X-Sums Sudoku (Daily Sudoku League #48)

The instruction booklet of the World Sudoku Championship 2014 is released yesterday. My League Sudoku posts till WSC2014 will be of Sudoku types that are appearing in this year's World Sudoku Championship.
Irregular Sudoku and X-Sums Sudoku are the two types appearing in WSC 2014. So this X-Sums Sudoku is a mix of these two types.

This X-Sums Sudoku is my 48th contribution to The League of Extraordinary Ladies and Gentlemen. Can you solve this X-Sums Sudoku puzzle?

Rules of X-Sums Sudoku

Irregular Sudoku Rules apply. Additionally, the clues outside the grid indicate the sum of the first X numbers placed in the corresponding direction, where X is equal to the first number placed in that direction.