Relative Bladder Volume Research Articles

Individual lymph node position variation for rectal cancer patients treated with long course chemoradiotherapy

Background and purposeDelivery of high precision radiotherapy lymph node boosts requires detailed information on the interfraction positional variation of individual lymph nodes. In this study we characterized interfraction positional shifts of suspected malignant lymph nodes for rectal cancer patients receiving long course radiotherapy. Furthermore, we investigated parameters which could affect the magnitude of the position variation. Materials and MethodsFourteen patients from a prospective clinical imaging study with a total of 61 suspected malignant lymph nodes in the mesorectum, presacral, and lateral regions, were included. The primary gross tumor volume (GTVp) and all suspected malignant lymph nodes were delineated on six magnetic resonance imaging scans per patient. Positional variation was calculated as systematic and random errors, based on shifts of center-of-mass, and estimated relative to either bony structures or the GTVp using a hierarchical linear mixed model. ResultsDepending on location and direction, systematic and random variations (relative to bony structures) were within 0.6–2.8 mm and 0.6–2.9 mm, respectively. Systematic and random variations increased when evaluating position relative to GTVp (median increase of 0.6 mm and 0.5 mm, respectively). Correlations with scan time-point and relative bladder volume were found in some directions. ConclusionsUsing linear mixed modeling, we estimated systematic and random positional variation for suspected malignant lymph nodes in rectal cancer patients treated with long course radiotherapy. Statistically significant correlations of the magnitude of the lymph node shifts were found related to scan time-point and relative bladder volume.

Impact of head-down-tilt body position on abdomen resistance for urinary bladder monitory applications

Tissue electrical impedance (or bioimpedance) is a quantity related to the passive, frequency-dependent electrical properties of a biological tissue and is a promising modality for continuous monitoring of relative bladder volume and bladder activity. In this study, the impact of body position [specifically 6° head-down tilt (HDT)] intended to induce fluid redistribution and, therefore, result in a change in the electrical resistance of the abdomen is evaluated. The abdomen resistance (10 kHz–100 kHz) of nine healthy young adults was measured before and after 240 min in a 6° HDT position. Over this period, the resistance increase was not statistically significant even though the average bladder volume increased by 506 mL. It was expected that the abdomen resistance would decrease with an increase in bladder volume over this period. The masking of the expected resistance decrease is attributed to the shift in the fluid from the legs/abdomen to the neck/chest caused by the HDT body position over this period. Overall, this suggests that methods to differentiate bladder volume changes from other types of fluid shifts in the body are needed for resistance-based monitoring under free-living conditions.

Full daily re-optimization improves plan quality during online adaptive radiotherapy

Background and purposeDaily online treatment plan adaptation requires a fast workflow and planning process. Current online planning consists of adaptation of a predefined reference plan, which might be suboptimal in cases of large anatomic changes. The aim of this study was to investigate plan quality differences between the current online re-planning approach and a complete re-optimization. Material and methodsMagnetic resonance linear accelerator reference plans for ten prostate cancer patients were automatically generated using particle swarm optimization (PSO). Adapted plans were created for each fraction using (1) the current re-planning approach and (2) full PSO re-optimization and evaluated overall compliance with institutional dose-volume criteria compared to (3) clinically delivered fractions. Relative volume differences between reference and daily anatomy were assessed for planning target volumes (PTV60, PTV57.6), rectum and bladder and correlated with dose-volume results. ResultsThe PSO approach showed significantly higher adherence to dose-volume criteria than the reference approach and clinical fractions (p < 0.001). In 74 % of PSO plans at most one criterion failed compared to 56 % in the reference approach and 41 % in clinical plans. A fair correlation between PTV60 D98% and relative bladder volume change was observed for the reference approach. Bladder volume reductions larger than 50 % compared to the reference plan recurrently decreased PTV60 D98% below 56 Gy. ConclusionComplete re-optimization maintained target coverage and organs at risk sparing even after large anatomic variations. Re-planning based on daily magnetic resonance imaging was sufficient for small variations, while large variations led to decreasing target coverage and organ-at-risk sparing.

