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An Analysis of the Deep Inspiration Breath Hold (DIBH) Treatment Delivery Uncertainties

X Tang*, T Cullip, J Dooley, X Zhu, J Lian, M Lawrence, T Zagar, E Jones, L Marks, S Chang, UNC School of Medicine, Chapel Hill, NC

SU-E-J-222 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Depends on how stable the patient can hold her breath during beam on time, there are always some degrees of uncertainties associated with the Deep Inspiration Breath Hold (DIBH) delivery. We herein analyze 1) how much motion patients have during delivery; 2) how much dosimetric uncertainties are resulted due to motion.

Methods: The data from three tangential-field DIBH breast patients were studied. AlignRT (Vision RT Ltd., London, UK), a 3D surface matching-based system was used for the DIBH clinical implementation. AlignRT calculated and recorded, in real-time, the differences between the treatment surface and planned surface, including 3 translational and 3 rotational displacements (RTDs). We programmed our in-house TPS to read RTDs and calculate the final dose distribution and DVHs patients have received. The received dose and DVHs were compared with the planned ones. We also calculated the mean (m) and standard deviation (σ) of the RTDs, trying to correlate them to the delivery uncertainties.

Results: All patients had <0.2mm and 0.7° σ. Patient A had m_A = (-0.02mm, -0.05mm, 0.02mm, 1.11°, -0.36°, 0.45°). Her delivered dose distribution is slightly different than the plan with 3D max dose difference of 0.4%. No noticeable differences on the DVHs. Patients B and C had larger rotational displacement with m_B = (-0.07mm, 0.01mm, 0.12mm, 1.80°, 2.17°, 1.06°) and m_C = (-0.04mm, -0.04mm, -0.04mm, 2.09°, -0.22°, 0.97°). The resulted 3D max dose differences are both 1%. Although dose distributions in the center treatment regions are as planned, there are different hot spots and cold spots in the peripheral areas. Both patients had slightly lower received heart, lung, and target DVHs.

Conclusion: No significant translational motion was observed, and its impact to the delivery uncertainties seems small. Larger rotational displacements seem to cause some dosimetric uncertainties. More data need to be collected for quantitative results.

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