Actinotherapy & Superficial Heat: IRR, LASER, UVR
💡 The Core Concept: This section covers Phototherapy (Light Therapy). The effects depend entirely on the Wavelength and Frequency of the radiation on the electromagnetic spectrum.
1. Infra-Red Radiation (IRR)
Electromagnetic radiation with wavelengths longer than visible red light. Primarily used for superficial thermal effects.
| Type | Wavelength Range | Source | Penetration |
|---|---|---|---|
| IR-A (Near IR) | 770 nm - 1500 nm | Luminous Generators (Tungsten filament) | Deeper (Epidermis/Dermis) ~5-10mm |
| IR-B/C (Far IR) | 1500 nm - 15,000 nm+ | Non-Luminous Generators (Ceramic coil) | Superficial (Epidermis only) ~2mm |
Physics Laws (Exam Critical)
- Inverse Square Law: Intensity is inversely proportional to the square of the distance. (Distance doubled = Intensity 1/4th).
- Cosine Law: Absorption is maximum when rays strike at 90° (perpendicular).
- Grothus-Draper Law: Only radiation absorbed by the tissue is effective; reflected/transmitted radiation has no effect.
⚠️ IRR Dangers:
- Burn: If sensation is impaired.
- Gangrene: In patients with Arterial Insufficiency (Heat increases metabolic demand which blood supply cannot meet).
- Eye Damage: IR-A can cause Cataracts/Retinal damage.
2. LASER (Light Amplification by Stimulated Emission of Radiation)
Unique Properties of Laser Light
- Monochromaticity: Single wavelength (one color).
- Coherence: Waves are in phase (peaks and troughs match).
- Collimation: Parallel beam, minimal divergence.
Common Therapeutic Lasers (Cold Lasers / LLLT)
| Type | Medium | Wavelength | Penetration |
|---|---|---|---|
| He-Ne (Helium Neon) | Gas | 632.8 nm (Visible Red) | Superficial (Skin/Wounds) |
| GaAs (Gallium Arsenide) | Semiconductor | 904 nm (Invisible IR) | Deep (Musculoskeletal) |
| GaAlAs | Semiconductor | 830 nm (Invisible IR) | Deepest |
Laser Classification (Safety)
- Class 3B: Therapeutic use. Power < 500 mW. Direct eye exposure is dangerous.
- Class 4: Surgical/High Power. Power > 500 mW. Causes skin burns and fire hazards.
Dosage Parameters (The "Numbers")
- Energy Density (Fluence): Measured in Joules per cm² (J/cm²).
- Formula: Energy (J) = Mean Power (W) × Time (s).
- Acute Conditions: Low dose (2-4 J/cm²).
- Chronic Conditions: High dose (High intensity or longer duration).
3. Ultraviolet Radiation (UVR)
Electromagnetic waves shorter than visible violet light. Known for photochemical effects.
| Band | Wavelength | Common Name | Primary Effect |
|---|---|---|---|
| UVA | 315 - 400 nm | Long Wave | Pigmentation, PUVA Therapy |
| UVB | 280 - 315 nm | Middle Wave | Erythema (Sunburn), Vitamin D synthesis |
| UVC | < 280 nm | Short Wave | Germicidal (Kills bacteria), Wound Healing |
Dosimetry: The Test Dose (MED)
Before treatment, a Minimal Erythema Dose (MED) test is mandatory to determine patient sensitivity.
- E1 (1st Degree Erythema): Mild pink, disappears in 24 hours. (Standard treatment dose).
- E2 (2nd Degree): Red, sore, mild peeling. Fades in 2-3 days.
- E3 (3rd Degree): Intense red, hot, peeling, edema. Fades in 1 week.
- E4 (4th Degree): Destructive, blistering, exudation.
🏆 AIIMS "Golden Points"
- PUVA: Psoralen (drug) + UVA Radiation. Used for Psoriasis.
- Germicidal Peak: UVC at 254 nm is most effective for killing bacteria in open wounds.
- Contraindication: Systemic Lupus Erythematosus (SLE) and Xeroderma Pigmentosum are absolute contraindications for UVR.
