Quantifying the sensitivity of target dose on intra-fraction displacement in intra-cranial stereotactic radiosurgery.

Abstract

BACKGROUND/PURPOSE

Mask-immobilized stereotactic radiosurgery (SRS) using a gating window is an emerging technology. However, the amount of intracranial tumor motion that can be tolerated during treatment while satisfying clinical dosimetric goals is unknown. The purpose of this study was to quantify the sensitivity of target dose to tumor motion.

CONCLUSION

Simulated target displacements showed that sensitivity of tumor dose to motion depends on both target volume and target location. Suggesting that patient- and target-specific thresholds may be implemented for optimizing the balance between dosimetric plan accuracy and treatment prolongation caused by out-of-tolerance motion.

RESULTS

The effect on dose metrics is statistically larger for translational displacements compared to rotational displacements, and the effect of pitch rotations is statistically larger compared to yaw rotations. The mixed-effect model for translations showed that displacement and target volume are statistically significant variables, for rotation the variable target distance to rotation axis is additionally significant. For mean target volume (12.6cc) and translational nose-marker displacements of 0.5mm, 1.0mm, and 1.5mm, D99 decreased by 2.2%, 7.1% and 13.0%, and coverage by 0.4%, 1.8% and 4.4%, respectively. For mean target volume, mean distance midpoint-target to pitch axis (7.6cm), and rotational nose-marker displacement of 0.5mm, 1.0mm, and 1.5mm, D99 decreased by 1.0%, 3.6% and 6.9%, and coverage by 0.2%, 0.8% and 1.9%, respectively. For rotational yaw axis displacement, mean distance midpoint-target axis (4.2cm), D99 decreased by 0.3%, 1.2% and 2.5%, and coverage by 0.1%, 0.2% and 0.5%, respectively.

METHODS

In clinical SRS plans, where a nose marker was tracked as surrogate for target motion, translational and rotational target movements were simulated using nose-marker displacements of ±0.5mm, ±1.0mm or ±1.5mm. The effect on minimum dose to 99% of the target (D99) and percent target coverage by prescription dose was quantified using mixed-effect modelling with variables: displacement, target volume and location.

More about this publication

Practical radiation oncology
  • Publication date 17-12-2021

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