(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: The aim of this study is to evaluate the dosimetric benefits of hydrogel spacer in Linac-based prostate stereotactic body radiation therapy (SBRT) treatment for the organ at risk (OAR) volumes.
Methods: Ten patients were selected for this study. They were underwent CT and MRI studies. The first five patients were injected SpaceOAR hydrogel spacer with transperineal approach by using transrectal ultrasonography (TRUS). All patients were prescribed to 36.25 Gy. in 5 fractions. RapidArc (Eclipse version 13.7.16, Varian Inc.) plans were generated by using two or three full arcs depending on the dose constraints to be met. Plan acceptance criteria were minimum 95% and maximum 107% of prescription dose to planning target volume (PTV) along with acceptable conformity index(<1.2). The dose to rectum, bladder and femoral heads were evaluated. The conformity indices and PTV-rectum overlap volume were also tabulated.
Results: The treatment plans with hydrogel spacer shows superior OAR sparing especially in rectum compared to non-spacer plans due to mechanical separation provided by the spacer. The mean PTV-rectum overlap is 0.04 cc and 5.1 cc respectively for spacer and non-spacer plans. Rectal doses were significantly lower for all the dose constraints for spacer vs non-spacer plans. (Dmax= 31.3 Gy. vs 36.8 Gy. , D90%=1.3 Gy. vs 2.7 Gy. , D80%=2.0 Gy. vs 5.1 Gy. , D50%= 8.2 Gy. vs 12.3 Gy.). Bladder and femoral head maximum doses were not significantly different (35.6 Gy. vs 37.6 Gy. and 15.6 Gy. vs 17.9 Gy.).
Conclusion: Significant dose reduction to rectum were observed and this may, in turn, lead to reduced rectal toxicities for patients with hydrogel spacers. Although maximum dose to bladder and femoral heads were lower for patients with spacers, these were not notable as expected.
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