Uncertainty analysis for 3D image-based cervix cancer brachytherapy by repetitive MR imaging: Assessment of DVH-variations between two HDR fractions within one applicator insertion and their clinical relevance (original) (raw)
Related papers
2017
Objective: This study observed the dose-volume histogram (DVH) parameter changes caused by applicator shifting that result from patient movement during image acquisition for magnetic resonance imaging guided brachytherapy for cervical cancer patients. Materials and Methods: Nine cervical cancer plans with insertion of a Fletcher computed tomography (CT)/magnetic resonance (MR) applicator were retrospectively studied. The MR sequences were T2 fast spin echo on parasagittal, para-axial, and para-coronal planes, respectively. The applicator library was used for applicator reconstruction in each image data set. The tip of the applicator (2 ovoids + 1 tandem) was identified, and the difference from the reference image (axial view) was recorded. The DVH parameters were as follows: D90 of high-risk clinical target volume (HR-CTV) and D2cc of the bladder and rectum for each image data set were compared with the reference image. Results: The tandem showed less applicator shift on the coronal plane than the reference image. The applicator shifts for tandem were 0.0 ± 0.4, 0.0 ± 1.0, and-0.5 ± 1.0 mm in the left-right, superior-inferior, and anterior-posterior directions, respectively. The mean percentage dose differences in DVH parameters on the coronal and sagittal planes were 3.04% and 1.23% for D90 of HR-CTV, 2.73% and 3.88% for D2cc of the bladder, and 2.60% and 3.49% for D2cc of the rectum, respectively. Conclusion: An image acquisition time of approximately 15 minutes for three-dimensional MR brachytherapy provided a mean applicator reconstruction shift within 1.3 mm, with minor effects on the DVH parameter of approximately 3%.
Radiotherapy and Oncology, 2003
The purpose of this comparative prospective study was to assess the effect of CT and MR based individualisation and adaptation on the dose distribution in the target volume and organs at risk compared to a radiography based procedure. In 15 patients MR scans, in 10 patients additional axial CT-scans with compatible tube-ring applicator in situ were performed and digitally transferred to the PLATO(R) planning system. Considering clinical examination and MR-scan before radiotherapy individual 3-D dose distribution was calculated and adapted based on (1) two orthogonal radiographs; (2) isodoses superimposed on the CT images; and (3) isodoses superimposed on the MR images. Adaptation was strictly limited by the dose level at 2 cm(3) bladder or rectum volume (D(2)) to allow comparison of CT and MR plans. All three individualised dose distributions were superimposed on the MR images and cumulative dose-volume histograms were calculated for comparison. 3-D individualisation based on sectional imaging enabled higher dose to the target volume (isodose enclosing 95% of the CTV=CTV(95)) compared to individualised treatment plans based on orthogonal radiographs by a mean factor of 1.2 (1-1.7). The dose to bladder and/or rectum wall was at the same time not increased beyond the prescribed tolerance level (71% of the prescribed target dose). In a subgroup of 10 patients MRI based treatment plans were superior to CT based treatment plans allowing for a higher dose (138% vs. 124%). Sectional imaging based treatment planning, in particular using MR, was superior to radiography allowing for a clinical meaningful dose escalation without increasing the dose to bladder and rectum beyond the tolerance level.
Asian Pacific Journal of Cancer Prevention, 2014
Background: CT based brachytherapy allows 3-dimensional (3D) assessment of organs at risk (OAR) doses with dose volume histograms (DVHs). The purpose of this study was to compare computed tomography (CT) based volumetric calculations and International Commission on Radiation Units and Measurements (ICRU) reference-point estimates of radiation doses to the bladder and rectum in patients with carcinoma of the cervix treated with high-dose-rate (HDR) intracavitary brachytherapy (ICBT). Materials and Methods: Between March 2011 and May 2012, 20 patients were treated with 55 fractions of brachytherapy using tandem and ovoids and underwent post-implant CT scans. The external beam radiotherapy (EBRT) dose was 48.6Gy in 27 fractions. HDR brachytherapy was delivered to a dose of 21 Gy in three fractions. The ICRU bladder and rectum point doses along with 4 additional rectal points were recorded. The maximum dose (D Max) to rectum was the highest recorded dose at one of these five points. Using the HDRplus 2.6 brachyhtherapy treatment planning system, the bladder and rectum were retrospectively contoured on the 55 CT datasets. The DVHs for rectum and bladder were calculated and the minimum doses to the highest irradiated 2cc area of rectum and bladder were recorded (D 2cc) for all individual fractions. The mean D 2cc of rectum was compared to the means of ICRU rectal point and rectal D Max using the Student's t-test. The mean D 2cc of bladder was compared with the mean ICRU bladder point using the same statistical test .The total dose, combining EBRT and HDR brachytherapy, were biologically normalized to the conventional 2 Gy/fraction using the linear-quadratic model. (α/β value of 10 Gy for target, 3 Gy for organs at risk). Results: The total prescribed dose was 77.5 Gyα/β10. The mean dose to the rectum was 4.58±1.22 Gy for D 2cc , 3.76±0.65 Gy at D ICRU and 4.75±1.01 Gy at D Max. The mean rectal D 2cc dose differed significantly from the mean dose calculated at the ICRU reference point (p<0.005); the mean difference was 0.82 Gy (0.48-1.19Gy). The mean EQD2 was 68.52±7.24 Gy α/β3 for D 2cc , 61.71±2.77 Gy α/β3 at D ICRU and 69.24±6.02 Gy α/β3 at D Max. The mean ratio of D 2cc rectum to D ICRU rectum was 1.25 and the mean ratio of D 2cc rectum to D Max rectum was 0.98 for all individual fractions. The mean dose to the bladder was 6.00±1.90 Gy for D 2cc and 5.10±2.03 Gy at D ICRU. However, the mean D 2cc dose did not differ significantly from the mean dose calculated at the ICRU reference point (p=0.307); the mean difference was 0.90 Gy (0.49-1.25Gy). The mean EQD2 was 81.85±13.03 Gy α/β3 for D 2cc and 74.11±19.39 Gy α/β3 at D ICRU. The mean ratio of D 2cc bladder to D ICRU bladder was 1.24. In the majority of applications, the maximum dose point was not the ICRU point. On average, the rectum received 77% and bladder received 92% of the prescribed dose. Conclusions: OARs doses assessed by DVH criteria were higher than ICRU point doses. Our data suggest that the estimated dose to the ICRU bladder point may be a reasonable surrogate for the D 2cc and rectal D Max for D 2cc. However, the dose to the ICRU rectal point does not appear to be a reasonable surrogate for the D 2cc .
