Rectal Point Dose Research Articles

Quality Metric to Assess Adequacy of Hydrogel Rectal Spacer Placement for Prostate Radiation Therapy and Association of Metric Score With Rectal Toxicity Outcomes

Although hydrogel spacer placement (HSP) minimizes rectal dose during prostate cancer radiation therapy, its potential benefit for modulating rectal toxicity could depend on the achieved prostate-rectal separation. We therefore developed a quality metric associated with rectal dose reduction and late rectal toxicity among patients treated with prostate stereotactic body radiation therapy (SBRT). A quality metric consisting of prostate-rectal interspace measurements from axial T2-weighted magnetic resonance imaging simulation images was applied to 42 men enrolled in a multi-institutional phase 2 study using HSP with prostate SBRT (45 Gy in 5 fractions). A score of 0, 1, or 2 was assigned to a prostate-rectal interspace measurement of <0.3 cm, 0.3 to 0.9 cm, or ≥1 cm, respectively. An overall spacer quality score (SQS) was computed from individual scores at rectal midline and ±1 cm laterally, located at the prostate base, midgland, and apex. Associations of SQS with rectal dosimetry and late toxicity were evaluated. The majority of the analyzed cohort had an SQS of 1 (n=17; 41%) or 2 (n=18; 43%). SQS was associated with maximum rectal point dose (rectal Dmax; P=.002), maximum dose to 1 cc of rectum (D1cc; P=.004), and volume of rectum receiving ≥100% of prescription dose (V45; P=.046) and ≥40 Gy (V40; P=.005). SQS was also associated with a higher incidence of (P=.01) and highest-graded late rectal toxicity (P=.01). Among the 20 men who developed late grade ≥1 rectal toxicity, 57%, 71%, and 22% had an SQS of 0, 1, and 2, respectively. Men with an SQS of 0 or 1 compared with 2 had 4.67-fold (95% CI, 0.72-30.11) or 8.40-fold (95% CI, 1.83-38.57) greater odds, respectively, of developing late rectal toxicity. We developed a reliable and informative metric for assessing HSP, which appears to be associated with rectal dosimetry and late rectal toxicity after prostate SBRT.

Dosimetric Impact of Perirectal Hydrogel Spacer for Focal Intraprostatic Lesion Ablative Microboost: Which Patients Benefit?

<h3>Purpose/Objective(s)</h3> Recent trials have demonstrated a benefit in biochemical free survival with focal ablative microboost (FAM) to the dominant intraprostatic lesion (DIL) in localized prostate cancer (LPC). Full DIL coverage was not always achieved due to prioritization of organs at risk. A dosimetric study was conducted to characterize the advantage of iodinated hydrogel (HG) spacer placement based on lesion location in both the IMRT and SBRT setting. <h3>Materials/Methods</h3> Ten prostate patients with pre- and post- HG placement imaging were evaluated. A GU-radiologist delineated all DILs on post-HG placement MRIs. IMRT (77-95 Gy/35 fx) and SBRT (36.25-40-50 Gy/5 fx) plans were generated on both pre- and post-HG imaging, with and without urethral constraints. Normal tissue constraints were utilized from prior randomized trials. Full coverage of the DIL was defined as D95 and V95 ≥95% of volume. Additional plans with theoretical DILs in varying positions throughout the prostate were created to develop a generalized model of HG benefit for FAM radiotherapy. The model was then applied to 125 patients with biopsy-confirmed DILs from the Prostate-MRI-US-Biopsy (PMUB) dataset to better approximate the real-world benefit of HG placement. <h3>Results</h3> The mean prostate-rectal separation with HG placement at mid prostate was 12.8 mm (<i>SD</i> 2.85). The mean lesion size was 9 mm (range 4.3-14.8). There were no post-operative complications from HG placement. In the majority of patients both pre- and post-HG plans were able to achieve pre-specified dose-constraints for both SBRT and IMRT plans. In two patients (20%), full coverage of the DIL was not able to be achieved until after HG placement due to proximity of the rectum for both SBRT and IMRT. Post-HG plans had lower maximum rectal point dose, D0.1cc, and achieved significant reduction of D1cc to the rectum for SBRT (<i>p</i>=0.045) and IMRT (<i>p</i>=0.015). In the model, DIL coverage was compromised when the DIL was located within 1.5 mm of the urethra, 2.0 mm of the rectum or 1.5 mm of the bladder. In the PMUB dataset, an estimated 32 (25.6%) patients could potentially benefit from HG placement to improve DIL coverage if planned for FAM with either SBRT or IMRT. <h3>Conclusion</h3> We developed a model to assess the benefit of HG spacer for FAM in LPC. Our data suggest HG spacer placement may provide benefit in improving DIL coverage for select patients, typically for LPC with DILs that are within 2.0 mm of the posterior prostate-rectum interface. The majority of prostate patients do not require HG placement to achieve both full DIL coverage and standard dose constraints.

A comparison of dosimetric parameters in high-dose-rate intracavitary brachytherapy using tandem and ring applicators: is the combination of a rectal retractor and radio-opaque vaginal packing better than rectal retractor alone for rectum sparing in cervical cancer?

