Abstract
The definite indication of flattening filter free Rapid-ARC is still unclear yet. Our study compared the dose distribution of target volumes, dose fall, protection of normal organs at risk (OAR) and monitor unit (MU) of 3 radiotherapy techniques (Rapid-ARC FFF, IMRT FF and Rapid-ARC FF) in superficial tumors of head and neck. Nine patients were enrolled. The three RT plans mentioned above were designed for each patient with 6MV X-ray. The prescribed dose was 54Gy/30f/1.8Gy to PTV concurrent with 64.2Gy/30f/2.14Gy to PGTV. The target volume coverage indicators included conformity and homogeneity index (CI, HI). The dose fall indicators included V40 and V20 (the covered volume by 40Gy and 20Gy, respectively). OARs included the brainstem and spinal cord. All the optimized parameters and target values for plans were consistent. Rapid-ARC FFF provided significantly improved conformity (0.762±0.013) and homogeneity (1.073±0.022) of PGTV than IMRT FF (CI= 0.677±0.076, p<0.01; HI= 1.116±0.048, p<0.05), and Rapid-ARC FF (CI= 0.717±0.077, HI= 1.080±0.018, p<0.05). Rapid-ARC FFF has a better CI (0.800±0.049) of PTV compared with IMRT FF (0.754±0.071, p<0.05) and Rapid-ARC FF (0.768±0.074, p<0.05) respectively.Furthermore, RapidArc FFF had a rapider dose fall. RapidArc FFF remarkably reduced V40 (445.85±213.60cm3) and V20(972.42±428.70cm3) compared with IMRT FF (V40= 472.62±219.63cm3, V20= 1000.18±445.74cm3, p<0.01) and Rapid-ARC FF (V40= 454.51±221.50cm3, V20= 1018.17±475.67cm3, p<0.01). However, the dose of brain stem was increased in RapidArc FFF (D1cc=2669.46±927.05cGy) but kept in the nomal threshold compared with IMRT FF (2593.97±872.12cGy, p<0.05) and Rapid-ARC FF (2656.97±909.73cGy,p<0.05). Similarly, the dose of cord was increased in RapidArc FFF (D1cc=3031.25±438.77cGy) but kept in the nomal threshold compared with IMRT FF (3027.76±426.03cGy,p<0.05) and Rapid-ARC FF (3025.33±487.39cGy,p<0.05). RapidArc FFF greatly reduced MU (344.00±40.62) compared with IMRT FF (613.50±100.06, p<0.01) but slightly increased MU compared with RapidArc FF (325.75±31.15,p<0.05). Rapid-ARC FFF is superior to IMRT FF or RapidArc FF in superficial tumors of head and neck for better target coverage and rapider dose fall. Rapid-ARC FFF can be the first option for superficial tumors of head and neck.
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