Catatan Pelatihan Teknis Dasar Elekta Linac

Konsep Dasar Linac

• Tujuan utama:

  • Menghasilkan beam berenergi tinggi (elektron atau foton)

  • Mempercepat partikel menggunakan gelombang RF (travelling‐wave guide)

  • Semua komponen utama terpasang pada gantry drum yg dapat berputar $+180^{\circ}$ s.d. $-180^{\circ}$

• Sebutan/rujukan:

  • “Linac” = Linear Accelerator

  • Pelatihan teknis dasar Elekta Linac (20–22 Sept 2016)

Clinical Beam

• Jenis & kisaran energi

  • Elektron: $4\;\text{–}\;22\;\text{MeV}$ → lesi ≤ $50\;\text{mm}$ dalam

  • Foton: $4\;\text{–}\;25\;\text{MV}$ → lesi ≤ kedalaman jaringan dalam

Proses Produksi Clinical Beam

1. Beam Generation

• Rangkaian utama (gambar area): HT → Magnetron → Waveguide dsb.

• Komponen penting:

  • High-Voltage Pulse

  • Sumber 3-fase (aktif bila interlock aman: pintu ruang, dll.)

  • HT PSU (Area 17) menyearahkan & step-up lalu mengisi $8$ kapasitor PFN

  • Modulator (Area 30) → discharge PFN → pulsa tegangan tinggi menuju thyratron & magnetron

  • Magnetron

  • Sumber RF; elektron dari katoda ke anoda di rongga magnetron menghasilkan gelombang RF

  • Frekuensi RF ditentukan dimensi rongga; disetel via tuner software (Fast Tune Magnetron – FTM, Area 37)

  • Electron Gun (Area 21)

  • Filamen tungsten spiral; dipanaskan (arus diatur via software) utk emisi elektron

  • Waveguide (Area 22)

  • Tembaga, L > $2\;\text{m}$; dibagi sel terpisah disc

  • RF memasuki sel 1 dg kecepatan $0.4c$; di ujung mencapai $0.998c$ bersama elektron

  • Desain jarak antar‐disc menaikkan fase & mempercepat elektron

2. Beam Control

• Fungsi utama

  • Beam Focusing (1R & 1T)

  • Beam Steering (1R & 1T, 2R & 2T)

  • Beam Bending: Triple Magnet System (Primer & Sekunder)

3. Beam Shaping

• Target (tungsten, $1\;\text{mm}$):

  • Mode X-ray → elektron menabrak target menghasilkan foton

  • Mode Electron → elektron lolos via nickel window

• Primary Filter: $6$ port (5 electron, 1 photon “open”)

• Collimator: 2 tipe (electron & photon energi rendah, photon energi tinggi)

• Secondary Filter: $5$ port (2 photon, 3 electron)

• Monitoring → Ion Chamber: mengukur uniformity & dosis (mis. $d<em>1, d</em>2$; spesifikasi profil 90 % & 50 %)

• Aksesoris & modifikasi:

  1. Wedge (lead alloy) – memiringkan distribusi dosis

  2. Shutter (aluminium) – menahan back-scatter agar tdk masuk ion chamber

  3. Diaphragm (tungsten/nickel/iron) – membatasi lapangan

  4. Shadow Tray (photon) & Applicator (electron)

Machine Geography

• Orientasi anatomi: ceiling (anterior), floor (posterior), G-end (superior), T-end (inferior), A-side (kanan), B-side (kiri)

• Area kode penting (ringkasan):

  • 10 Heat Exchanger, 11 HP Phase Shift, 12 RHCA, 13 LV PSU, 14 Gantry interlock relay, 15 Motor Drive PSUs, 16 HT Control, 17 Flyback HT PSU, 18 Ion Pump PSU, 19 Laser Back Pointer, 20 Gantry Arm & RF, 21 Electron Gun, 22 Waveguide, 23 Bending Magnet, 24 Flight Tube & Target, 25 Collimator, 26 BLD, 30 Modulator, 32 Thyratron Pulser, 33 Filament PSU, 37 FTM Rack, 40 Misc. Gantry Drum, 42 Cable Reel, 43 Phase Error Detector, 44 Gantry Rim, 45 Gantry Base, 50 Gantry Base.

Control System (LCC)

• Tiga Area Kontrol serial (link A & B):

  • ICCA Area 72 (Interface/Console)

  • RHCA Area 12 (Radiation Head)

  • HTCA Area 16 (High Tension)

• PCB yg dapat diswap antarzona: MTU, AI12, ROC, AO8, AO12, Aux PSU

• PCB yg tidak boleh diswap: SCC, DIE

Interlock System

• Kategori:

  • LT Interlock

  • Movement Interlock

  • HT Interlock (CON J / K / D)

  • PRF Interlock (segmen radiasi)

• Beberapa interlock dpt di-bypass saat servis/kalibrasi (harus dicatat untuk keselamatan!)

