Conventional margins not sufficient for post-prostatectomy prostate bed coverage: An analysis of 477 cone-beam computed tomography scans

doi:10.1016/j.radonc.2013.12.004

Radiotherapy and Oncology

Volume 110, Issue 2, February 2014, Pages 235-239

https://doi.org/10.1016/j.radonc.2013.12.004 Get rights and content

Abstract

Purpose

To study prostate bed deformation, and compare coverage by 5 mm and 10 mm posterior expansion PTV margins.

Method

Fifty patients who completed post-prostatectomy radiotherapy had two expansion margins applied to the planning CT CTV: PTV10 (10 mm isometrically) and PTV5 (5 mm posteriorly, 10 mm all other directions). The CTV was then contoured on 477 pre-treatment CBCTs, and PTV5 and PTV10 coverage of each CBCT-CTVs was assessed. The maximum distance from the planning CT CTV to the combined CTV of all CBCTs including the planning CT CTV was measured for the superior part of the prostate bed, and the inferior part of the prostate bed, for every patient.

Results

The mean difference between largest and smallest CBCT-CTVs per patient was 18.7 cm³ (range 6.3–34.2 cm³). Out of 477 CBCTs, there were 43 anterior geometric geographical misses for either PTV with a mean volume of 2.25 cm³ (range 0.01–18.88 cm³). For PTV10, there were 26 posterior geometric geographical misses with a mean volume of 1.37 cm³ (0.01–11.02 cm³). For PTV5, there were 46 posterior geometric geographical misses with a mean volume of 3.22 cm³ (0.01–19.82 cm³). The maximum edge-to-edge distance for the superior prostate bed was anterior 19 mm, posterior 16 mm, left and right 7 mm. The maximum edge-to-edge distance for the inferior prostate bed was anterior 4 mm, posterior 12 mm, left and right 7 mm.

Conclusion

This study supports differential margins for the superior and inferior portions of the prostate bed. Because of the large deformation of CTV volume seen, adaptive radiotherapy solutions should be investigated further.

Section snippets

Method

This study was conducted on fifty consecutive post-prostatectomy patients treated at one academic cancer centre between August 2009 and May 2011. All patients enrolled had completed treatment.

For simulation, and also prior to each fraction, the patients were instructed to empty their bladder and bowels one hour before and then to drink approximately 750 ml of water. Immobilisation was conducted in the supine position with knee stocks and a footrest (Combifix-Sinmed, Civco, Kalona, IA). All

Results

On the planning CT, the mean CTV volume for the 50 patients was 81.1 cm³ (range 38.2–153.1 cm³). The mean CBCT combined CTV volume was 123.2 cm³ (range 58.57–212.49 cm³). The mean difference between largest and smallest CTV for individual patients during treatment was 18.7 cm³ (range 6.3–34.2 cm³). The largest individual CTV volume during treatment was on average 16% (range 0–61.1%) larger than the planning CT CTV volume, and smallest individual CTV volume during treatment was on average 8% (range

Discussion

The margin for prostate bed deformation has been measured using three methods in this study. In the first method, we measured the volume of geographical miss by subtracting each individual CBCT CTV from the planning CT CTV with two posterior margins of 5 mm and 10 mm. This method is probably the most comprehensive method to estimate margins, because information from each individual CBCT was assessed individually. By using this method, we have deduced that the number of posterior geographical

Conclusion

The prostate bed displacement and deformation when analysed with volumetric segmentation appears greater than was previously believed based on studies looking at point displacement. This study supports further investigation of adaptive radiotherapy solutions to manage prostate bed deformations.

Disclosure

No conflict of interest.

