Standard national high-resolution computed tomography (HRCT) Protocol
Authors: Trisiripanit Nannapat , Suntornsawat Soraya , Phonkaew Worapan 
Published: August 2021

Diffuse interstitial lung diseases (ILDs) include more than hundreds of diseases which have different causes or underlying, target groups, signs and symptoms, clinical courses, radiographic appearances, treatments, and prognosis. Among them, idiopathic pulmonary fibrosis (IPF) is the most fatal, with prognosis worse than many cancers. After decades of no specific treatment, new medications that may help slow the progression of the fibrosis have been introduced and approved in some countries.  Similar to corticosteroid, anti-inflammatory and immunosuppressive drugs which are used to treat some ILDs; these antifibrotic medications could cause certain side effects. In contrast, the cost of treatment is much higher.

To monitor ILDs in terms of incidence, demographic and geographic distributions, and life expectancy;  T.S.T. is developing a national ILD database. To ensure that this data base will provide the most accurate information, diagnosis should be as much precise as possible.

However, the diagnoses of most ILDs are multidisciplinary. With the facts that surgical lung biopsies are available in patients fewer than 20% in most countries1, HRCT plays important role in showing disease characters and extension. Certain HRCT patterns are accepted to replace surgical lung biopsies (SLB) in some diseases.

Unfortunately typical diagnostic HRCT patterns to replace SLB are not possible in all cases; for example, only about half of usual interstitial pneumonia2. Initially, diagnosis could not be made in some cases whose HRCT patterns are not specific and other clinical information is not sufficient. Longitudinal study by following up HRCTs and adding subsequently exhibited clinical data, or even surgical lung biopsy, could eventually establish the diagnosis.  These patients need a system that provide regular clinical and HRCT follow up, also the multidisciplinary team to evaluate those newly acquired clinical and radiographic information .

As an important role in managing patients with ILDs, standard HRCT is required to ensure that the initial examination will provide sufficient radiographic information, both the initial and follow-up examinations could be compared,  the interpretation of all examinations is reproducible, and it could be performed in most institutes.

To develop national standard HRCT protocol; current situation of interstitial lung diseases in Thailand,the purpose to develop the protocol, and a probable draft of the standard protocol (made by the committee from RCRT) were presented to a panel consisted of thoracic radiologist experts from all parts of Thailand in a meeting held on 11 January 2019 by Foundation of Orphan and Rare Lung Disease (FORD) and Imaging Academic Outreach Center (iAOC).  Knowledge sharing, benefits and disadvantages of the drafted protocol were discussed. Adjustment was done based on feasibility, coverage of all lung diseases, diagnostic accuracy, and radiation safety.

The panel provided a standard protocol describing scan coverage, technique, collimation, rotation time, pitch, radiation dose, and reconstruction images. The standard protocol recommends a mandatory acquisition for the first HRCT and optional or additional ones for the follow-up or particular cases.