Cervical HDR Research Articles

527: A novel integrated measure of cervical HDR brachytherapy plan quality

527: A novel integrated measure of cervical HDR brachytherapy plan quality

529: Use of a radar plot to assess cervical HDR brachytherapy plans and correlate with clinical outcomes

529: Use of a radar plot to assess cervical HDR brachytherapy plans and correlate with clinical outcomes

A Novel Method for Intracavitary Cervical HDR Brachytherapy: Express Finger-Guided Implant Insertion at Simulation Table without Speculum, Cervical Dilatation, Sleeve, Anesthesia, or Sedation

Our purpose is to develop a fast, effective, and independent intracavitary brachytherapy implant insertion method that does not need sleeve insertion, anesthesia or conscious sedation, and that can be performed at the front edge of the simulation table (CT or MRI), using finger guidance without a need for speculum or cervical dilatation. From February 2022 to January 2023, we treated 27 locally advanced cervical cancer patients. In the last week of EBRT, we assessed patients with MRI and pelvic exam to determine their eligibility: 89% (24 patients) met the two inclusion criteria for the express insertion which are: the ability to cover any residual disease with intracavitary brachytherapy, and the accessibility of cervix external os. Each patient had 3 HDR express insertions (8Gy x3). A total of 72 consecutive express implant insertions were performed. Each insertion is evaluated for the success of procedure, number of attempts, and time taken. Patients started on laxative 3 days prior to the procedure, and paracetamol & Ibuprofen taken at home 2 hours before the procedure. On arrival, patients used the bathroom, and IM/SC morphine given. Patients were prepared at the front edge of the simulation table and topical lidocaine applied to the cervix. The external os identified with the index finger of one hand which also guided the tandem insertion using the other hand. No cervical dilatation was used. CT simulation was performed to confirm adequate implant placement and to contour and plan CTV-HR and OARs as per GEC-ESTRO/ABS guidelines. The success rate was 100% in all the 72 express insertions. >90% (66 insertions) were smooth and fast, i.e., completed in 1 attempt that took <20 minutes. <10% (6 insertions) were challenging but successful, in 2 patients: one patient had an acute anteverted uterus for which suprapubic abdominal pressure facilitated the procedure that took <3 attempts and completed in <40 minutes, the other patient had an acute retroverted uterus which was associated with the most challenging procedure that took >3 attempts and completed in >40 minutes. The success rate was not affected by the type of applicator used. 85% of our applications used multichannel tandem and cylinder, 10% used tandem and ovoids, and 5% used tandem and ring applicators. Express finger-guided intracavitary brachytherapy implant insertion at the simulation table without speculum, cervical dilatation, sleeve, anesthesia, or sedation is fast, effective, and an independent method that can be used in most cervical cancer patients to complete their planned brachytherapy treatment regardless of limited resources. Practice and dissemination of this innovative method is important especially when operative rooms and anesthesia support are limited (e.g., epidemics and closures) and in centers lacking such support. Further studies are warranted to optimize the procedure and to highlight its significant medical and socioeconomic benefits.

OC-0132 Near-to-target-aware OARs segmentation in cervical HDR brachytherapy via deep learning

OC-0132 Near-to-target-aware OARs segmentation in cervical HDR brachytherapy via deep learning

OC-0131 Deep learning-based segmentation in cervical HDR brachytherapy with two types of applicators

OC-0131 Deep learning-based segmentation in cervical HDR brachytherapy with two types of applicators

PHSOR03 Presentation Time: 10:10 AM: Practical Needle Placement and Dosimetry Improvements with Hybrid Intracavitary/Interstitial Ring Applicators

Purpose: Hybrid intracavitary/interstitial (IC/IS) applicators have been shown to improve local control for HRCTV > 30cc and dosimetry in all volume HRCTV compared to traditional intracavitary (IC) cervical HDR brachytherapy. Standard needle insertion patterns have not been well-established for hybrid IC/IS applicators. We quantify dosimetric benefits of the Vienna-style IC/IS applicator compared to IC-alone and aim to establish standard interstitial needle-loading and insertion depth patterns for non-bulky HRCTV.

