Author: Awens Alphonse, Nebi Demez, Michael Kasper, Noufal Manthala Padannayil, Shyam Pokharel, Suresh Rana, Lauren A. Rigsby, Tino Romaguera, Hina Saeed, Nishan Shrestha, Somol Sunny 👨🔬
Affiliation: Lynn Cancer Institute, Boca Raton Regional Hospital, Baptist Health South Florida 🌍
Purpose: In radiation therapy, patient setup errors have been a primary concern impacting dose delivery accuracy. A robust treatment plan is essential to mitigate these errors. This study aimed to evaluate the impact of translational errors on the robustness of MR Linac-based stereotactic body therapy (SBRT) plans for prostate cancer.
Methods: Ten prostate cancer patients, previously treated with 5 fractions delivering 40 Gy to PTV_40 and 36.25 Gy to PTV_36.25, were retrospectively analyzed. Translational setup errors of ±2 mm and ±3 mm were applied independently in the three translational planes to the nominal plans without altering optimization parameters or monitor units. Target coverage (V100) and maximum doses (D0.03cc) to organs at risk (OARs) were compared between the simulated and nominal plans.
Results: In the nominal plans, V100 for PTV_40 and PTV_36.25 was 97.3±1.4% and 95.5±0.8%, respectively. V100 for PTV_40 dropped to 89.0±4.0%, 82.2±6.0%, 93.4±3.5%, and 88.7±5.2% for 2 mm, 3 mm, -2 mm, and -3 mm setup errors, respectively, while V100 for PTV_36.25 decreased to 92.5±2.5%, 88.2±4.4%, 88.0±2.6% and 82.5±3.4% for the same errors. For a +3 mm setup error, the D0.03cc to the bladder, sigmoid, and urethra increased by up to 13.9±5.0%, 46.8±38.0%, and 9.0±5.6%, respectively, while rectal dose decreased by up to 18.1±13.9%. For -3 mm setup error, the D0.03cc to the rectum and urethra increased by 19.3±9.0% and 6.7±3.8%, respectively, whereas the bladder and sigmoid doses decreased by 12.8±8.0% and 21.9±18.1%, respectively.
Conclusion: Preliminary findings suggest that translational setup errors, as small as 2 mm, can compromise target coverage and cause notable deviations in OAR doses, with larger errors, such as 3 mm, further amplifying these effects.