Improvement in bladder volume reproducibility using A-mode portable ultrasound bladder scanner in moderate-hypofractionated volumetric modulated arc therapy for prostate cancer patients.

PurposeThis study introduced an A‐mode portable ultrasound bladder scanner, the Lilium® α‐200 (here after Lilium; Lilium Otsuka, Kanagawa, Japan), for the treatment of prostate cancer patients with hypofractionated volumetric modulated arc therapy to improve the reproducibility of bladder volume (BV).Materials and methodsThirty patients were advised to maintain full BV prior to computed tomography (CT) simulation and daily treatment. Among these, the BV of 15 patients was measured using Lilium until a BV of 80% in the simulation was achieved (with the Lilium group). Daily cone‐beam CT (CBCT) was performed for treatment. The correlation between BV measured by CBCT and Lilium was assessed. The differences in the BV and dosimetric parameters of the bladder in the CBCT versus planning CT were compared between the groups with and without Lilium.ResultsThere was a significantly strong relationship (r = 0.796, p < 0.05) between the BVs measured using CBCT and Lilium. The relative BV ratios to simulation CT < 0.5 and > 2 were observed in 10.3% and 12.7%, respectively, of treatment sessions without Lilium group, while these ratios were 1% and 2.8%, respectively, in the Lilium group. The mean absolute difference in the range of V30Gy to V40Gy without Lilium sessions was significantly larger (p < 0.05) than that in the Lilium group.ConclusionThe use of the A‐mode portable ultrasound bladder scanner significantly improved the reproducibility of the BV, resulting in few variations in the dosimetric parameters for the bladder.

Evaluation of the ITV-margin and variables affecting bladder and mesorectal deformation during long course neoadjuvant radiotherapy for rectal cancer.

Internal target volume (ITV) margins were estimated by evaluating the movement of mesorectum and bladder during neoadjuvant long-course radiation therapy (RT) for rectal cancer. In this prospective study, 23 patients with rectal cancer had planning CT (pCT) and weekly cone beam CT (CBCT) in supine position during preoperative long-course RT. Mesorectal wall motion was analyzed based on the coordinates of the most anterior, posterior, left and right points on the pCT and CBCT. Overlap volume (OV) between the pCT bladder and CBCT mesorectum was generated. Variables that might affect relative bladder volume (ratio of CBCT to pCT bladder volumes), anterior mesorectal wall position, and OV were studied. ITV margins were also calculated. In females, smaller OV and less movement of the upper anterior mesorectal wall were identified, suggesting smaller ITV margins might be required compared to males. The relative bladder volume did not change significantly over time and was correlated with OV: the larger the relative bladder volume, the less the OV. ITV margin of 0.8 to 1.1 cm in right-left direction is satisfactory. Posteriorly, only 8 to 9 mm margin is required for upper and mid rectal regions but double of this is required for inferior third. Anteriorly, 1.3 cm margin is adequate for lower and mid rectal regions and 2.4 cm is required superiorly. An anisotropic ITV expansion of clinical target volume (CTV) for rectal cancer radiotherapy contouring provides a robust method to encompass the deformation of bladder and mesorectum. The ITV margin should take into account sex and distance from the anal verge.

Strict bladder filling and rectal emptying during prostate SBRT: Does it make a dosimetric or clinical difference?

