Associations between volume changes and spatial dose metrics for the urinary bladder during local versus pelvic irradiation for prostate cancer

Dose-volume relationships of planned versus estimated delivered radiation doses to pelvic organs at risk and side effects in patients treated with salvage radiotherapy for recurrent prostate cancer

Purpose

To investigate estimated delivered dose distributions using weekly cone-beam computed tomography (CBCT) scans for pelvic organs at risk (OARs) in salvage radiotherapy (SRT) after radical prostatectomy. Furthermore, to compare them with the originally planned dose distributions and analyse associations with gastrointestinal (GI) and genitourinary (GU) side effects.

Methods

This study is part of a phase II trial involving SRT for recurrent prostate cancer. Treatment was personalised based on PSA response during SRT, classifying patients as PSA responders or non-responders. Estimated radiation dose distributions were obtained using deformable image registration from weekly CBCT scans. GI and GU toxicities were assessed using the RTOG toxicity scale, while patient-reported symptoms were monitored through self-assessment questionnaires.

Results

The study included 100 patients, with similar treatment-related side effects observed in both responders and non-responders. Differences in dose-volume metrics between the planned and estimated delivered doses for the examined OARs were mostly modest, although generally statistically significant. We identified statistically significant associations between QUANTEC-recommended dose-volume constraints and acute bowel toxicity, as well as late urinary patient-reported symptoms, for both the estimated delivered and planned dose distributions.

Conclusion

We found small but statistically significant differences between estimated delivered and planned doses to OARs. These differences showed trends toward improved associations for estimated delivered dose distributions with side effects. Enhanced registration methods and imaging techniques could potentially further enhance the assessment of truly delivered doses and yield more reliable dose-volume constraints for future therapies.

Advantages and robustness of partial VMAT with prone position for neoadjuvant rectal cancer evaluated by CBCT-based offline adaptive radiotherapy

BACKGROUND AND PURPOSE

This study aims to explore the advantages and robustness of the partial arc combined with prone position planning technique for radiotherapy in rectal cancer patients. Adaptive radiotherapy is recalculated and accumulated on the synthesis CT (sCT) obtained by deformable image registration between planning CT and cone beam CT (CBCT). Full and partial volume modulation arc therapy (VMAT) with the prone position on gastrointestinal and urogenital toxicity, based on the probability of normal tissue complications (NTCP) model in rectal cancer patients were evaluated.

MATERIALS AND METHODS

Thirty-one patients were studied retrospectively. The contours of different structures were outlined in 155 CBCT images. First, full VMAT (F-VMAT) and partial VMAT (P-VMAT) planning techniques were designed and calculated using the same optimization constraints for each individual patient. The Acuros XB (AXB) algorithm was used in order to generate more realistic dose distributions and DVH, considering the air cavities. Second, the Velocity 4.0 software was used to fuse the planning CT and CBCT to obtain the sCT. Then, the AXB algorithm was used in the Eclipse 15.6 software to conduct re-calculation based on the sCT to obtain the corresponding dose. Furthermore, the NTCP model was used to analyze its radiobiological side effects on the bladder and the bowel bag.

RESULTS

With a CTV coverage of 98%, when compared with F-VMAT, P-VMAT with the prone position technique can effectively reduce the mean dose of the bladder and the bowel bag. The NTCP model showed that the P-VMAT combined with the prone planning technique resulted in a significantly lower complication probability of the bladder (1.88 ± 2.08 vs 1.62 ± 1.41, P = 0.041) and the bowel bag (1.28 ± 1.70 vs 0.95 ± 1.52, P < 0.001) than the F-VMAT. In terms of robustness, P-VMAT was more robust than F-VMAT, considering that less dose and NTCP variation was observed in the CTV, bladder and bowel bag.

