Impact dosimétrique de la pose d’un espaceur rectal dans le traitement de cancer de la prostate localisé par irradiation en conditions stéréotaxiques

PurposeStereotactic body radiotherapy (SBRT) of prostate cancer is associated with rectal toxicities, which can be reduced by using a hydrogel spacer. The object of this retrospective study was to show the feasibility of spacer placement under local anesthesia and utility of hydrogel spacer to reduce the dose to the rectal wall.Material and methodsWe collected data from all patients with localised prostate cancer treated with SBRT (40 Gy in 5 fractions) between 2018 and 2020. A hydrogel spacer (SpaceOAR®) was placed depending on the availability of the product. We collected dosimetric data for target volumes and organs at risk. We calculated mean values, which were compared using non-parametric tests.ResultsAmong 35 patients, mean age was 75 years. Seventeen had a spacer placed, with a mean space created of 10 mm. No complication was reported during the intervention. High doses to the rectal wall were significantly lower in spacer group (V38: 0.39 cm³ vs. 0.72 cm³; P = 0.02). PTV were better covered in spacer group (P = 0.07). Doses to the bladder wall were similar in both groups.ConclusionSpacer procedure under local anesthesia was well tolerated. Hydrogel spacer allowed to reduce doses to the rectum while improving PTV coverage.     

Feasibility of Same-Day Prostate Fiducial Markers,Perirectal Hydrogel Spacer Placement,and Computed Tomography and Magnetic Resonance Imaging Simulation for External Beam Radiation Therapy for Low-Risk and Intermediate-Risk Prostate Cancer

PurposeThe use of prostate fiducial markers and perirectal hydrogel spacers can reduce the acute and late toxic effects associated with prostate radiation therapy. These procedures are usually performed days to weeks before simulation during a separate clinic visit to ensure resolution of procedure-related inflammation. The purpose of this study was to assess whether same-day intraprostatic fiducial marker placement, perirectal hydrogel injection, and computed tomography (CT) and magnetic resonance imaging (MRI) simulation were feasible without adversely affecting hydrogel volume, perirectal spacing, or rectal dose. If feasible, performing these procedures on the same day as simulation would expedite the start of radiation therapy, improve patient convenience, and reduce costs.Methods and MaterialsTwenty-one patients with clinically localized prostate cancer who were enrolled on a prospective clinical trial (NCT01617161) underwent same-day marker placement, hydrogel injection, and CT and MRI simulation, then underwent T2 MRI verification scans 3 to 4 weeks later. The MRI scans were fused to the CT planning scans by clinical target volumes (CTVs) to generate comparison treatment plans (70 Gy in 28 fractions). Hydrogel volume and symmetry, perirectal spacing, CTV dose, and organ-at-risk dose were evaluated.ResultsVerification scans occurred a mean of 24.9 ± 4.6 days after simulation and 9.3 ± 4.9 days after treatment start. Prostate volume did not change between scans (median, 67.3 ± 22.1 cm³ vs 64.1 ± 21.8 cm³; P = .64). The median hydrogel change between simulation and verification was ⁻1.8% ± 4.5% (P = .27). No significant differences in perirectal spacing (midgland: 1.33 ± 0.45 cm vs 1.3 ± 0.7 cm; 1 cm superior: 1.25 ± 0.95 cm vs 1.43 ± 0.91 cm; 1 cm inferior: 1.16 ± 0.28 cm vs 1.41 ± 0.49 cm) were identified. No significant differences in rectal V66 (median 2.3 ± 2.18% vs 2.3 ± 2.28%; P = .99), V35 (median 14.79 ± 7.61 vs 14.67 ± 8.4; P = .73), or D1cc (65.7 ± 9.2 Gy vs 68.2 ± 9.0 Gy; P = .80) were found. All plans met CTV and organ-at-risk constraints.ConclusionSame-day placement of intraprostatic fiducial markers, perirectal hydrogel, and simulation scans was feasible and did not significantly affect hydrogel volume, position, CTV coverage, or rectal dose.     

