Prevalens penyakit paru obstruksi kronik (PPOK) dan emfisema berdasarkan pemeriksaan spirometri dan computed tomography scanning (CT-scan) toraks pada pasien kanker paru di Rumah Sakit Umum Pusat Persahabatan = Prevalence of chronic obstructive pulmonary disease and emphysema based on spirometry and thorax CT-scan among lung cancer patients treated at Persahabatan Hospital Jakarta, Indonesia