BackgroundTo evaluate inter-fractional variations in bladder and rectum during prostate stereotactic body radiation therapy (SBRT) and determine dosimetric and clinical consequences.MethodsEighty-five patients with 510 computed tomography (CT) images were analyzed. Median prescription dose was 40 Gy in 5 fractions. Patients were instructed to maintain a full bladder and empty rectum prior to simulation and each treatment. A single reviewer delineated organs at risk (OARs) on the simulation (Sim-CT) and Cone Beam CTs (CBCT) for analyses.ResultsBladder and rectum volume reductions were observed throughout the course of SBRT, with largest mean reductions of 86.9 mL (19.0%) for bladder and 6.4 mL (8.7%) for rectum noted at fraction #5 compared to Sim-CT (P < 0.01). Higher initial Sim-CT bladder volumes were predictive for greater reduction in absolute bladder volume during treatment (ρ = − 0.69; P < 0.01). Over the course of SBRT, there was a small but significant increase in bladder mean dose (+ 4.5 ± 12.8%; P < 0.01) but no significant change in the D2cc (+ 0.8 ± 4.0%; P = 0.28). The mean bladder trigone displacement was in the anterior direction (+ 4.02 ± 6.59 mm) with a corresponding decrease in mean trigone dose (− 3.6 ± 9.6%; P < 0.01) and D2cc (− 6.2 ± 15.6%; P < 0.01). There was a small but significant increase in mean rectal dose (+ 7.0 ± 12.9%, P < 0.01) but a decrease in rectal D2cc (− 2.2 ± 10.1%; P = 0.04). No significant correlations were found between relative bladder volume changes, bladder trigone displacements, or rectum volume changes with rates of genitourinary or rectal toxicities.ConclusionsDespite smaller than expected bladder and rectal volumes at the time of treatment compared to the planning scans, dosimetric impact was minimal and not predictive of detrimental clinical outcomes. These results cast doubt on the need for excessively strict bladder filling and rectal emptying protocols in the context of image guided prostate SBRT and prospective studies are needed to determine its necessity.

Dosimetric correlations with urinary quality of life in patients receiving post-prostatectomy radiation therapy

Acute urinary toxicity is well-documented in individuals receiving post-prostatectomy radiation. However, dosimetric correlations between bladder dose and acute urinary symptoms in the post-prostatectomy setting have not been well-studied. We examined the relationship between bladder dosimetry and acute changes in individual urinary symptoms among men receiving post-prostatectomy radiation therapy. Patient-reported urinary symptoms were prospectively collected for 90 consecutive prostate cancer patients receiving post-prostatectomy radiation using the validated quality of life instrument Prostate Cancer Symptom Indices. Data were collected prior to treatment and weekly during treatment. Individual symptom scores were examined and a change in severity of an individual symptom (from baseline) of ≥ 2 points was considered clinically significant. DVHs were generated for all the patients. Receiver operating characteristic curves were generated to evaluate the ability of different dose-volume metrics to identify patients who developed individual urinary symptoms during radiation treatment from those who did not. Logistic regression was used to examine the relationship between dose-volume parameters and worsening of individual urinary symptoms. Worsening of individual urinary symptoms during radiation treatment was reported by 7% (urinary flow) to 29% (urgency) of patients. The relative bladder volume receiving moderate doses of radiation was associated with urgency (AUC 0.67 for V30 Gy). Dose-volume parameters were not significantly associated with flow, frequency, nocturia, or dysuria. There is an acute worsening of urinary symptoms among men receiving modern post-prostatectomy radiation. Worsening of urgency is associated with bladder dosimetry while flow, frequency, nocturia, and dysuria are not. This data can be used during treatment planning to reduce acute urinary toxicity during post-prostatectomy radiation.

Radical prostatectomy restores detrusor contraction pattern according to pressure flow parameters.