PurposeTo describe a novel packing technique of combining radio-opaque vaginal packing (VP) with rectal retractor (RR) blade to displace rectum and to compare the standard International Commission on Radiation Units & Measurements-38 (ICRU-38) rectal, bladder point doses and volume parameters with the conventional technique of using RR alone with tandem and ring (T&R) applicators in high-dose-rate (HDR) intracavitary brachytherapy (ICB) for cervical cancer.Materials and methodsA retrospective analysis of the treatment plans of a cohort of 24 consecutively treated patients with locally advanced cervical cancer was performed. All patients received external beam radiotherapy with a dose of 45–50.4 Gy, in fractions of 1.8–2 Gy, to the whole pelvis with concurrent weekly chemotherapy, followed by HDR-ICB. The treatment plans for each brachytherapy session using T&R applicators that these patients received were included for analysis. A total of 17 treatment plans in which the combination of RR and radio-opaque VP was used for rectum separation were included in the combination (RR+VP) group, and 21 treatment plans in which a RR alone was used were included in the conventional (RR) group.ResultsThe mean dose to the ICRU rectal point was 39.7% of the point A dose (range, 28.8%–50.4%; median 38.6%) in the RR+VP group and 52.7% (range, 46.9%–63.6%; median 51.7%) in the RR group. This 13% reduction in the mean dose to the ICRU rectal point was statistically significant (p = 0.001). The mean dose to the ICRU bladder point was 55.4% of the point A dose (range, 26.3%–73.6%; median 57.4%) in the RR+VP group and 45.3% (range, 23.7%–72.7%; median 46.9%) in the RR group. This 10.1% increase in the mean dose to the ICRU bladder point was also significant (p = 0.024). The other point dose and volume parameters were similar between groups.ConclusionCompared to the conventional use of a RR blade alone for rectum separation, combining a RR blade with radio-opaque VP significantly reduced the ICRU rectal point dose.

Quality Metric to Assess Adequacy of Hydrogel Rectal Spacer Placement for Prostate Radiotherapy and Association of Metric Score With Dosimetric and Gastrointestinal Toxicity Outcomes

<h3>Purpose/Objective(s)</h3> Hydrogel rectal spacer placement (HSP) has been shown to minimize rectal dose during prostate cancer radiotherapy, yet its potential benefit for modulating rectal toxicity could in large part depend upon the quality of prostate-rectal separation achieved from HSP. We therefore developed a practical quality metric to evaluate HSP, validating its association with rectal dose reduction, as well as physician- and patient-reported rectal toxicity using a prospective dataset of men treated with prostate stereotactic body radiotherapy (SBRT). <h3>Materials/Methods</h3> Using the axial T2-weighted MRI images from a small pilot cohort of men with HSP who had been treated at our institution with prostate SBRT, a hydrogel spacer quality metric was devised from prostate-rectal space thickness (PRST) measurements. A score of 0, 1, or 2 was assigned to a PRST of < 0.3 cm, 0.3-0.9 cm, or ≥1 cm, respectively; an overall spacer quality score (SQS) was computed from individual scores (total of 9) at rectal midline and 1 cm to the right and left, located at the level of the prostate base, midgland, and apex. This quality metric was then applied to MRI simulation scans of 43 men with low/intermediate risk prostate cancer who had been enrolled on a multi-institutional phase II study to assess safety and efficacy of HSP during prostate SBRT. Associations between SQS and rectal dosimetry, late gastrointestinal (GI) toxicity, and EPIC bowel quality of life were quantified in these men treated with 45 Gy in 5 fractions. <h3>Results</h3> Among this cohort, the majority had a SQS of 1 (n = 18; 42%) or 2 (n = 18; 42%). SQS was associated with maximum rectal point dose (rectal Dmax; <i>P</i> = 0.001), maximum dose to 1 cc of rectum (D1cc; <i>P</i> = 0.003), and volume of rectum receiving ≥100% of prescription dose (V45; <i>P</i> = 0.03). For those with SQSs of 0, 1 and 2, the median rectal Dmax (cGy) was 4683, 4600, and 3921, respectively. SQS was associated with incidence of late GI toxicity (<i>P</i> = 0.03) and highest late GI toxicity score (<i>P</i> = 0.02). Among the 20 men who developed late GI toxicity, 57%, 67% and 22% with Grade ≥1 had a SQS of 0, 1, and 2, respectively. Men with SQSs of 2 compared to 0-1 had 1.36 times lower odds of an increased rectal Dmax (95% CI: 1.14-1.63); and 1.20 times lower odds of an increased rectal D1cc (95% CI: 1.07-1.34). Men with SQSs of 2 versus 0-1 had 3.30 times lower odds of a higher late GI toxicity score (95% CI: 1.18-9.28). While evidence of a significant difference in baseline EPIC bowel summary score between SQSs was not observed (<i>P</i> = 0.07) as expected, men with SQSs of 2 compared to 0-1 had 3.52 times higher odds (95% CI: 0.91-13.64) of a superior bowel summary score 12 months from prostate SBRT. <h3>Conclusion</h3> We developed a reliable, easy to use, and informative metric for assessing HSP, which appears to be associated with rectal dosimetry and late GI toxicity in men treated with prostate SBRT.