CONCLUSION

This study analyzed the advantages and robustness of the P-VMAT in the prone position from three aspects, based on the sCT fused by CBCT. Whether it is in regards to dosimetry, radiobiological effects or robustness, P-VMAT in the prone position has shown comparative advantages.

Predictors for late genitourinary toxicity in men receiving radiotherapy for high-risk prostate cancer using planned and accumulated dose

Background and purpose

Significant deviations between bladder dose planned (D_P) and dose accumulated (D_A) have been reported in patients receiving radiotherapy for prostate cancer. This study aimed to construct multivariate analysis (MVA) models to predict the risk of late genitourinary (GU) toxicity with clinical and D_P or D_A as dose-volume (DV) variables.

Materials and methods

Bladder D_A obtained from 150 patients were compared with D_P. MVA models were built from significant clinical and DV variables (p < 0.05) at univariate analysis. Previously developed dose-based-region-of-interest (DB-ROI) metrics using expanded ring structures from the prostate were included. Goodness-of-fit test and calibration plots were generated to determine model performance. Internal validation was accomplished using Bootstrapping.

Results

Intermediate-high D_A (V_{30-65 Gy} and DB-ROI-20-50 mm) for bladder increased compared to D_P. However, at the very high dose region, D_A (D_{0.003 cc}, V_{75 Gy,} and DB-ROI-5-10 mm) were significantly lower. In MVA, single variable models were generated with odds ratio (OR) < 1. DB-ROI-50 mm was predictive of Grade ≥ 1 GU toxicity for D_A and D_P (D_A and D_P; OR: 0.96, p: 0.04) and achieved an area under the receiver operating curve (AUC) of > 0.6. Prostate volume (OR: 0.87, p: 0.01) was significant in predicting Grade 2 GU toxicity with a high AUC of 0.81.

Conclusions

Higher D_A (V_{30-65 Gy}) received by the bladder were not translated to higher late GU toxicity. DB-ROIs demonstrated higher predictive power than standard DV metrics in associating Grade ≥ 1 toxicity. Smaller prostate volumes have a minor protective effect on late Grade 2 GU toxicity.

Application of an automated dose accumulation workflow in high-risk prostate cancer - validation and dose-volume analysis between planned and delivered dose

Inter-fraction organ variations cause deviations between planned and delivered doses in patients receiving radiotherapy for prostate cancer. This study compared planned (D_P) vs accumulated doses (D_A) obtained from daily cone-beam computed tomography (CBCT) scans in high-risk- prostate cancer with pelvic lymph nodes irradiation. An intensity-based deformable image registration algorithm used to estimate contours for D_A was validated using geometrical agreement between radiation oncologist's and deformable image registration algorithm propagated contours. Spearman rank correlations (r_s) between geometric measures and changes in organ volumes were evaluated for 20 cases. Dose-volume (DV) differences between D_A and D_P were compared (Wilcoxon rank test, p < 0.05). A novel region-of-interest (ROI) method was developed and mean doses were analyzed. Geometrical measures for the prostate and organ-at-risk contours were within clinically acceptable criteria. Inter-group mean (± SD) CBCT volumes for the rectum were larger compared to planning CT (pCT) (51.1 ± 11.3 cm³vs 46.6 ± 16.1 cm³), and were moderately correlated with variations in pCT volumes, rs = 0.663, p < 0.01. Mean rectum DV for D_A was higher at V30-40 Gy and lower at V70-75 Gy, p < 0.05. Mean bladder CBCT volumes were smaller compared to pCT (198.8 ± 55 cm³vs 211.5 ± 89.1 cm³), and was moderately correlated with pCT volumes, rs = 0.789, p < 0.01. Bladder D_A was higher at V30-65 Gy and lower at V70-75 Gy (p < 0.05). For the ROI method, rectum and bladder D_A were lower at 5 to 10 mm (p < 0.01) as compared to D_P, whilst bladder D_A was higher than D_P at 20 to 50 mm (p < 0.01). Generated D_A demonstrated significant differences in organ-at-risk doses as compared to D_P. A well-constructed workflow incorporating a ROI DV-extraction method has been validated in terms of efficiency and accuracy designed for seamless integration in the clinic to guide future plan adaptation.

