A Dosimetric Comparison of Intensity-Modulated Proton Therapy (IMPT), Cyberknife (CK), and Non-Coplanar Volumetric Modulated Arc Therapy (nCo-VMAT) for Orbital Lymphoma
Abstract
Purpose
To compare the differences among various treatment techniques in the treatment of orbital lymphoma, this study performed a dosimetric comparison among Intensity-Modulated Proton Therapy (IMPT), CyberKnife (CK), and non-coplanar Volumetric Modulated Arc Therapy (nCo-VMAT) for orbital lymphoma.
Methods
Ten patients with orbital lymphoma were included, and treatment plans were generated for each of the three modalities: CK, IMPT, and nCo-VMAT. Dosimetric parameters related to target coverage and organ-at-risk (OAR) sparing were evaluated, including conformity index (CI), gradient index (GI), homogeneity index (HI), dose distributions in the clinical target volume (CTV) and planning target volume (PTV), as well as maximum dose (Dmax) and mean dose to relevant OARs.
Results
All three techniques achieved clinically acceptable target coverage for CTV and PTV. Regarding plan quality, CK and nCo-VMAT provided better conformity (CI: 0.87±0.09 and 0.87±0.07, respectively) than IMPT (CI: 0.75±0.07; p=0.008). CK also demonstrated the steepest dose gradient (GI: 2.55±0.35), which was significantly sharper than that of nCo-VMAT (2.90±0.48) and IMPT (4.14±0.59; p<0.001). In contrast, IMPT yielded the most homogeneous dose distribution (HI: 1.14±0.03), followed by nCo-VMAT (1.17±0.08) and CK (1.23±0.05; p=0.004). For OAR sparing, IMPT was generally superior, significantly reducing doses to the contralateral lens, contralateral optic nerve, brainstem, and whole brain (p<0.001). However, IMPT delivered a higher dose to the ipsilateral lens compared to the other two techniques (p<0.001). nCo-VMAT spared the ipsilateral optic nerve better than CK (p=0.003). No significant differences were observed for the optic chiasm (p=0.087).
Conclusion
IMPT offered comparable target coverage to CK and nCo-VMAT while demonstrating better sparing of most adjacent critical structures, despite a higher dose to the ipsilateral lens. CK provided the sharpest dose fall-off, and nCo-VMAT represents a widely accessible clinical option. These findings underscore the distinct dosimetric advantages of each modality in the treatment of orbital lymphoma.