SQL improving

Hi,

Could some one help improve below query. DB -11.2.0.3

SELECT ap.agency_id,
       ap.vac_ref,
       kc.kpi_id,
       SUM(CASE
             WHEN (( ( SYSDATE - ap.application_status_date ) > ( CASE
                               WHEN af.type_id = 1 THEN Nvl(
                               ak.custom_orange_days_medical
                               + ak.custom_green_days_medical,
kc.default_orange_days_medical
+ kc.default_green_days_medical
)
ELSE Nvl(ak.custom_orange_days
+ ak.custom_green_days, kc.default_orange_days
        + kc.default_green_days
)
          END ) )) THEN 1
ELSE 0
END) AS kpi_overdue_count
FROM   application ap
       inner join kpi_criteria kc
               ON ap.application_status_id = kc.application_status_id
       left outer