Comparison of ICRU 38 rectal reference point dose estimates with measured dose in vivo in cobalt-60 HDR brachytherapy for cervical cancer

The objective of this study was to compare the ICRU 38 calculated rectal dose with in vivo dosimetry measured doses in cobalt-60 HDR brachytherapy for cervical cancer. A total of 48 brachytherapy insertions done on 15 patients treated from January to March 2017 at our institution were included in this prospective cross-sectional study. The results demonstrated no significant difference between the computed ICRU rectal point dose and in vivo maximum measured rectal dose ((r) 0.6208, p < 0.0001 [S]; t test p = 0.1578 [NS] 95% CI − 0.78 to 0.46), but a significant difference between ICRU rectal point and in vivo mean measured rectal dose ((r) 0.6033, p < 0.0001 [S]; t test p < 0.0001 [S] 95% CI − 0.81 to 0.35). These findings were seen even when sub-analyzed for the two used fraction sizes of 7 Gy and 8 Gy. The results also showed no significant differences in the maximum ((r) 0.9029, p < 0.0001 [S]; t test p = 0.2576 [NS], 95% CI − 0.21 to 0.06) and mean ((r) 0.9766, p < 0.0001 [S]; t test p = 0.2786 [NS], 95% CI − 0.93 to 0.03) doses taken from treatment planning system assigned dose points coinciding with the imaged probes of the in vivo dosimeter. Overall, this study was able to provide additional evidence that in vivo dosimetry can be validly used in the clinical setting to estimate the dose to the rectum during Co-60 HDR brachytherapy. Use of this technique allows for an additional quality assurance method that can contribute to reductions of errors in dose delivery.

Analysis of Volumetric Dosimetry of Target Volumes and Organs at Risk on ICRU Point-Based Dose Planning in CT-Guided HDR Intracavitary Brachytherapy to Carcinoma Cervix

Intracavitary brachytherapy (ICBT) has been historically planned based on orthogonal X-rays with point A as prescription point and surrogate rectal and bladder points to determine the approximate dose to organs at risk. This was standardized based on ICRU report 38. However, with the availability of better imaging modalities (CT, MRI), it became obvious that those points were poor surrogates for the tumor or the organ at risk. The current study analyzes the volumetric dose distribution to tumor volume and risk organs, from CT image-guided point-based planning done for intracavitary high-dose-rate brachytherapy using Fletcher–Suit–Delclos applicator in locally advanced carcinoma cervix patients. Fifty-one patients with locally advanced carcinoma cervix who were treated with ICBT were included. Point A-based dose planning was done based on CT images, on Oncentra™ treatment planning software. The doses to bladder point and rectal point were determined and were used for the purpose of dose prescription and optimization. Relevant target volumes and risk organ volumes were determined over the same plans, and dose measurements are taken. They were then analyzed for correlation and linear regression model using IBM SPSS Statistics version 23. The point A-based prescription dose did not adequately cover the target volume. CTV 90 obtained only 53.23% (95% CI 49.21–57.25) of the prescribed dose. The bladder point dose correlated well with all sub-volumes, especially D2cc bladder dose (r = 0.525, p = < 0.001). It satisfied linear regression model with standardized beta of 0.665. On the contrary, the correlation with rectal point and D2cc rectal dose was not strong (r = 0.284, p = 0.055). The point-based dose underestimates bladder dose by 18.24 ± 7.77% and overestimates rectal dose by 5.46 ± 4.55%, both being statistically significant. CT image-guided point A-based dose planning, without any volume-based optimization, has poor target volume coverage. There is disproportionate overestimation of dose to rectum and rectal wall while calculating from rectal point dose. The bladder point dose has good mathematical prediction for dose to bladder. However, volumetrically, it underestimates the actual dose. While point A-based planning on tomographic imaging can be a stepping stone toward image-guided brachytherapy, volume-based planning is necessary for optimizing the dose to primary tumor and managing risk organ dose properly.

Assessment of cartesian co-ordinates-based bladder and rectal dose and variability with tandem-ring angles first Nigerian experience in high-dose-rate brachytherapy.

This study assessed bladder and rectal dose based on Cartesian-coordinates in intracavitary brachytherapy and examined the variations resulting from use of tandem-ring (T-R) of different angles. Cartesian-co-ordinates of bladder and rectum points were derived on orthogonal-radiographs of 90 patients who had high-dose-rate brachytherapy for cervical cancer at the Department of Radiation Oncology, University College Hospital, Ibadan, Nigeria. The patients were classified in three groups of 30, based on T-R angles 30°, 45° and 60° used, bearing same lengths and diameters across sets. The measured co-ordinates and the related percentage doses to points of interest in the two organs were analysed using EViews and SPSS statistical softwares. The mean rectal point dose (RPD) obtained was 68.97 ± 13.57 % of the prescribed doses as against 56.57 ± 11.83% for bladder point dose. While the maximums of the mean RPD were 95.7, 90.5 and 82.5% for T-R angles 30°, 45° and 60° respectively; corresponding values for the bladder point were 72.8, 87.8 and 62.3%. The baseline data obtained in this study served as guidelines for subsequently achieving acceptable values of bladder point dose and RPD at University College Hospital, Nigeria. Special attention should be paid to the application of 2 cm-tandems in relation to the RPD. This is one of the few studies assessing the influence of T-R angles on organs-at-risk. The increase in RPD with the use of intrauterine tandem-2 cm is found to be most pronounced with T-R 300, and this trend reduced with larger angles.

