Relative Biological Effectiveness and Its Impact on Dose Calculation in Proton Therapy
2017; Elsevier BV; Volume: 99; Issue: 2 Linguagem: Inglês
10.1016/j.ijrobp.2017.06.2060
ISSN1879-355X
AutoresA. Madkhali, Camilla H. Stokkevåg, Mike Partridge,
Tópico(s)Advanced Radiotherapy Techniques
ResumoIn proton therapy (PT), a relative biological effectiveness (RBE) of 1.1 (RBE1.1) is often applied clinically. In reality, RBE depends on dose, linear energy transfer (LET), biological end point, and tissue type. Using RBE1.1 may lead to inaccurate dose calculation and hence, influence modelled outcome. We used in-house built software to calculate biological dose using voxel-by-voxel dose maps (Timlin et al. 2015). A published RBE model was implemented to calculate structure-specific RBE, recalculate organ dose and compare it with planned dose calculations using RBE1.1. Dose was analyzed for a number of structures from PT plans for six pediatric patients diagnosed with medulloblastoma. Variable RBE (RBEMinMax) was calculated using the Carabe-Fernandez model (Carabe-Fernandez et al. 2007) which is a function of dose (d), α and β and RBEMin and RBEMax: RBE=(-α+√(αˆ2+4βd(〖RBE〗_max α+〖RBE〗_(min)ˆ2 βd)))/2βd. The table shows that the effect of using RBEMinMax was more evident in some patients and structures than others. In the selected organs, mean dose varied between 2.9% and 7.2% (average =5%) while the mean dose varied between 0.3% and 4.9% (average = 2.2%). Variations seen could be a result of age-related structural/volume differences.Abstract 3443ThyroidHeartLiverPatientMeanD (RBE1.1)MeanD (RBEMinMax)Difference in MeanD %MeanD (RBE1.1)MeanD (RBEMinMax)Difference in MeanD %MeanD (RBE1.1)MeanD (RBEMinMax)Difference in MeanD %A0.730.786.82%0.490.525.26%0.160.164.77%B0.450.487.20%0.530.565.22%0.720.742.85%C0.300.327.00%0.810.864.95%0.430.453.46%D0.500.537.01%0.550.585.12%0.590.613.15%E0.931.006.97%0.420.444.61%0.480.503.11%F1.571.665.49%0.560.594.91%0.450.463.27%PatientMaxnD (RBE1.1)MaxD (RBEMinMax)Difference in MaxD %MaxnD (RBE1.1)MaxD (RBEMinMax)Difference in MaxD %MaxnD (RBE1.1)MaxD (RBEMinMax)Difference in MaxD %A11.5712.043.87%18.0618.462.13%18.0618.462.13%B10.1810.634.23%16.6817.092.38%16.6817.092.38%C7.868.274.91%17.7918.192.18%17.7918.192.18%D7.848.254.92%19.6520.021.86%19.6520.021.86%E10.5010.964.14%22.2322.561.46%22.2322.561.46%F17.6218.082.58%22.6722.991.40%22.6722.991.40% Open table in a new tab Using RBE1.1 may contribute to making PT dose and dose-dependent predictions less accurate. Our results using an RBE calculation model show systematic differences in dose. This may have clinical implications and can influence predicted risk of secondary cancer as well as normal tissue complication probability.
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