ESTRO 2023 - Abstract Book

S1840

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ESTRO 2023

Table 1: Median, first and third quartiles (in brackets) are shown. All results are given as a percentage of the prescribed dose or a percentage of the organ volume Figure1: Boxplot representation of the values shwon in table 1. Y-axis as a percentage of the of the prescribed dose or a percentage of the organ volume

Conclusion Hybrid techniques, combining static and modulated arcs are a good dosimetric solution for the irradiation of patients with internal mammary nodes affected. However, VMAT techniques may be preferable compared to a hybrid technique in cases where V20Gy to the homolateral lung needs to be lowered

PO-2064 Separated single arc VMAT with rectangular collimation (SA-VMAT) for prostate SBRT.

H. Nagano 1 , H. Yokoyama 1 , M. Kato 2 , H. Hashimoto 1 , T. Shimo 2 , M. Watanabe 1 , M. Nakanishi 1 , H. Suzuki 1 , Y. Kaneko 1 , K. Kobayashi 1 , C. Takano 1 , S. Tanaka 1 , Y. Goto 1 , E. Horikoshi 1 , M. Notani 1 1 Shonan Fujisawa Tokushukai Hospital, Radiation oncology, Fujisawa, Japan; 2 Tokyo-West Tokushukai Hospital, Radiation oncology, Akishima, Japan Purpose or Objective In the cases of the prostate VMAT-SBRT we used multiple arcs (MA-VMAT) for the sake of realizing ideal clinical goals (CGs). As the number of arc increases, the goals may get closer but estimated treatment time (ETT) should increase. We tried separated single arc (gantry angle; 181 - 290, 290 - 70, 70 - 179 degrees) with rectangularly (5, 95, 5 degrees) collimated VMAT (SA-VMAT), and reported time saving ability of this method under the same CGs used for the MA-VMAT. Materials and Methods From June 2022, thirty five patients were retrospectively selected from our database. Median of age was 77 (range 55 - 86) years. High, intermediate and low risks were distributed as 26, 7 and 2, respectively. Initial PSA value was ranged from 4.014 to 339.0 (median 9.862) ng/ml. GS was 4 to 9 and median value was 8. Numbers of patients diagnosed as T1, T2 and T3 were 5, 20 and 10, respectively. Median volume of prostate was 27.8 (range 13.08 - 82.55) ml. These 35 MA-VMAT plans were recalculated by SA-VMAT using the same CGs with some modifications of constrains. Values of CGs and ETT were compared and estimated by paired t-test. Dose calculation was done using RayStation 10. CRAN R and Rstudio used for statistical calculation.

Results