The rationale for intensity-modulated proton therapy in geometrically challenging cases

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Treatment

Background:

• Field patching is a standard, simplified form of intensity-modulated proton therapy (IMPT) using binary dose modulation.
• IMPT with beam scanning offers continuous dose modulation but is available at fewer centers.
• This study investigates limitations of field patching and dosimetric benefits of continuous IMPT.

Purpose of the Study:

• To compare the dosimetric performance of field patching in three-dimensional conformal proton therapy (3DCPT) versus intensity-modulated proton therapy (IMPT).
• To evaluate the robustness of both techniques against setup and range uncertainties in challenging patient geometries.

Main Methods:

• Identified two challenging target and organ-at-risk (OAR) geometries from paraspinal and skull-base tumor cases.
• Performed treatment planning comparisons between 3DCPT with field patching and IMPT using commercial and in-house software.
• Analyzed plan robustness against systematic setup errors (±1 mm) and range errors (±2.5 mm).

Main Results:

• IMPT demonstrated superior OAR sparing and target dose coverage compared to field patching in the evaluated challenging cases.
• Both techniques showed sensitivity to setup and range errors, with IMPT exhibiting a larger effect.
• Despite uncertainties, IMPT plans maintained dosimetric superiority in target coverage and OAR sparing.

Conclusions:

• IMPT can significantly improve target coverage and OAR sparing in complex cases, surpassing even field patching.
• IMPT plans are more sensitive to delivery uncertainties, but robust planning techniques can mitigate this.
• The dosimetric advantages of IMPT generally hold even when considering delivery uncertainties.