  Purpose: There is growing interest in the use of modern 3D printing
technology to implement intensity-modulated radiation therapy (IMRT) on the
preclinical scale which is analogous to clinical IMRT. However, current
3D-printed IMRT methods suffer from complex modulation patterns leading to long
delivery times, excess filament usage, and inaccurate compensator fabrication.
In this work, we have developed a total variation regularization (TVR) approach
to address these issues.
  Methods: TVR-IMRT, a technique designed to minimize the intensity difference
between neighboring beamlets, was used to optimize the beamlet intensity map,
which was then converted to corresponding compensator thicknesses in
copper-doped PLA filament. IMRT and TVR-IMRT plans using five beams were
generated to treat a mouse heart while sparing lung tissue. The individual
field doses and composite dose were delivered to film and compared to the
corresponding planned doses using gamma analysis.
  Results: TVR-IMRT reduced the total variation of both the beamlet intensities
and compensator thicknesses by around 50% when compared to standard 3D printed
compensator IMRT. The total mass of compensator material consumed and radiation
beam-on time were reduced by 20-30%, while DVHs remained comparable. Gamma
analysis passing rate with 3%/0.3mm criterion was 89.07% for IMRT and 95.37%
for TVR-IMRT.
  Conclusion: TVR can be applied to small animal IMRT beamlet intensities in
order to produce fluence maps and subsequent 3D-printed compensator patterns
with less total variation, simplifying 3D printing and reducing the amount of
filament required. The TVR-IMRT plan required less beam-on time while
maintaining the dose conformity when compared to a traditional IMRT plan.