- Vitamin D: Synthesized primarily by UVB rays (280-315 nm).
📝 40 High-Yield MCQs (Practice Now)
Click an option to check your answer immediately.
Part 1: LASER Therapy
Q1. Which unit is used to define LASER Dosage (Energy Density)?
Rationale: Energy density describes the amount of energy delivered per unit area of tissue, calculated as (Power × Time) / Area.
Q2. The He-Ne (Helium Neon) Laser emits light in which spectrum?
Rationale: He-Ne is a gas laser that produces a visible red beam at exactly 632.8 nm.
Q3. Which property of Laser refers to all waves being "in phase" (peaks and troughs matching)?
Rationale: Coherence means all the photons are vibrating in unison (same space and time phase), which allows the beam to carry high energy.
Q4. Therapeutic Lasers (LLLT) generally fall under which Safety Class?
Rationale: Class 3B includes lasers with power between 5mW and 500mW, used for therapy. Class 4 (>500mW) is surgical/destructive.
Q5. Gallium Arsenide (GaAs) Laser is primarily used for:
Rationale: GaAs emits at 904 nm (Infrared), which penetrates deeper (3-5 cm) than visible red lasers, making it suitable for deep tissues.
Q6. What is "Photobiomodulation"?
Rationale: LLLT works not by heat, but by stimulating chromophores (like Cytochrome C Oxidase) in the mitochondria to increase ATP production. This is photobiomodulation.
Q7. Which of the following is an absolute contraindication for Laser therapy?
Rationale: Lasers can cause immediate and permanent retinal damage. Both patient and therapist must wear protective goggles. Metal implants are NOT a contraindication for cold laser.
Q8. "Grid Scanning" technique in Laser is used for:
Rationale: For large areas, the treatment zone is divided into a grid of 1cm squares, and each square is treated sequentially.
Q9. The wavelength of GaAlAs (Gallium Aluminum Arsenide) laser is typically:
Rationale: GaAlAs is a continuous wave semiconductor laser emitting in the near-infrared range (780-830 nm), offering good penetration.
Q10. Class 4 Lasers (>500mW) are primarily used for:
Rationale: Class 4 lasers produce significant heat and are used for surgical cutting (CO2 lasers) or High Intensity Laser Therapy (HILT). They are fire hazards.
Q11. Which parameter determines the depth of laser penetration?
Rationale: Wavelength dictates absorption. Longer wavelengths (Near IR) penetrate deeper than shorter wavelengths (Visible Red).
Q12. "Monochromaticity" means the laser beam has:
Rationale: Mono = One, Chroma = Color. Laser light consists of only one specific wavelength, unlike white light which is a mix.
Q13. For treating an open wound, the laser probe should be:
Rationale: To maintain sterility and prevent cross-contamination, the probe is held just off the surface or a clear sterile barrier is used.
Part 2: Ultraviolet Radiation (UV-R)
Q14. Which band of UVR is responsible for the "Germicidal" effect (killing bacteria)?
Rationale: UVC (Short wave, <280nm) damages bacterial DNA. The peak germicidal wavelength is 254 nm.
Q15. PUVA therapy combines a Psoralen drug with which radiation?
Rationale: PUVA = Psoralen + UVA. Psoralen sensitizes the skin to UVA, effective for treating Psoriasis.
Q16. Vitamin D synthesis in the skin is primarily stimulated by:
Rationale: UVB rays (280-315 nm) convert 7-dehydrocholesterol in the skin into Vitamin D3 (Cholecalciferol).
Q17. The test dose "E1" (1st Degree Erythema) is defined as:
Rationale: E1 is the minimal perceptible erythema that disappears within 24 hours. It is the baseline for calculating dosage.
Q18. Which condition is an ABSOLUTE contraindication for UVR therapy?
Rationale: SLE is an autoimmune condition characterized by extreme photosensitivity. UVR can trigger severe systemic flare-ups.
Q19. What is the wavelength range of UVC?
Rationale: UVC corresponds to short-wave UV (< 280 nm). It is mostly absorbed by the ozone layer but produced artificially for sterilization.