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, 2019
Introduction 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. Materials and Methods 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 TM 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. Results 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. Conclusions 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.
Radiation Oncology Investigations, 1998
The purpose of this work is to compare bladder and rectal dose rates in brachytherapy for carcinoma of the cervix using two different dosimetry systems: traditional orthogonal radiograph-based dosimetry vs. computed axial tomography tandem and ovoids (CATTO) dosimetry. Twenty-two patients with carcinoma of the uterine cervix received the brachytherapy component of their radiotherapy with a computedtomography compatible Fletcher-Suit-Delclos device. A total of 27 implants were performed. The average maximum bladder dose (B max ) for the implants was 85.8 cGy/hr using the CATTO system as compared to 42.6 cGy/hr using traditional dosimetry, (P < 0.005). The average maximum rectal dose (R max ) using the CATTO system was 59.2 cGy/hr as compared with 46.3 cGy/hr using the traditional system (P < 0.05). The traditional methods for choosing points to determine bladder and rectal dose rates underestimated the true B max in all cases and the R max in most. Based on the complication rates published in the literature, it is likely that the maximum tolerance dose of both the rectum and bladder, but especially the bladder, is higher than previously thought.
Asian Pacific Journal of Cancer Prevention, 2014
Background: Dosimetric comparison of two dimensional (2D) radiography and three-dimensional computed tomography (3D-CT) based dose distributions with high-dose-rate (HDR) intracavitry radiotherapy (ICRT) for carcinoma cervix, in terms of target coverage and doses to bladder and rectum. Materials and Methods: Sixty four sessions of HDR ICRT were performed in 22 patients. External beam radiotherapy to pelvis at a dose of 50 Gray in 27 fractions followed by HDR ICRT, 21 Grays to point A in 3 sessions, one week apart was planned. All patients underwent 2D-orthogonal and 3D-CT simulation for each session. Treatment plans were generated using 2D-orthogonal images and dose prescription was made at point A. 3D plans were generated using 3D-CT images after delineating target volume and organs at risk. Comparative evaluation of 2D and 3D treatment planning was made for each session in terms of target coverage (dose received by 90%, 95% and 100% of the target volume: D90, D95 and D100 respectively) and doses to bladder and rectum: ICRU-38 bladder and rectum point dose in 2D planning and dose to 0.1cc, 1cc, 2cc, 5cc, and 10cc of bladder and rectum in 3D planning. Results: Mean doses received by 100% and 90% of the target volume were 4.24±0.63 and 4.9±0.56 Gy respectively. Doses received by 0.1cc, 1cc and 2cc volume of bladder were 2.88±0.72, 2.5±0.65 and 2.2±0.57 times more than the ICRU bladder reference point. Similarly, doses received by 0.1cc, 1cc and 2cc of rectum were 1.80±0.5, 1.48±0.41 and 1.35±0.37 times higher than ICRU rectal reference point. Conclusions: Dosimetric comparative evaluation of 2D and 3D CT based treatment planning for the same brachytherapy session demonstrates underestimation of OAR doses and overestimation of target coverage in 2D treatment planning.
Applicator reconstruction and applicator shifts in 3D MR-based PDR brachytherapy of cervical cancer
Radiotherapy and Oncology, 2009
To evaluate the methods of applicator reconstruction in 3D MR-based planning for brachytherapy of cervical cancer, and to investigate applicator shifts and changes in DVH parameters during PDR treatment. Methods: For each application MR scans with applicator in situ were made: three T2-weighted (4.5 mm slices) Turbo Spin Echo (TSE) scans and a balanced Steady State Free Precession scan (1.5 mm). Three observers tested two applicator reconstruction methods: (A) directly on the bSSFP scan and (B) on a resampled combination of the three T2-weighted scans. For 10 patients MR imaging was repeated on the second day of each PDR fraction to determine applicator shifts and changes in DVH parameters. Results: For both applicator reconstruction methods the interobserver variation for the DVH parameters was comparable (average <1.5% in dose). Differences between the two methods were larger (up to 6.4% for target) and were related to position differences during MR scanning. The average applicator shift relative to the pelvic structures was 5-6 mm into the ventral direction and 3-4 mm cranially. For a single PDR fraction, the average D90 (HR-CTV) on 'day 2' was 0.2 (SD 2.0) Gy lower than that for day 1. The average increase in D 2cc (bladder) was 1.0 (SD 3.0) Gy ab3 for a single PDR fraction. If the effect of both fractions was combined, for 1 patient a total decrease of D90 of 7 Gy ab10 was found, whereas for another patient the total increase in bladder dose was 12 Gy ab3. Conclusions: Applicator reconstruction on MR data is feasible. In the overall accuracy during PDR brachytherapy the reconstruction uncertainty is of minor importance. Applicator and/or organ movement during the course of the PDR fraction produce larger uncertainties.