Characterization of an Iodinated Rectal Spacer for Prostate Photon and Proton Radiation Therapy

PurposeConventional rectal spacers (nonI-SPs) are low-contrast on computed tomography (CT), often necessitating magnetic resonance imaging for accurate delineation. A new formulation of spacers (I-SPs) incorporates iodine to improve radiopacity and CT visualization. We characterized placement, stability, and plan quality of I-SPs compared to nonI-SPs.Methods and MaterialsPatients with intact prostate cancer (n = 50) treated with I-SPs and photons were compared to randomly selected patients (n = 50) with nonI-SPs (photon or proton therapy). The I-SP was contoured on the planning CT and cone beam CTs at 3 timepoints: first, middle, and final treatment (n = 200 scans). I-SPs Hounsfield units (HU), volume, surface area (SA), centroid position relative to prostate centroid, and distance between prostate/rectum centroids were compared on the planning CTs between each cohort. I-SP changes were evaluated on cone beam CTs over courses of treatment. Dosimetric evaluations of plan quality and robustness were performed. I-SP was tested in a phantom to characterize its relative linear stopping power for protons.ResultsI-SPs yielded a distinct visible contrast on planning CTs compared to nonI-SPs (HU 138 vs 12, P < .001), allowing delineation on CT alone. The delineated volume and SA of I-SPs were smaller than nonI-SPs (volume 8.9 vs 10.6 mL, P < .001; SA 28 vs 35 cm², P < .001), yet relative spacer position and prostate-rectal separation were similar (P = .79). No significant change in HU, volume, SA, or relative position of the I-SPs hydrogel occurred over courses of treatment (all P > .1). Dosimetric analysis concluded there were no significant changes in plan quality or robustness for I-SPs compared to nonI-SPs. The I-SP relative linear stopping power was 1.018, necessitating HU override for proton planning.ConclusionsI-SPs provide a manifest CT contrast, allowing for delineation on planning CT alone with no magnetic resonance imaging necessary. I-SPs radiopacity, size, and relative position remained stable over courses of treatment from 28 to 44 fractions. No changes in plan quality or robustness were seen comparing I-SPs and nonI-SPs.     

Separation Effect and Development of Implantation Technique of Hydrogel Spacer for Prostate Cancers

PurposeThe purpose of this study is to improve the placement of a hydrogel spacer in patients with prostate cancer receiving radiation therapy.Methods and MaterialsA total of 160 patients with prostate cancer were classified into 3 groups: No spacer (group 1; n = 30), spacer placed using conventional technique (group 2; n = 100), and spacer placed using new technique (group 3; n = 30). When placing the spacer, the tip of the needle is placed at the middle of the prostate gland (group 2), or at a level corresponding to a cranial:caudal ratio of 6:4 and as close to the prostate gland as possible (group 3). The separation effect was examined and compared among the groups.ResultsThe separation in group 2 was larger than that in group 1 from the base to the apex level of the prostate (4 mm), but the separation in group 3 was larger than that in group 2 from the middle to the apex level of the prostate (4 mm). The separation values for the middle to the apex, the spacer thickness from the apex level to the apex (10 mm), the rectal exclusion from the middle to the apex, and the laterality were correlated with the 50 and 60 Gy relative biologic effectiveness (Gy[RBE]) rectal dose (P = 4.1 × 10⁻⁹ – .046). The separation vales were strongly correlated with the spacer thickness at the apex (10 mm) and the apex (4 mm; P = 1.1 × 10⁻¹⁸ – 1.8 × 10⁻¹⁷). The rectal volumes at 10 to 60 Gy(RBE) differed among the groups (P = 5.1 × 10⁻¹⁹ – 5.4 × 10⁻³). The rectal volumes in group 2 were smaller than those in group 1 at all dose levels, but those in group 3 were smaller than those in group 2 at dose levels of 30 to 50 Gy(RBE).ConclusionsThe separation, spacer thickness, and rectal exclusion from the middle to the apex of the prostate and the laterality of the hydrogel spacer affected the reduction in the rectal dose. The rectal dose can be further reduced by implanting a spacer on the caudal and prostate side.     