Q20. E3 (3rd Degree Erythema) is characterized by:
Rationale: E3 is a severe reaction involving pain, heat, edema, and blistering. It takes about a week to fade.
Q21. The "Kromayer Lamp" is a source of:
Rationale: The Kromayer lamp is a water-cooled mercury vapor lamp used for local/contact application of UVR (e.g., to an ulcer or sinus).
Q22. Which law states "Absorption is maximum when rays strike perpendicular"?
Rationale: Lambert's Cosine Law states that absorption is proportional to the cosine of the angle of incidence. At 90 degrees (perpendicular), cosine is 1 (maximum).
Q23. Why are the therapist's eyes at risk during UVR application?
Rationale: UVR absorption by the conjunctiva and cornea causes inflammation known as Photokeratitis (Snow Blindness) or Conjunctivitis.
Q24. The "Leeds Regimen" is associated with the treatment of:
Rationale: The Leeds Regimen is a specific protocol using Dithranol cream and UVB radiation to treat Psoriasis.
Q25. Which skin condition acts as an Indication for UVR?
Rationale: UVR slows down skin cell turnover (useful for Psoriasis) and stimulates melanocytes (useful for Vitiligo).
Part 3: Infra-Red Radiation (IRR)
Q26. Non-Luminous (Ceramic) generators produce which type of IR?
Rationale: Non-luminous generators produce long-wave (Far) Infrared (1500nm+), which is absorbed very superficially in the skin.
Q27. Which generator penetrates deeper into the tissues?
Rationale: Luminous generators emit Near-IR (Short wave), which can penetrate to the dermis/subcutaneous layer. Non-luminous is absorbed almost entirely in the epidermis.
Q28. The "Inverse Square Law" implies that if you move the lamp from 50cm to 100cm, the intensity becomes:
Rationale: Doubling the distance (x2) results in intensity decreasing by the square ($1/2^2 = 1/4$).
Q29. Why is IRR contraindicated in "Arterial Insufficiency" (e.g., PVD)?
Rationale: Heating increases cellular metabolism, requiring more oxygen. In arterial insufficiency, arteries cannot dilate to supply this extra oxygen, leading to ischemia and potentially gangrene.
Q30. The therapeutic effect of IRR is primarily due to:
Rationale: IRR is a heating modality. Its effects (pain relief, relaxation) are secondary to the heating of superficial tissues.
Part 4: Mixed High-Yield
Q31. Which wavelength corresponds to "Visible Red" light?
Rationale: Visible light ranges from 400nm (Violet) to 700nm (Red).
Q32. What is the risk of applying IRR over an area with defective sensation?
Rationale: The patient cannot report if the heat is too intense, leading to burns. This is the most common accident with heating modalities.
Q33. For calculating Laser dosage, the formula is:
Rationale: Energy Density ($J/cm^2$) = Total Energy (Joules) divided by Area ($cm^2$).
Q34. "Abiotic" UVR refers to which band?
Rationale: UVC is often called "Abiotic" because it is incompatible with life (germicidal, damaging to cells).
Q35. A "Cluster Probe" in Laser therapy contains:
Rationale: Cluster probes combine multiple diodes (e.g., 5 laser diodes + 10 LEDs) to treat larger areas more quickly.
Q36. Which law explains why we must clean the skin (remove oil/dirt) before UVR/IRR application?
Rationale: Grothus-Draper law states that rays must be absorbed to be effective. Oil/dirt can reflect or block rays, preventing absorption.
Q37. The latent period (time before redness appears) for UVR Erythema is roughly:
Rationale: Unlike heat erythema (immediate), UV erythema is a photochemical reaction that has a latent period of several hours.
Q38. When treating with IRR, how should the lamp be positioned relative to the skin surface?
Rationale: According to the Cosine Law, maximum absorption occurs when the rays strike the surface at a right angle.
Q39. "Cold Laser" refers to:
Rationale: LLLT is called "Cold Laser" because the power output is low enough that it does not generate appreciable heat in the tissue.
Q40. A patient has a "Port Wine Stain". Which laser is commonly used for dermatological treatment?
Rationale: While not typical LLLT, dermatological lasers often target hemoglobin.
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