Comparison between DVH-based doses and ICRU point-based doses to the rectum and the bladder using CT-based high-dose rate brachytherapy to the cervix

Traditionally, doses to the bladder and the rectum were quantified using the bladder and rectal reference points defined by the International Commission on Radiation Units and Measurements (ICRU) in Report No. 38. In this study, we compared the 0.1-, 1.0-, 2.0-cc doses to the bladder and the rectum with the corresponding ICRU point doses using computed tomography (CT)-based planning in the intracavitary brachytherapy of carcinoma of the cervix. CT datasets of 136 consecutive intracavitary brachytherapy insertions between January and May 2015 were analyzed. The bladder and the rectum were contoured on consecutive CT slices as per Groupe Europeen de Curietherapie and the European Socie Ty for Radiotherapy and Oncology recommendations. Dose volume histograms were generated and doses of 0.1, 1.0, and 2.0 cc to the bladder and the rectum were recorded. ICRU bladder and rectal points were identified in the treatment plan. Mean doses of 0.1, 1.0, and 2.0 cc to the bladder was found to be 2.02, 1.57, and 1.35 times the ICRU point dose, respectively. The maximum dose received by the bladder was found to be 5.83 times the average ICRU point dose. Mean doses of 0.1, 1.0, and 2.0 cc to the rectum were found to be 1.12, 0.90, and 0.78 times the ICRU rectal point dose, respectively. The maximum dose received by the rectum was 4.79 times the average ICRU point dose. The Pearson correlation coefficient value (r) was found to be 0.639 for D2cc and ICRU bladder point values. The Pearson correlation coefficient value was found to be 0.752 for D2cc and ICRU rectal point values. Our results show that the ICRU bladder points underestimated the dose to the bladder, which is in agreement with other studies. ICRU rectal point doses were higher than the corresponding D2cc doses. However, there was a good correlation between D2cc and ICRU point doses for both the bladder and the rectum.

Comparative assessment of late toxicity in patients of carcinoma cervix treated by radiotherapy versus chemo-radiotherapy – Minimum 5 years follow up

BackgroundA randomised trial was carried out comparing chemo-radiation (CTRT) vs. radiotherapy (RT) in patients of carcinoma cervix and showed similar rates of pelvic disease control, disease free survival and overall survival. Late toxicity is presented. MethodsBetween December 2000 and July 2006, 180 patients of carcinoma cervix were randomly assigned to RT + weekly cisplatin (n = 94) or RT alone (n = 86). Late toxicity was prospectively scored using RTOG criteria in 156 evaluable patients, 79 and 77 respectively and is presented as crude incidence for rectum, bladder, small intestine, vagina, skin and bone and also as actuarial incidence for rectum and bladder. ResultsThe median follow up of surviving patients was 10.4 years (minimum – 6.5 years). Crude incidence, CTRT vs. RT, of late toxicities were: rectal (7.5% vs. 5%, p = 0.22), bladder (15% vs. 10.4%, p = 0.76), small bowel (3% vs. 1.2%, p = 0.51), vagina (25% vs. 35%, p = 0.35) while the actuarial risk of grades 3–5 rectal and bladder toxicities by 5 years were 13% vs. 10% (p = 0.698) and 16% vs. 14.8% (p = 0.783) respectively. Bladder toxicity appeared later then rectal toxicity (median 49.4 vs. 21.4 months). Severe bone toxicity (fractures) were higher in the CTRT arm, 5% vs. 0%, p = 0.018. On multivariate analysis vaginal involvement (p = 0.016) and bulky tumor (p = 0.020) were associated with severe vaginal morbidity while rectal point dose > 80% (p = 0.040) was associated with a higher incidence of rectal toxicity. ConclusionBone toxicity was significantly increased by addition of CT to RT and patients continued to experience toxicity at longer periods of follow up albeit disease free.

Image-Guided High-Dose Rate Brachytherapy in Cervix Carcinoma Using Balloon Catheter and Belt Immobilization System.

The efficacy of image-guided high-dose rate brachytherapy for cervical cancer is limited by the ineffective rectal sparing devices available commercially and the potential applicator movement. We developed a novel device using a balloon catheter and a belt immobilization system, serving for rectal dose reduction and applicator immobilization purposes, respectively. The balloon catheter is constructed by gluing a short inflatable tube to a long regular open-end catheter. Contrast agent (10) cm3 is injected into the inflatable end, which is affixed to the tandem and ring applicator, to displace the posterior vaginal wall. The belt immobilization system consists of a specially designed bracket that can hold and fix itself to the applicator, a diaper-like Velcro fastener package used for connecting the patient's pelvis to the bracket, and a buckle that holds the fasteners to stabilize the whole system. The treatment data for 21 patients with cervical cancer using both balloon catheter and belt immobilization system were retrospectively analyzed. Computed tomography and magnetic resonance images, acquired about 30 minutes apart, were registered to evaluate the effectiveness of the immobilization system. In comparison with a virtual rectal blade, the balloon decreased the rectal point dose by 34% ± 4.2% (from 276 ± 57 to 182 ± 38 cGy), corresponding to an extra sparing distance of 7.9 ± 1.1 mm. The maximum sparing distance variation per patient is 1.4 ± 0.6 mm, indicating the high interfractional reproducibility for rectum sparing. With the immobilization system, the mean translational and rotational displacements of the applicator set are <3 mm and <1.5°, respectively, in all directions. The rectal balloon provides significant dose reduction to the rectum and it may potentially minimize patient discomfort. The immobilization system permits almost no movement of the applicator during treatment. This work has the potential to be promoted as a standardized solution for high-dose rate treatment of cervical cancer.