Evaluation of rectal dose discrepancies between planned and in vivo dosimetry using MOSkin detector and PTW 9112 semiconductor probe during 60Co HDR CT-based intracavitary cervix brachytherapy

PurposeDose to the rectum during brachytherapy treatment may differ from an approved treatment plan which can be quantified with in vivo dosimetry (IVD). This study compares the planned with in vivo doses measured with MOSkin and PTW 9112 rectal probe in patients undergoing CT based HDR cervical brachytherapy with Co-60 source. MethodsDose measurement of a standard pear-shaped plan carried out in phantom to verify the MOSkin dose measurement accuracy. With MOSkin attached to the third diode, RP3 of the PTW 9112, both detectors were inserted into patients’ rectum. The RP3 and MOSkin measured doses in 18 sessions as well as the maximum measured doses from PTW 9112, RPmax in 48 sessions were compared to the planned doses. ResultsPercentage dose differences ΔD (%) in phantom study for two MOSkin found to be 2.22 ± 0.07% and 2.5 ± 0.07%. IVD of 18 sessions resulted in ΔD(%) of −16.3% to 14.9% with MOSkin and ΔD(%) of −35.7% to −2.1% with RP3. In 48 sessions, RPmax recorded ΔD(%) of −37.1% to 11.0%. MOSkin_measured doses were higher in 44.4% (8/18) sessions, while RP3_measured were lower than planned doses in all sessions. RPmax_measured were lower in 87.5% of applications (42/47). ConclusionsThe delivered doses proven to deviate from planned doses due to unavoidable shift between imaging and treatment as measured with MOSkin and PTW 9112 detectors. The integration of MOSkin on commercial PTW 9112 surface found to be feasible for rectal dose IVD during cervical HDR ICBT.

SU‐F‐T‐37: Dosimetric Evaluation of Planned Versus Decay Corrected Treatment Plans for the Treatment of Tandem‐Based Cervical HDR Brachytherapy

Purpose:This study evaluated dosimetric parameters for actual treatment plans versus decay corrected treatment plans for cervical HDR brachytherapy.Methods:125 plans of 25 patients, who received 5 fractions of HDR brachytherapy, were evaluated in this study. Dose was prescribed to point A (ICRU‐38) and High risk clinical tumor volume (HR‐CTV) and organs at risk (OAR) were, retrospectively, delineated on original CT images by treating physician. First HDR plan was considered as reference plan and decay correction was applied to calculate treatment time for subsequent fractions, and was applied, retrospectively, to determine point A, HR‐CTV D90, and rectum and bladder doses.Results:The differences between mean point A reference doses and the point A doses of the plans computed using decay times were found to be 1.05%±0.74% (−2.26% to 3.26%) for second fraction; −0.25%±0.84% (−3.03% to 3.29%) for third fraction; 0.04%±0.70% (−2.68% to 2.56%) for fourth fraction and 0.30%±0.81% (−3.93% to 2.67%) for fifth fraction. Overall mean point A dose difference, for all fractions, was 0.29%±0.38% (within ± 5%). Mean rectum and bladder dose differences were calculated to be −3.46%±0.12% and −2.47%±0.09%, for points, respectively, and −1.72%±0.09% and −0.96%±0.06%, for D2cc, respectively. HR‐CTV D90 mean dose difference was found to be −1.67% ± 0.11%. There was no statistically significant difference between the reference planned point A doses and that calculated using decay time to the subsequent fractions (p&lt;0.05).Conclusion:This study reveals that a decay corrected treatment will provide comparable dosimetric results and can be utilized for subsequent fractions of cervical HDR brachytherapy instead of actual treatment planning. This approach will increase efficiency, decrease workload, reduce patient observation time between applicator insertion and treatment delivery. This would be particularly useful for institutions with limited resources or large patient populations with limited access to care.

SU‐F‐T‐14: Dosimetric Impacts of Various Uncertainties in Cervical Cancer HDR Brachytherapy: Are Conventional Point Doses Good Surrogates for 3D Dosimetry?

