Assessment of unintended shifts during frame-based stereotactic radiosurgery using cone beam computed tomography image guidance.

PURPOSE: To investigate the frequency, magnitude and possible causes of frame-shifts that may occur between treatment planning and treatment delivery when performing Gamma Knife radiosurgery with rigid frame-based immobilization. METHODS: Differences between computed tomography (CT) framed fiducial stereotactic coordinate reference and cone beam computed tomography stereotactic coordinates after image registration were recorded for 49 frame-based GK radiosurgery cases performed using the Gamma Knife Icon. Parameters recorded include rotational shifts, translational shifts, and the GK-computed Maximum Shot Displacement (MSD) between the two stereotactic coordinate spaces. Other patient-specific parameters were collected and linear regression analysis was performed to evaluate predictors of increased displacement. RESULTS: The median values of rotational shifts were: pitch 0.14°, yaw 0.17°, and roll 0.13°. The median absolute values of translational shifts were: left-right 0.39 mm, anteroposterior 0.14 mm, and superior-inferior 0. 22 mm. The median value of MSD was 0.71 mm. Twelve cases (24.5%) had a MSD of greater than 1.0 mm. Male gender was associated with increased MSD (p = 0.013) and translational shifts (root-mean-squared value, p = 0.017). Cases with large differences between right and left sided pin lengths were also associated with increased MSD (p = 0.011). CONCLUSIONS: The use of CBCT image guidance in frame-based GK radiosurgery allows unintended frame shifts to be identified and corrected. A significant fraction (24.5%) of patients had large enough shifts to result in a MSD of greater than 1.0 mm. Male gender and eccentrically placed frames were associated with increased MSD, and particular care should be taken in these cases.

Impact of Patient Stage and Disease Characteristics on the proposed Radiation Oncology Alternative Payment Model (RO-APM).

PURPOSE: The proposed Radiation Oncology Alternative Payment Model (RO-APM) released on July 10, 2019, represents a dramatic shift from fee-for-service (FFS) reimbursement in radiation therapy (RT). This study compares historical revenue at Mayo Clinic to the RO-APM and quantifies the effect that disease characteristics may have on reimbursement. METHODS AND MATERIALS: FFS Medicare reimbursements were determined for patients undergoing RT at Mayo Clinic from 2015 to 2016. Disease categories and payment episodes were defined as per the RO-APM. Average RT episode reimbursements were reported for each disease site, except for lymphoma and metastases, and stratified by stage and disease subcategory. Comparisons with RO-APM reimbursements were made via descriptive statistics. RESULTS: A total of 2098 patients were identified, of whom 1866 (89%) were categorized per the RO-APM; 840 (45%) of those were aged >65 years. Breast (33%), head and neck (HN) (14%), and prostate (11%) cancer were most common. RO-APM base rate reimbursements and sensitivity analysis range were lower than historical reimbursement for bladder (-40%), cervical (-34%), lung (-28%), uterine (-26%), colorectal (-24%), upper gastrointestinal (-24%), HN (-23%), pancreatic (-20%), prostate (-16%), central nervous system (-13%), and anal (-10%) and higher for liver (+24%) and breast (+36%). Historical reimbursement varied with stage (stage III vs stage I) for breast (+57%, P < .01), uterine (+53%, P = .01), lung (+50%, P < .01), HN (+24%, P = .01), and prostate (+13%, P = .01). Overall, for patients older than 65 years of age, the RO-APM resulted in a -9% reduction in total RT reimbursement compared with historical FFS (-2%, -15%, and -27% for high, mid, and low adjusted RO-APM rates). CONCLUSIONS: Our findings indicate that the RO-APM will result in significant reductions in reimbursement at our center, particularly for cancers more common in underserved populations. Practices that care for socioeconomically disadvantaged populations may face significant reductions in revenue, which could further reduce access for this vulnerable population.