Planning target volume, biological dose, and radiological response following radiotherapy for bone metastases: An exploratory analysis

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Abstract

Planning target volume (PTV) is routinely used in radiotherapy planning, but its relationship with treatment response in bone metastases remains insufficiently characterized. This retrospective single-center study evaluated associations of PTV and biologically effective dose (BED10) with objective radiological response and pain reduction in 40 patients treated with radiotherapy between 2024 and 2025. Radiological response was evaluable in 28 patients; complete and partial responses were classified as response. Associations with objective response were assessed using Firth penalized logistic regression, the relationship between PTV and BED10 using Spearman correlation, and PTV discrimination using receiver operating characteristic analysis with bootstrap confidence intervals. Fifteen patients were responders and 13 were non-responders. PTV and BED10 were inversely correlated (Spearman’s ρ = −0.471, p = 0.011). In multivariable Firth regression, larger PTV was associated with lower odds of objective response after adjustment for BED10 (OR per 100-cm³ increase, 0.752; 95% CI, 0.532–0.978; p = 0.032), whereas BED10 was not independently associated with response (OR per 10-Gy increase, 0.827; 95% CI, 0.347–1.995; p = 0.661). PTV showed modest discrimination (AUC = 0.685; bootstrap 95% CI, 0.462–0.882), and an exploratory cutoff of 427.4 cm³ yielded 93.3% sensitivity and 53.8% specificity. PTV was not significantly associated with pain reduction. These exploratory findings suggest that treatment volume and biological dose should be considered jointly and that radiological and symptomatic outcomes represent distinct dimensions of treatment efficacy. Prospective validation is required.

Keywords

Biologically effective dose

Bone metastases

Planning target volume

Radiological response

Radiotherapy

Treatment volume

Funding

None.

Conflict of interest

The authors declare no conflicts of interest.

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Advances in Radiotherapy & Nuclear Medicine, Electronic ISSN: 2972-4392 Print ISSN: 3060-8554, Published by AccScience Publishing