A Dosimetric Analysis of MRI-Guided Combined Intracavitary and Interstitial Dynamic Adaptive Brachytherapy for Cervical Cancer with a Novel Split Ring Applicator

PurposeTo evaluate the dosimetric advantages of target volume coverage and normal tissue avoidance between standard intracavitary (IC) delivery of high-dose rate (HDR) brachytherapy for cervical cancer vs. fractions delivered with the addition of an interstitial (IS) needle, utilizing a novel combined IC-IS applicator.Materials & MethodsWith IRB approval, we reviewed all cases of HDR brachytherapy utilizing a split-ring & tandem applicator for the treatment of cervical cancer performed at our institution from January 2013 through December 2015. Using 3T multi-parametric MRI (mpMRI) series, high- and intermediate-risk (HR, IR) clinical target volumes (CTVs) as well as organs at risk (OARs) were delineated before each fraction. At least 90% of prescription dose delivered to the HR-CTV and 80% to the IR-CTV was deemed the minimal acceptable target coverage. If these objectives were unachievable with the standard IC applicator, additional IS needles were added at the discretion of the physician to improve dosimetric coverage of CTVs without overdosing OARs. Interstitial needles were placed in the paracervical tissues with either the Ellis Interstitial Applicator Cap or freehand. For those patients who had an IS needle placed during one or more fractions, dosimetric parameters for HR-CTV, IR-CTV, bladder, rectum, sigmoid and small bowel for each fraction were extrapolated. Target coverage and avoidance of OARs were compared between combined IC-IS and IC fractions alone.ResultsIn 5/17 (29.4%) patients, an IS needle was placed in addition to the IC applicator, with a total of 7 needle insertions: 1 had a single IS needle during 3 of 5 fractions, and 4 had single needle placement during 1 fraction each. Mean D90 (Gy) per fraction to the HR-CTV with and without an IS needle was 10.77 ± 2.36 vs. 7.92 ± 0.84, respectively, with a mean percent-dose increase of 36.6%, and for the IR-CTV, 8.59 ± 1.52 vs. 7.02 ± 1.45, respectively, with a mean percent-dose increase of 23.7%. Regarding OARs, mean D2cc (Gy) per fraction for fractions with and without an IS needle were: Bladder - 8.89 ± 0.88 vs. 9.37 ± 0.88; Rectum - 5.95 ± 2.28 vs. 4.95 ± 1.24; Sigmoid - 3.96 ± 1.91 vs. 2.53 ± 1.30; Small bowel - 5.76 ± 2.12 vs. 5.28 ± 2.13. For the series in which an IS needle was placed in 3 out of 5 fractions, comparison of mean D90 (Gy) per fraction with and without an IS needle yielded: HR-CTV 12.77 vs. 7.5 (+70.3%); IR-CTV 9.35 vs. 6.04 (+54.8%); D2cc (Gy) Bladder - 9.02 vs. 9.35 (-3.7%); Rectum - 4.17 vs. 5.29 (-26.9%); Sigmoid - 1.06 vs. 1.35 (-27.4%); Small bowel - 6.60 vs. 5.32 (+24.1%) (Figure 1). All patients tolerated the procedure well without any documented severe adverse events.Conclusions PurposeTo evaluate the dosimetric advantages of target volume coverage and normal tissue avoidance between standard intracavitary (IC) delivery of high-dose rate (HDR) brachytherapy for cervical cancer vs. fractions delivered with the addition of an interstitial (IS) needle, utilizing a novel combined IC-IS applicator. To evaluate the dosimetric advantages of target volume coverage and normal tissue avoidance between standard intracavitary (IC) delivery of high-dose rate (HDR) brachytherapy for cervical cancer vs. fractions delivered with the addition of an interstitial (IS) needle, utilizing a novel combined IC-IS applicator. Materials & MethodsWith IRB approval, we reviewed all cases of HDR brachytherapy utilizing a split-ring & tandem applicator for the treatment of cervical cancer performed at our institution from January 2013 through December 2015. Using 3T multi-parametric MRI (mpMRI) series, high- and intermediate-risk (HR, IR) clinical target volumes (CTVs) as well as organs at risk (OARs) were delineated before each fraction. At least 90% of prescription dose delivered to the HR-CTV and 80% to the IR-CTV was deemed the minimal acceptable target coverage. If these objectives were unachievable with the standard IC applicator, additional