Prostate bed and organ-at-risk deformation: Prospective volumetric and dosimetric data from a phase II trial of stereotactic body radiotherapy after radical prostatectomy

Yoon, Sangpil; Cao, Minsong; Aghdam, Nima; Shabsovich, David; Kahlon, Sartajdeep; Ballas, Leslie K.; Collins, Sean P.; Steinberg, Michael L.; Kishan, Amar U.

doi:10.1016/j.radonc.2020.04.007

Cited by 16 publications

(15 citation statements)

References 29 publications

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“…Comparing the results from the current study to previous studies is difficult due to the different equipment, methods and end points used to measure intra-fraction motion (Additional file 1). Two other studies used CBCT to measure intra-fraction motion with variations in the timing of acquisition [6,7]. Our study demonstrated a larger overall amount of IFD of 2.4 mm compared with 0.4 mm [6], and a similar mean motion [7].…”

Section: Discussionsupporting

confidence: 59%

“…[14] It is important to note that our study included 46 patients which, to our knowledge, is the largest patient cohort to date with the previous highest being 20 patients [8,9]. The only other studies that used CBCT scans to quantify intra-fraction motion included 14-18 patients [6,7]. Our study is also unique because, to our knowledge, it is the only study that has evaluated soft tissue and/or surgical clip marginal miss and its location.…”

Section: Discussionmentioning

confidence: 98%

“…Two other studies used CBCT to measure intra-fraction motion with variations in the timing of acquisition [6,7]. Our study demonstrated a larger overall amount of IFD of 2.4 mm compared with 0.4 mm [6], and a similar mean motion [7]. A number of groups used real-time monitoring to measure intrafraction motion of the prostate bed either by introducing electromagnetic transponders (Calypso, Varian Medical Systems, Palo Alto, CA, USA) [8][9][10] or transperineal ultrasound (Clarity, Elekta, Stockholm, Sweden) (Additional file 1) [11,12].…”

Section: Discussionmentioning

confidence: 99%

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Intra-fraction displacement of the prostate bed during post-prostatectomy radiotherapy

et al. 2021

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Background To measure intra-fraction displacement (IFD) in post-prostatectomy patients treated with anisotropic margins and daily soft tissue matching. Methods Pre-treatment cone beam computed tomography (CBCT) scans were acquired daily and post-treatment CBCTs for the first week then weekly on 46 patients. The displacement between the scans was calculated retrospectively to measure IFD of the prostate bed (PB). The marginal miss (MM) rate, and the effect of time between imaging was assessed. Results A total of 392 post-treatment CBCT’s were reviewed from 46 patients. The absolute mean (95% CI) IFD was 1.5 mm (1.3–1.7 mm) in the AP direction, 1.0 mm (0.9–1.2 mm) SI, 0.8 mm (0.7–0.9 mm) LR, and 2.4 mm (2.2–2.5 mm) 3D displacement. IFD ≥ ± 3 mm and ≥ ± 5 mm was 24.7% and 5.4% respectively. MM of the PB was detected in 33 of 392 post-treatment CBCT (8.4%) and lymph nodes in 6 of 211 post-treatment CBCT images (2.8%). Causes of MM due to IFD included changes in the bladder (87.9%), rectum (66.7%) and buttock muscles (6%). A time ≥ 9 min between the pre and post-treatment CBCT demonstrated that movement ≥ 3 mm and 5 mm increased from 19.2 to 40.5% and 5 to 8.1% respectively. Conclusions IFD during PB irradiation was typically small, but was a major contributor to an 8.4% MM rate when using daily soft tissue match and tight anisotropic margins.

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Section: Discussionsupporting

confidence: 59%

Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

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Intra-fraction displacement of the prostate bed during post-prostatectomy radiotherapy

et al. 2021

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“…The major concerns with hypofractionated postoperative RT have been the “invisible” nature of the clinical target volume (CTV) which is significantly influenced by several deformable organs at risk (OARs), such as the bladder and rectum, and the possibility that the vesicourethral anastomosis may be more prone to toxicity than the native urethra [ 12 , 13 , 14 , 15 ]. Relevant to the first concern, a retrospective analysis of cone beam CT (CBCT) setup images of patients enrolled in a prospective phase II trial evaluating SBRT in the post-prostatectomy setting, found the interfractional change in CTV volume to be relatively small [ 16 ]. However, the CTV coverage goal was only met in 70% of fractions, suggesting the shape of the target and OARs may have a more direct dosimetric impact.…”

