Doosan does not have a postseason-clinch number; they can miss the postseason even if they win all 12 of their remaining games.
Here is scenario in which Doosan wins 12 additional games (68 total) but does not reach the postseason.

Here are the final standings in the scenario:
            Team	W	L	D	PCT	GB
          Hanwha	85	56	3	0.6028	0.0
              LG	82	59	3	0.5816	3.0
              NC	74	64	6	0.5362	9.5
              KT	75	65	4	0.5357	9.5
         Samsung	69	71	4	0.4929	15.5
          Doosan	68	70	6	0.4928	15.5
             KIA	68	72	4	0.4857	16.5
           Lotte	65	71	8	0.4779	17.5
             SSG	65	75	4	0.4643	19.5
          Kiwoom	46	94	4	0.3286	38.5

To construct the scenario, we start with the current standings:
            Team	W	L	D	GL	PCT	GB
              LG	80	49	3	12	0.620	0.0
          Hanwha	76	53	3	12	0.589	4.0
             SSG	65	60	4	15	0.520	13.0
              KT	65	63	4	12	0.508	14.5
         Samsung	66	64	2	12	0.508	14.5
           Lotte	63	64	6	11	0.496	16.0
              NC	61	62	6	15	0.496	16.0
             KIA	61	65	4	14	0.484	17.5
          Doosan	56	70	6	12	0.444	22.5
          Kiwoom	43	86	4	11	0.333	37.0

The next two tables show, respectively, how many of their remaining games each team wins and ties against each of the other teams in the scenario:

					Scenario Additional Wins Against
Team	Doosan	Hanwha	KIA	Kiwoom	KT	LG	Lotte	NC	Samsung	SSG	Wins
Doosan	-	1	0	3	0	1	1	1	1	4	12
Hanwha	0	-	3	1	0	3	1	0	0	1	9
KIA	0	0	-	1	1	0	1	0	2	2	7
Kiwoom	0	0	0	-	1	0	1	0	0	1	3
KT	0	2	0	0	-	4	0	1	1	2	10
LG	0	0	0	0	0	-	1	0	1	0	2
Lotte	0	0	0	0	0	0	-	0	1	1	2
NC	0	0	4	1	0	2	2	-	1	3	13
Samsung	0	0	0	2	0	0	0	0	-	1	3
SSG	0	0	0	0	0	0	0	0	0	-	0
-----------------------------------------------------------------------------------
Losses	0	3	7	8	2	10	7	2	7	15

					Scenario Additional Draws (Ties) With
Team	Doosan	Hanwha	KIA	Kiwoom	KT	LG	Lotte	NC	Samsung	SSG	Total
Doosan	-	1	0	0	0	0	1	2	0	0	0
Hanwha	0	-	0	0	0	1	0	0	0	0	0
KIA	0	0	-	2	0	0	0	0	0	1	0
Kiwoom	0	0	0	-	0	0	0	1	0	1	0
KT	0	0	0	0	-	0	0	1	0	0	0
LG	0	0	0	0	0	-	2	0	0	0	0
Lotte	0	0	0	0	0	0	-	0	3	0	2
NC	0	0	0	0	0	0	0	-	0	1	0
Samsung	0	0	0	0	0	0	2	0	-	1	2
SSG	0	0	0	0	0	0	0	0	0	-	0
-----------------------------------------------------------------------------------
Total	0	0	0	0	0	0	2	0	2	0

The next two tables show, respectively, how many total games each team wins and ties against each of the other teams in the scenario:

					Scenario Total Wins Against
Team	Doosan	Hanwha	KIA	Kiwoom	KT	LG	Lotte	NC	Samsung	SSG	Wins
Doosan	-	9	6	12	4	7	8	6	7	9	68
Hanwha	6	-	12	14	9	8	10	9	8	9	85
KIA	9	4	-	8	9	5	9	6	9	9	68
Kiwoom	4	2	6	-	6	7	5	5	4	7	46
KT	11	7	7	10	-	8	6	7	11	8	75
LG	9	7	11	9	8	-	10	8	10	10	82
Lotte	7	6	7	11	8	4	-	7	8	7	65
NC	8	6	10	10	8	8	9	-	8	7	74
Samsung	9	8	7	12	5	6	5	8	-	9	69
SSG	7	7	6	8	8	6	9	8	6	-	65
-----------------------------------------------------------------------------------
Losses	70	56	72	94	65	59	71	64	71	75

					Scenario Total Draws (Ties) With
Team	Doosan	Hanwha	KIA	Kiwoom	KT	LG	Lotte	NC	Samsung	SSG	Total
Doosan	-	1	1	0	1	0	1	2	0	0	6
Hanwha	0	-	0	0	0	1	0	1	0	0	3
KIA	0	0	-	2	0	0	0	0	0	1	4
Kiwoom	0	0	0	-	0	0	0	1	0	1	4
KT	0	0	0	0	-	0	2	1	0	0	4
LG	0	0	0	0	0	-	2	0	0	0	3
Lotte	0	0	0	0	0	0	-	0	3	0	8
NC	0	0	0	0	0	0	0	-	0	1	6
Samsung	0	0	0	0	0	0	2	0	-	1	4
SSG	0	0	0	0	0	0	0	0	0	-	4
-----------------------------------------------------------------------------------
Total	6	3	4	4	4	3	8	6	4	4