3D printed collimators and dosimetry for spatially fractionated radiation therapy

Spatially fractionated radiation therapy (SFRT) has shown incredible potential in sparing normal tissues and activating mechanisms of tumor control distinct from conventional radiotherapy. However, the optimal spatial configuration of SFRT as well as the optimal peak and valley dose values have not been established. This poses a barrier to widespread clinical implementation and efficacy.

To facilitate greater SFRT optimization, this work establishes a simple, readily customizable, and cost-effective approach for fabricating SFRT collimators with different spatial configurations as well as peak and valley dose values.

The approach involves fabrication of custom SFRT collimators, each consisting of a 3D-printed plastic shell filled with tungsten. Once fabricated, the collimator dosimetry is characterized using a combination of Gafchromic film and ion chamber measurements. Monte Carlo simulations are used to verify SFRT dosimetry and assess positional uncertainties. The collimators are applied in preclinical mouse experiments demonstrating how they can be used to deliver SFRT.

Five collimators were fabricated for use at kilovoltage energies and one collimator was fabricated for use at megavoltage energies. Across all collimators, the peak widths ranged from 1.2 to 10.1 mm and the valley widths ranged from 1.1 to 10.6 mm. For the kilovoltage collimators, the highest peak-to-valley dose ratio was 32.4 at the surface and this dropped to 29.5 at 10 mm depth. For the megavoltage collimator, at 95 cm SSD, the peak-to-valley dose ratio was 2.7 at 15 mm depth and this dropped to 2.2 at 100 mm depth. In the mouse experiments, out of multiple SFRT parameters, the mean tumor valley dose had the strongest correlation with change in tumor volume (p = 0.02). The Monte Carlo simulations indicated a 5 mm translation of the mouse tumor relative to the beam led to a 44.8% change in the mean tumor dose, underlying the importance of precise positioning for SFRT.

This work establishes a novel approach for custom 3D printing of SFRT collimators and their subsequent characterization. The developed collimators are capable of SFRT delivery at both kilovoltage and megavoltage photon beam energies. This approach facilitates patient specific customization as well as optimization of the peak and valley doses for more effective SFRT.