112 - Initial Clinical Experience of Cherenkov Imaging in Sub-Total Total Skin Electron Therapy Identifies Opportunities to Improve Daily Set-Up QA

B. Byrd¹, Y. Zhu², D. A. Alexander³, M. Chelius⁴, G. M. Freedman⁵, M. J. LaRiviere⁶, J. P. Plastaras⁶, and T. Zhu⁷; ¹Penn Medicine Radiation Oncology Abramson Cancer Center, Philadelphia, PA, United States, ²Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, ³University of Pennsylvania, Philadelphia, PA, ⁴Memorial Sloan Kettering Cancer Center, New York, NY, ⁵Department of Radiation Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA, ⁶Department of Radiation Oncology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, ⁷Department of Radiation Oncology, Penn Medicine, Philadelphia, PA

Purpose/Objective(s): Total skin electron therapy (TSET) is a prevalent treatment modality for patients with cutaneous T-cell lymphomas. However, patient-specific QA measures for these TSET patients are lacking. Unlike isocentric treatments, there are no prior CT scans to utilize for planning, nor are there automated motion-management systems in place to ensure consistent and accurate patient positioning from day-to-day and while the patient is standing for treatment. To add additional variability, sub-total skin electron therapy patient treatments are commonly performed without treatment planning systems available to simulate and verify field edges. Materials/

Methods: To address this unmet need for patient-specific QA, we deployed a clinical Cherenkov imaging system which utilizes three cameras to capture the Cherenkov emission on the patient’s skin surface from one frontal and two lateral directions. There were 52 TSET subjects enrolled under an ongoing IRB-approved clinical Cherenkov imaging study. Amongst the 52 enrolled subjects, 7 patients were withdrawn, 7 subjects were repeat study enrollments, imaged in two separate TSET study cases, and 24/52 (46%) treatments were sub-total skin electron therapy cases. All 52 TSET Cherenkov study cases were manually examined to identify potential clinically relevant differences between the planned vs. observed treatment fields within the standard Stanford 6-position treatment scheme.
Results: Among the 52 Cherenkov TSET cases examined, two cases exhibited reduced dose to the upper extremities due to partial blocking, and one case saw increased dose in the subject’s left arm due to patient movement during treatment delivery. In four cases involving head blocking in the posteroanterior (PA) position, the subjects’ forearms were suboptimally aligned, parallel to the beam, rather than perpendicular to it. These specific observations were corroborated by Monte Carlo simulations, which also found reduced dose in a patient’s forearm region after accumulating skin dose from all 6 positions. Lastly, in one subject, Cherenkov imaging detected suboptimal hand positioning in the right anterior oblique (RAO) position, which was subsequently corrected for in the left anterior oblique (LAO) position. Notably, all instances of dose discrepancies or suboptimal patient positions occurred in cases with partial body blocking planned as part of the treatment, i.e. sub-total skin electron therapy.
Conclusion: When blocking is clinically indicated, modifications to the standard Stanford 6-position treatment are often required. As shown in this analysis, these modifications may increase the difference in planned vs. delivered dose to specific blocked or unblocked anatomic regions. To address these challenges, Cherenkov imaging represents a highly useful record-and-verify tool for ensuring proper patient positioning and field coverage during these more complex TSET cases.