Comparison Study of the Measured Rectal Point Dose by Detector In Vivo and the Recommended Point Dose of Rectum in Brachytherapy of Cervical Cancer

To explore the difference and the relevance of the measured rectal point dose by detector in vivo and the recommended point dose of rectum to estimate radiation doses to rectum in patients with cervical cancer treated with 3-dimensional (3D) brachytherapy. Between January 2012 and December 2014, 150 cervix cancer patients (320 person-time) in our hospital who were treated with radical radiation therapy (RT) combined with the high-dose-rate (HDR) brachytherapy after external beam RT (EBRT) for total dose of 45 to 50 Gy in 25 fractions were analyzed. The computed tomography (CT)-based and ultrasound-guided 3D brachytherapy was performed using an applicator with 112 cases for interstitial combined with intracavity brachytherapy and 38 cases for intracavity only. The prescribed dose of brachytherapy was 7 Gy in 3 to 4 fractions. The reference point of rectal dose recommended by the International ICRU Report 38 (DICRU), the rectal D2cc values recommended by the GEC-ESTRO, the measured rectal point dose in vivo by an IDF1-3G detector (P), which were inserted into the rectum at the level of ICRU reference point and the calculated dose of the same point on the detector in planning system (P1) were recorded for all individual fractions respectively as indicators for the rectal dose evaluation. The features and the relevance of these indicators were determined by the paired t test and Pearson test. The P value was 3.48±0.68 Gy, it was higher than P1 (3.25±0.69 Gy) in the same point (P<.05). Both the P and P1 were significantly lower than the DICRU (3.71±0.62 Gy) and the D2cc (3.87±0.68 Gy). Moreover, the P value has a high relationship with the DICRU (P=.000; correlation coefficient=0.722), but not with D2cc (P=.002; correlation coefficient=0.284). The rectal point dose determined with the use of rectal detector in vivo has a big deviation with the same point in planning system, and it underestimated the rectal dose comparing with the DICRU and D2cc. Therefore, we did not recommend it as a perfect indicator for rectal dose evaluation for treatment planning. However, we argued that it is a good method in monitoring the real-time rectal dose for quality control and quality assurance during brachytherapy.

English

Conventional two-dimensional (2D) treatment planning of intracavitary brachytherapy is still a common practice at the radiotherapy center. The purpose of this study was to evaluate the organ at risk (OAR) doses estimated based on International Commission on Radiation Units and Measurements (ICRU) reference-point in patients with cervical cancer treated with high-dose-rate (HDR) intracavitary brachytherapy (ICBT). Between January 2010 and April 2014, 21 cervical cancer patients were treated with 42 fractions of brachytherapy using tandem and ovoids and underwent post-implant two-dimensional (2D) radiograph scans. HDR brachytherapy was delivered to a dose of 18 Gy in two fractions. Using the Oncentra brachytherapy treatment planning system (BTPS) software version 4.1 (Nucletron, Netherlands), the bladder and rectum points were retrospectively reconstructed based on 42 orthogonal radiographs datasets. The ICRU bladder and rectum point doses were recorded. As for results, the mean percentage dose of rectum and bladder for selected patients treated with intracavitary brachytherapy treatment (ICBT) were 47.27 and 75.59%, respectively. Combinations of ovoid’s size, length of tandem and anatomy variation between each patient were factors that affected the dose to the OAR. Therefore, the ICRU reference points can still be used with the 2D brachytherapy treatment planning in evaluating the OAR doses.

Dosimetric Comparison of Fixed and Flexible Geometry ICRT Applicators in Patients Treated for Carcinoma Cervix

In intracavitary radiotherapy (ICRT) for cancer cervix, applicator geometry has the potential to impact the doses to organs at risk (OARs) and the coverage of the target volume. At our centre two Varian made Fletcher-style applicator sets, namely defined (fixed) geometry and flexible geometry, are used for ICRT. In the present work, the two types of applicators were compared dosimetrically as per the recommendations of the International Commission on Radiation Units and Measurements (ICRU-38) while delivering high dose rate brachytherapy. Twenty four patients who underwent ICRT were considered for this study. Radiographic method was used for treatment planning on Abacus planning system. ICRU-38 recommended parameters were estimated and compared. Flexible geometry applicator showed 8.8% and 16% higher bladder and rectum point doses as compared to the fixed geometry one but the difference was statistically not significant. The thickness of the pear-shaped isodose volume was larger for the flexible geometry implant also indicating towards higher doses to OARs. The higher bladder and rectum point doses in the case of flexible applicator will need to be validated by a larger data set.

Bladder and rectum dose estimations on digitized radiographs for vaginal brachytherapy after hysterectomy.

