Zend Pdf round corners in rectangle section

I wrote the below code to show rectangle in pdf file

        $page->setFillColor(new Zend_Pdf_Color_GrayScale(0.92)); 
        $page->setLineColor(new Zend_Pdf_Color_GrayScale(0.92));
        $page->drawRectangle($x, $oldY+20, ($pageWidth/2)-50, $this->y-10);
        $page->setFillColor(new Zend_Pdf_Color_GrayScale(0));
        $page->setLineColor(new Zend_Pdf_Color_GrayScale(0));

AND Output is

But I need round corners in rectangle how can I do this in Magento 2 Zend pdf.I wanna output like this

Expected output: