ORL = otorrinolaringología

Cupo appears to mean entry-level doctors (MIR). Originally I imagine it referred to the number of such doctors in any particular department.

In this CV you can see that this doctor first did 3 years as MIR and then became "jefe del cupo de cirugía" and then "Medico Adjunto"
http://www.hospiten.es/hospiten/HOSPITEN/published/DEFAULT/c...

In this document, on page 10 "cupo" is the last column in a table showing numbers of doctors for each department, ordered by senior to junior:
http://www.senado.es/legis5/publicaciones/pdf/senado/bocg/I0...

In other contexts it would be catchment area, but I don't think that works here.

In my answer "residents" would be for a US audience and FY (Foundation Year doctors) would be for the UK.

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Note added at 1 hr (2012-05-28 18:31:23 GMT)
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Well, on further investigation, I think I was barking up the wrong tree:)

I've found a definition that says,
El término cupo hace referencia a que su tarea consiste en atender a un determinado «cupo» de pacientes.
http://www.lne.es/sociedad-cultura/2011/12/16/navia-osorio-a...

Here's a hospital that lists "especialista de cupo" as someone who is apparently higher up than MIR.
http://hugu.sescam.jccm.es/servicio/radiodiagnostico/quien

How about "Head of the ENT catchment area" or even just ""Head of the ENT area"?

Confidence level down to 1 now...

One idea. I finally sat down to study this as the article I posted earlier as a reference was about a situation here in the city I live in. I was surprised to discover that this isn't an exclusively Spanish thing. Apparently some doctors have a base pay that is augmented by service units rendered. The quota refers to the number of these "above baseline" services they are now allowed to provide. Keeping track of an employee's allotted working hours is basically a human resources function, so I'd state it that way. An example in Asia: URL:http://www.auditpaper.com/marketing-audit/17078969.shtml
Based on the policy circumstance of quota regulation of hospitals,the paper analyzed the human resources status and the quota of Shanghai Chest Hospital,then discussed the problems including the separation between the quota and the workload,the irrationality of structure of the technical post,the outdated quota regulation,and the conflicting management.It also gave some suggestions to solve the problems from the hospital and administrative perspectives.
If this is for a general audience, I'd suggest an explanatory footnote. If it's directed towards hospital employees, they'll probably understand what it's all about. Apparently when doctors (at least in Spain) entered the system years ago, they accepted a low base salary on the premise that the difference would always be made up by the hours they worked in excess of the core officially contracted for. To cut costs, the hospitals are suddenly drastically reducing these "extra" hours - a disaster for doctors in their 50s or 60s for whom it's too late to re-channel careers to the private sector. Since there are other kinds of quotas related to hospital, I'd make sure some reference to human resources was included.