Image-guided brachytherapy for cervical cancer: Analysis of D2 cc hot spot in three-dimensional and anatomic factors affecting D2 cc hot spot in organs at risk

PurposeTo analyze the D_{2 cc} hot spot in three-dimensional CT and anatomic factors affecting the D_{2 cc} hot spot in organs at risk (OARs).Methods and MaterialsThirty-one patients underwent pelvic CT scan after insertion of the applicator. High-dose-rate treatment planning was performed with standard loading patterns. The D_{2 cc} structures in OARs were generated in three dimensional if the total equivalent dose in 2 Gy exceeded our defined dose limits (hot spot). The location of D_{2 cc} hot spot was defined as the center of the largest D_{2 cc} fragment. The relationship between the hot spot and the applicator position was reported in Digital Imaging and Communication in Medicine coordinates.ResultsThe location of sigmoid, small bowel, and bladder D_{2 cc} hot spots was around the endocervix: The mean location of sigmoid hot spot for lateral view was 1.6 cm posteriorly and 2.3 cm superiorly (Y, 1.6 and Z, 2.3), small bowel was 1.6 cm anteriorly and 2.7 cm superiorly (Y, −1.6 and Z, 2.7). The mean location of bladder hot spot was 1.6 cm anteriorly and 1.6 cm superiorly (Y, −1.6 and Z, 1.6). These hot spots were near the plane of Point A (X, 2.0 or −2.0; Y, 0; and Z, 2.0). The mean location of rectal hot spot was 1.6 cm posteriorly and 1.9 cm inferiorly (Y, 1.6 and Z, −1.9). D_{2 cc} hot spot was affected by uterine wall thickness, uterine tandem position, fibroids, bladder fullness, bowel gas, and vaginal packing.ConclusionsBecause of the location of the D_{2 cc} hot spots, larger tumors present a challenge for adequate tumor coverage with a conventional brachytherapy applicator without an interstitial implant. Additionally, anatomic factors were identified which affect the D_{2 cc} hot spot in OARs.