Deformable image registration-based contour propagation yields clinically acceptable plans for MRI-based cervical cancer brachytherapy planning.

To study the dosimetric impact of deformable image registration-based contour propagation on MRI-based cervical cancer brachytherapy planning. High-risk clinical target volume (HRCTV) and organ-at-risk (OAR) contours were delineated on MR images of 10 patients who underwent ring and tandem brachytherapy. A second set of contours were propagated using a commercially available deformable registration algorithm. "Manual-contour" and "propagated-contour" plans were optimized to achieve a maximum dose to the most minimally exposed 90% of the volume (D90) (%) of 6 Gy/fraction, respecting minimum dose to the most exposed 2cc of the volume (D2cc) OAR constraints of 5.25 Gy and 4.2 Gy/fraction for bladder and rectum/sigmoid (86.5 and 73.4 Gy equivalent dose in 2 Gy fractions [EQD2] for external beam radiotherapy [EBRT] + brachytherapy, respectively). Plans were compared using geometric and dosimetric (total dose [EQD2] EBRT + brachytherapy) parameters. The differences between the manual- and propagated-contour plans with respect to the HRCTV D90 and bladder, rectum, and sigmoid D2cc were not statistically significant (per-fraction basis). For the EBRT + brachytherapy course, the D2cc delivered to the manually contoured OARs by the propagated-contour plans ranging 98-107%, 95-105%, and 92-108% of the dose delivered by the manual-contour plans (max 90.4, 70.3, and 75.4 Gy for the bladder, rectum, and sigmoid, respectively). The HRCTV dose in the propagated-contour plans was 97-103% of the dose in the manual-contour plans (maximum difference 2.92 Gy). Increased bladder filling resulted in increased bladder dose in manual- and propagated-contour plans. When deformable image registration-propagated contours are used for cervical brachytherapy planning, the HRCTV dose is similar to the dose delivered by manual-contour plans and the doses delivered to the OARs are clinically acceptable, suggesting that our algorithm can replace manual contouring for appropriately selected cases that lack major interfractional anatomical changes.

Chapman CH ，Polan D ，Vineberg K ，Jolly S ，Maturen KE ，Brock KK ，Prisciandaro JI ... -  《-》

Image-based 3D treatment planning for vaginal cylinder brachytherapy: dosimetric effects of bladder filling on organs at risk.

To investigate the dosimetric effects of bladder filling on organs at risk (OARs) using three-dimensional image-based treatment planning for vaginal cylinder brachytherapy. Twelve patients with endometrial or cervical cancer underwent postoperative high-dose rate vaginal cylinder brachytherapy. For three-dimensional planning, patients were simulated by computed tomography with an indwelling catheter in place (empty bladder) and with 180 mL of sterile water instilled into the bladder (full bladder). The bladder, rectum, sigmoid, and small bowel (OARs) were contoured, and a prescription dose was generated for 10 to 35 Gy in 2 to 5 fractions at the surface or at 5 mm depth. For each OAR, the volume dose was defined by use of two different criteria: the minimum dose value in a 2.0-cc volume receiving the highest dose (D(2cc)) and the dose received by 50% of the OAR volume (D(50%)). International Commission on Radiation Units & Measurements (ICRU) bladder and rectum point doses were calculated for comparison. The cylinder-to-bowel distance was measured using the shortest distance from the cylinder apex to the contoured sigmoid or small bowel. Statistical analyses were performed with paired t tests. Mean bladder and rectum D(2cc) values were lower than their respective ICRU doses. However, differences between D(2cc) and ICRU doses were small. Empty vs. full bladder did not significantly affect the mean cylinder-to-bowel distance (0.72 vs. 0.92 cm, p = 0.08). In contrast, bladder distention had appreciable effects on bladder and small bowel volume dosimetry. With a full bladder, the mean small bowel D(2cc) significantly decreased from 677 to 408 cGy (p = 0.004); the mean bladder D(2cc) did not increase significantly (1,179 cGy vs. 1,246 cGy, p = 0.11). Bladder distention decreased the mean D(50%) for both the bladder (441 vs. 279 cGy, p = 0.001) and the small bowel (168 vs. 132 cGy, p = 0.001). Rectum and sigmoid volume doses were not affected by bladder filling. In high-dose rate vaginal cylinder brachytherapy, treatment with a distended bladder preferentially reduces high dose to the small bowel around the vaginal cuff without a significant change in dose to the bladder, rectum, or sigmoid.

Hung J ，Shen S ，De Los Santos JF ，Kim RY ... -  《-》

A novel two-step optimization method for tandem and ovoid high-dose-rate brachytherapy treatment for locally advanced cervical cancer.

