Prediction of Dose Discrepancies Using Differences in Plan Normalization Values of Head-And-Neck VMAT Plans
M Sasaki1*, H Ikushima2, S Kobuchi3, K Kuwahara4, A Kajino5, D Sato6, W Sugimoto7, M Oita8, (1) Department of Therapeutic Radiology, Institute of Biomedical Sciences, Tokushima University Graduate School, Tokushima,JP (2) Department of Therapeutic Radiology, Institute of Biomedical Sciences, Tokushima University Graduate School, Tokushima, JP (3)Graduate School of Health Sciences, Tokushima University, Tokushima, JP (4)Graduate School of Health Sciences, Tokushima University, Tokushima, JP (5)Graduate School of Health Sciences, Tokushima University, Tokushima, JP (6)Graduate School of Health Sciences, Tokushima University, Tokushima, JP (7)Department of Radiological Technology, Tokushima Prefectural Central Hospital, Tokushima, JP (8) Okayama University Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama, JP
Presentations
PO-GePV-M-212 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: This study evaluated whether plan normalization value (PNV) differences could be used as predictors of potential discrepancies between planned and delivered doses.
Methods: Forty-five patients who underwent volumetric-modulated arc therapy (VMAT) for head-and-neck cancer at our institution were included. The absolute dose and dose distribution were verified using ionization chamber and a GafChromic film and Delta4 PT, respectively. The VMAT plan to change the PNV used computed-tomography images and a simulated head-and-neck radiotherapy structure-set provided by the American Association of Physicists in Medicine Task Group (TG) 119. Seven treatment plans with varying PNVs were selected: 95%, 97%, 99%, 100%, 101%, 103%, and 105% PNV. For dose distribution verification, we used Delta4 PT in clinical cases.
Results: PNV ranged from 98% to 102% in 38 (84.4%) of the 45 cases of head-and-neck VMAT. Further, PNVs ranged from 98% to 102% with 14 measurement locations exceeding ±2.0%, and five measurement locations exceeded ±3%. All GafChromic film and Delta4 PT gamma analysis (GA) results were above 90%, regardless of the PNV range. There was no apparent difference between the results of PNV and dose verification for 45 cases of head-and-neck VMAT. The 2 mm/2% result for GA in TG119 showed a trend of decreasing GA pass rates as the PNV moved away from 100%.
Conclusion: The linear accelerator beam did not hold in the 95–105% PNV range, and the delivery was accurate with little effect on the accuracy of the planned and delivered doses.
ePosters
Keywords
Treatment Planning, Quality Assurance
Taxonomy
TH- External Beam- Photons: Quality Assurance - IMRT/VMAT
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