Pressure flow studies are regarded as the gold standard for evaluating both bladder outlet obstruction and detrusor contractility, but none of the current methods for evaluating bladder contraction patterns are well validated. Impaired bladder contraction results in a lower peak Watts factor and poorly sustained detrusor contractions. From this viewpoint, the maximum Watts factor and its pattern should be considered separately. To examine detrusor contraction pattern in patients after radical prostatectomy by using multiple parameters. A total of 37 patients with clinically localized prostate cancer underwent both pre- and post-radical prostatectomy urodynamic evaluations. The examined urodynamic parameters included the maximum flow rate, post-void residual volume, detrusor pressure at maximum flow, maximum Watts factor and relative volume (maximum Watts factor). Some parameters were defined from the Watts factor curve throughout micturition. Relative volume (maximum Watts factor) was the relative bladder volume at the maximum Watts factor. A normal detrusor contractility pattern involves an increase in Watts factor at the initiation followed by further gradual increases until the end of micturition. Maximum flow rate increased significantly after radical prostatectomy (pre: 13.0±6.5, post: 17.3±7.7mL/min; P<0.01), whereas detrusor pressure at maximum flow and post-void residual volume decreased significantly (pre: 49.6±21.6 and 31.4±18.2cmH2 O; post: 48.6±66.1 and 10.1±28.5mL; P<0.05). Maximum Watts factor did not change significantly after radical prostatectomy (pre: 10.5±3.1W/m2 , post: 11.0±3.2W/m2 ), but relative volume (maximum Watts factor) decreased significantly (pre: 0.48±0.3, post: 0.20±0.20; P<0.001). Maximum Watts factor represents the maximum power of bladder contraction at a particular point in time, whereas relative volume (maximum Watts factor) can be used to detect changes in detrusor contraction pattern. Evaluation of relative volume (maximum Watts factor) confirms that radical prostatectomy restores the normal detrusor contractility pattern in prostate cancer patients.

Optimal bladder volume at treatment planning for prostate cancer patients receiving volumetric modulated arc therapy

PurposeTo investigate optimal bladder volumes at treatment planning (TP) in prostate cancer patients who undergo volumetric modulated arc therapy (VMAT). Methods and materialsTo determine the minimum value, 122 patients were classified into 6 groups according to the bladder volume at TP: <100 mL (group 1), 100-149 mL (group 2), 150-199 mL (group 3), 200-249 mL (group 4), 250-299 mL (group 5), and ≥300 mL (group 6). Bladder volumes receiving more than 70 Gy (V70Gy) and V50Gy were calculated in each subgroup and compared with the bladder dose-volume constraints specified in our institution. To determine the maximum value, 64 patients who underwent uniform nursing interventions were classified into the same 6 groups. Bladder volumes on cone beam computed tomography (CBCT) images were measured once weekly during treatment, for a total of 8 measurements. Relative bladder volumes (bladder volume on CBCT image [mL]/bladder volume at TP [mL] × 100%) were evaluated in each of the 6 subgroups. ResultsThe upper bounds of the 95% confidence intervals of the mean V70Gy and V50Gy values in group 1 exceeded the dose constraints at our institution. The mean relative bladder volumes were 104%, 91%, 77%, 81%, 63%, and 59% in groups 1, 2, 3, 4, 5, and 6, respectively. The institutional criterion of 70% for the mean relative bladder volume was achieved in groups 1-4, but it could not be achieved in groups 5-6. Therefore, the patients in groups 2-4 met both institutional dose constraints for the bladder at TP and the institutional criterion for the mean relative bladder volume during treatment. ConclusionsThe optimal bladder volumes at TP were between 100 and 250 mL in this setting. Nursing intervention needs to be implemented before treatment planning to ensure that patients achieve the optimal bladder volume range.

Evaluating Variations of Bladder Volume Using an Ultrasound Scanner in Rectal Cancer Patients during Chemoradiation: Is Protocol-Based Full Bladder Maintenance Using a Bladder Scanner Useful to Maintain the Bladder Volume?