Purpose:In the context of evaluating dosimetric impacts of a variety of uncertainties involved in HDR Tandem‐and‐Ovoid treatment, to study the correlations between conventional point doses and 3D volumetric doses.Methods:For 5 cervical cancer patients treated with HDR T&amp;O, 150 plans were retrospectively created to study dosimetric impacts of the following uncertainties: (1) inter‐fractional applicator displacement between two treatment fractions within a single insertion by applying Fraction#1 plan to Fraction#2 CT; (2) positional dwell error simulated from −5mm to 5mm in 1mm steps; (3) simulated temporal dwell error of 0.05s, 0.1s, 0.5s, and 1s. The original plans were based on point dose prescription, from which the volume covered by the prescription dose was generated as the pseudo target volume to study the 3D target dose effect. OARs were contoured. The point and volumetric dose errors were calculated by taking the differences between original and simulated plans. The correlations between the point and volumetric dose errors were analyzed.Results:For the most clinically relevant positional dwell uncertainty of 1mm, temporal uncertainty of 0.05s, and inter‐fractional applicator displacement within the same insertion, the mean target D90 and V100 deviation were within 1%. Among these uncertainties, the applicator displacement showed the largest potential target coverage impact (2.6% on D90) as well as the OAR dose impact (2.5% and 3.4% on bladder D2cc and rectum D2cc). The Spearman correlation analysis shows a correlation coefficient of 0.43 with a p‐value of 0.11 between target D90 coverage and H point dose.Conclusion:With the most clinically relevant positional and temporal dwell uncertainties and patient interfractional applicator displacement within the same insertion, the dose error is within clinical acceptable range. The lack of correlation between H point and 3D volumetric dose errors is a motivator for the use of 3D treatment planning in cervical HDR brachytherapy.

Dosimetric Analysis of an Additional Rectal Point in Cervical HDR Brachytherapy

Dosimetric Analysis of an Additional Rectal Point in Cervical HDR Brachytherapy

The Stability of Intracavitary Applicator Placement during Patient Transfer for Cervical HDR Brachytherapy

limiting factor in fractionated radiotherapy for pancreatic cancer. Interand intra-fraction motion due to residual setup errors, respiratory motion and deformation results in deviations between planned and delivered doses. This motion and the dose deviations they cause prevent the widespread adoption of intensity modulated radiation therapy (IMRT) and smaller margins in pancreatic radiotherapy which could be used to reduce the planned OAR doses and toxicity risks. Daily cone beam CT (CBCT) image-guidance is currently used to minimize setup errors, which can be corrected using a simple 3D shift of the treatment couch. However, other types of 3D and 4D motion cannot be corrected in this manner. Deformable image registration (DIR) is a novel technique that allows residual motion in internal anatomy to be incorporated into the dose distribution, thus improving estimates of the normal tissue doses. This study aims to evaluate the accuracy of DIR algorithms to model organ deformation and evaluate the clinical impact of this technique by comparing deviations between planning doses and delivered doses estimated using DIR of CBCT. Method/Process: Weekly CBCT images of 20 patients treated with IMRT for locally advanced pancreatic cancer will be retrospectively evaluated in the treatment planning system (RayStation). OARs will be delineated manually on CBCT. DIR of the planning CT to each CBCT will be performed to auto-propagate planning OAR contours to each CBCT. Accuracy of the DIR will be quantified by calculating the discrepancy of the two deformed contours (manual vs. DIR generated). The cumulative dose will be calculated by summing the DIR doses of the weekly CBCT. Differences in clinically relevant dose metrics will be evaluated using paired t-tests (where P<0.05 is considered significant). Results/Benefits/Challenges: Pending. Conclusion/Impact/Outcomes: DIR and dose accumulation will improve our estimate of the delivered dose to patients. This allows us to apply margin reduction in treatment planning and enhance normal tissue sparing which consequently can decrease toxicity.

