(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: Lowering heart doses for patients receiving breast irradiation has become a priority. The reduction in heart dose seen by implementing voluntary breath hold with OSMS monitoring/gating and PerFraction verification is discussed.
Methods: Patients were simulated in free-breathing and breath-hold states. Dosimetry contoured the heart, lung, and body on each scan and measured the separation from the heart to the chest wall. The physician chosen treatment scan was sent to OSMS. The treatment plan, structure set, and dose were sent to PerFraction and an integrated image was scheduled for the first three fractions of treatment. Patients were treated using the OSMS software for patient positioning, monitoring, and gating with a 3mm tolerance. The integrated images were analyzed in the PerFraction software using γ analysis. Fractions 2 and 3 were compared to the fraction 1 baseline. Some patients were treated free-breathing without OSMS and were analyzed in PerFraction for comparison. The mean heart dose calculated by PerFraction for left breast patients treated with OSMS was recorded.
Results: The median γ pass rate using a 3%/2mm/local normalization analysis criteria was 93.4% for free-breathing patients treated without OSMS. The pass rate for free-breathing patients with OSMS was 94.0%. For breath hold patients, the pass rate increased to 98.5%. The calculated heart dose was 1.43 Gy for free breathing patients compared to 0.95 Gy for breath hold patients.
Conclusion: The measured γ pass rates increased for free-breathing and breath-hold patients with an ~5% increase for breath-hold patients. Python simulations gave similar γ pass rates for each case, 91% (no OSMS), 94.2% (OSMS free-breathing), and 98.7% (OSMS breath-hold). The average calculated heart does was 30% lower for breath-hold patients. Increased ɣ pass rates and lower heart doses allows smaller margins and quicker treatments.
Keywords
Electronic Portal Imaging, Patient Positioning
Taxonomy
TH- External beam- photons: Motion management (intrafraction)
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