On 15 January 2021, legislation was passed for low dose HRCT scan to replace chest X-ray in Western Australia as the radiological screening test for occupational exposure to silica. This means that chest X-rays are no longer used for this purpose.

Schedule 14 of the Work Health and Safety (General) Regulations 2022 and Schedule 14 of the Work Health and Safety (Mines) Regulations 2022 require the following:

Low dose high resolution computed tomography of the chest at less than 1 millisievert (mSv) equivalent dose for the entire study. The study must image the whole of each lung on inspiration at 1.5 mm slice thickness or less, without an interslice gap, and must include expiratory imaging. The images must be of adequate quality to detect subtle abnormalities, including ground glass opacities and small nodules.

Note: Supine views only; prone views are not required. No contrast should be used.

A standard diagnostic HRCT chest scan (2-5 mSv) is not suitable due to the higher radiation exposure.

This is an occupational lung disease caused by the inhalation of fine silica dust particles (also called respirable crystalline silica). Silicosis is a progressive disease which can remain asymptomatic for decades. There is no effective treatment even after cessation of exposure.

Hazardous silica dust is released into the air from drilling, chipping, cutting, grinding, sanding, polishing or crushing and screening natural rock and ore as in granite, sandstone, slate quarries and in mining. Similarly, workers are exposed to hazardous silica dust when products containing silica such as engineered stone, concrete, and masonry are drilled, chipped, cut, ground, sanded, polished or crushed.

The silica content in natural stone varies from 5% for marble, 20-40% for slate, 25-60% for granite and 70-90% for sandstone.  Engineered stone contains 80-95% silica.

Silica exposure has historically been associated with chronic silicosis from exposure to relatively low levels of dust. Chronic silicosis, which develops slowly over decades (10-30 years), may become symptomatic towards the end of the worker’s working life or after retirement. A small proportion of chronic silicosis may go on to develop complications of progressive massive fibrosis (PMF) and respiratory impairment.

In more recent times, the use of engineered stone products for kitchen and bathroom benchtops has led to the emergence of accelerated silicosis among workers (in their 30’s, 40’s and 50’s) following work exposures of 5-10 years. Rapid progression from simple silicosis to complicated silicosis can occur with onset of progressive massive fibrosis resulting in respiratory failure and death.  Engineered stone, also known as artificial stone, is a composite material made up of silica held in a matrix with polymeric resin. As engineered stone is relatively easy to fabricate compared to the much harder granite (natural stone), far less training and skills are required.

Acute silicosis is rare. It is also known as silico-proteinosis in which alveoli fill with lipid and proteinaceous material. This condition is an acute illness that can occur after exposure to very high concentrations of silica dust resulting in severe symptoms within a few weeks to a few years of initial exposure. Clinically, there is progressive breathlessness, pleuritic chest pain, fever, cough, fatigue, weight loss and rapid progression to death from respiratory failure.

Respirable crystalline silica particles (5 µm or less) penetrate deep within the lungs. When they reach the alveoli, the particles are ingested by macrophages. This induces proliferation of concentric fibrous tissue (often hyaline) surrounding birefringent silica particles, and the formation of tiny silicotic nodules. Fibrosis may progress to obliterate the lumen of respiratory bronchioles and pulmonary blood vessels. These nodules concentrate subpleurally and coalesce to form larger nodules and masses. Silica is also carried to the lymph nodes in the hilum. Enlargement and calcification of the lymph nodes can develop.

Silicosis is associated with increased risk of:

• chronic bronchitis
• tuberculosis
• rheumatic disorders (rheumatoid arthritis, SLE)
• sarcoidosis 
• lung cancer (silica is a Group 1 carcinogen in humans (IARC)).

Spirometry should be performed by trained personnel using a spirometer that is calibrated and maintained in line with TSANZ or ATS guidelines. Requirements include:

• at least 3 acceptable manoeuvres
• two largest FVC values are within 0.15L of each other
• two largest FEV₁ values are within 0.15L of each other
• maximal continuous expiration for ≥ 6 seconds

Spirometry print-outs, including flow-volume graphs, must be submitted DMIRS with the health monitoring notification form.

Chest X-rays are no longer required as they are not sensitive enough to detect silicosis nor associated early changes. A low dose CT high resolution chest scan (LDCT) with a dose limit of 1 mSv or less, provides an image quality sufficient to detect silicosis and early changes. No contrast should be used. A standard diagnostic HRCT chest scan (2-5 mSv) is not suitable as an occupational screening test due to the higher radiation exposure.

A LDCT is to be repeated at 2 to 5 yearly intervals depending on the specified Category. It is important that radiation exposures are kept as low as possible.  The LDCT scan must be read by a radiologist with expertise in reading such scans. In addition to the standard report on the scan,  the modified Kusaka ICOERD classification must be included together with the  dose length product (DLP) for the scan. The conversion factor for dose length product (DLP) to mSv for chest CT scan is 0.014.

If this service is not available in your regional area, there is scope for the worker to undertake the screening in a facility that has this capability within 3-6 months of the date of referral. A full dose HRCT and/or chest X-ray are not acceptable substitutes if the radiology provider cannot provide a low dose CT scan service.