Section: Introductionmentioning

confidence: 99%

Interfractional Geometric Variations and Dosimetric Benefits of Stereotactic MRI Guided Online Adaptive Radiotherapy (SMART) of Prostate Bed after Radical Prostatectomy: Post-Hoc Analysis of a Phase II Trial

Cao

Gao

Yoon

et al. 2021

Cancers

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Purpose: To evaluate geometric variations of patients receiving stereotactic body radiotherapy (SBRT) after radical prostatectomy and the dosimetric benefits of stereotactic MRI guided adaptive radiotherapy (SMART) to compensate for these variations. Materials/Methods: The CTV and OAR were contoured on 55 MRI setup scans of 11 patients treated with an MR-LINAC and enrolled in a phase II trial of post-prostatectomy SBRT. All patients followed institutional bladder and rectum preparation protocols and received five fractions of 6−6.8 Gy to the prostate bed. Interfractional changes in volume were calculated and shape deformation was quantified by the Dice similar coefficient (DSC). Changes in CTV-V95%, bladder and rectum maximum dose, V32.5Gy and V27.5Gy were predicted by recalculating the initial plan on daily MRI. SMART was retrospectively simulated if the predicted dose exceeded pre-set criteria. Results: The CTV volume and shape remained stable with a median volumetric change of 3.0% (IQR −3.0% to 11.5%) and DSC of 0.83 (IQR 0.79 to 0.88). Relatively large volumetric changes in bladder (median −24.5%, IQR −34.6% to 14.5%) and rectum (median 5.4%, IQR − 9.7% to 20.7%) were observed while shape changes were moderate (median DSC of 0.79 and 0.73, respectively). The median CTV-V95% was 98.4% (IQR 94.9% to 99.6%) for the predicted doses. However, SMART would have been deemed beneficial for 78.2% of the 55 fractions based on target undercoverage (16.4%), exceeding OAR constraints (50.9%), or both (10.9%). Simulated SMART improved the dosimetry and met dosimetric criteria in all fractions. Moderate correlations were observed between the CTV-V95% and target DSC (R2 = 0.73) and bladder mean dose versus volumetric changes (R2 = 0.61). Conclusions: Interfractional dosimetric variations resulting from anatomic deformation are commonly encountered with post-prostatectomy RT and can be mitigated with SMART.

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“…The impact of possible shifts between the prostate bed and the symphysis are limited because: (1) Patients followed specific rectal and bladder filling preparation each day. Therefore, a lower impact of those volumes on the target volume is expected translating into less significant movements of the CTV [13] , [14] , [15] ; 2) No extreme hypofractionated radiotherapy is delivered in the post-prostatectomy setting. At the time of the development of this study, there were no guidelines or consensus on the choice of matching structures/volumes while treating PBI.…”

Section: Methodsmentioning

confidence: 99%

Evaluation of the XVI dual registration tool for image-guided radiotherapy in prostate cancer

Sousa

Jourani

Begin

et al. 2021

Technical Innovations & Patient Support in Radiation Oncolo

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Highlights The dual registration tool (DRT) aims to improve the accuracy by using two automatic image registrations sequentially; For prostate irradiation, DRT could be considered in combination with additional verification, as manual correction by the RTTs is less often needed after DRT than after chamfer matching; For prostate bed irradiation with matching on the pubic symphysis, the chamfer match together with additional verification of the RTTs remains the best choice, as it is fast and accurate.

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Prostate bed and organ-at-risk deformation: Prospective volumetric and dosimetric data from a phase II trial of stereotactic body radiotherapy after radical prostatectomy

Cited by 16 publications

References 29 publications

Intra-fraction displacement of the prostate bed during post-prostatectomy radiotherapy

Intra-fraction displacement of the prostate bed during post-prostatectomy radiotherapy

Interfractional Geometric Variations and Dosimetric Benefits of Stereotactic MRI Guided Online Adaptive Radiotherapy (SMART) of Prostate Bed after Radical Prostatectomy: Post-Hoc Analysis of a Phase II Trial

Evaluation of the XVI dual registration tool for image-guided radiotherapy in prostate cancer

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