Evaluation of a Novel Absorbable Radiopaque Hydrogel in Patients Undergoing Image Guided Radiation Therapy for Borderline Resectable and Locally Advanced Pancreatic Adenocarcinoma

PurposeWe assessed the feasibility and safety of placing a radiopaque hydrogel in the pancreaticoduodenal groove via endoscopic ultrasound guidance in patients with borderline resectable/locally advanced pancreatic cancer (BR/LAPC).Methods and MaterialsHydrogel injections were done at time of fiducial placement to form blebs in the pancreaticoduodenal groove. Patients subsequently underwent simulation computed tomography (sim-CT) followed by hypofractionated stereotactic body radiotherapy (SBRT; 33 Gy in 5 fractions). Four to 8 weeks after SBRT, patients underwent CT re-evaluation for surgical candidacy and assessment of hydrogel location and size. Hydrogel placement was considered successful if identified in the pancreaticoduodenal groove on sim-CT scan. Stability was evaluated using equivalence testing analyses, with a null hypothesis of the presence of a ≥20% mean percentage change in volume and ≥2 mm change in the median and mean interbleb surface distance with a P value <.05 required to reject the null hypothesis and conclude equivalence. For patients undergoing pancreaticoduodenectomy, hydrogel sites were histologically examined for location and local inflammatory reactions.ResultsHydrogel placement was successful in 6 of the 6 evaluable patients. The average changes in median and mean interbleb distances were −0.43 mm and −0.35 mm, respectively, with P < .05. The average change in volume from sim-CT to post-SBRT CT was −1.0%, with P < .05. One patient experienced grade 3 nausea after fiducial/hydrogel placement, with no other adverse events to date.ConclusionsThese data demonstrate feasibility and safety of injecting a hydrogel marker in the pancreaticoduodenal groove in patients with BR/LAPC and set the stage for a follow-up clinical trial to place hydrogel as a spacer between the pancreatic tumor and dose-limiting, radiosensitive duodenum.     

Minimum Required Interval Between Hydrogel Spacer Injection and Treatment Planning for Stereotactic Body Radiation Therapy for Prostate Cancer

PurposeThe present study evaluated the short-term characteristics (<3 days) of a hydrogel spacer from the time of injection during stereotactic body radiation therapy (SBRT) for prostate cancer.Methods and MaterialsFifteen patients treated with SBRT via the CyberKnife system (36.25 Gy/5 fractions) were enrolled in this retrospective study. Two magnetic resonance (MR) images were obtained with a hydrogel spacer: one on a computed tomography (CT) simulation day (MR pretreatment [MR_pre]) and the other on the last treatment day (MR posttreatment [MR_post]). Two medical physicists contoured the hydrogel spacer on each MR image. The changes of the shapes and the volume for the hydrogel spacer between 2 MR images were evaluated.ResultsThe median period between hydrogel spacer injection and CT simulation was 1 day (range, 1-9 days). The median period between CT simulation and the last treatment was 17 days (range, 14-25 days). Regarding the volume change of the hydrogel spacer, the 2 observers observed significant differences between the volumes of the hydrogel spacer on the MR_pre and MR_post. However, the average volume difference between them was less than 1 cm³. The average dice similarity coefficient between the MR_pre and MR_post to compare the shape was more than 0.83. In addition, no clear correlation was confirmed between the volume change and the period from hydrogel spacer injection to CT simulation.ConclusionsA single day is an acceptable interval between hydrogel spacer injection and treatment planning for SBRT for prostate cancer.     

Proposed Hydrogel-Implant Quality Score and a Matched-Pair Study for Prostate Radiation Therapy

PurposeSpaceOAR hydrogel has been Food and Drug Administration approved to reduce rectal toxicity in prostate radiation therapy. Training and certification for this procedure is performed by the manufacturer, without independent quality measures. We propose a Hydrogel-Implant Quality Score (HIQS) as a surrogate to quantify hydrogel placement accuracy, to assist clinicians in tracking their implant proficiency, and to support quality improvement. A matched-pair study was designed to investigate the benefit of SpaceOAR in rectal dose reduction for low-dose-rate brachytherapy and to validate the principle of the proposed HIQS.MethodsEighty-one prostate patients were retrospectively selected for this study. Each patient had SpaceOAR implantation under manufacturer supervision. Postprocedure computed tomography and T2-weighted magnetic resonance imaging were acquired for radiation planning. A HIQS system was proposed to evaluate the hydrogel placement quality. Hydrogel implantation was performed immediately after LDR seed placement. For each LDR patient, a non-SpaceOAR patient was matched based upon intraoperative rectal dose and prostate coverage. Intraoperative and postoperative rectal dose reduction was compared between SpaceOAR and non-SpaceOAR groups.ResultsThe average HIQS was 77 ± 10.8 (range, 49-97). Rectal anatomic distortions were seen in 17 cases. Significant rectal dose reductions between intraoperative and postoperative plans were found for SpaceOAR patients compared with non-SpaceOAR patients (25.1 Gy vs −5.0 Gy for ΔD_2cc and 65.7 Gy vs 13.0 for ΔD_0.1cc). Additional rectal dose reductions (8.4 Gy for ΔD_2cc and 12.7 Gy for ΔD_0.1cc) were found for patients without rectal distortion when SpaceOAR was used.ConclusionsThe proposed HIQS system measured the hydrogel placement quality and provided insights into clinician learning and DVH outcome. SpaceOAR was shown to be effective in reducing rectal dose for LDR patients.     