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2024, Physics and Imaging in Radiation Oncology
Magnetic Resonance Imaging (MRI)-guided Stereotactic body radiotherapy (SBRT) treatment to prostate bed after radical prostatectomy has garnered growing interests. The aim of this study is to evaluate intra-fractional anatomic and dose/volume metric variations for patients receiving this treatment.
Nineteen patients who received 30–34 Gy in 5 fractions on a 0.35T MR-Linac were included. Pre- and post-treatment MRIs were acquired for each fraction (total of 75 fractions). The Clinical Target Volume (CTV), bladder, rectum, and rectal wall were contoured on all images. Volumetric changes, Hausdorff distance, Mean Distance to Agreement (MDA), and Dice similarity coefficient (DSC) for each structure were calculated. Median value and Interquartile range (IQR) were recorded. Changes in target coverage and Organ at Risk (OAR) constraints were compared and evaluated using Wilcoxon rank sum tests at a significant level of 0.05.
Bladder had the largest volumetric changes, with a median volume increase of 48.9 % (IQR 28.9–76.8 %) and a median MDA of 5.1 mm (IQR 3.4–7.1 mm). Intra-fractional CTV volume remained stable with a median volume change of 1.2 % (0.0–4.8 %). DSC was 0.97 (IQR 0.94–0.99). For the dose/volume metrics, there were no statistically significant changes observed except for an increase in bladder hotspot and a decrease of bladder V_32.5 Gy and mean dose. The CTV V_95% changed from 99.9 % (IQR 98.8–100 %) to 99.6 % (IQR 93.9–100 %).
Despite intra-fractional variations of OARs, CTV coverage remained stable during MRI-guided SBRT treatments for the prostate bed.
A feasibility study of adaptive radiation therapy for postprostatectomy prostate cancer
2023, Medical Dosimetry
Postoperative prostate radiotherapy requires large planning target volume (PTV) margins to account for motion and deformation of the prostate bed. Adaptive radiation therapy (ART) can incorporate image-guidance data to personalize PTVs that maintain coverage while reducing toxicity. We present feasibility and dosimetry results of a prospective study of postprostatectomy ART. Twenty-one patients were treated with single-adaptation ART. Conventional treatments were delivered for fractions 1 to 6 and adapted plans for the remaining 27 fractions. Clinical target volumes (CTVs) and small bowel delineated on fraction 1 to 4 CBCT were used to generate adapted PTVs and planning organ-at-risk (OAR) volumes for adapted plans. PTV volume and OAR dose were compared between ART and conventional using Wilcoxon signed-rank tests. Weekly CBCT were used to assess the fraction of CTV covered by PTV, CTV D99, and small bowel D_1cc. Clinical metrics were compared using a Student's t-test (p < 0.05 significant). Offline adaptive planning required 1.9 ± 0.4 days (mean ± SD). ART decreased mean adapted PTV volume 61 ± 37 cc and bladder wall D50 compared with conventional treatment (p < 0.01). The CTV was fully covered for 96% (97%) of fractions with ART (conventional). Reconstructing dose on weekly CBCT, a nonsignificant reduction in CTV D99 was observed with ART (94%) compared to conventional (96%). Reduced CTV D99 with ART was significantly correlated with large anterior-posterior rectal diameter on simulation CT. ART reduced the number of fractions exceeding our institution's small bowel D1c limit from 14% to 7%. This study has demonstrated the feasibility of offline ART for post-prostatectomy cancer. ART facilitates PTV volume reduction while maintaining reasonable CTV coverage and can reduce the dose to adjacent normal tissues.
Prostate bed and organ-at-risk deformation: Prospective volumetric and dosimetric data from a phase II trial of stereotactic body radiotherapy after radical prostatectomy
2020, Radiotherapy and Oncology
Citation Excerpt :
On the other hand, interfractional changes were notable with nearly 20% of treatments requiring shifts due to interfractional motion related to suboptimal bladder and/or rectal preparation. Median shifts were anisotropic, and were similar to the shifts reported for conventionally fractionated regimens [23,25,27]. To our knowledge, this is the first study evaluating the dosimetric implications of target and pelvic OAR deformation when delivering SBRT postoperatively for prostate cancer.
Stereotactic body radiotherapy (SBRT) in the post-prostatectomy setting is investigational. A major concern is the deformable prostate bed clinical target volume (CTV) and the closely juxtaposed organs-at-risk (OARs). We report a volumetric and dosimetric analysis of kilovoltage cone-beam CT (CBCT) data from the first 18 patients enrolled on a phase II trial of post-prostatectomy SBRT. With instructions on bladder filling and rectal preparation, we hypothesized acceptable CTV coverage while minimal overdosing to OARs could be achieved.
All patients received 5 fractions of 6–6.8 Gy to the prostate bed. CBCT were taken prior to and halfway through each fraction. CTV and OARs were contoured for each CBCT. Changes in inter- and intra-fraction volume and dose were calculated. Relative changes in CTV V95%, bladder V32.5 Gy, and rectal V32.5 Gy and V27.5 Gy were evaluated.
Interfraction CTV volume remained stable, with median change +5.69% (IQR −1.73% to +9.84%). CTV V95% exhibited median change −0.74% (IQR −9.15% to −0.07%). Volumetric and dosimetric changes were minor from interfraction rotation and intrafraction motion. CTV V95% was ≥93% in 13 of 18 (72%) patients; in the remaining five, median change was −14.09% (IQR −16.64% to −13.56%). Interfraction CTV volume change was significantly larger among patients with CTV V95% <93% (+25.04% vs. +2.85%, p = 0.002).
With specific bladder and rectum filling protocols, CTV underdosing and overdosing to bladder and rectum are avoided in majority of patients. Changes in CTV shape may account for the underdosing that may be observed.
Clinical to planning target volume margins in prostate cancer radiotherapy
