Author: Laura Buchanan, Samantha G. Hedrick, Stephen L. Mahan, Isabella Pfeiffer, Chester R. Ramsey 👨🔬
Affiliation: Thompson Proton Center 🌍
Purpose: Proton therapy plans can be highly sensitive to both anatomical changes and positional errors, making the acquisition of Quality Assurance CT (QACT) images a routine clinical practice during treatment. At our institution, the plan adaptation rate exceeded that reported at other proton facilities, leading to an investigation of adaptation triggers and opportunities for improvement.
Methods: A chart review was performed for head-and-neck patients who completed proton therapy. For each patient, the number of fields, the number of plans, the frequency of treatment plan adaptations, QACT acquisition dates, and related adaptation reports were collected. Adaptation triggers were classified from the medical record as patient-related non-controllable (e.g., tumor volume changes, weight changes, swelling, other anatomical variations) or controllable (e.g., shoulder positioning, mask fit, head pitch, MD plan changes).
Results: Data was collected for 102 head-and-neck patients, comprising 189 original treatment plans. A total of 298 QACT scans (2.9 per patient) were performed resulting in 70 plan adaptations. Overall, 37% of the original plans required adaptation, with the physics team having a 30% adapt rate and physicians/therapists having a 7% adapt rate. Of all adaptations, 47% were patient-related and were primarily driven by tumor volume and weight changes. The remaining 53% were controllable, most attributed to shoulder positioning, mask fit, head pitch, and MD plan changes. These findings have prompted further efforts to refine patient setup and immobilization strategies during the initial treatment planning CT. One such change is the use of a new mask system that contains integrated shims that allow for adjustments to the mask fit during treatment.
Conclusion: While patient-related changes are often unavoidable, setup-related issues present opportunities for improvement through improved immobilization protocols. By addressing these factors, it may be possible to reduce the rate of plan adaptations, thereby reducing the treatment planning workload.