The Linear Accelerator Shortage Index (LSI) is a practical tool for prioritising the deployment of linear accelerators (LINACs) in various regions within a country. The LSI reflects the ratio of LINAC demand to current availability. The aim of this study was to use the LSI to predict global LINAC needs and classify countries according to the degree of radiotherapy shortage (LINAC shortage grade).

In this cross-sectional, population-based study of globally representative, country-level data, we sourced regional LINAC distribution, numbers of radiotherapy centres, and cancer incidence data for 181 countries from the Directory of Radiotherapy Centers and Global Cancer Observatory 2022 databases. Current gross domestic product and gross national income per capita in US dollars were obtained from the World Bank. We calculated an LSI for each country to assess the relative demand and supply of radiotherapy by dividing LINAC use by 450 and multiplying by 100. An LSI of 100 or less indicates no shortage (450 or fewer patients per LINAC), whereas an LSI greater than 100 signals a shortage, with higher values indicating more severe deficits. We categorised countries by LINAC shortage grade: grade 0 (LSI ≤100, no shortage), grade 1 (LSI 101–130, low need), grade 2 (LSI 131–300, high need), grade 3 (LSI >300, excessive need), or grade 4 (no existing LINACs). We estimated LINAC requirements until 2045 using the LSI and Global Cancer Observatory data. We determined future investment costs according to the LSI for each country.

As of the data cutoff on Sept 15, 2024, the global median LSI was 130 (IQR 96–319), suggesting a shortage of 30% in radiotherapy capacity. Significant disparities in median LSI were observed across income levels: low-income countries had a median LSI of 1523 (528–2247), lower-middle-income countries 399 (183–685), upper-middle-income countries 133 (104–198), and high-income countries 96 (83–127; p<0·0001). The distribution of countries across LINAC shortage grades was 40 (22%) of 181 as grade 0, 32 (18%) as grade 1, 35 (19%) as grade 2, 38 (21%) as grade 3, and 36 (20%) as grade 4 (no LINACs). Most LINAC shortage grade 4 countries were low income (12 [33%]) or lower-middle income (16 [44%]). The median number of new LINACs needed per country by 2045 was estimated at 6 (1–13) for grade 0, 21 (4–102) for grade 1, 22 (8–80) for grade 2, 52 (26–113) for grade 3, and three (2–14) for grade 4. To meet these demands, also including the replacement of obsolete devices, an estimated 30 470 LINACs will be needed by 2045. The median total investment required for new and replacement machines and radiotherapy centres to meet the 2045 demand is projected at US$162 million (49–369) for grade 0, $216 million (54–772) for grade 1, $143 million (64–580) for grade 2, $238 million (126–561) for grade 3, and $16 million (9–59) for grade 4. A significant change in LINAC shortage grade composition between 2020 and 2045 is predicted, with distribution of 40 (22%) versus seven (4%) for grade 0, 32 (18%) versus 23 (13%) for grade 1, 35 (19%) versus 63 (35%) for grade 2, 38 (21%) versus 52 (29%) for grade 3, and 38 (20%) versus 38 (20%) for grade 4 (p<0·0001).

The LSI and LINAC shortage grade systems are effective for evaluating, monitoring, and forecasting global LINAC needs. The LSI and LINAC shortage grade highlight the substantial disparities in radiotherapy availability and underscore the urgent need for investment in radiotherapy capacity building, particularly in many low-income and middle-income countries.

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