Assessing the Clinical Impact of the Special Physics Consult (SPC)

Abstract

<h3>Purpose/Objective(s)</h3> Progress in cancer care has improved the survival rates of treated cancer patients. With patients living longer, radiation oncologists are more likely to manage patients who have had prior courses of adjacent or overlapping radiation. To facilitate and improve the safety of re-irradiation, the special physics consult (SPC) was adopted in certain clinics. SPCs are ordered by physicians and performed by physicists to address complex planning and physics considerations (including physics evaluation of patients with implantable devices, anatomical changes during treatment, and monitoring surface dose). Results are used to inform clinical decision-making in patients who may be at an increased risk of complications. This study aims to evaluate the clinical impact of using SPCs by evaluating the extent to which results can alter management. <h3>Materials/Methods</h3> We evaluated 100 consecutive SPC orders entered over a 5-month period. The purpose for ordering the SPC and its impact on management were recorded for all cases. For re-irradiation SPCs, the dose from prior treatments was applied onto the current CT dataset using rigid or deformable registration, then all dose was scaled to equivalent dose in 2-Gy fractions (EQD₂) and summed. Patients with implantable devices were evaluated following the recommendations of AAPM TG 203. When in-vivo dosimetry was ordered, it was performed on patients using an optically stimulated luminescence dosimeter system. In the case of anatomical changes to a patient throughout the course of treatment, an adaptive plan was created using the daily imaging CBCT and the dose was compared to the originally planned dose. The results of all SPCs were reviewed with the ordering physician prior to final clinical decision-making. <h3>Results</h3> The majority of SPCs were ordered for re-irradiation cases (88.0%). SPCs were otherwise ordered to evaluate implantable devices (8.0%), adaptive replanning (3.0%) and in-vivo dosimetry (1.0%) as shown in table 1. Across all SPCs, 37.0% yielded one or more adjustments to the treatment plan. For re-irradiation cases, the SPC results produced one or more planning changes in 38.6% of cases. These changes include re-optimization (29.5%), target contour revisions (9.1%), replanning (5.7%), modality change (4.5%), OAR contour revisions (2.3%), and fractionation changes (1.1%). <h3>Conclusion</h3> Our data shows that SPC results can impact management in more than a third of evaluated cases. Re-irradiation is the most common reason for ordering an SPC, highlighting it as a valuable tool for ensuring patient safety and quality of care. Future studies are needed to further evaluate the benefits of SPCs.