IS needles were added at the discretion of the physician to improve dosimetric coverage of CTVs without overdosing OARs. Interstitial needles were placed in the paracervical tissues with either the Ellis Interstitial Applicator Cap or freehand. For those patients who had an IS needle placed during one or more fractions, dosimetric parameters for HR-CTV, IR-CTV, bladder, rectum, sigmoid and small bowel for each fraction were extrapolated. Target coverage and avoidance of OARs were compared between combined IC-IS and IC fractions alone. With IRB approval, we reviewed all cases of HDR brachytherapy utilizing a split-ring & tandem applicator for the treatment of cervical cancer performed at our institution from January 2013 through December 2015. Using 3T multi-parametric MRI (mpMRI) series, high- and intermediate-risk (HR, IR) clinical target volumes (CTVs) as well as organs at risk (OARs) were delineated before each fraction. At least 90% of prescription dose delivered to the HR-CTV and 80% to the IR-CTV was deemed the minimal acceptable target coverage. If these objectives were unachievable with the standard IC applicator, additional IS needles were added at the discretion of the physician to improve dosimetric coverage of CTVs without overdosing OARs. Interstitial needles were placed in the paracervical tissues with either the Ellis Interstitial Applicator Cap or freehand. For those patients who had an IS needle placed during one or more fractions, dosimetric parameters for HR-CTV, IR-CTV, bladder, rectum, sigmoid and small bowel for each fraction were extrapolated. Target coverage and avoidance of OARs were compared between combined IC-IS and IC fractions alone. ResultsIn 5/17 (29.4%) patients, an IS needle was placed in addition to the IC applicator, with a total of 7 needle insertions: 1 had a single IS needle during 3 of 5 fractions, and 4 had single needle placement during 1 fraction each. Mean D90 (Gy) per fraction to the HR-CTV with and without an IS needle was 10.77 ± 2.36 vs. 7.92 ± 0.84, respectively, with a mean percent-dose increase of 36.6%, and for the IR-CTV, 8.59 ± 1.52 vs. 7.02 ± 1.45, respectively, with a mean percent-dose increase of 23.7%. Regarding OARs, mean D2cc (Gy) per fraction for fractions with and without an IS needle were: Bladder - 8.89 ± 0.88 vs. 9.37 ± 0.88; Rectum - 5.95 ± 2.28 vs. 4.95 ± 1.24; Sigmoid - 3.96 ± 1.91 vs. 2.53 ± 1.30; Small bowel - 5.76 ± 2.12 vs. 5.28 ± 2.13. For the series in which an IS needle was placed in 3 out of 5 fractions, comparison of mean D90 (Gy) per fraction with and without an IS needle yielded: HR-CTV 12.77 vs. 7.5 (+70.3%); IR-CTV 9.35 vs. 6.04 (+54.8%); D2cc (Gy) Bladder - 9.02 vs. 9.35 (-3.7%); Rectum - 4.17 vs. 5.29 (-26.9%); Sigmoid - 1.06 vs. 1.35 (-27.4%); Small bowel - 6.60 vs. 5.32 (+24.1%) (Figure 1). All patients tolerated the procedure well without any documented severe adverse events. In 5/17 (29.4%) patients, an IS needle was placed in addition to the IC applicator, with a total of 7 needle insertions: 1 had a single IS needle during 3 of 5 fractions, and 4 had single needle placement during 1 fraction each. Mean D90 (Gy) per fraction to the HR-CTV with and without an IS needle was 10.77 ± 2.36 vs. 7.92 ± 0.84, respectively, with a mean percent-dose increase of 36.6%, and for the IR-CTV, 8.59 ± 1.52 vs. 7.02 ± 1.45, respectively, with a mean percent-dose increase of 23.7%. Regarding OARs, mean D2cc (Gy) per fraction for fractions with and without an IS needle were: Bladder - 8.89 ± 0.88 vs. 9.37 ± 0.88; Rectum - 5.95 ± 2.28 vs. 4.95 ± 1.24; Sigmoid - 3.96 ± 1.91 vs. 2.53 ± 1.30; Small bowel - 5.76 ± 2.12 vs. 5.28 ± 2.13. For the series in which an IS needle was placed in 3 out of 5 fractions, comparison of mean D90 (Gy) per fraction with and without an IS needle yielded: HR-CTV 12.77 vs. 7.5 (+70.3%); IR-CTV 9.35 vs. 6.04 (+54.8%); D2cc (Gy) Bladder - 9.02 vs. 9.35 (-3.7%); Rectum - 4.17 vs. 5.29 (-26.9%); Sigmoid - 1.06 vs. 1.35 (-27.4%); Small bowel - 6.60 vs. 5.32 (+24.1%) (Figure 1). All patients tolerated the procedure well without any documented severe adverse events. Conclusions