Hyaluronic acid spacer in focal prostate reirradiation: A single centre experience

PurposeThe optimal management of locally recurrent prostate cancer after curative radiotherapy is still unknown. In this study, we evaluated the preliminary results of reirradiation using stereotactic body radiotherapy for locally recurrent prostate cancer after initial definitive local radiotherapy.Materials and methodsBetween April 2016 and February 2019, 11 patients with recurrent disease at the previously irradiated prostate were treated. Local recurrence was detected by radiological with or without functional imaging modalities including prostate multiparametric/pelvic MRI or positron-emission tomography–computerised tomography with (⁶⁸Ga)-labelled prostate-specific membrane antigen performed after rising prostate specific antigen serum level during follow-up. All patients received stereotactic body radiotherapy to the recurrent nodule to a total dose of 30 Gy in five fractions. Hyaluronic acid spacer was injected between prostate and rectum in seven patients to decrease the rectal dose. Acute toxicity was evaluated by using Common Terminology Criteria for Adverse Events version 4.0, and late toxicity was evaluated by using Radiation Therapy Oncology Group/European Organisation for Research and Treatment of Cancer late radiation morbidity scoring schema.ResultsAt the diagnosis, the median age was 64 years, and the mean prostate specific antigen serum concentration was 17.7 ng/mL. The median interval time between local recurrence and initial definitive radiotherapy was 63 months. Mean prostate specific antigen concentration nadir value during follow-up was 0.43 ng/mL. With a median follow up of 19 months, three patients developed either local or distant relapse. One patient had grade 3 acute rectal toxicity, and one patient had grade 2 late urinary toxicity. We did not observe any acute or late toxicity due to hyaluronic acid spacer injection.ConclusionReirradiation after local recurrence following initial definitive radiotherapy together with hyaluronic acid spacer use seems to be effective and safe.     

Délimitation des volumes-cibles et des organes critiques pour la radiothérapie conformationnelle du cancer de la prostate : expérience des essais français d’escalade de dose

The delineation of target volume and organs at risk depends on the organs definition, and on the modalities for the CT-scan acquisition. Inter-observer variability in the delineation may be large, especially when patient’s anatomy is unusual. During the two french multicentric studies of conformal radiotherapy for localized prostate cancer, it was made an effort to harmonize the delineation of the target volumes and organs at risk. Two cases were proposed for delineation during two workshops. In the first case, the mean prostate volume was 46,5 mL (extreme : 31,7-61,3), the mean prostate and seminal vesicles volume was 74,7 mL (extreme : 59,6-80,3), the rectal and bladder walls varied respectively in proportion from 1 to 1,45 and from 1 to 1,16 ; in the second case, the mean prostate volume was 53,1 mL (extreme : 40,8-73,1), the volume of prostate plus seminal vesicles was 65,1 mL (extreme : 53,2-89), the rectal wall varied proportionally from 1 to 1, 24 and the vesical wall varied from 1 to 1,67. For participating centers to the french studies of dose escalation, a quality control of contours was performed to decrease the inter-observer variability. The ways to reduce the discrepancies of volumes delineation, between different observers, are discussed. A better quality of the CT images, use of urethral opacification, and consensual definition of clinical target volumes and organs at risk may contribute to that improvement.     

Impact of magnetic resonance imaging on computed tomography-based treatment planning and acute toxicity for prostate cancer patients treated with intensity modulated radiation therapy