PurposeThe maintenance of full bladder is important to reduce radiation-induced toxicities and maintain the therapeutic consistency in locally advanced rectal cancer patients who underwent radiotherapy (RT). So, the aim of this study was to evaluate the effectiveness of protocol-based full bladder maintenance by assessing bladder volume variation using an ultrasound bladder scanner to maintain bladder volume.Materials and MethodsFrom March 2011 to May 2011, twenty consecutive rectal cancer patients receiving external beam RT participated in this prospective study. Protocol-based full bladder maintenance consisted of education, training and continuous biofeedback by measuring bladder volume. Bladder volume was measured by bladder scan immediately before simulation CT scan and before each treatment three times weekly during the RT period. The relative bladder volume change was calculated. Intra-patient bladder volume variations were quantified using interquartile range (IQR) of relative bladder volume change in each patient. We compared intra-patient bladder volume variations obtained (n=20) with data from our previous study patients (n=20) performing self-controlled maintenance without protocol.ResultsBladder volumes measured by bladder scan highly correlated with those on simulation CT scan (R=0.87, p<0.001). Patients from this study showed lower median IQR of relative bladder volume change compared to patients of self-controlled maintenance from our previous study, although it was not statistically significant (median 32.56% vs. 42.19%, p=0.058). Upon logistic regression, the IQR of relative bladder volume change was significantly related to protocol-based maintenance [relative risk 1.045, 95% confidence intervals (CI) 1.004-1.087, p=0.033]. Protocol-based maintenance included significantly more patients with an IQR of relative bladder volume change less than 37% than self-controlled maintenance (p=0.025).ConclusionOur findings show that bladder volume could be maintained more consistently during RT by protocol-based management using a bladder scan.

Contouring and Constraining Bowel on a Full-Bladder Computed Tomography Scan May Not Reflect Treatment Bowel Position and Dose Certainty in Gynecologic External Beam Radiation Therapy

To evaluate, in a gynecologic cancer setting, changes in bowel position, dose-volume parameters, and biological indices that arise between full-bladder (FB) and empty-bladder (EB) treatment situations; and to evaluate, using cone beam computed tomography (CT), the validity of FB treatment presumption. Seventeen gynecologic cancer patients were retrospectively analyzed. Empty-bladder and FB CTs were obtained. Full-bladder CTs were used for planning and dose optimization. Patients were given FB instructions for treatment. For the study purpose, bowel was contoured on the EB CTs for all patients. Bowel position and volume changes between FB and EB states were determined. Full-bladder plans were applied on EB CTs for determining bowel dose-volume changes in EB state. Biological indices (generalized equivalent uniform dose and normal tissue complication probability) were calculated and compared between FB and EB. Weekly cone beam CT data were available in 6 patients to assess bladder volume at treatment. Average (±SD) planned bladder volume was 299.7 ± 68.5 cm(3). Median bowel shift in the craniocaudal direction between FB and EB was 12.5 mm (range, 3-30 mm), and corresponding increase in exposed bowel volume was 151.3 cm(3) (range, 74.3-251.4 cm(3)). Absolute bowel volumes receiving 45 Gy were higher for EB compared with FB (mean 328.0 ± 174.8 vs 176.0 ± 87.5 cm(3); P=.0038). Bowel normal tissue complication probability increased 1.5× to 23.5× when FB planned treatments were applied in the EB state. For the study, the mean percentage value of relative bladder volume at treatment was 32%. Full-bladder planning does not necessarily translate into FB treatments, with a patient tendency toward EB. Given the uncertainty in daily control over bladder volume for treatment, we strongly recommend a "planning-at-risk volume bowel" (PRV_Bowel) concept to account for bowel motion between FB and EB that can be tailored for the individual patient.

