We developed "sandglass" technique using volumetric arc therapy (VMAT) with two avoidance sectors and make comparison between two intensity-modulated radiotherapy (IMRT) techniques, "butterfly" with three anterior and two posterior beams, and "rainbow" with five anterior beams. Conformity index (CI), homogeneity index (HI), organ of risk doses, and monitor unit (MU) values are used as evaluation tools.
METHODS
IMRT and VMAT plans generated for 15 mediastinal lymphoma patients. Sandglass technique consists
of two full arc with avoidance sectors (240°-300° and 60°-120°), butterfly technique with five static fields
(0°, 40°, 160°, 190°, and 330°), and rainbow technique has five static fields (0°, 20°, 40°, 320°, and 345°).
The prescribed treatment dose was 30.6 Gy in 17 fractions. Dosimetric data were compared using crosspaired
sample t-test.
RESULTS
Lung V5 doses were 41.62-50.74%, V20 doses were 12.72-16.21%, heart mean doses were between 454
and 509 cGy, spinal cord max point doses were between 2210 and 2798 cGy, esophagus mean doses were
between 1309 and 1409 cGyHI, CI, and MU values were calculated. Lung V20, mean esophagus, and mean
heart and spinal cord max. point doses were observed significantly lower at sandglass technique (p=0.001,
p=0.02, p=0.013, and p=0.001). CI is significantly better than other two techniques (rainbow p=0.000 and
butterfly p=0.001). On the other hand, lung V5 doses significantly lower at rainbow technique (p=0.035),
besides, HI has significant advantage with respect to others. Sandglass has lower MU value with 484 MU.
CONCLUSION
Sandglass technique has remarkable advantageous for lung V20, heart, esophagus, spinal cord, CI, and
MU. Treatment plans with lower critical organ doses have great importance in terms of late side effects
in patients with long survival expectancy. Sandglass plan was preferable for mediastinal lymphoma.