SU‐E‐T‐237: Deformable Image Registration and Deformed Dose Composite for Volumetric Evaluation of Multimodal Gynecological Cancer Treatments

Purpose:Radiotherapy plans for patients with cervical cancer treated with EBRT followed by HDR brachytherapy are optimized by constraining dose to organs at risk (OARs). Risk of treatment related toxicities is estimated based on the dose received to the hottest 2cc (D2cc) of the bladder, bowel, rectum, and sigmoid. To account for intrafractional variation in OAR volume and positioning, a dose deformation method is proposed for more accurate evaluation of dose distribution for these patients.Methods:Radiotherapy plans from five patients who received 50.4Gy pelvic EBRT followed by 30Gy in five fractions of HDR brachytherapy, using split‐ring and tandem applicators, were retrospectively evaluated using MIM Software version 6.0. Dose accumulation workflows were used for initial deformation of EBRT and HDR planning CTs onto a common HDR planning CT. The Reg Refine tool was applied with user‐specified local alignments to refine the deformation. Doses from the deformed images were transferred to the common planning CT. Deformed doses were scaled to the EQD2, following the linear‐quadratic BED model (considered α/β ratio for tumor as 10, and 3 for rest of the tissues), and then combined to create the dose composite. MIM composite doses were compared to the clinically‐reported plan assessments based upon the American Brachytherapy Society (ABS) guidelines for cervical HDR brachytherapy treatment.Results:Bladder D2cc exhibited significant reduction (−11.4%±3.85%, p&lt; 0.02) when evaluated using MIM deformable dose composition. Differences observed for bowel, rectum, and sigmoid D2cc were not significant (−0.58±7.37%, −4.13%±13.7%, and 8.58%±4.71%, respectively and p&gt;0.05 for all) relative to the calculated values used clinically.Conclusion:Application of deformable dose composite techniques may lead to more accurate total dose reporting and can allow for elevated dose to target structures with the assurance of not exceeding dose to OARs. Further study into deformable dose composition and correlation with clinical outcomes is warranted.

Effect of Bladder Distension on Dosimetry of Organs at Risk During Intracavitary Cervical HDR Brachytherapy Using Dose-Volume and Dose-Surface Histograms

Effect of Bladder Distension on Dosimetry of Organs at Risk During Intracavitary Cervical HDR Brachytherapy Using Dose-Volume and Dose-Surface Histograms

SU‐F‐BRF‐09: A Non‐Rigid Point Matching Method for Accurate Bladder Dose Summation in Cervical Cancer HDR Brachytherapy

Purpose:To propose and validate a deformable point matching scheme for surface deformation to facilitate accurate bladder dose summation for fractionated HDR cervical cancer treatment.Method:A deformable point matching scheme based on the thin plate spline robust point matching (TPSRPM) algorithm is proposed for bladder surface registration. The surface of bladders segmented from fractional CT images is extracted and discretized with triangular surface mesh. Deformation between the two bladder surfaces are obtained by matching the two meshes' vertices via the TPS‐RPM algorithm, and the deformation vector fields (DVFs) characteristic of this deformation is estimated by B‐spline approximation. Numerically, the algorithm is quantitatively compared with the Demons algorithm using five clinical cervical cancer cases by several metrics: vertex‐to‐vertex distance (VVD), Hausdorff distance (HD), percent error (PE), and conformity index (CI). Experimentally, the algorithm is validated on a balloon phantom with 12 surface fiducial markers. The balloon is inflated with different amount of water, and the displacement of fiducial markers is benchmarked as ground truth to study TPS‐RPM calculated DVFs' accuracy.Results:In numerical evaluation, the mean VVD is 3.7(±2.0) mm after Demons, and 1.3(±0.9) mm after TPS‐RPM. The mean HD is 14.4 mm after Demons, and 5.3mm after TPS‐RPM. The mean PE is 101.7% after Demons and decreases to 18.7% after TPS‐RPM. The mean CI is 0.63 after Demons, and increases to 0.90 after TPS‐RPM. In the phantom study, the mean Euclidean distance of the fiducials is 7.4±3.0mm and 4.2±1.8mm after Demons and TPS‐RPM, respectively.Conclusions:The bladder wall deformation is more accurate using the feature‐based TPS‐RPM algorithm than the intensity‐based Demons algorithm, indicating that TPS‐RPM has the potential for accurate bladder dose deformation and dose summation for multi‐fractional cervical HDR brachytherapy.This work is supported in part by the National Natural ScienceFoundation of China (no 30970866 and no 81301940).

