(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: This work investigated the dose effect of delivery errors on volumetric-modulated arc therapy (VMAT) for nasopharynx cancer (NPC) and cervical cancer.
Methods: Ten NPC and ten cervical cancer with double full arcs VMAT treatment plans were selected, and gantry rotation angle, MU, collimator position, and multi-leaf collimator (MLC) leaf position errors were simulated, respectively. The dose differences were compared between simulated and original plans for DVH-based dosimetry parameters. Homogeneity index (HI) and conformity index (CI) of PTV were also evaluated.
Results: There was no discernible dosimetry effect for gantry angle, MU, collimator position and MLC shift errors up to 2°, 2%, 3mm and 2mm, respectively. For NPC and cervical cancer, maximum dose deviations of PTV were less than 2.11% and 1.96%, respectively, and of organs at risks (OARs) were 2.12% and 3.22%, respectively. The CI and HI were barely changed. However, the dose gradients of PGTV74-Dmean, brainstem-D0.1cc, and left and right parotid gland-Dmean for NPC were 5.09%, 7.46%, 7.74%, and 7.50% per millimeter of MLC close and open errors, respectively. And the dose gradients of Dmean of PTV, bladder and rectum for cervical cancer were 7.53%, 3.20%, and 3.53% per millimeter, respectively. The dose deviations of PTV and OARs showed a strong linear correlation with MLC open or close errors (R>0.95, P<0.05).
Conclusion: The dosimetry effect of gantry angle, MU, collimator position and MLC shift errors were negligible, while MLC close or open errors had significant dosimetry effects for both NPC and cervical cancer. Therefore, it should be given more attention on MLC leaf open or close position errors to ensure the treatment accuracy.
Funding Support, Disclosures, and Conflict of Interest: This research work was supported by National Natural Science Foundation of China (Grant No. 81472807).
Keywords
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TH- External beam- photons: Quality Assurance - VMAT
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