligible for SBRT.

Methods: Consensus maximum PTV size (50 cc) was determined from recent clinical trials and our own clinical experience. PTV as a function of GTV was found for four treatment scenarios: 1 cm motion, no tracking; 0.5 cm motion, no tracking; no motion, no tracking; and, arbitrary motion, with tracking. We included a 0.5 cm/1.0 cm asymmetric CTV to PTV margin for no tracking (RTOG recommendation) and a 0.3 cm margin for tracking, as suggested by the results of Rottmann (2010). No GTV to CTV margin is included. A large population study is used to determine the increase in numbers of patients eligible for SBRT.

Results: PTV < 50 cc corresponds to a maximum GTV of 11, 13, 17 and 33 cc, for 1 cm motion (no tracking), 0.5 cm motion (no tracking), no motion (no tracking) and arbitrary motion (with tracking). With tracking, empirically-derived normal tissue dose constraints can be maintained while increasing the volumes of tumors that we could treat with SBRT by >250%, going from a limit of 13 cc, for tumors moving more than 5 mm, to 33 cc for all motions. This translates to a ~50% increase in the numbers of patients eligible for lung SBRT.

Conclusions: Restrictions on PTV size limit patient eligibility for SBRT, excluding patients with smaller GTVs and respiratory motion. Real-time motion management will enable a substantial increase in the numbers of patients eligible for SBRT.

Funding Support, Disclosures, and Conflict of Interest: The project described was supported, in part, by Award Number R21CA156068 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health.

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