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Improving IMRT dose accuracy via deliverable Monte Carlo optimization for the treatment of head and neck cancer patients
Author(s) -
Dogan Nesrin,
Siebers Jeffery V.,
Keall Paul J.,
Lerma Fritz,
Wu Yan,
Fatyga Mirek,
Williamson Jeffrey F.,
SchmidtUllrich Rupert K.
Publication year - 2006
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2357835
Subject(s) - nuclear medicine , medicine , radiation therapy , head and neck cancer , dosimetry , monte carlo method , radiology , mathematics , statistics
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 ( SC opt ) , B: anSC optplan recalculated with Monte Carlo [ MC ( SC opt ) ] , and C: an MC optimized plan ( MC opt ) . For each structure, DPEs and OCEs were estimated asDPE SC = D B − D AandOCE SC = D C − D Bwhere 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 ofDPE SCin the GTVD 98varied from − 1.9 % to − 4.9 % , while theOCE SCranged from 0.9% to 7.0%. TheDPE SCin the contralateral parotidD 50reached 8.2%, while theOCE SCin the contralateral parotidD 50varied from 0.91% to 6.99%. TheDPE SCin cordD 2reached − 3.0 % , while theOCE SCreached to − 7.0 % . The magnitude of theDPE SCandOCE SCdifferences demonstrate the importance of using the most accurate available algorithm in the deliverable IMRT optimization process, especially for the estimation of normal structure doses.