Dose different between original treatment planning and planned adaptive calculation during helical tomotherapy in patients with nasopharyngeal cancer
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Abstract
Background: Changing anatomic and volumetric occur in nasopharyngeal cancer (NPC) patients during fractioned radiotherapy cause the delivered dose considerably different from the original plan.
Objectives: The study purpose was to evaluate dose difference between original plan and planned adaptive software calculation during the course of radiotherapy in NPC patients treated with Tomotherapy HiArtTM system.
Materials and methods: Three NPC patients treated with helical tomotherapy underwent daily positional correction using megavoltage CT imaging. Both parotid glands and spinal cord of patients were recontoured on daily MVCT images. MVCT images were used to recalculate dose distribution for all 33 fractions by planned adaptive software. The original plan dose and recalculate dose were compared.
Results: Percent dose difference between original plan and planned adaptive dose of PTV70 (D95%), left and right parotid glands (D50%) were 1.74%±0.32%, 35.19%±12.67% and 24.60%±15.21%, respectively. The structure dose difference were statistically significant (p<0.05) after fraction number 2nd, 8th and 7th, respectively. Percentage of spinal cord dose (D2%) difference between original plan and planned adaptive was 8.76%±10.15% with no statistically significance. Volume reduction in percentage of PTV70, left and right parotid glands volumes compare to original plan were 9.43%, 29.00% and 27.29%, respectively. Volume of spinal cord was not change during the treatments.
Conclusion: Anatomic and volumetric variations in nasopharyngeal cancer patients caused PTV70 and parotid glands in receiving treatment dose more than original plan. Adaptive planning should be considered to correct for delivery dose.
Journal of Associated Medical Sciences 2017; 50(2): 286-292. Doi: 10.14456/jams.2017.28
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Personal views expressed by the contributors in their articles are not necessarily those of the Journal of Associated Medical Sciences, Faculty of Associated Medical Sciences, Chiang Mai University.
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