PurposeTo evaluate rectal and bladder dosimetric and clinical acute toxicity endpoints for prostate patients treated with intensity modulated radiation therapy (IMRT) using magnetic resonance images (MRI) registered to computed tomographic (CT) simulation images versus CT alone.Materials and MethodsThe charts of 155 consecutive prostate cancer patients at our institution from 2004 to 2008 were reviewed. A cohort of 15 IMRT treatment plans was created to compare dosimetric endpoints for CT-MRI vs CT alone. A subsequent clinical comparison involved 81 patients (CT-MRI [n = 28] vs CT alone [n = 53]). Acute genitourinary and rectal toxicity rates for the CT-MRI and CT cohorts were compared; also, univariate and multivariate regression analyses were performed using all major demographic, disease, and treatment factors as covariates.ResultsContoured prostate volumes were 43.0 vs 55.7 cm³ (P < .001, n = 15) for CT-MRI vs CT definition, with significant reductions in all bladder dose endpoints and rectal V20, V30, and V70. Grades 0, 1, and 2 toxicity rates for CT-MRI (n = 28) vs CT (n = 53) were, respectively, 25%, 25%, and 50% vs 8%, 21%, and 72% (acute genitourinary [GU], P = .024) and 39%, 29%, and 32% vs 32%, 28%, and 40% (acute rectal, P = .495). On univariate regression, only MRI use and International Prostate Symptom Scores reached significance for acute GU toxicity. On multivariate regression, age, prostate volume, and MRI use reached statistical significance for acute GU toxicity. No factor reached significance for rectal toxicity.ConclusionsThis study demonstrates a statistically significant reduction in clinical acute GU toxicity with the clinical implementation of MRI in the treatment planning process.     

Who Benefits From a Prostate Rectal Spacer? Secondary Analysis of a Phase III Trial

PurposePreviously a phase III trial of a hydrogel rectal spacer during prostate radiation therapy found decreased toxicity and a clinically significant improvement in bowel quality of life (QOL) at 3 years by the Expanded Prostate Cancer Index. We performed a secondary analysis to identify men less likely to benefit.Methods and MaterialsClinical and dosimetric data for the 222 patients enrolled on the SpaceOAR phase III trial were analyzed. The volume of rectum treated to 70 Gy (V70) and the quantitative analysis of normal tissue effects in the clinic (QUANTEC) rectal dose goals were used as surrogates for clinical benefit and plan quality. Mean bowel QOL was assessed at 15 and 36 months posttreatment and the likelihood of 1× (5 points) or 2× (10 points) minimally important difference changes were assessed.ResultsRectal V70 was correlated with physician scored toxicity (P = .033) and was used as a surrogate for plan quality. There was no correlation between prostate volume and rectal V70 (r = 0.077). Rectal V70 pre- and post-hydrogel was 13% and 3% for the smallest prostates (<40 mL) and 12% and 2% for the largest (>80 mL). The relative reduction in rectal V70 of 78% did not vary by prespacer V70, but the absolute reduction was greater for a higher V70. All spacer plans met the 5 QUANTEC rectal dose constraints, although 92% of control plans met all constraints. At 3 years, those not meeting all QUANTEC goals had a 15.0-point (standard deviation 15.1) decline, control patients meeting QUANTEC goals had a 4.0-point (9.5) decline, and spacer had >0.5 (7.6; P < .01). Previous surgery was not correlated with QOL (P = .8). Across prognostic groups, including age, body mass index, previous surgery, target volume, or quality of radiation plans, there was no statistically significant heterogeneity in the relative benefit of spacer in decreasing the risk of 1× or 2× the minimally important difference declines.ConclusionsThere was little heterogeneity in the likelihood of spacer reducing the risk of declines in bowel QOL across clinical and dosimetric variables. Even for the >95% of plans meeting QUANTEC rectal criteria, hydrogel spacer provided potentially meaningful benefits.     

Use of an intravaginal spacer in young girls treated with brachytherapy for bladder neck rhabdomyosarcoma: Dosimetric impact for organs at risk sparing and acute tolerance

