There are dosimetric advantages associated with the use of multi-channel (MC) cylinders for intracavitary gynecologic brachytherapy, including reduced dose to organs at risk (OAR) and the ability to shape target coverage. Single-channel (SC) cylinders have been shown to have reproducible doses to OAR between fractions (i.e., inter-fraction variability), but this has not been shown for MC cylinders. This study aimed to assess doses to OAR and inter-fraction variability amongst three different MC cylinders and one SC cylinder for HDR brachytherapy. Forty-eight women (38 endometrial cancer, 10 cervical cancer) were included. MC vaginal cylinders were used in 27 (7 13-channel applicator, 11 CET MC Cylinder [CET], 9 Ovoid and Cylinder [O&C]) and one SC cylinder (electronic applicator) was used in 21 patients. The CET cylinder is an MC cylinder designed in-house with 4 outer channels and 1 central channel. CT scans were obtained at treatment planning and prior to each fraction. D0.1 cc, D1 cc and D2 cc doses were recorded for the OAR including the rectum (R), bladder (B) and sigmoid (S) for each CT scan. Re-optimization of plans was not performed between fractions. OAR doses from the treatment planning CT (CT[p]) were compared to the average of OAR doses calculated at each treatment (CT[t]). One hundred seventy-eight fractions were delivered with a median dose per fraction of 6 Gy. Patients were treated with a median of 3 fractions to an average vaginal length of 4 cm and median prescription depth of 2 mm (range, 0 - 5 mm). Mean OAR doses for each applicator are shown in the Table. No significant difference was noted between OAR doses calculated at CT(p) and CT(t) for any applicator. Multivariate analysis was carried out adjusting for age, number of fractions, treatment length and prescription depth, assessing OAR doses for the CET MC cylinder versus the others. Rectal D0.1, 1 and 2 cc doses determined from the CT(t) scan dosimetry were 9.7%, 9.7%, and 9.3% (p < 0.05) less, respectively, for the CET MC cylinder compared with the other applicators. Differences in bladder and sigmoid doses between applicators were not observed. OAR doses did not significantly vary between planning and treatment delivery for any of the applicators. This suggests that after verifying a reproducible insertion, re-planning is not required between fractions for MC cylinders. Comparison of OAR doses between applicators revealed that the CET MC cylinder was associated with the lowest dose to the rectum.Poster Viewing Abstract 2568; TableMean OAR D0.1, 1, and 2 cc doses as % of prescription dose (with standard error) at CT(t) and CT(p)13-channel applicator (CT[p])13-channel applicator (CT[t])CET (CT[p])CET (CT[t])O&C (CT[p])O&C (CT[t])Electronic Applicator (CT[p])Electronic Applicator (CT[t])RD0.1 cc85.9 (+/-6.2)83.2 (+/-6.0)69.7 (+/-4.9)71.9 (+/-4.8)81.8 (+/-5.5)82.1 (+/-5.3)91.6 (+/-3.6)98.2 (+/-3.4)RD1.0 cc72.8 (+/-5.0)71.7 (+/-4.5)57.6 (+/-4.0)59.6 (+/-3.6)70.0 (+/-4.4)69.7 (+/-4.0)72.7 (+/-2.9)77.9 (+/-2.6)RD2.0 cc66.2 (+/-4.7)65.5 (+/-4.2)51.7 (+/-3.8)53.6 (+/-3.3)63.5 (+/-4.2)63.3 (+/-3.7)64.2 (+/-2.7)69.0 (+/-2.4)BD0.1 cc80.8 (+/-7.4)77.0 (+/-8.7)66.8 (+/-5.9)68.2 (+/-7.0)85.6 (+/-6.5)79.7 (+/-7.7)87.6 (+/-4.3)81.9 (+/-5.0)BD1.0 cc70.6 (+/-6.2)67.2 (+/-6.2)57.0 (+/-5.0)57.3 (+/-5.0)74.8 (+/-5.4)68.9 (+/-5.4)69.9 (+/-3.6)64.4 (+/-3.6)BD2.0 cc65.9 (+/-5.8)62.7 (+/-5.5)53.9 (+/-4.6)52.5 (+/-4.4)69.0 (+/-5.1)63.6 (+/-4.8)62.1 (+/-3.4)56.9 (+/-3.2)SD0.1 cc53.6 (+/-12.8)59.6 (+/-11.9)63.5 (+/-10.4)57.2 (+/-9.5)38.9 (+/-13.2)39.3 (+/-11.9)47.6 (+/-12.3)60.0 (+/-11.1)SD1.0 cc46.2 (+/-8.4)48.8 (+/-8.1)45.5 (+/-6.8)43.5 (+/-6.5)30.8 (+/-8.7)30.7 (+/-8.1)34.0 (+/-8.3)38.5 (+/-7.6)SD2.0 cc45.0 (+/-7.2)45.0 (+/-6.9)39.4 (+/-5.9)38.2 (+/-5.5)27.5 (+/-7.4)27.5 (+/-6.9)26.4 (+/-7.2)31.2 (+/-6.4) Open table in a new tab
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