Effect of Body Mass Factors on Setup Displacement for Gynecological Cancers and Subsequent Impact on PTV Margin

ABSTRACT

To analyze the impact of body mass factors (BMFs) including body mass index (BMI), umbilical circumference (UC), and hip circumference (HC), on setup errors in gynecological tumors, and whether the planned tumor volumes (PTVs) are adequate for obese patients. A retrospective study was conducted among 46 consecutive women with gynecological tumors, who were treated with Volumetric Modulated Arc Therapy (VMAT) at the radiotherapy (RT) unit. Setup accuracy was verified using daily cone-beam computed tomography (CBCT). BMFs were measured at baseline for all patients, and at fractions #10 and #20. Total vector errors (TVEs) were computed and linear regression was used to analyze their relationship with baseline BMFs. Accuracy was determined for each fraction by testing two different PTVs (Cutoff I ≤0.7cm and II ≤1.0cm). A pooled analysis was conducted to test the association of accuracy levels (within vs beyond-PTV) with the mean and variance of BMI, UC, and HC, considering the repeated measures. Receiver operating characteristics (ROC) curve analysis was carried out to test the sensitivity of BMI, UC, and HC in predicting inaccurate setup The mean (SD) TVE was 0.86 (0.34) cm and 0.79 (0.30) cm in systematic and random settings respectively. Random TVE showed weakly positive relationships with BMI (B=0.005 [95%CI=0.001-0.010];R2=0.090;p=0.042) and UC (B=0.013 [95%CI=0.002-0.025];R2=0.119;p=0.019. The pooled analysis showed a higher mean BMI with setups beyond the PTV compared to within PTV, with a mean difference of approximately 3.50 kg/m2, (p=0.001), in the lateral direction. Similarly, measures of UC (mean difference ∼10 cm) and HC (∼8 cm) were significantly higher in setups beyond the PTV compared with accurate setups (p<0.001). With respect of the vertical direction, BMI (mean difference=7.4 kg/m2, p=0.001), UC (5.3 cm, p<0.001), and HC (16.0 cm, p<0.001) were higher in setups beyond the PTV versus those within PTV;however, this was only observed using Cutoff I. Using Cutoff II, only HC showed a statistically significant difference, with a mean difference of 11.7 cm between inaccurate setups and accurate setups (0=0.041). ROC curve analysis showed that a BMI>31.4 kg/m2 was predictive for inaccurate setup in the vertical direction with 90.0% sensitivity, with respect of Cutoff I. Furthermore, a BMI>30.3 kg/m2 was predictive for inaccurate setup in the lateral direction with 92.5% sensitivity, with respect of Cutoff II. The accuracy of RT setups in gynecological tumors are highly sensitive to patients' BMI, notably in the lateral and vertical directions. To facilitate workflow during the Covid-19 crisis, we suggest that daily CBCT should be applied on patients with a BMI>30.3 kg/m2 or the PTVs should be adapted for obese patients to enhance setup accuracy of RT [ FROM AUTHOR] Copyright of International Journal of Radiation Oncology, Biology, Physics is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full . (Copyright applies to all s.)