PurposeInterstitial brachytherapy is indicated as part of a conservative strategy for children with bladder and/or prostate rhabdomyosarcoma (RMS), providing high local control probability with acceptable functional results. Vaginal and/or rectal complications were however reported, due to the close proximity to the implanted volume. We investigated the dosimetric impact of a vaginal spacer in terms of rectal and vaginal doses.Methods and patientsMedical records of 12 consecutive female patients with bladder neck RMS, median age 32 months (range: 1.3–6 years), were reviewed. Five patients were treated prior to 2017 without a vaginal spacer and seven patients treated after 2017 had their brachytherapy delivered with a vaginal spacer placed at time of implant.ResultsMinimal doses delivered to the most exposed 2 cm³, 1 cm³, and 0.5 cm³ of the rectum were all statistically significantly lower among patients treated with a vaginal spacer, as compared to those treated without a spacer. Median rectal D2cm³ was 22 Gy_EQD2 versus 38 Gy_EQD2 (P = 0.02), D1cm³ was 29 Gy_EQD2 versus 51 Gy_EQD2 (P = 0.013), and D0.5cm³ was 32 Gy_EQD2 versus 61 Gy_EQD2 (P = 0.017), with and without the vaginal spacer, respectively. The posterior vaginal wall D0.5cm³ dose was also significantly decreased, with median D0.5cm³ of 92 Gy_EQD2 versus 54 Gy_EQD2 (P < 0.0001), with and without the spacer, respectively. Acute tolerance was excellent in all patients, with no need for replanning and no acute complication.ConclusionsThe use of vaginal spacers in brachytherapy of female pediatric patients with bladder neck RMS resulted in significantly decreased doses to the rectum and the posterior vaginal wall. Though the clinical impact of such dose reduction remains undemonstrated, routine utilization of a vaginal spacer could be a method to decrease long-term morbidity in these patients.     

The Feasibility and Utility of Cystoscopy-Guided Hydrogel Marker Placement in Patients With Muscle-Invasive Bladder Cancer

PurposeFiducial markers at the borders of bladder tumors are useful to facilitate target delineation radiation therapy (RT) and offer the possibility of image guided RT for a focal boost. Our purpose was to evaluate the feasibility and technical performance of cystoscopy-guided placement of hydrogel markers in patients with bladder cancer referred for RT.Methods and MaterialsOurs was a prospective, multicenter, feasibility, and utility study. Thirty-two consecutive patients with muscle-invasive bladder cancer, referred for RT, underwent cystoscopy-guided implantation of hydrogel markers. Feasibility, clinical performance of the markers, and adverse events were registered. Computer tomography (CT) scans and cone beam CT (CBCT) scans acquired during RT were analyzed to evaluate the visibility and stability of the markers during the radiation period.ResultsA total of 107 hydrogel spots were implanted in 32 patients with bladder cancer. There were no procedure-related adverse events. On the simulation CT scan 76.6% of the implanted markers were sufficient for tumor delineation. At start of treatment 52.3% were visible on the CBCT and adequate for positional verification on a routine basis. The washout rate during treatment was 9.3%. At the end of treatment 46.7% of implanted spots were visible on CBCT scan and adequate for routine positional verification. At patient level, in 31.2% of cases, use of hydrogel fiducials showed adequate performance throughout the whole course.ConclusionsCystoscopy-guided placement of hydrogel markers is both safe and feasible for muscle-invasive bladder tumors. Adequate performance for radiation purposes throughout the whole course (implantation, delineation, and positional verification) was 46.7% of all implanted markers, leaving room for improvement.     

CT and MRI in target delineation in primary hepatocellular carcinoma

PurposeTo compare the quality of computed tomography (CT) and magnetic resonance imaging (MRI) in target delineation of hepatocellular carcinoma.Patients and methodsThirty-one patients with hepatocellular carcinoma received CT and MRI (including diffusion-weighted imaging [DWI]) before surgery. The maximal measurement on axial imaging and pathologic examination were extracted for statistical analysis.ResultsCT, MRI, DWI-based tumour size correlated well with pathologic sizes, r = 0.974, 0.969, 0.964 respectively. But Wilcoxon signed-ranked test showed that differences did exist. CT overestimated the tumour size by 2.9 mm compared to pathology (95% CI: -13.2 to 7.4 mm). The agreement of MRI-pathology seemed to be worse than CT, with a mean difference of 3.6 mm (95% CI: -14.7 to 7.7 mm). The worst agreement was in DWI-pathology, with a mean difference of 5 mm (95% CI: -17.9 to 7.9 mm). But significant difference was found neither between CT and MRI (P = 0.477) nor between MRI and DWI (P = 0.079).ConclusionsCT and MRI-based tumour size correlated well with pathologic size, but differences did exist. Most of the lesions were overestimated by CT and MRI. CT and MRI were similar in the guidance of target delineation, and DWI had added little value to MRI. A margin of 10 mm around the gross tumour volume to become the clinical target volume is likely not sufficient.     

