CARBON-SUSTAIN study: Visit-sparing, low-emission hypofractionated radiation therapy in a traffic-dense Indian megacity.

Abstract

e23117 Background: In megacities, serial radiation therapy (RT) visits markedly augment healthcare-related carbon emissions due to traffic congestion, yet this burden remains poorly quantified. Bengaluru city illustrates this challenge, where each additional visit amplifies emissions, travel time, and patient burden. CARBON SUSTAIN STUDY aimed to quantify climate impact of RT delivery, assess if evidence-based hypo-fractionation(HF) can enable guideline concordant, low emission, carbon efficient, climate sensitive care model without compromising treatment precision. Methods: Electricity related emissions were estimated from measured per-fraction energy consumption (kWh/fraction) using direct clamp-meter measurements at uninterruptible power supply output (415-V, three phase; power factor (0.9) and Bengaluru Electricity Supply Company grid emission factor (0.71 kg CO₂/kWh). Measured energy use per fraction was 13.14 kWh (Ethos), 20.15 kWh (TomoTherapy), and 12.30 kWh (CyberKnife). Travel-related emissions were modeled using home to hospital distance bands (≤5 km, 6–10 km, 11–20 km, >20 km) with congestion-adjusted emission factors for weekday peak traffic. Primary endpoint was total carbon dioxide equivalent (CO₂e) emissions from electricity and travel. Secondary endpoints included Care Access Days Saved (CADS), defined as fraction-visits avoided, and regimen-level carbon efficiency. Statistical analysis included descriptive statistics, CADS with 95% confidence intervals, Kruskal–Wallis testing for CO₂e comparisons, and multivariable linear regression with robust standard errors. Results: In a total of 786 patients, delivered fractions were 12,185 compared with 20,859 expected under conventional schedule, resulting in 8,674 fraction-visits avoided (CADS) and 41.6% reduction in hospital visits. Electricity-related CO₂e avoided was 37.1 metric tons. Travel-related CO₂e avoided was at 95.4 metric tons, yielding total reduction of 132.5 metric tons of CO₂e. On multivariable analysis, number of fractions was strongest independent predictor of total CO₂e (p < 0.001),while travel-distance band contributed additional variance (p < 0.001). Conclusions: In traffic-dense megacities, meaningful decarbonisation of RT is driven primarily by reducing visit frequency. Visit-sparing HFRT substantially lowers carbon emissions maintaining treatment precision, offering scalable, low-emission, climate-sensitive framework. These reductions were attained using guideline-concordant HF without altering oncologic outcomes. Fraction reduced and CADS by disease site. Cancer site Patient (n) Delivered fractions Conventional fractions (CADS) %reduction Breast ca 542 8,976 16,260 7,284 44.8 Prostate ca 53 961 2,014 1,053 52.3 Glottic ca 27 868 945 77 8.1 Bone metastasis 164 1,380 1,640 260 15.9 Total 786 12,185 20,859 8,674 41.6