Improving IMRT dose accuracy via deliverable Monte Carlo optimization for the treatment of head and neck cancer patients

<jats:p>The purpose of this work is to investigate the effect of dose‐calculation accuracy on head and neck (H&N) intensity modulated radiation therapy (IMRT) plans by determining the systematic dose‐prediction and optimization‐convergence errors (DPEs and OCEs), using a superposition/convolution (SC) algorithm. Ten patients with locally advanced H&N squamous cell carcinoma who were treated with simultaneous integrated boost IMRT were selected for this study. The targets consisted of gross target volume (GTV), clinical target volume (CTV), and nodal target volumes (CTV nodes). The critical structures included spinal cord, parotid glands, and brainstem. For all patients, three IMRT plans were created: A: an SC optimized plan<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0001.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0001"/>, B: an<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0002.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0002"/>plan recalculated with Monte Carlo<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0003.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0003"/>, and C: an MC optimized plan<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0004.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0004"/>. For each structure, DPEs and OCEs were estimated as<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0005.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0005"/>and<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0006.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0006"/>where A, B, and C stand for the three different optimized plans as defined above. Deliverable optimization was used for all plans, that is, a leaf‐sequencing step was incorporated into the optimization loop at each iteration. The range of<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0007.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0007"/>in the GTV<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0008.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0008"/>varied from<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0009.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0009"/>to<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0010.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0010"/>, while the<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0011.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0011"/>ranged from 0.9% to 7.0%. The<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0012.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0012"/>in the contralateral parotid<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0013.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0013"/>reached 8.2%, while the<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0014.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0014"/>in the contralateral parotid<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0015.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0015"/>varied from 0.91% to 6.99%. The<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0016.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0016"/>in cord<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0017.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0017"/>reached<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0018.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0018"/>, while the<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0019.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0019"/>reached to<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0020.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0020"/>. The magnitude of the<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp7835-math-0021.png" xlink:title="urn:x-wiley:0094-2405:media:mp7835:mp7835-math-0021"/>and<jats:inline-graphic xmlns:xlink="htt ...