Radiotherapy for esophageal cancer using simultaneous integrated boost techniques: dosimetric comparison of helical TomoTherapy, Volumetric-modulated Arc Therapy (RapidArc) and dynamic intensity-modulated radiotherapy.
This study compared TomoTherapy (TM), with Volumetric-Modulated Arc Therapy (RapidArc, RA), and dynamic intensity-modulated radiotherapy (dIMRT) for locally advanced esophageal cancer (LAEC) with a simultaneous integrated boost (SIB) technique with regard to the target coverage and sparing of organs at risk (OARs). Twelve patients receiving four-dimensional computed tomography simulation were enrolled for dosimetric comparison. Gross tumor volume was contoured with the maximum intensity projection method. Using an SIB method, Planning target volume low (PTVL) and planning target volume high (PTVH) were prescribed as 54 Gy and 60 Gy, respectively, each administered in 30 fractions. We compared the results of statistical analysis for target coverage, homogeneity index (HI) and conformity index (CI) of PTVs, parameters of OARs and monitor unit (MU) were compared for analysis. The HI for PTVH varied significantly for the 3 techniques of TM, RA, and dIMRT (4.38 ± 0.86, 6.40 ± 0.86, and 6.11 ± 0.68, respectively; P , 0.001). The CI scores for PTVH also differed across TM, RA, and dIMRT (0.64 6 0.06, 0.53 6 0.06, and 0.59 ± 0.05, respectively; P < 0.001). The HI for PTVL showed a significant difference among TM, RA, and dIMRT (15.44 ± 0.88, 20.88 ± 1.03 and 18.65 ± 1.42, respectively; P < 0.001). The percentage of lung volume receiving 5 Gy (V5) and 20 Gy (V20) (for V5: TM 54.4 ± 8.0%; RA 67.5 ± 14.5%, P < 0.01; dIMRT 44.8 ± 8.2%; for V20: 13.6 6 3.3%, 12.2 ± 3.6%, 18.1 6 3.4%, P = 0.001, respectively). For RA, the lung V5 ? 65% was observed in 6 patients and the V10 ? 50 % in one patient. TM, RA and dIMRT provided comparable coverage of the target and sparing of OARs. TM demonstrated superior CI and HI for tumor coverage and lowered the specified dose parameters for lung. RA provided an advantage in terms of the lowest MU and V20 of the lung, but its higher lung V5 was of some concern about lung toxicity.