The purpose of this study was to evaluate the feasibility of assessing bladder and rectal point doses, using orthogonal radiographs without treatment planning, for vaginal cylinder applicator (VC), high‐dose‐rate (HDR) vaginal cuff brachytherapy (BT) after hysterectomy. Thirty‐three VC HDR BT treatment plans from 31 postoperative endometrial cancer patients were retrospectively analyzed. Single‐channel VC with four differing diameters — 2.0 cm, 2.3 cm, 2.6 cm, and 3.0 cm — were analyzed. Dose‐distance modeling was performed to estimate bladder and rectal point doses by measuring distances on each orthogonal radiograph without treatment planning. The estimated doses were then compared with doses calculated on treatment planning system (TPS). Their percent (%) dose differences were recorded. Analysis was performed for each VC size, ICRU bladder and rectal points, and the closest rectal point. The estimated doses obtained from dose‐distance modeling displayed on average less than 2.5% difference when compared with TPS doses at ICRU bladder and rectal points for each VC size. Dose percent differences between estimated values and TPS values were on average 1.9% and 2.5% for ICRU bladder and rectal point, respectively, regardless of VC sizes. Dose‐distance modeling for closest rectal point presented on average 5.4% dose difference when compared with TPS values of all VC sizes. It was feasible to estimate rectal and bladder point doses by measuring distances on orthogonal radiographs without treatment planning. Percent dose differences were 2.5% less for both ICRU bladder and rectal points, regardless of VC sizes. The use of closest rectal point is not recommended for estimating rectal dose.PACS number: 87.53.‐j, 87.53.Jw, 87.55.‐x, 87.55.D‐, 87.55dk

Assessing the Need for Dose Calculations to Organs at Risk Using MRI Planning in Vaginal Brachytherapy

With the overall low morbidity of adjuvant vaginal brachytherapy (VB) and its relatively fixed geometry, the need for individual calculation of doses to organs at risk (OARs) such as the bladder and rectum has been questioned, and ICRU bladder and rectal point dose calculations have been previously recommended. Using T1 and T2-weighted MRI simulation scans during VB, we evaluated patient anatomic variability and doses to OARs. Nineteen MRI simulation scans from 9 endometrial cancer patients undergoing adjuvant VB were obtained. In this retrospective study, all cases were planned to treat the proximal 4cm of vagina to a total dose of 21 Gy in 3 fractions prescribed to 5mm. The urethra, bladder, rectum, and sigmoid were contoured and the minimum dose in Gy to the most exposed 0.1cc, 1cc, and 2cc of the organ (D0.1cc, D1cc, D2cc) and the ICRU 38 bladder and rectal points were calculated. Additionally, patient anatomic variability in relation to OARs was assessed. The mean D2cc to the bladder, sigmoid, and rectum per 7Gy treatment fraction prescribed to 5mm were 5.6 Gy (3.3 - 7.32 Gy), 2.4 Gy (0.6 - 5.9 Gy), and 6.0 Gy (4.1 - 7.1 Gy), respectively. The mean D0.1cc to the urethra was 5.2 Gy (2.0 - 7.7 Gy). MRI scans revealed that significant variability can exist in the dose to the sigmoid colon, especially when positioned superiorly at the apex of the vaginal cylinder. Due to the anatomy of the internal urethral sphincter, the urethra deviates from the bowel at the location of the vaginal vault. However, even when treating the proximal 4cm of the vagina, the D0.1cc urethra exceeds 75% and 100% of the prescription dose in 36.8% and 15.8% of cases, respectively. The bladder and rectal ICRU points underestimated D0.1cc to their respective structures by more than 10% of the prescription dose in 68.4% and 78.9% of cases, respectively. An initial MRI simulation scan may guide VB treatment regarding vaginal length and prescription (surface or 5mm) relative to the location of critical structures. In cases when bowel is located above the vaginal apex, or the urethral point dose approaches the prescription dose, a more prolonged treatment course and prescription to the vaginal surface can be considered. Based on this study, it appears that the ICRU bladder and rectum points underestimate the dose to 0.1cc of the organ by greater than 10% of the prescription dose in most cases.

Comparative analysis of rectal dose parameters in image-guided high-dose-rate brachytherapy for cervical cancer with and without a rectal retractor

The objective of this study was to determine if use of a rectal retractor (RR) in high-dose-rate intracavitary brachytherapy for cervical cancer reduces rectal dose parameters. We reviewed data obtained from patients treated with intracavitary brachytherapy for cervical cancer with and without an RR. Treatment plans for each brachytherapy fraction were separated into two groups; R group with use of an RR and P group with use of vaginal packing. Dose-volume parameters for high-risk clinical target volume (HR-CTV), rectum, sigmoid, small bowel, and vaginal surface were collected for each fraction. Rectal D2cc and International Commission on Radiation Units & Measurements (ICRU) rectal point doses were compared between groups using Student's t tests. Predictors of higher rectal D2cc were determined by univariate and multivariate regression analyses. Four hundred sixty-three brachytherapy fractions from 114 patients were used for analysis, 377 fractions with a RR (R group) and 86 with vaginal packing only (P group). Bothgroups were similar except for slightly higher mean HR-CTV and mean bladder volume in P group. Both mean ICRU rectal point dose (241.1 vs. 269.9cGy, p= 0.006) and rectal D2cc (240.6 vs. 283.6cGy, p < 0.001) were significantly higher in P group. Point A dose, HR-CTV, stage, and use of an RR were significant predictors of rectal D2cc on multivariate analysis. Our data show that use of an RR leads to lower rectal dose parameters compared with vaginal packing. Further study is needed to determine if this will lead to less long-term toxicity.