Optimal Bladder Volume at Treatment Planning for Prostate Cancer Patients Receiving Volumetric Modulated Arc Therapy

Purpose: To investigate optimal bladder volumes at treatment planning (TP) in prostate cancer patients who undergo volumetric modulated arc therapy (VMAT). Methods and materials: To determine the minimum value, 122 patients were classified into 6 groups accordingtothe bladdervolumeat TP:b100mL(group1),100-149mL(group2),150-199mL(group 3), 200-249 mL (group 4), 250-299 mL (group 5), and ≥300mL(group6).Bladdervolumesreceiving more than 70 Gy (V70Gy )a nd V50Gy were calculated in each subgroup and compared with the bladder dose-volumeconstraintsspecifiedinourinstitution.Todeterminethemaximumvalue,64patientswho underwent uniform nursing interventions were classified into the same 6 groups. Bladder volumes on cone beam computed tomography (CBCT) images were measured once weekly during treatment, for a total of 8 measurements. Relative bladder volumes (bladder volume on CBCT image [mL]/bladder volume at TP [mL] × 100%) were evaluated in each of the 6 subgroups. Results: The upper bounds of the 95% confidence intervals of the mean V70Gy and V50Gy values in group1exceededthedoseconstraintsatourinstitution.Themeanrelativebladdervolumeswere104%, 91%,77%,81%,63%, and59%ingroups1,2,3,4,5,and6,respectively. Theinstitutional criterionof 70% for the mean relative bladder volume was achieved in groups 1-4, but it could not be achieved in groups 5-6. Therefore, the patients in groups 2-4 met both institutional dose constraints for the bladder at TP and the institutional criterion for the mean relative bladder volume during treatment. Conclusions:TheoptimalbladdervolumesatTPwerebetween100and250mLinthissetting.Nursing intervention needs to be implemented before treatment planning to ensure that patients achieve the optimal bladder volume range.

SU‐E‐T‐376: Is the Bladder Foley Point Dose Still An Effective Dose Factor for Three‐Dimensional Image‐Based Vaginal Brachytherapy?

Purpose: To evaluate the use of the bladder foley point dose as an effective factor for 3D image‐based vaginal brachytherapy. Methods: Twenty‐one endometrial cancer patients who received postoperative intracavitary vaginal brachytherapy were included in this study (69 fractions). The radiation was delivered through a segmented cylinder applicator with a high dose rate (HDR) afterloader. The prescription dose was either 550 cGy or 700 cGy to a reference line which was 0.5 cm from the applicator surface. The posterior aspect of the foley balloon was identified as the bladder dose point. The bladder was contoured by a radiation oncologist. Two dose‐volume histograms (DVH) were collected for each fraction: 1) absolute bladder volume vs relative dose (% of prescription dose) and 2) relative bladder volume (% of bladder volume) vs relative dose. D2cc (the dose received by 2 cc bladder), D1cc, D0.1cc, and D50% (the dose received by 50% of bladder volume) were collected for each fraction, and the correlation coefficients were calculated between the bladder point dose and these dose factors. The correlation coefficients were also calculated between the bladder point dose and the DVH. The statistical significance of each correlation was determined with statistical significance identified as p‐value &lt; 0.05. Results: : There were significant linear correlations between the bladder point dose and the DVH metrics, between V14% and V68% (p‐value &lt;0.05). Additionally, there were significant linear correlations between bladder point dose and D50%, D2cc, D1cc, and D0.1cc, with p‐ values &lt; 0.001 Conclusions: : In this study, there were a significant linear correlations between the bladder point dose and the bladder DVH, D50%, D2cc, D1cc, and D0.1cc. Subsequently, the bladder point dose remains an effective factor for 3D image‐based vaginal brachytherapy.