Supplies & Services

Sumber Daya

• 3-phase supply → HT PSU

• LV PSU (Areas 11, 13, RHCA)

• HT PSU (Area 17)

• Aux PSU (Area 14)

• Movement Table: Area 15, EIM Area 75

Pendingin & Lingkungan

• Water: eksternal chiller, internal $12.5\;\text{psi}$

• Gas dielectric: $0.8\;\text{bar}$ (self filling saat start-up)

• Vacuum: Vac Gun, Vac Target $\approx -6\;\text{xx}\;\text{mbar}$ + Ion Pumps

LCS (Linac Control System)

Hardware

• Mainboard, Display Processor, Control Processor

• LIB, SIB, LCD Dose Module, Storage, berbagai PCI card

Software (Integrity)

• Mode: Service (biru) / Clinical (pink)

  • Akses Service: user = "service", password = "service"

• Tiga fokus tampilan: Machine State, Inhibit, Interlock

Item & Part

• “Item” = komponen fisis (Vac Gun, Gun I ctrl)

• “Part” = parameter terukur/setpoint (set value, actual value, limit, offset, gain)

Radiation Head & MLC

BLD (Beam Limiting Device)

• Tipe:

  • Asymmetric Diaphragm (non-MLC)

  • MLCi, MLCi2

  • Beam Modulator

MLC (Multileaf Collimator)

• Fungsi: membentuk lapangan sesuai kontur tumor

• Spesifikasi:

  • $40$ leaf per bank (Y1 & Y2)

  • Ketebalan leaf di isocenter $1\;\text{cm}$

• Komponen:

  • Leaf (tungsten alloy)

  • Reflector (stiker)

  • Lead Screw & Motor

  • Optik: Projector + Mirror + Camera, lampu halogen $13.8\;\text{V},\;50\;\text{W}$

• Kontrol & Servis umum:

  • Calibrate Reference Reflectors

  • Calibrate Video Lines

  • Optic Optimization (threshold lebar reflector 30–70 %, status OK/Warning/Error)

  • Display Shape Codes

Precise Table

• Komponen Mekanik:

  1. Table Tops

  2. Gerak $X/Y$ (motorized)

  3. Gerak $Z$ (tinggi)

  4. Column (Z) & Iso-rotation (motorized)

  5. Column rotation manual

• EIM (Electrical Interface Module) di ruang mesin

  • Menyediakan tegangan $\pm26\;\text{V}$, $\pm15\;\text{V}$, $+5\;\text{V}$, $+90\;\text{V}$

  • LED Bar Graph untuk diagnosis pergerakan

  • PCB kunci troubleshoot: LED PCB, LCU

iViewGT (MV EPID)

• Komponen:

  • Detector Panel (Perkin Elmer a-Si): $1024\times1024$ px, 16-bit, $41\times41\;\text{cm}$ (≈ $26\times26\;\text{cm}$ di isocenter)

  • Mechanical Arm dgn 6 gerakan (Extend, Retract, Open, Close, dll.) dikendalikan ACB

  • Control PC, DCB, PSU, CAN Bus

• Prinsip Kerja

  • Arm Control PSU $+24\;\text{V}$, Detector PSU

  • Data ➔ CAN data cable; Image ➔ Fibre-optic

  • Indikator LED: hijau kontinu (supply OK), hijau berkedip (sync internal), amber berkedip (sync eksternal)

• Fungsi: verifikasi posisi pasien (portal imaging) sebelum &/atau saat iradiasi

MOSAIQ (EMR System)

• Integrated Clinical & Management

• Komponen:

  1. Server (24/7) berisi DB & software

  2. DICOM/Namer gateway (24/7) konversi TPS→MOSAIQ

  3. Workstation (approval, scheduling, billing, record dose)

  4. Sequencer ↔ Linac (kirim field, dosis, data pasien)

Common Problems (Ringkasan)

• Linac/LCS: swap board ROC/AI12, fibreoptic, interlock fault, chiller, gas/water pressure, laser/ODI lamp, database integrity, software bug, Demux PCB kotor, hang, kalibrasi

• MLC: lamp mati, reflector kotor, isocenter meleset, optic mis-align

• iViewGT: detector movement error, image noise, connection lost, backup gagal

• Table: clutch/brake slip, LED PCB error, software bug

Monthly Maintenance (15 Task)

1. Cek Isocenter

2. Cek Laser

3. Cek Suhu Ruang

4. Cek Kelembapan Ruang

5. Cek Dehumidifier

6. Cek Tekanan Air Internal

7. Cek Tekanan Gas

8. Cek Level Chiller

9. Cek Suhu Air

10. Bersihkan Gantry Rims

11. Bersihkan Filter Inlet LCS

12. Catat LT Hours

13. Catat HT Hours

14. Catat Level Kamera BK

15. Database Routine Maintenance

Catatan detail ini mencakup seluruh poin besar & kecil, nilai numerik, struktur area, serta implikasi praktis (pemeliharaan, troubleshoot, keselamatan). Digunakan sebagai pengganti transkrip asli untuk persiapan ujian teknisi Elekta Linac.