2792 - Skeletal Muscle Loss after Short ADT Duration in Prostate Cancer Patients Treated with Radiation Therapy

R. K. Gadam¹, S. M. Gibson², Y. Cao³, and X. Shen³; ¹Department Of Radiation Oncology, University of Kansas Medical Center, Kansas City, KS, ²Kansas City University College Of Osteopathic Medicine, Kansas City, KS, ³Department of Radiation Oncology, University of Kansas Medical Center, Kansas City, KS

Purpose/Objective(s): Androgen deprivation therapy (ADT) improves survival in many patients treated with radiation therapy (RT) for prostate cancer but carries morbidity including body composition change. Severe loss of lean muscle mass, a condition known as sarcopenia, has been shown to predict treatment toxicity and is associated with poor outcomes in advanced prostate cancer. It is unknown how quickly ADT cause these changes. We hypothesize that even short-term exposure to ADT leads to significant loss in skeletal muscle mass. Materials/

Methods: We selected a convenience sample of patients who were treated with radiation therapy along with ADT for prostate cancer at a single institution. Pre-ADT diagnostic CT images and simulation CT after initiation of ADT were analyzed. Skeletal muscle index (SMI) comparison was performed using the average skeletal muscle cross-sectional areas of sequential CT slices at the L3 vertebral level between the pre-ADT and after ADT initiation CT scans. The image analysis was performed by trained observers using Sliceomatic software with a Hounsfield unit threshold of -29 to 150 to define skeletal muscle. Sarcopenia was defined as SMI<43 if BMI was < 25 and SMI< 53 if BMI was > 25. Per prior studies, clinically significant SMI decline was defined as SMI decrease of 5 cm²/m². Patient baseline factors including age, race, co-morbidity, and time from ADT to post-treatment scan were collected. Paired t-test was used to compare change in SMI. Univariate logistic regression was used to evaluate for predictors of significant change in SMI.
Results: 34 patients were included in the analysis. Median age was 67 years (Range 51 -80, IQR 63 to 72). Baseline median BMI was 30.50 kg/m² (range 20.23 -63.05, IQR 26.80 to 35.61). 23 were White,11 Black race. Median time interval from initiation of ADT to post-ADT CT scan was 2.94 months (Range 0.80 - 7, IQR 1.67 -3.33). All patients had reduced SMI after ADT, with median loss of 5.16 cm²/m² (range 0.9 to 16.3, IQR 3.44 to 7.69, p <0.01). Median SMI loss was 9.41% (range 2%-24.86%, IQR 5.73%-12.42%). Of patients without baseline sarcopenia,15/28 (53.7%) became sarcopenic after ADT. Clinically significant SMI decline occurred in 18/34 (52.9%). Patient factors including race, age, co-morbidity, baseline BMI, baseline SMI, time since initiation of ADT were not associated with degree of SMI loss. Abstract 2792 – Table 1
Conclusion: All patients developed rapid muscle mass loss within 2 months after the initiation of ADT with 54% having clinically significant muscle loss. This change carries significant morbidity. We did not identify any predictive factors for significant skeletal muscle loss. Future work will focus on association between quality of life and sarcopenia, and prospective strategies to reduce body composition change in patients undergoing ADT.

Change in SMI after ADT (Median 2.9 months exposure)

Total Patients	N = 34
Any Decrease in SMI	34/34 (100%)
Median Decrease in SMI	9.41%
Clinically significant decrease in SMI	18/34(52.9%)
Sarcopenia onset after ADT	15/28(53.7%)