Evaluating the relationship between vaginal apex "dog ears" and patterns of recurrence in endometrial cancer following adjuvant image guided vaginal cuff brachytherapy.

PURPOSE: The aim of this investigation is to characterize vaginal apex "dog ears" and their association with patterns of treatment failure in patients with endometrial cancer treated with adjuvant high-dose-rate (HDR) single-channel vaginal cuff brachytherapy (VCB). METHODS: A retrospective review of patients treated with HDR VCB from 2012 to 2021 for medically operable endometrial cancer at a single institution was conducted. Dog ears, defined as tissue at the apex extending at least 10 mm from the brachytherapy applicator were identified on CT simulation images. Fisher exact test and a multivariate logistic regression model evaluated the association between factors of interest with treatment failure. Vaginal cuff failure free survival (VCFFS) was calculated from first brachytherapy to vaginal cuff recurrence (VCR). RESULTS: A total of 219 patients were reviewed. In this sample, 57.5% of patients met criteria for having dog ears. In total, 13 patients (5.9%) developed a VCR. There was no statistically significant difference in the rate of VCR between patients with and without dog ears (7.1% vs. 4.3%, p = 0.56). There was a trend toward increased risk of recurrence with higher grade histology identified in the multivariate logistic regression model (p = 0.085). The estimated 3-year probability of VCFFS was 86%. CONCLUSIONS: Vaginal apex dog ears are prevalent but are not found to statistically increase the risk of VCR after VCB in our single institution experience. However, while local failure remains low in this population, we report an absolute value of over twice as many VCRs in patients with dog ears, indicating that with improved dog ear characterization this may remain a relevant parameter for consideration in treatment planning.

Scripted spot removal in PBS proton therapy planning.

BACKGROUND: It is well known in proton therapy that the relative biological effectiveness (RBE) is not constant across the entire Bragg peak, with higher RBE at the distal end of the Bragg peak due to higher linear energy transfer (LET). Treatment planning systems are moving toward LET optimization to mitigate this potentially higher biological impact at a track end. However, using a simple script, proton users can begin to simulate this process by deleting spots from critical structures during optimization. In most cases, nominal target coverage and plan robustness remain satisfactory. METHODS: In our clinic, we developed a script that allows the user to delete spots in all organs at risk (OARs) of interest for one or more treatment beams. The purpose of this script is to potentially reduce side effects by eliminating Bragg peaks within OARs. The script was first used for prostate patients where spots in the rectum and sigmoid, outside of the overlap with the target, were deleted. We then began to use the script for head and neck (H&N) and breast/chestwall patients to reduce acute side effects of the skin by removing spots in a 0.5-cm skin rind. CONCLUSIONS: By utilizing a simple script for deleting spots in critical structures, we have seen excellent clinical results thus far. We have noted reduced skin reactions for nearly all H&N and breast patients.