Relation between DIR recalculated dose based CBCT and GI and GU toxicity in postoperative prostate cancer patients treated with VMAT

BACKGROUND AND PURPOSE

To investigate the relationship between deformable image registration (DIR) recalculated dose on cone beam computed tomography (CBCT) and gastrointestinal and genitourinary toxicity in postoperative prostate cancer patients treated with volumetric modulated arc therapy and its actual delivered dose.

MATERIAL AND METHODS

A total of 114 patients were retrospectively studied. Delineation of rectum and bladder was performed on each CBCT image. Actual delivered dose on CBCT available fraction was recalculated using DIR. Dosimetric parameters of rectum and bladder were then evaluated by Quantitative Analyses of Normal Tissue Effects in the Clinic study. Differences in mean volume between patients with grade 0-1 and grade 2-5 CTCAEv5.0 toxicities were compared. Relationship between toxicity and radiation volume was analyzed using logit analysis.

RESULTS

Significant differences between the actual and planned dose-volume were observed in nearly all doses of rectum. High-grade acute rectal toxicity was significantly associated with planned dose-volume in V50 and V75, and actual dose in all doses. High-grade chronic rectal toxicity was significantly associated with all planned and actual rectal dose-volume parameters. There was no significant association between all dose-volume parameters and acute or chronic bladder toxicity.

CONCLUSION

Significant differences between actual and planned dose-volume, and significant association between actual dose-volume and acute rectal toxicity, but not planned dose-volume suggests that actual dose-volume may more precisely reflect toxicity due to daily variation in the rectum during the treatment course. Adaptive planning should be considered as a novel approach for reducing toxicity.

Bladder volume reproducibility after water consumption in patients with prostate cancer undergoing radiotherapy: A systematic review and meta-analysis

Background

To minimize toxicity due to radiotherapy in patients with prostate cancer, high bladder volume reproducibility is essential. Water consumption is often used to increase bladder volume reproducibility, but the optimal amount of water required to be consumed remains unclear. We aimed to analyzed the relationship between water consumption and bladder volume reproducibility in patients undergoing radiotherapy for prostate cancer.

Methods

We conducted a systematic review and meta-analysis of randomized controlled trials and cohort studies that assessed bladder volume change after water consumption in patients with prostate cancer undergoing radiotherapy. MEDLINE, Embase, and Cochrane Central Register of Controlled Trials were searched for relevant studies published from database inception up until July 4, 2020. The Newcastle–Ottawa Scale was used to evaluate the risk of bias in the included studies. The outcome was the mean difference (MD) of bladder volume after water consumption, evaluated through meta-analysis using a random-effects model.

Results

Ten cohort studies and one randomized controlled trial with a total of 417 patients were included. For 300–400 ml water consumption, the bladder volume MD between during treatment and at computer tomography-simulation (95% confidence interval [CI]) was −11.97 (−51.68 to 27.74), was −45.99 (−82.85 to −9.13) for 500–540 ml water consumption and −45.92 (−78.86 to −12.98) for water consumption until full-bladder sensation was reached.

Conclusion

Consuming 300–400 ml of water potentially leads to the best bladder volume reproducibility; moreover, the higher the water consumption volume, the lower the bladder volume reproducibility.

[Individual control of urine volume to improve stability of bladder volume in radiotherapy of urinary tumor]

OBJECTIVE

To explore the training mode of individual urine volume control, to take indi-vidual expected urine volume as the goal of bladder control in patients with urinary system tumors, and to improve the accuracy of bladder control during radiotherapy by active training of bladder receptivity.