Behavior of Lipiodol Markers During Image Guided Radiotherapy of Bladder Cancer

To investigate the stability of a novel type of markers used in partial bladder tumor irradiation and tumor deformation as indicated by the markers. In 15 patients with solitary bladder cancer, lipiodol was injected in the bladder wall during flexible cystoscopy to identify the tumor. A planning CT scan was made, followed by daily cone-beam CT (CBCT) scans during treatment. To study the accuracy of using these markers for image guidance, uncertainties U1 and U2 were calculated, which were defined as the difference between submask registration (covering single marker) and the average of all submask registrations and the difference between the submask registration and the general mask registration (including all markers), respectively. Finally, to study tumor deformation, the relative movement of each marker pair was correlated with the relative bladder volume (RBV). The analyzed patients had 2.3 marker injections on average. The lipiodol spot size was 0.72 +/- 1.1 cm(3). The intensity of spots in both CT and CBCT was significantly higher than the surrounding bladder tissue. The uncertainties U1 and U2 were comparable, and the uncertainties in left-right direction (0.14-0.19 cm) were smaller than those in cranial-caudal and anterior-posterior directions (0.19-0.32 cm). The relative marker movement of within-zone marker pairs was much smaller (and has less dependence on the RBV) than across-zones marker pairs. Lipiodol markers are a feasible method to track bladder tumor by using online CBCT. Tumor deformation is observed, especially for tumors that cross the defined bladder zones.

Ultrasound Imaging to Assess Inter- and Intra-fraction Motion during Bladder Radiotherapy and its Potential as a Verification Tool

Aims Organ motion is the principle source of error in bladder cancer radiotherapy. The aim of this study was to evaluate ultrasound bladder volume measurement as a surrogate measure of organ motion during radiotherapy: (1) to assess inter- and intra-fraction bladder variation and (2) as a potential treatment verification tool. Materials and methods Twenty patients receiving radical radiotherapy for bladder cancer underwent post-void ultrasound bladder volume measurement at the time of radiotherapy treatment planning (RTP), and immediately before (post-void) and after receiving daily fractions. Results Ultrasound bladder volume measurement was found to be a simple and acceptable method to estimate relative bladder volume changes. Six patients showed significant changes to post-void bladder volume over the treatment course ( P < 0.05). The mean inter-fraction post-void bladder volume of five patients exceeded their RTP ultrasound bladder volume by more than 50%. Intra-fraction bladder volume increased on 275/308 (89%) assessed fractions, with the mean intra-fraction volume increases of seven patients exceeding their RTP ultrasound bladder volume by more than 50%. Conclusions Both day-to-day bladder volume variation and bladder filling during treatment should be considered in RTP and delivery. Ultrasound may provide a practical daily verification tool by: supporting volume limitation as a method of treatment margin reduction; allowing detection of patients who may require interventions to promote bladder reproducibility; and identifying patients with prominent volume changes for the selective application of more advanced adaptive/image-guided radiotherapy techniques.

Modeling correlation indices between bladder and Foley′s catheter balloon dose with CT-based planning using limited CT slices in intracavitary brachytherapy for carcinoma of cervix

To derive and validate an index to correlate the bladder dose with the catheter balloon dose using limited computed tomography (CT) slices. Applicator geometry reconstructed from orthogonal radiographs were back-projected on CT images of the same patients for anatomy-based dosimetric evaluation. The correlation indices derived using power function of the catheter balloon dose and the bladder volume dose were validated in 31 patients with cervical cancer. There was significant correlation between International Commission on Radiation Units (ICRU)-38 balloon reference dose (Dr) and the dose received by 25% bladder volume (D(25)) (P< 0.0001). Significant correlation was also found between the reference dose of mid-balloon point (D(rm)) and the dose to D(25) (P < 0.0001). Average percentage difference [100 x (observed index - expected index)/ expected index] of observed value of I'25 (index for the dose to D25 bladder with respect to mid-balloon reference point) from that of expected value was 0.52%, when the index was modeled with reference dose alone. Similarly the average percentage difference for I'10cc (index for the dose to 10 cc volume of bladder with respect to mid balloon point) was 0.84%. When this index was modeled with absolute bladder volume and reference dose, standard deviation of the percentage difference between observed and expected index for D(rm) reduced by approximately 2% when compared to D(r). For clinical applications, correlation index modeled with reference dose and volume predicts dose to absolute volume of bladder. Correlation index modeled with reference dose gives a good estimate of dose to relative bladder volume. From our study, we found D(rm) to be a better indicator of bladder dose than D(r).