The association of rectal equivalent dose in 2 Gy fractions (EQD2) to late rectal toxicity in locally advanced cervical cancer patients who were evaluated by rectosigmoidoscopy in Faculty of Medicine, Chiang Mai University.

PurposeTo evaluate association between equivalent dose in 2 Gy (EQD2) to rectal point dose and gastrointestinal toxicity from whole pelvic radiotherapy (WPRT) and intracavitary brachytherapy (ICBT) in cervical cancer patients who were evaluated by rectosigmoidoscopy in Faculty of Medicine, Chiang Mai University.Materials and MethodsRetrospective study was designed for the patients with locally advanced cervical cancer, treated by radical radiotherapy from 2004 to 2009 and were evaluated by rectosigmoidoscopy. The cumulative doses of WPRT and ICBT to the maximally rectal point were calculated to the EQD2 and evaluated the association of toxicities.ResultsThirty-nine patients were evaluated for late rectal toxicity. The mean cumulative dose in term of EQD2 to rectum was 64.2 Gy. Grade 1 toxicities were the most common findings. According to endoscopic exam, the most common toxicities were congested mucosa (36 patients) and telangiectasia (32 patients). In evaluation between rectal dose in EQD2 and toxicities, no association of cumulative rectal dose to rectal toxicity, except the association of cumulative rectal dose in EQD2 >65 Gy to late effects of normal tissue (LENT-SOMA) scale ≥ grade 2 (p = 0.022; odds ratio, 5.312; 95% confidence interval, 1.269-22.244).ConclusionThe cumulative rectal dose in EQD2 >65 Gy have association with ≥ grade 2 LENT-SOMA scale.

Dosimetric Comparison of Tandem and Ovoids Versus Tandem Alone Intracavitary Applicators for Treatment of Locally-Advanced Cervical Cancer

Standard therapy for locally advanced cervical cancer includes intracavitary brachytherapy. Tandem and ovoids (TO) are traditionally used in the US, but when the vaginal fornices are obliterated by tumor, ovoid placement is difficult. Practice patterns surveys in Canada reveal 9% of practitioners there use tandem only. This study compares the dosimetry of TO versus tandem (T) alone insertions with respect to the dose to ICRU points A, B, bladder and rectum, volumetric dose to bladder and rectum and volume of tissue receiving various dose gradients. One hundred eight brachytherapy cases from 27 women with stage II-IV cervical cancer were treated consecutively for cervical cancer with HDR brachytherapy with 4 applicator insertions. The prescribed dose of each insertion was 7 Gy to ICRU point A with additional goals of minimizing bladder and rectal doses. Patients were treated with either TO or T alone at physician discretion based on the clinical evaluation of the vaginal fornices at the time of the procedure. Parameters compared were ICRU point A and B doses, volume receiving 95%, 85%, 50%, and 20% of the prescription dose, ICRU bladder and rectal point doses, and maximal dose to 2 cc of bladder and rectum (D2 cc). The Mann-Whitney U test was used to compare these parameters. The mean dose to ICRU point A was not significantly different between the TO and T applicators, 681 cGy vs 670 cGy (p = 0.09). The mean dose to ICRU point B was significantly higher with the TO applicator than T alone, 200 Gy vs 177 cGy (p = 10-7). Dose distribution was different between the two applicators, with significantly increased volume receiving 95%, 85%, 50%, and 20% of the prescription dose using the TO applicator. The mean V95 was 109.5 cc for TO vs 96.4 cc for T (p = 0.001) and the mean V20 was 1041.7 cc for TO vs 923.9 cc for T (p = 0.009). There was no significant difference in ICRU rectal point doses between the applicators, 361.8 cGy TO vs 375.1 cGy T (p = 0.7). However, there were significantly increased doses to the ICRU bladder point, and D2 cc of the rectum and bladder with the T alone. The bladder point dose was 294.9 cGy TO vs 360.6 cGy T (p = 0.02), bladder D2 cc 403.7 cGy TO vs 632.7 cGy T (p = 0.001) and rectal D2 cc 289.7 cGy TO vs 224.8 cGy T (p = 0.01). TO and T applicator insertions for cervix brachytherapy provide equivalent doses to the ICRU point A, however, the volumetric distribution is significantly different between the 3 channel applicator and single channel tandem. The TO applicator provides increased volumetric dose within the patient, but allows better sparing of the rectum and bladder. In trained providers, T may be considered when the vaginal fornices prohibit appropriate placement of ovoid applicators to provide equivalent Point A doses.

