Author: Philip Blumenfeld, Jon Feldman, Yair Hillman, Michael Marash, Aron Popovtzer, Alexander Pryanichnikov, Shimshon Winograd, Marc Wygoda, Vered Zivan 👨🔬
Affiliation: Institute of Biomedical Engineering, Karlsruhe Institute of Technology (KIT), P-Cure Ltd./Inc., Sharett Institute of Oncology, Hadassah Medical Center, Hebrew University of Jerusalem 🌍
Purpose:
Image-guided adaptive proton therapy (IGAPT) allows tailored dose adjustments to account for anatomical and physiological changes during treatment. Recent efforts have developed a cost-effective gantry-less proton therapy systems with integrated CT scanner primarily for upright treatments. This study evaluates an offline adaptive workflow and its dosimetric implications in a novel gantry-less IGAPT approach for head and neck (H&N) and central nervous system (CNS) cancers.
Methods:
A total of 34 patients treated with the gantry-less IGAPT system were analyzed. Primary diagnoses included squamous cell carcinoma of the oral cavity (n=12), oropharynx (n=8), and sino-nasal region (n=5), glioblastoma (n=3), oligodendroglioma (n=2), and other tumors (n=4). Dose fractionation ranged from 50.4 Gy in 28 fractions to 70 Gy in 35 fractions. All patients underwent daily upright CT prior to each fraction. Offline adaptive replanning sessions were triggered by tumor progression, anatomical changes, or treatment-related complications.
Results:
Of these patients, 24 (71%) required at least one adaptive replanning session (16 had one, 6 had two, and 2 had three). Triggers for replanning included tumor progression (n=5), significant anatomical changes (n=15), and treatment complications (n=4). A total of 19 patients (54%) received boost fractions to optimize target coverage. Replanning was performed between fractions 5 and 30, with dose escalation proving particularly beneficial in sino-nasal cases to mitigate toxicity while maintaining tight margins.
Conclusion:
This gantry-less IGAPT approach effectively adapts to the evolving anatomy of H&N and CNS cancers within the standard fractionated scheme, allowing for highly conformal dose delivery and limiting exposure to critical structures. The timing and frequency of replanning were key factors in achieving optimal target coverage and reducing side effects. Future developments will focus on automated and online (while the patient is still in the treatment room after daily CT) plan adaptation to further improve workflow efficiency and treatment precision.