SU‐F‐T‐415: Differences in Lung Sparing in Deep Inspiration Breath‐Hold and Free Breathing Breast Plans Calculated in Pinnacle and Monaco

Abstract

Purpose:Deep inspiration breath‐hold (DIBH) is used for left‐sided breast radiotherapy to spare the heart and lung. The magnitude of sparing has been shown to be significant. Monte Carlo, furthermore, has the potential to calculate most accurately the dose in the heterogeneous lung medium at the interface with the lung wall. The lung dose was investigated in Monaco to determine the level of sparing relative to that calculated in Pinnacle3.Methods:Five patients undergoing DIBH radiotherapy on an Elekta Versa HD linear accelerator in conjunction with the Catalyst C‐RAD surface imaging system were planned using Phillips Pinnacle3. Free breathing plans were also created to clinically assure a benefit. Both plans were re‐calculated in Monaco to determine if there were any significant differences. The mean heart dose, mean left lung, and mean total lung dose were compared in addition to the V20 for left and both lungs. Dose was calculated as dose to medium as well as dose to water with a statistical precision of 0.7%.Results:Mean lung dose was significantly different (p < 0.003) between the two calculations for both DIBH (11.6% higher in Monaco) and free breathing (14.2% higher in Monaco). V20 was also higher in Monaco (p < 0.05) for DIBH (5.7% higher) and free breathing (4.9% higher). The mean heart dose was not significantly different between the dose calculations for either DIBH or free breathing. Results were no more than 0.1% different when calculated as dose to water.Conclusion:The use of Monte Carlo can provide insight on the lung dose for both free breathing and DIBH techniques for whole breast irradiation. While the sparing (dose reductions with DIBH as compared to free breathing) is equivalent for either planning system, the lung doses themselves are higher when calculated with Monaco.