Evaluation of Planning Target Margins In Head and Neck Cancer Radiotherapy: A Multicentric Experience from Bangladesh
Abstract
Purpose
Head and neck cancers (HNC) pose unique challenges due to anatomical complexity and setup uncertainties during radiotherapy. In resource-limited settings like Bangladesh, standardized planning target volume (PTV) margins may inadequately address institutional variations in imaging and setup protocols. This multicentric study evaluates PTV margins across four Bangladeshi institutions, quantifying systematic (Σ) and random (σ) errors to optimize precision.
Methods
Forty (40) HNC patients underwent intensity-modulated radiotherapy (IMRT) or volumetric modulated arc therapy (VMAT) at four centers (May–September 2024). Translational setup deviations (left-right [LR], anterior-posterior [AP], superior-inferior [SI]) were measured using electronic portal imaging devices (EPID) or cone-beam computed tomography (CBCT). Σ (standard deviation of mean displacements) and σ (root mean square of daily variations) errors were calculated. PTV margins were derived using van Herk’s (2.5Σ + 0.7σ) and Stroom’s (2.0Σ + 0.7σ) formulas. Planning organ-at-risk volume (PRV) margins followed McKenzie’s method (1.3Σ + 0.5σ). Results were compared to 16 global studies (737 patients).
Results
Significant institutional disparities were observed. PTV margins ranged from 4.7 mm (CBCT-equipped center) to 8.0 mm (mean: 6.8 ± 1.2 mm), aligning with literature (weighted mean: 6.8 mm; range: 3.6–9.9 mm). PORV margins varied from 2.6–4.4 mm. Institutions using CBCT demonstrated smaller margins (p<0.05, Kruskal-Wallis/Dunn’s test), with lower Σ errors (1.2 ± 0.3 mm vs. 1.4 ± 0.5 mm in EPID-only centers). Daily CBCT reduced PTV margins by 3.3 mm, correlating with advanced imaging’s role in error mitigation.
Conclusion
Institution-specific PTV margins, tailored to local imaging capabilities, are critical in resource-constrained settings to balance tumor coverage and organ sparing. Daily CBCT enables margin reduction, directly supporting toxicity reduction strategies. These findings advocate for adaptive protocols and context-specific guidelines to enhance global radiotherapy equity, emphasizing technology integration in low-resource environments.