SU-E-T-699: Dosimetric Evaluation of Tandem-Based Cervical HDR Brachytherapy Treatment Planning Using ABS 2011 Recommendations

Purpose: This study evaluated dosimetric parameters for cervical HDR brachytherapy treatment using varying dose prescription methods. Methods: We evaluated 20 unique tandem‐based cervical HDR brachytherapy treatment plans. Radiotherapy dose was originally prescribed to a defined point (Point A, ICRU‐report 38) for all plans. For this study, tumor volumes (HR‐CTV) and organs at risk (OAR) were retrospectively delineated on the original 3D treatment planning CT datasets by the original treating physicians. We also carefully redefined the dose prescription point using ABS 2011 criteria. The coverage index (V100) for each HR‐CTV was calculated using DVH parameters. A plot between HR‐CTV volume (V) and V100 was generated using the best fit linear regression line (least‐square fit analysis). Results: Mean prescribed dose to Point A (average of Rt and Lt point A doses) was 590.47 cGy ± 28.65cGy (range 499.10–612.45cGy; 95%CI 586.73–594.22cGy). Mean prescribed dose to ABS 2011 point A (average of Rt and Lt points) was 593.35 cGy ± 30.42cGyrange 501.00–625.50cGy; 95%CI 589.38–597.32cGy). There was no statistically significant difference between the original planned point A and new calculated ABS point A doses (p=0.23, paired t‐student test). The plot between V and V100 was well defined and was described by the best fit linear regression line: V100= −0.0064V+1.0858, with correlation coefficient of 0.9519. Therefore, as V increases the coverage index decreases: when V 95%; when V>20cc and 29cc, V100<90%. Conclusion: For cervical HDR brachytherapy, dose prescription to an arbitrarily defined point (e.g., point A) does not provide consistent coverage of HR‐CTV. The difference in coverage between the two dose prescription approaches increases with increasing CTV volume. Our ongoing work evaluates the dosimetric consequences of volumetric dose prescription approaches for these patients.

SU‐E‐T‐461: Cervical HDR Optimization Using Oncentra Masterplan's IPSA Algorithm

Purpose: Traditionally, cervical HDR planning was done using standard loading techniques, and prescription points defined in 2D. Currently, widespread availability of 3D imaging allows for structure contouring, inverse plan optimization, and structure based dose prescriptions. However, many institutions still use traditional techniques for some portion of HDR planning. The goal of this research is to compare inverse‐optimized plans with structure based dose prescriptions, to forward‐optimized plans with point A based prescriptions. Methods: 41 clinical cervical HDR plans (12 patients), originally optimized using forward‐planning techniques, were retrospectively optimized using Oncentra MasterPlans (Nucletron, Veenendal, the Netherlands) inverse planning simulated annealing (IPSA) algorithm. Dose objectives for the high risk CTV (HRCTV) and Organs at risk (OARs) were used in the inverse optimization. The inverse optimization plans were normalized to match the HRCTV D90 dose with their forward‐planned counterparts. For each plan, the following values were recorded: the dose to Point A, D90 for intermediate risk CTV (IRCTV); D2cc, D0. 1cc for OARs (rectum, bladder, sigmoid colon, small bowel) and total treatment time. Results: Inverse optimization changed the dose to point A and IRCTV D90 by −12.77+/−32.86% and −17.17+/−31.52%, respectively. Changes in the OARs [D2cc, D0.1cc] were: [−15.89+/−27.10%,−12.87 +/− 31.40%] for rectum, [−14.88+/−23.70%, −11.50+/−27.69%] for bladder, [− 18.32+/−38.81%, −17.52+/−41.35%] for sigmoid colon, and [−24.10+/− 36.61%,−22.47+/−39.64%] for small bowel. The treatment time changed by — 25.49 +/−24.44%. Conclusion: On average, the IPSA optimized plans decreased the dose to the IRCTV, point A, and OARs. However, the large standard deviations in the dosimetric changes indicate that the performance of the IPSA optimization is highly case dependent. Further IPSA studies are needed to determine whether dose can be increased to IRCTV and point A, while maintaining OAR sparing.

Prospective Study of Cervical HDR Brachytherapy with Intra-operative Ultrasound Guidance

Prospective Study of Cervical HDR Brachytherapy with Intra-operative Ultrasound Guidance