METHODS

Twenty-five patients of urinary system tumors were enrolled from May 2019 to September 2019, of whom, 21 patients had prostate cancer, and 4 had bladder cancer. Training of bladder filling started before CT simulation. The patients were required to take the individual bladder filling as the training goal, and the optimal bladder volume range was suggested to be 200－400 mL. After 2－4 weeks of training, the prescribed volume of the bladder was determined according to the patient's bladder receptivity. The volume of the bladder was measured by images of plain CT and images 8-minutes after intravenous contrast injection. The patient's bladder volume was measured using BladderScan before treatment. CBCT (Cone-beam CT) was performed, and bladder volume was measured before treatment. The bladder volume was measured again using BladderScan after treatment.

RESULTS

The mean bladder volume of simulation (V_CT01) was (262±130) mL, ranging from 78 mL to 505 mL. The mean self-evaluation bladder volume before radiotherapy (V_EVA01) was (238±107) mL, ranging from 100 mL to 400 mL. The mean BladderScan measured volume before radiotherapy (V_BVI01) was (253±123) mL, ranging from 60 mL to 476 mL. The mean cone-beam CT measured volume before radiotherapy (V_CBCT) was (270±120) mL, ranging from 104 mL to 513 mL. There was a correlation between V_EVA01 and V_BVI01, V_CT01 and V_BVI01, V_CT01, and V_BVI01, and there was no significant difference in paired t-test. There was a correlation between differences of self-evaluation bladder volume before radiotherapy(V_EVA01) and simulation CT (V_CT01) and differences of self-evaluation bladder volume before radiotherapy (V_EVA01) and cone-beam CT (V_CBCT), and there was no significant difference in paired samples by t-test.

CONCLUSION

During radiotherapy for urinary system tumors, such as prostate cancer and bladder cancer, with the assistance of BladderScan, the patients could try to hold their urine moderately according to their conditions, and individualized bladder prescription may be beneficial to achieve stable bladder volume during radiotherapy.

Influence of different urinary bladder filling levels and controlling regions of interest selection on deformable image registration algorithms

PURPOSE

Evaluation of Raystation ANAtomically CONstrained Deformation Algorithm (ANACONDA) performance to different urinary bladder filling levels in male pelvis anatomic site varying the controlling Regions Of Interest (ROIs).

METHODS

Different image datasets were obtained with ImSimQA (Oncology System Limited, Shrewsbury, UK) to evaluate ANACONDA performances (RaySearch Laboratories, Stockholm, Sweden). Deformation vector fields were applied to a synthetic man pelvis and a real patient computed tomography (CT) dataset (reference CTs) resulting in deformed CTs (target CTs) with various bladder filling levels. Different deformable image registrations (DIRs) were generated between each target CTs and reference CTs varying the controlling ROIs subset. Deformed ROIs were mapped from target CT to reference CT and then compared to reference ROIs. Evaluation was performed by Dice Similarity Coefficient (DSC), Correlation Coefficient (CC), Mean Distance to Agreement (MDA), maximum Distance to Agreement (maxDA) and with the introduction of global DSC (global_DSC) and global CC (global_CC) parameters.

RESULTS

In both synthetic and real patient CT cases, DSC scored less than 0.75 and MDA greater than 3 mm when no ROIs or only bladder were exploited as controlling ROI. DSC and CC increased by increasing the number of controlling ROIs selected whereas, an opposite behavior was observed for MDA and maxDA.

CONCLUSIONS

ANACONDA performances can be influenced by bladder filling fluctuation if no controlling ROIs are selected. Global_DSC and global_CC are useful parameters to quantitatively compare DIR algorithms. DIR performances improve by increasing the number of controlling ROIs selected, reaching a saturation level after a defined ROIs subset selection.

Dosimetric impact of organ at risk daily variation during prostate stereotactic ablative radiotherapy

OBJECTIVE

Prostate stereotactic ablative radiotherapy (SABR) delivers large doses using a fast dose rate. This amplifies the effect geometric uncertainties have on normal tissue dose. The aim of this study was to determine whether the treatment dose-volume histogram (DVH) agrees with the planned dose to organs at risk (OAR).