2016, Cancer/Radiotherapie
La connaissance des mouvements et déformations intrapelviens entre et pendant les fractions des différents volumes cibles (prostate, vésicules séminales, loge de prostatectomie et aires ganglionnaires) ainsi que celle des principaux organes à risque (vessie et rectum) permettent de définir des marges entre les volumes cibles anatomoclinique et prévisionnel rationnelles en fonction des différentes techniques d’irradiation et de leurs incertitudes. En cas de radiothérapie guidée par l’image, les marges prostatiques et des vésicules séminales peuvent se situer entre 5 et 10 mm. Les marges autour de la loge de prostatectomie varient de 10 à 15 mm et celles autour du volume cible anatomoclinique ganglionnaire entre 7 et 10 mm, selon les directions de l’espace. Les techniques de radiothérapie stéréotaxique permettent une réduction des marges, qui sont de 3 à 5 mm autour de la prostate.
The knowledge of inter- and intrafraction motion and deformations of the intrapelvic target volumes (prostate, seminal vesicles, prostatectomy bed and lymph nodes) as well as the main organs at risk (bladder and rectum) allow to define rational clinical to planning target volume margins, depending on the different radiotherapy techniques and their uncertainties. In case of image-guided radiotherapy, prostate margins and seminal vesicles margins can be between 5 and 10 mm. The margins around the prostatectomy bed vary from 10 to 15 mm and those around the lymph node clinical target volume between 7 and 10 mm. Stereotactic body radiotherapy allows lower margins, which are 3 to 5 mm around the prostate. Image-guided and stereotactic body radiotherapy with adequate margins allow finally moderate or extreme hypofractionation.
Evaluating deviations in prostatectomy patients treated with IMRT
2016, Reports of Practical Oncology and Radiotherapy
Citation Excerpt :
Defining inappropriate margins can lead to underdosing in target volumes and also an overdosing in healthy tissues, increasing the morbility.15 Some studies show that surgical bed in patients submitted to prostatectomy presents larger mobility compared with patients that were not subjected to surgery.20–22 There are imaging strategies, such as portal image, to correct geometric uncertainties that allow the verification of bony anatomy, although this may be insufficient for the correction of uncertainties.21
To evaluate the deviations in prostatectomy patients treated with IMRT in order to calculate appropriate margins to create the PTV.
Defining inappropriate margins can lead to underdosing in target volumes and also overdosing in healthy tissues, increasing morbidity.
223 CBCT images used for alignment with the CT planning scan based on bony anatomy were analyzed in 12 patients treated with IMRT following prostatectomy. Shifts of CBCT images were recorded in three directions to calculate the required margin to create PTV.
The mean and standard deviation (SD) values in millimetres were −0.05 ± 1.35 in the LR direction, −0.03 ± 0.65 in the SI direction and −0.02 ± 2.05 the AP direction. The systematic error measured in the LR, SI and AP direction were 1.35 mm, 0.65 mm, and 2.05 mm with a random error of 2.07 mm; 1.45 mm and 3.16 mm, resulting in a PTV margin of 4.82 mm; 2.64 mm, and 7.33 mm, respectively.
With IGRT we suggest a margin of 5 mm, 3 mm and 8 mm in the LR, SI and AP direction, respectively, to PTV1 and PTV2. Therefore, this study supports an anisotropic margin expansion to the PTV being the largest expansion in the AP direction and lower in SI.
Evaluation of a new transperineal ultrasound probe for inter-fraction image-guidance for definitive and post-operative prostate cancer radiotherapy
2016, Physica Medica
Citation Excerpt :
The image quality of CBCT acquisitions could also affect the accuracy of soft-tissue CT/CBCT registration. In particular, for post-prostatectomy patients, accurate localization of the vesico-ureteric anastomosis is known to be difficult on CBCT images [19]. Conversely, on US images, the RPV is only defined in the inferior direction, and arbitrarily truncated in the superior direction.
The aim of this study was to evaluate a new system based on transperineal ultrasound (TP-US) acquisitions for prostate and post-prostatectomy pre-treatment positioning by comparing this device to cone-beam computed tomography (CBCT).
The differences between CBCT/CT and TP-US/TP-US registrations were analyzed on 427 and 453 sessions for 13 prostate and 14 post-prostatectomy patients, respectively. The inter-operator variability (IOV) of the registration process, and the impact and variability of the probe pressure were also evaluated.
CBCT and TP-US shift agreements at ± 5 mm were 76.6%, 95.1%, 96.3% and 90.3%, 85.0%, 97.6% in anterior-posterior, superior-inferior and left-right directions, for prostate and post-prostatectomy patients, respectively. IOV values were similar between the 2 modalities. Displacements above 5 mm due to strong pressures were observed on both localizations, but such pressures were rarely reproduced during treatment courses.
High concordance between CBCT/CT and TP-US/TP-US localization of prostates or prostatic beds was found in this study. TP-US based prepositioning is a feasible method to ensure accurate treatment delivery, and represents an attractive alternative to invasive and/or irradiating imaging modalities.

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Prostate radiotherapyConventional margins not sufficient for post-prostatectomy prostate bed coverage: An analysis of 477 cone-beam computed tomography scans

Abstract

Purpose

Method

Results

Conclusion

Section snippets

Method

Results

Discussion

Conclusion

Disclosure

Radiother Oncol

Int J Radiat Oncol Biol Phys

Radiother Oncol

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Radiother Oncol

Prostate radiotherapy
Conventional margins not sufficient for post-prostatectomy prostate bed coverage: An analysis of 477 cone-beam computed tomography scans