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Intensity modulation in radiotherapy: photons versus protons in the paranasal sinus
Anthony John Lomax1, Michael Goitein, Judy Adams
1Division of Radiation Oncology, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland.
Summary
Intensity modulated proton therapy (IMPT) offers superior critical structure sparing compared to intensity modulated X-ray therapy (IMXT) for paranasal sinus tumors. IMPT achieves this while maintaining target dose homogeneity, unlike IMXT where tighter constraints compromise results.
Area of Science:
- Radiation Oncology
- Medical Physics
- Radiotherapy Planning
Background:
- Intensity modulated radiation therapy (IMRT) is a common technique for head and neck cancers.
- Proton therapy offers potential advantages in dose distribution compared to photon therapy.
Purpose of the Study:
- To compare intensity modulated X-ray therapy (IMXT) and intensity modulated proton therapy (IMPT) for paranasal sinus tumors.
- To investigate if optimizing IMXT by tightening normal tissue constraints can achieve clinical comparability with IMPT.
Main Methods:
- Calculated photon and proton intensity modulated plans for a paranasal sinus case.
- Applied nominal dose constraints and subsequently tightened constraints for photon plans to match proton plan dose-volume histograms.
Main Results:
- Tightening constraints in photon plans to spare critical structures (orbits) increased target dose heterogeneity.
- Further constraint tightening compromised target dose homogeneity and conformity.
- Photon plans showed increased integral dose to non-critical tissues as critical structures were more spared.
Conclusions:
- Both IMXT and IMPT provided comparable target conformation and critical structure sparing at nominal constraints.
- IMPT uniquely allowed critical structure sparing across all dose levels with acceptable target dose homogeneity.
- IMXT struggles to match IMPT's ability to simultaneously spare critical structures and maintain target homogeneity.