To present a novel method allowing fast volumetric optimization of tandem and ovoid high-dose-rate treatments and to quantify its benefits. Twenty-seven CT-based treatment plans from 6 consecutive cervical cancer patients treated with four to five intracavitary tandem and ovoid insertions were used. Initial single-step optimized plans were manually optimized, approved, and delivered plans created with a goal to cover high-risk clinical target volume (HR-CTV) with D90 >90% and minimize rectum, bladder, and sigmoid D2cc. For the two-step optimized (TSO) plan, each single-step optimized plan was replanned adding a structure created from prescription isodose line to the existent physician delineated HR-CTV, rectum, bladder, and sigmoid. New, more rigorous dose-volume histogram constraints for the critical organs at risks (OARs) were used for the optimization. HR-CTV D90 and OAR D2ccs were evaluated in both plans. TSO plans had consistently smaller D2ccs for all three OARs while preserving HR-CTV D90. On plans with "excellent" CTV coverage, average D90 of 96% (91-102%), sigmoid, bladder, and rectum D2cc, respectively, reduced on average by 37% (16-73%), 28% (20-47%), and 27% (15-45%). Similar reductions were obtained on plans with "good" coverage, average D90 of 93% (90-99%). For plans with "inferior" coverage, average D90 of 81%, the coverage increased to 87% with concurrent D2cc reductions of 31%, 18%, and 11% for sigmoid, bladder, and rectum, respectively. The TSO can be added with minimal planning time increase but with the potential of dramatic and systematic reductions in OAR D2ccs and in some cases with concurrent increase in target dose coverage. These single-fraction modifications would be magnified over the course of four to five intracavitary insertions and may have real clinical implications in terms of decreasing both acute and late toxicities.

Sharma M ，Fields EC ，Todor DA 《-》

Practically achievable maximum high-risk clinical target volume doses in MRI-guided intracavitary brachytherapy for cervical cancer: a planning study.

To explore maximum high-risk clinical target volume (HR-CTV) doses that can be practically achieved when organs at risk (OARs; bladder, rectum, and sigmoid) doses are allowed to equal current recommended thresholds in MRI-based intracavitary brachytherapy (BT) planning for cervical cancer. Planning MRI sets were retrieved for 21 patients who received pulsed-dose-rate BT boost. Plans were generated using manual optimization (MO) by adjusting dwell positions and times to obtain the prescribed HR-CTV isodose that includes 90% of target (D90) coverage of 35 Gy while limiting OAR doses to below recommended tolerances (prescribed dose target [TGT] plans). Additional planning was performed with automatic volume optimization (VO) to evaluate target coverage relative to the MO plans. The MO and VO approaches were then applied with the objective of obtaining the highest possible HR-CTV coverage when OAR doses were allowed to equal threshold tolerance values (maximized [MAX] plans). A two-tailed paired t test was performed to determine the statistical significance of the results; significance level set at p < 0.013. MO and VO planning techniques could conform HR-CTV D90 to the prescribed dose quite similarly for TGT plans. Using the MAX approach, the HR-CTV D90 could be increased by 30% and 37% for MO and VO, respectively, without exceeding OAR thresholds. Sigmoid and often rectum were the dose-limiting structures during MAX planning. Simple differences in the approach to volumetric MRI-based cervix BT treatment planning can impact HR-CTV D90. Consequently, dose escalation for MRI-guided cervix BT appears feasible in this manner should clinical circumstances warrant.

Menon G ，Huang F ，Sloboda R ，Pearcey R ，Ghosh S ... -  《-》

Feasibility study of toxicity outcomes using GEC-ESTRO contouring guidelines on CT based instead of MRI-based planning in locally advanced cervical cancer patients.

To report late rectal and bladder toxicity outcomes of a CT-based image-guided brachytherapy (IGBT) technique for treatment of cervical cancer. Between 2008 and 2014, 95 women with International Federation of Gynecology and Obstetrics stage IB to IVA cervical carcinoma treated with definitive concurrent cisplatin-based chemotherapy and external beam radiation therapy 50.4 Gy in 28 fractions followed by planned prescription dose of 7 Gy × 4 fractions of high-dose-rate IGBT was retrospectively reviewed. At each implantation, all patients had a urinary catheter in situ and received bowel enema before undergoing planning CT simulation. A high-risk clinical target volume (HRCTV) as per GEC-ESTRO guidelines and the entire cervix, rectum, and bladder was contoured on the simulation CT according to Radiation Therapy Oncology Group Gynaecology Contouring Atlas. Reported doses to HRCTV and organs at risk were recorded. Toxicities were recorded using National Cancer Institute Common Terminology Criteria for Adverse Events version 3. The median followup time was 29 months. The mean HRCTV equivalent dose in 2 Gy fractions (EQD2) of external beam radiation therapy combined with brachytherapy was 80 Gy (standard deviation [SD], 11), and the rectal doses to 2 cm3 (D2cc) EQD2 and bladder D2cc EQD2 were 74 Gy (SD, 6) and 79 Gy (SD, 15), respectively. Twenty-two patients (23%) had grade 2 proctitis and 10 patients (11%) had grade 3 proctitis. Four patients (4%) had grade 2 cystitis and two patients (2%) had grade 3 cystitis. No patients had ≥ grade 4 toxicity. Despite CT-based brachytherapy planning, reported organ at risk toxicity was still significant compared with reported MRI-based planning series. Coimplementation of interstitial IGBT using the European Study on MRI-guided Brachytherapy in Locally Advanced Cervical Cancer (EMBRACE) protocol or using intensity-modulated radiation therapy during the external beam phase treatment might help to limit these late toxicities.

Koh V ，Choo BA ，Lee KM ，Tan TH ，Low JH ，Ng SY ，Ilancheran A ，Shen L ，Tang J ... -  《-》