Impact of pelvic irradiation on fiducial tracking prior to SBRT for high-risk prostate cancer
PO-1455
Abstract
Impact of pelvic irradiation on fiducial tracking prior to SBRT for high-risk prostate cancer
Authors: Jonathan Lischalk1, Vianca F. Santos1, Mary Coakley2, Meredith Akerman3, Astrid Sanchez4, Christopher Mendez4, Todd Carpenter4, Aaron Katz5, Anthony Corcoran5, Hillel Y. Marans6, Owen Clancey7, Matthew Witten7, Samir S. Taneja6, Jonathan A. Haas4
1Perlmutter Cancer Center at New York University Langone Hospital - Long Island, Radiation Oncology, New York, USA; 2Perlmutter Cancer Center at New York University Langone Hospital - Long Island, Radiation oncology, New York, USA; 3NYU Langone Hospital - Long Island, Mineola, Research and Academic Center, Mineola, USA; 4Perlmutter Cancer Center at New York University Langone Hospital - Long Island, Radiation Oncology, Mineola, USA; 5Perlmutter Cancer Center at New York University Langone Hospital - Long Island, Urology, Mineola, USA; 6NYU Grossman School of Medicine, Urology, New York, USA; 7Perlmutter Cancer Center at New York University Langone Hospital-Long Island, Radiation Oncology, Mineola, USA
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Purpose or Objective
Pelvic nodal irradiation is commonly utilized in the management of high-risk prostate cancer. A novel method of dose escalation in lieu of an LDR brachytherapy implant is the use of a 3-fraction robotic radiosurgical SBRT boost using fiducial tracking. This theoretically achieves more comprehensive coverage of extracapsular extension or seminal vesicle invasion, which can be common in high-risk disease. In the present study, we investigate the impact of upfront nodal irradiation on subsequent fiducial tracking for the SBRT boost portion of treatment.
Material and Methods
In this single institutional analysis, we prospectively collected fiducial tracking information for patients who were treated with upfront conventionally fractionated pelvic nodal radiation followed by a 3-fraction boost. As a control group, during the same period we identified patients treated sans nodes with 5-fraction SBRT. Monte Carlo estimates (MC) to the Fisher’s Exact Test was used to assess temporal loss of fiducial tracking across treatment fractions. Volatility was defined as a deviation from the most common “state” of fiducial tracking, and was corrected for number of fractions. The 5- and 3-fraction cohorts were compared using the Mann-Whitney Test (MWT). Analysis of fiducial tracking changes and their association with pre-treatment factors was performed using two techniques: (1) pattern of tracking change from first to last fraction using the Kruskal-Wallis test and MC, and (2) deviation from ideal tracking as a function of fiducial tracking loss aggregated over all fractions using Spearman Correlation Coefficient and MWT.
Results
A total of 233 patients were treated with either 5-fraction SBRT (n = 186, 79%) or a 3-fraction SBRT boost after nodal irradiation (n = 49, 21%) from April 2021 to July 2022. Over five treatment fractions, there was a significant (p < 0.001) loss of fiducial tracking fidelity as demonstrated by progressive loss of one tracked fiducial. In contrast, there was no similar tracking loss for the three fraction regimen that proceeded nodal treatment (p = 0.9). Moreover, there was significantly more volatility observed in the 5-fraction versus 3-fraction boost treatment (median volatility 2.2 vs. 0.0, p < 0.001). There were no significant associations between fiducial tracking, independently for 3- or 5-fractions, using either analysis method for the following parameters: neoadjuvant ADT, time from fiducial placement to SBRT, clinical target volume, and QOD vs. daily SBRT delivery.
Conclusion
Pelvic nodal treatment has no impact on 3-fraction SBRT boost fiducial tracking quantity or quality. In contrast, 5-fraction treatments demonstrated a significant progressive loss of fiducial tracking over time and increased volatility of those fiducials tracked, thus we recommend placement of a minimum of four fiducials. Finally, no pre-treatment factors were significantly associated with changes in fiducial tracking for 3- or 5- fraction SBRT.