Room: AAPM ePoster Library
Purpose: Multi-shield intracavitary rotating shield brachytherapy (RSBT) using ¹6?Yb has the potential to non-invasively deliver tumor-conformal dose distributions to cervical cancer patients. In this study we determined the dosimetric impact of angular and translational positioning errors on RSBT dose distributions to define tolerances for the mechanical components of RSBT applicators.
Methods: In a 37-patient treatment planning study with high-risk clinical target volume (HR-CTV) volumes of 79 ± 37 cm³ (avg. ± std. dev.), optimized treatment plans were created for each patient to meet the 85 Gy HR-CTV D90 planning goal (GEC-ESTRO), with organ-at-risk (OAR) D2cc tolerance doses of 90 Gy, 75 Gy, and 75 Gy for bladder, rectum, and sigmoid colon, respectively. Positional and rotational errors in the flexible tip of the shield-containing catheter were modeled as systematic ±5 mm, and ±10 mm proximal and distal shifts of the tandem dwell positions, and 5° and 10° shield rotation errors.
Results: For HR-CTV D90 values, 90% of patients had underdoses of <5% in cases with ±5 mm shifts and <10% with ±10 mm shifts. For bladder, 90% of patients had overdoses of <5% with ±5 mm and <12% with ±10 mm shifts. For rectum, 90% of patients had overdoses of <9% with ±5 mm and <18% with ±10 mm shifts. For sigmoid colon, 90% of patients had overdoses of <9% with ±5 mm and <19% with ±10 mm shifts. Angular shifts of 5° and 10° were responsible for <1% HR-CTV D90 underdose and <5%, <2%, and <9% overdose of bladder, rectum, and sigmoid, respectively.
Conclusion: Multi-shield, helical RSBT using ¹6?Yb appears to be robust to rotational and shifting errors that are minor and within clinical tolerance. OAR D2cc values appear to be more sensitive to applicator displacement and rotation than HR-CTV D90 values.
Funding Support, Disclosures, and Conflict of Interest: Research reported in this abstract was supported by the National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health under award number R01 EB020665. RTF is the founder of pxAlpha, LLC, which is developing rotating shield brachytherapy technology.