Respiratory motion effects and plan robustness for lattice radiation therapy

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Lattice radiation therapy (LRT), a form of spatially fractionated radiation therapy (SFRT), shows promise for bulky tumors by creating high-dose (hot) and low-dose (cold) regions.
• The peak-to-valley dose ratio (PVDR) is crucial for LRT efficacy, but the impact of respiratory motion on PVDRs has been largely overlooked.

Purpose of the Study:

• To quantify the effect of respiratory motion on LRT dose distributions.
• To inform motion management strategies for improving clinical outcomes in LRT.

Main Methods:

• Simulated respiratory motion (0.3-2 cm amplitude) in 1 and 1.5 cm sphere lattice plans using dose perturbations in phantoms.
• Analyzed retrospective patient plans to assess motion response considering anatomical variations.
• Compared deformed and rigid dose transformations to evaluate tumor deformation effects.

Main Results:

• Increasing motion reduced hot sphere coverage and altered cold sphere doses, decreasing the VTVH/VTVL D95% ratio.
• 1.5 cm sphere plans were less sensitive to motion than 1 cm sphere plans.
• Patient data generally corroborated phantom findings; significant dose changes observed with 1 cm motion.

Conclusions:

• Large tumor motion can compromise LRT dose distributions and treatment efficacy.
• Proposed motion cutoffs: >1 cm for 1.5 cm spheres and >0.5 cm for 1 cm spheres necessitate motion management.
• Tumor deformation may unpredictably alter dose distributions, requiring careful consideration.