METHODS

41 low-intermediate risk prostate cancer patients were treated with SABR using a linac based technique. Dose prescribed was 35 Gy in five fractions delivered on alternate days, planned using volumetric modulated arc therapy (VMAT) with 10X flattening filter free (FFF). On treatment, prostate was matched to fiducial markers on cone beam CT (CBCT). OAR were retrospectively delineated on 205 pre-treatment CBCT images. Daily CBCT contours were overlaid on the planning CT for dosimetric analysis. Verification plan used to evaluate the daily DVH for each structure. The daily doses received by OAR were recorded using the D%.

RESULTS

The median rectum and bladder volumes at planning were 67.1 cm3 (interquartile range 56.4-78.2) and 164.4 cm3 (interquartile range 120.3-213.4) respectively. There was no statistically significant difference in median rectal volume at each of the five treatment scans compared to the planning scan (p = 0.99). This was also the case for median bladder volume (p = 0.79). The median dose received by rectum and bladder at each fraction was higher than planned, at the majority of dose levels. For rectum the increase ranged from 0.78-1.64Gy and for bladder 0.14-1.07Gy. The percentage of patients failing for rectum D35% < 18 Gy (p = 0.016), D10% < 28 Gy (p = 0.004), D5% < 32 Gy (p = 0.0001), D1% < 35 Gy (p = 0.0001) and bladder D1% < 35 Gy (p = 0.001) at treatment were all statistically significant.

CONCLUSION

In this cohort of prostate SABR patients, we estimate the OAR treatment DVH was higher than planned. This was due to rectal and bladder organ variation.

ADVANCES IN KNOWLEDGE

OAR variation in prostate SABR using a FFF technique, may cause the treatment DVH to be higher than planned.

Precision of T2 TSE MRI-CT-image fusions based on gold fiducials and repetitive T2 TSE MRI-MRI-fusions for adaptive IGRT of prostate cancer by using phantom and patient data

INTRODUCTION

To increase precision of radiation treatment (RT) delivery in prostate cancer, MRI-based RT as well as the use of fiducials like gold markers (GMs) have shown promising results. Their combined use is currently under investigation in clinical trials. Here, we aimed to evaluate a workflow of image registration based on GMs between CT and MRI as well as weekly MRI-MRI adaption based on T2 TSE sequence.

MATERIAL AND METHODS

A gel-phantom with two inserted GMs was scanned with CT and three different MR-scanners of 1.5 and 3 T (T2 TSE and T1 VIBE-Dixon, isotropic, voxel size 2 × 2 × 2 mm). After image fusion, deviations for fiducial and gel match were measured and artifacts were evaluated. Additionally, CT-MRI-match deviations and MRI-MRI-match deviations of 10 Patients from the M-basePro study using GMs were assessed.

RESULTS

GMs were visible in all imaging modalities. The outer gel contours were matched with <1 mm deviation, contour volumes varied between 0 and 1%. The deviations of the GMs were less than 2 mm in any direction of MRI/CT. Shifts of peripherally or centrally located GMs were randomly distributed. The average MRI-CT-match precision of 10 patients with GMs was 1.9 mm (range 1.1-3.1 mm).

CONCLUSIONS

Match inaccuracies for GMs between reference CT and voxel-isotropic T2-TSE sequences are small. Spatial deviations of CT- and MR-contoured fiducials were less than 2 mm, i.e., below SLT of the applied modalities. In patients, the average CT-MRI-match precision for GMs was 1.9 mm supporting their use in MR-guided high precision RT.

A case-control study using motion-inclusive spatial dose-volume metrics to account for genito-urinary toxicity following high-precision radiotherapy for prostate cancer

Background and purpose

Material and methods

Results

Conclusions