A primer on treatment planning aspects for temporally modulated pulsed radiation therapy

<h2>Abstract</h2><h3>Purpose</h3> Develop and validate treatment planning guidelines for temporally modulated pulsed radiotherapy (TMPRT) to robustly deliver conventional fraction doses in temporally separated pulses of low doses ( <mml:math><mml:mrow><mml:mo><</mml:mo><mml:mn>30</mml:mn>cGy</mml:mrow></mml:math> ) yielding fraction-effective dose rates of around <mml:math><mml:mrow><mml:mn>6.7</mml:mn>cGymi<mml:msup><mml:mrow><mml:mi>n</mml:mi></mml:mrow><mml:mrow><mml:mo>−</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>. <h3>Methods and Materials</h3> Volumetric modulated arc therapy (VMAT) and 3D-CRT planning techniques for TMPRT, were developed following the guidelines of the proposed XXXX trial. Plans were evaluated with respect to homogeneity index, conformality, and adherence to dose constraints. Deliverability of plans was assessed using in-phantom measurements for absorbed dose accuracy at low dose rates and using EPID for isodose verification. <h3>Results</h3> For VMAT only single arc plans were found to be acceptable due to otherwise unacceptably heterogeneous field doses, while for dynamic conformal arc machine limtations on the number of monitor units per degree require the use of partial arcs for each pulse. Delivery of plans at low dose rates ( <mml:math><mml:mrow><mml:mo>≤</mml:mo><mml:mn>100</mml:mn>MU<mml:mo>/</mml:mo>min</mml:mrow></mml:math> ) was accurate with high <mml:math><mml:mi>Γ</mml:mi></mml:math> pass rates on modern LINACs and moderate pass rates on legacy LINACs, in line with their general performance. <h3>Conclusion</h3> Generally, VMAT is preferred to achieve optimal homogeneity, conformality, and OAR sparing, while the use of 3D-CRT can increase the availability of TMPRT for more patients and clinics.