# Dosimetric and Radiobiological Evaluation of Inhomogeneity-Corrected Dose Distribution in Prophylactic Radiotherapy for Heterotopic Ossification

## TL;DR

This study shows that ignoring tissue inhomogeneities in radiation dose planning for heterotopic ossification leads to less effective treatment outcomes.

## Contribution

The study introduces a radiobiological evaluation of inhomogeneity-corrected dose distributions in prophylactic radiotherapy for heterotopic ossification.

## Key findings

- Homogeneous dose plans overestimate dose conformity and uniformity compared to inhomogeneity-corrected plans.
- Inhomogeneity-corrected plans showed higher biological effectiveness but steeper dose gradients.
- Plans without inhomogeneity correction may lead to suboptimal biological outcomes in HO prophylaxis.

## Abstract

Background/Objectives: The aim of this study was to evaluate the impact of inhomogeneity correction (IC) of dose distribution on the dosimetric and radiobiological efficacy of radiation treatment for heterotopic ossification (HO). Methods: This study involved a retrospective analysis of 21 patients treated using a homogeneous dose distribution plan for hip prophylactic HO. These IC-off plans were evaluated against an IC-on dose distribution plan. Dosimetric and corresponding radiobiological parameters (gEUD, LQ-EUD, LQ, EQD2 for α/β = 3 and 10 Gy) were calculated. These parameters were compared for both treatment plans. Additionally, Monte Carlo simulations were performed using mean and standard deviation values from baseline data to generate 10,000 synthetic datasets, allowing for robust statistical modeling of variability in dose distributions and biological outcomes. Results: The homogeneous (IC-off) plans demonstrated overestimation of dose conformity and uniformity, reflected in lower HI values (0.10 ± 0.05 vs. 0.18 ± 0.05) and higher D90%–D98% coverage. Radiobiologically, these plans yielded higher gEUD (7.02 Gy vs. 6.80 Gy) and EQD2 values across all α/β scenarios (e.g., EQD2[α/β=3]_gEUD = 14.07 Gy vs. 13.35 Gy), with statistically significant differences (p < 0.001). Although IC-on plans demonstrated steeper dose gradients (higher GIs), this came at the expense of internal dose variability and potentially compromised biological effectiveness. Conclusions: Our results suggest that plans without IC deliver suboptimal biological effectiveness if continued preferentially in routine HO prophylaxis. With advanced radiation dose calculation algorithms available in all centers, inhomogeneity-corrected doses warrant prospective validation.