Cumulative dose and skin damage Colin Martin and David Sutton

Skin effects Histologic view of the skin Transient erythema: May occur 1 to 24 hours after irradiation > 3 Gy Erythema: Occurs after 2-3 weeks for doses of 3-10 Gy Alopecia(loss or absence of hair): 2-3 weeks, >3 Gy is reversible; 20 Gy is irreversible. Dry or moist desquamation: after 3-5 weeks for doses 8-15 Gy. DERMIS EPIDERMIS From “Atlas de Histologia...”. J. Boya Basal stratum cells, highly mitotic, more susceptible to radiation damage

Back Scattered Radiation The skin receives a higher dose as some radiation is scattered back from underlying tissues. Entrance surface dose is 30% higher than the incident air kerma. X-rays Tissue Backscatter

ICRP Report 85 (2001): Avoidance of Radiation Injuries from Interventional Procedures ICRP recommend: Warn patient of risk, if maximum skin dose exceeds 3 Gy Identify patients who have repeated interventions where the dose exceeds 1 Gy and warn them of risk

Use of a single projection concentrates dose and increases skin damage Complex procedures may lead to high skin doses. Multiple coronary angiography and angioplasty procedures performed. Evidence of injury 6-8 weeks after procedures. Skin injury 18 months after procedures Images reproduced with permission from Wagner LK and Archer BR. Minimizing Risks from Fluoroscopic Radiation, R. M. Partnership, Houston, TX 2004, and T Shope from ICRP Publication 85 (2000).,

Distribution of Interventional skin exposure Different shape and size of the fields, films show changes in collimation and beam angle during the procedure.

Lesions from overlapping fields Examinations generally use beams from different directions. There are risks of high doses from overlapping fields Lesion required grafting

Erythema from Cardiology procedures Skin erythema after fluoroscopy Cumulative build-up of dose from steeply angled beams through large patient Images reproduced with permission from Wagner LK and Archer BR. Minimizing Risks from Fluoroscopic Radiation, R. M. Partnership, Houston, TX 2004, and T Shope from ICRP Publication 85 (2000).,

Cumulative Dose Interventional Reference Point (IEC,60601-2-43, 2000) 15 cm in front of iso-centre 15 cm Isocenter IRP Cumulative dose does not take account of movement of X-ray tube

Method for MESAK evaluation: radiochromic large area detector Example: Radiochromic films type Gafchromic XR R 14”x17” usefull dose range: 0.1-10 Gy minimal photon energy dependence (60 - 120 keV) acquisition with a flatbed scanner:b/w image, 12-16 bit/pixel or, measure of OD measurement with a reflection densitometer

Relationship between Peak Skin Dose and Cumulative dose Neuroradiology Interventional Cardiology Reasonable link between peak skin dose and cumulative dose

Proposed follow-up for of skin injury in other Interventional Radiology Set “trigger values” for cumulative skin dose that roughly equates to peak skin dose of 3 Gy 2-3 Gy Neuroradiology 3-5 Gy Cardiology Identify where procedures are repeated on the same patient giving a skin dose in this range. Introduce a follow-up protocol for patients who could have received high skin doses

Cumulative dose distribution for Angiography and Stent procedures A few percent of procedures have cumulative doses above 5 Gy

Doses to the skin depend on area irradiated and focus to skin distance

Patients follow up Clinics The cumulative dose should be recorded in the patient’s notes, so that it can be referred to during follow-up clinic visits. The clinicians conducting the follow-up should be aware if the patient’s dose has exceeded the threshold Clinicians should be able to recognise radiation skin effects

Patient dosimetry in IR Dosimetry for quality assurance Air kerma area product (KAP, PKA) Dosimetry for stochastic risk evaluation dose equivalent to selected organs effective dose Dosimetry to prevent deterministic effects of radiation (maximum skin dose assessment) Maximum skin dose (MSD or Dskin,max)