The impact of body mass index on rectal dose in locally advanced cervical cancer treated with high-dose-rate brachytherapy

The impact of body mass index (BMI) on rectal dose in brachytherapy for cervical cancer is unknown. We assessed the association of BMI on rectal dose and lower gastrointestinal (GI) toxicity. Between 2007 and 2010, 51 patients with 97 brachytherapy planning images were reviewed. Volumetric measurements of the maximum percentage, mean percentage, dose to 2cc (D2cc), and dose to 1cc (D1cc) of the rectum, and the Internal Commission on Radiation Units and Measurement (ICRU) rectal point were recorded. Linear mixed effect models, analysis of variance, and regression analyses were used to determine the correlation between multiple observations or to detect a difference in the mean. The GI acute and late toxicity were prospectively recorded and retrospectively analyzed. The average BMI (kg/m(2)) was 27.7 with a range of 17.4-46.6. Among the patients, 8% were morbidly obese, 25% obese, 25% overweight, 40% normal weight, and 2% underweight. The mean D1cc, D2cc, mean rectal dose (%), maximum rectal dose (%), and ICRU rectum was 3.03Gy, 2.78Gy, 20%, 60%, and 2.99Gy, respectively. On multivariate analysis, there was a significant decrease in the D1cc and D2cc rectal dose (p=0.016), ICRU rectal point dose (p=0.022), and mean rectal dose percentage (p=0.021) with an increase in BMI. There was, however, no statistically significant relationship between BMI and GI toxicity. Obesity decreases the rectal dose given in high-dose-rate brachytherapy for locally advanced cervical cancer because of an increase in fatty tissue in the recto-uterine space. There is no significant correlation between BMI and acute or late GI toxicity.

Does Inability to Use Rectal Paddle Affect Rectal Dose Parameters in Tandem and Ring HDR Brachytherapy for Cervical Cancer?

PurposeIntracavitary (IC) HDR brachytherapy for cervical cancer can utilize many different methods to seperate normal tissues from the applicators. Most centres use a standard application approach. At BCCA Vancouver, a rectal paddle was used in a standard fashion to distance the rectal mucosa from the applicators. With this rectal paddle being recalled, 1 patient had treatment both with and without the rectal paddle. We wished to evaluate the effect of the recall of rectal paddle appartus on rectal DVH parameters hypothesizing that the rectal paddle would consiteantly lower rectal dose compared to other methods.Materials and MethodsDVH parameters and ICRU rectal dose point were measured for the rectum. This was compared between fractions.ResultsThe patient had stage 2b SCC of the cervix and received 5 IC brachytherapy treatments of 600cGy. She had 4 fractions of IC brachytherapy with a rectal paddle and 1 fraction with vaginal packing only. The mean rectal D2cc for the 4 fractions with a rectal paddle was 204 cGy and 254 cGy with packing only. This was 226 cGy and 204cGy for ICRU rectal point dose.ConclusionsThe data for this single patient seems to agree with our hypothesis for D2cc to the rectum. We cannot however say if this is a clinically relevant difference. We are planning a larger scale retrospective study of patients with vaginal packing vs the rectal paddle because of these findings to determine if there is benefit to use rectal paddle as a standard. PurposeIntracavitary (IC) HDR brachytherapy for cervical cancer can utilize many different methods to seperate normal tissues from the applicators. Most centres use a standard application approach. At BCCA Vancouver, a rectal paddle was used in a standard fashion to distance the rectal mucosa from the applicators. With this rectal paddle being recalled, 1 patient had treatment both with and without the rectal paddle. We wished to evaluate the effect of the recall of rectal paddle appartus on rectal DVH parameters hypothesizing that the rectal paddle would consiteantly lower rectal dose compared to other methods. Intracavitary (IC) HDR brachytherapy for cervical cancer can utilize many different methods to seperate normal tissues from the applicators. Most centres use a standard application approach. At BCCA Vancouver, a rectal paddle was used in a standard fashion to distance the rectal mucosa from the applicators. With this rectal paddle being recalled, 1 patient had treatment both with and without the rectal paddle. We wished to evaluate the effect of the recall of rectal paddle appartus on rectal DVH parameters hypothesizing that the rectal paddle would consiteantly lower rectal dose compared to other methods. Materials and MethodsDVH parameters and ICRU rectal dose point were measured for the rectum. This was compared between fractions. DVH parameters and ICRU rectal dose point were measured for the rectum. This was compared between fractions. ResultsThe patient had stage 2b SCC of the cervix and received 5 IC brachytherapy treatments of 600cGy. She had 4 fractions of IC brachytherapy with a rectal paddle and 1 fraction with vaginal packing only. The mean rectal D2cc for the 4 fractions with a rectal paddle was 204 cGy and 254 cGy with packing only. This was 226 cGy and 204cGy for ICRU rectal point dose. The patient had stage 2b SCC of the cervix and received 5 IC brachytherapy treatments of 600cGy. She had 4 fractions of IC brachytherapy with a rectal paddle and 1 fraction with vaginal packing only. The mean rectal D2cc for the 4 fractions with a rectal paddle was 204 cGy and 254 cGy with packing only. This was 226 cGy and 204cGy for ICRU rectal point dose. ConclusionsThe data for this single patient seems to agree with our hypothesis for D2cc to the rectum. We cannot however say if this is a clinically relevant difference. We are planning a larger scale retrospective study of patients with vaginal packing vs the rectal paddle because of these findings to determine if there is benefit to use rectal paddle as a standard. The data for this single patient seems to agree with our hypothesis for D2cc to the rectum. We cannot however say if this is a clinically relevant difference. We are planning a larger scale retrospective study of patients with vaginal packing vs the rectal paddle because of these findings to determine if there is benefit to use rectal paddle as a standard.