(Saturday, 4/4/2020) [Mountain Time (GMT-6)]
Purpose: Vendor-provided guidelines recommend correcting dwell positions for ring applicators for HDR brachytherapy. These corrections have been validated through imaging and video analysis and are currently the standard of practice for use of tandem and ring applicators for treatment of cervical cancer. The aim of this report is to study the dosimetric significance of these corrections and how they vary between different ring sets.
Methods: Eleven cervical cancer patient plans treated in a one year period with the same T&R set were recalculated with and without the vendor-recommended dwell position corrections applied to the ring applicator in Eclipse TPS. Prescription doses were 6 Gy/fraction to the physician-contoured HR-CTV. Dosimetric parameters were compared including HR-CTV coverage, D2cc of bladder, rectum, and sigmoid, and dose to point A. This data was also compared to the same data from eleven patient plans treated with a different T&R set.
Results: The average percentage absolute difference in HR-CTV coverage was 0.5%. The average percentage absolute difference in D2cc of the bladder, rectum, and sigmoid were 0.9%, 0.9%, and 0.5% respectively. The largest absolute difference in dose was 15cGy in D2cc to the bladder. The largest and only statistically significant average difference was found in the dose to Point A which ranged from -1.9% to 2.3%. Results for the second ring set were comparable with the average differences within a standard deviation from the original set.
Conclusion: No studied parameter apart from dose to Point A showed statistically significant differences between corrected and uncorrected T&R plans for either studied ring set. Other sources of error such as contouring and manual correction of the dwell positions in HDR have the potential to be much larger than the differences found in this report. A full cost and benefit analysis of dwell position corrections is under further investigation.
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