Room: AAPM ePoster Library
Purpose: Volumetric modulated arc therapy (VMAT) is an advanced radiotherapy technique that offers high conformity of the dose which makes it highly sensitive to patient setup error. The human lens is very sensitive to radiation and their highly mobility can lead to deviation between the planned and delivered dose. This study aims to prove the benefit for using lens planning risk volumes (PRV), and the effect of lens PRV present on target evaluation parameters [homogeneity index (HI), conformity index (CI) and paddic conformity index (PCI)] in glioblastoma.
Methods: Ten GBM patients are selected, accepted VMAT plans (L plan) are reoptimized by lens PRV instead of the lens (LPRV plan), for both plans recalculating after applying simulation position uncertainty 3 mm isocenter shift (L shifted plan and LPRV shifted plan) and evaluate uncertainty effect on lens maximum dose. Also we statistically compared target evaluation parameters (HI, CI, and PCI) between both basic plans (L plan and LPRV plan).
Results: The study revealed that the maximum dose to both lens decreased by using lens PRV in optimization process instead of the lens only, for uncertainty effect the lens maximum dose in (L shifted plan) increased higher than tolerance limit 7 Gy in about 60% of the patients, while for (LPRV shifted plan) the maximum dose exceeds tolerance limit in only 5%. On the other hand measurements of the lens PRV effect on target evaluation parameters between (L plan and LPRV) plan show that the average percentage error for HI, CI, and PCI was (0.021, 0.137, and 1.76) respectively.
Conclusion: The present study show that using the lens PRV structure for the lens has no effect on target evaluation parameters, also this PRV has a large benefit for reducing maximum dose to the lens and position uncertainty effect.