Image-guided radiotherapy of bladder cancer: Bladder volume variation and its relation to margins

Background and purpose To control and account for bladder motion is a major challenge in radiotherapy (RT) of bladder cancer. This study investigates the relation between bladder volume variation and margins in conformal and image-guided RT (IGRT) for this disease. Materials and methods The correlation between the relative bladder volume (RBV, defined as repeat scan volume/planning scan volume) and the margins required to account for internal motion was first studied using a series of 20 bladder cancer patients with weekly repeat CT scanning during treatment. Both conformal RT (CRT) and IGRT were simulated; in the latter translational movement of the bladder was accounted for by isocentre shifting. Further analysis of bladder volumes and margins was performed using a second series of eight patients with twice-weekly repeat CT scanning. In an attempt to control bladder volume variation these patients were given fluid intake restrictions on alternating weeks during treatment. Results IGRT gave the strongest correlation between the RBV and margin size ( R 2 = 0.75; p < 0.001). Using IGRT, isotropic margins >10 mm were required in only 1% of the situations when the RBV ⩽ 1, whereas isotropic margins >10 mm were required in 55% of the situations when the RBV > 1. Less marked correlation was found using CRT ( R 2 in the range 0.43–0.53, p < 0.001) for four different methods used to assess the margins required in the six directions, although a strong correlation was found for the superior margin ( R 2 = 0.63; p < 0.001). Fluid intake restriction gave a small reduction in both bladder volume (average absolute volume reduced from 126 to 121 cm 3; RBV from 0.83 to 0.80) and bladder volume variation, but not sufficient to translate into margin reduction. Conclusions The study showed the potential for a large margin reduction in bladder RT if the bladder volume is controlled and this potential was even greater for IGRT. An attempt to control the bladder volume by restricting fluid intake prior to the treatment session failed to give any reduction in the margins required.

Drugs acting on calcium channels modulate the diuretic and micturition effects of dexmedetomidine in rats

The purpose of this study was to assess the effects of calcium channel antagonist, verapamil, and agonist, Bay K 8644, on the α 2-adrenoceptor agonist, dexmedetomidine-induced (300 μg kg −1 subcutaneously) diuresis and overflow incontinence, in rats. Ultrasonography study revealed that verapamil (2.5 mg kg −1 subcutaneously) or Bay K 8644 (0.5 mg kg −1 intraperitoneally) coadministrations delayed dexmedetomidine-induced bladder filling and significantly prolonged the latency of urination (P < 0.05). Bay K 8644 decreased relative bladder volume and stopped continuous urination from dexmedetomidine, whereas verapamil had neither effect. However, none of the drugs eliminated the overflow incontinence. Dexmedetomidine alone increased the hourly and total (for 4 hours) urine volume. Bay K 8644 (0.5 or 1 mg kg −1) dose-dependently decreased the diuretic effect of dexmedetomidine (P < 0.001). Verapamil (0.5, 1 or 2.5 mg kg −1) dose-dependently decreased urine volume in the first hour (P < 0.01), and thereafter potentiated the diuretic effect of dexmedetomidine. Simultaneous determinations of mean arterial blood pressure (MAP) and urine output after dexmedetomidine and the highest dose of verapamil coadministration demonstrated a significant correlation between these variables (r = 0.537; P < 0.001). MAP of 100 mmHg or less was associated with a urine output significantly lower (P < 0.001) than that at higher pressures. Thus, hypotension during the first hour after dexmedetomidine-verapamil may explain the transient reduction in urination during this period. We conclude that modulation of calcium channels affects dexmedetomidine actions on both urine formation and micturition. Since both α 2-adrenoceptor agonists and calcium channel blockers have frequently been used for antihypertensive therapy and as adjuvant drugs during anesthesia, these interactions may have some practical importance.