Comparison of Motion-Insensitive T2-Weighted MRI Pulse Sequences for Visualization of the Prostatic Urethra During MR Simulation

PurposeThe use of magnetic resonance imaging (MRI) for radiation therapy simulation is growing because of its ability to provide excellent delineation of target tissue and organs at risk. With the use of hypofractionated schemes in prostate cancer, urethral sparing is essential; however, visualization of the prostatic urethra can be challenging because of the presence of benign prostatic hyperplasia as well as respiratory motion artifacts. The goal of this study was to compare the utility of 2 motion-insensitive, T2-weighted MRI pulse sequences for urethra visualization in the setting of MRI-based simulation.Methods and MaterialsTwenty-two patients undergoing MRI simulation without Foley catheters were imaged on a 3 Tesla MRI scanner between October 2018 and January 2019. Sagittal multislice data were acquired using (1) MultiVane XD radial sampling with parallel imaging acceleration (MVXD) and (2) single-shot fast-spin-echo (SSFSE) sequences with acquisition times of 2 to 3 minutes per sequence. For each examination, 2 genitourinary radiologists scored prostatic urethra visibility on a 1-to-5 scale and rated the signal-to-noise ratio and the presence of artifacts in each series.ResultsUrethral visibility was scored higher in the MVXD series than in the SSFSE series in 18 of 22 cases (Reader 1) and 17 of 22 cases (Reader 2). The differences in scores between MVXD and SSFSE were statistically significant for both readers (P < .0001 for both, paired Student's t-test) and interobserver agreement was high (Cohen's kappa = 0.67). Both readers found the signal-to-noise ratio of the MVXD sequence to be superior in all cases. The MVXD sequence was found to generate more artifacts than the SSFSE sequence, but these tended to appear in the periphery and did not affect the ability to visualize the urethra.ConclusionsA radial T2-weighted multislice pulse sequence was superior to an SSFSE sequence for visualization of the urethra in the setting of magnetic resonance simulation for prostate cancer.     

Planification de la radiothérapie du cancer de la prostate par l’imagerie par résonance magnétique

PurposeMagnetic resonance imaging (MRI) plays an increasing role in radiotherapy dose planning. Indeed, MRI offers superior soft tissue contrast compared to computerized tomography (CT) and therefore could provide a better delineation of target volumes and organs at risk than CT for radiotherapy. Furthermore, an MRI-only radiotherapy workflow would suppress registration errors inherent to the registration of MRI with CT. However, the estimation of the electronic density of tissues using MRI images is still a challenging issue. The purpose of this work was to design and evaluate a pseudo-CT generation method for prostate cancer treatments.Materials and methodsA pseudo-CT was generated for ten prostate cancer patients using an elastic deformation based method. For each patient, dose delivered to the patient was calculated using both the planning CT and the pseudo-CT. Dose differences between CT and pseudo-CT were investigated.ResultsMean dose relative difference in the planning target volume is 0.9% on average and ranges from 0.1% to 1.7%. In organs at risks, this value is 1.8%, 0.8%, 0.8% and 1% on average in the rectum, the right and left femoral heads, and the bladder respectively.ConclusionThe dose calculated using the pseudo-CT is very close to the dose calculated using the CT for both organs at risk and PTV. These results confirm that pseudo-CT images generated using the proposed method could be used to calculate radiotherapy treatment doses on MRI images.     

Évaluation dosimétrique d’un outil de délinéation automatique des organes pelviens à partir d’images IRM pour la radiothérapie du cancer prostatique

PurposeAn automatic segmentation tool of pelvic structures from MRI images for prostate cancer radiotherapy was developed and dosimetric evaluation of differences of delineation (automatic versus human) is presented here.Materials and methodsCTV, rectum and bladder were defined automatically and by a physician in 20 patients. Treatment plans based on “automatic” volumes were transferred on “manual” volumes and reciprocally. Dosimetric characteristics of PTV (V₉₅, minimal, maximal and mean doses), rectum (V₅₀, V₇₀, maximal and mean doses) and bladder (V₇₀, maximal and mean doses) were compared.ResultsAutomatic delineation of CTV did not significantly influence dosimetric characteristics of “manual” PTV. Rectal V₅₀ and V₇₀ were not significantly different; mean rectal dose is slightly superior (43.2 versus 44.4 Gy, p = 0.02, Student test). Bladder V₇₀ was significantly superior too (19.3 versus 21.6, p = 0.004). Organ-at-risk (OAR) automatic delineation had little influence on their dosimetric characteristics; rectal V₇₀ was slightly underestimated (20 versus 18.5 Gy, p = 0.001).ConclusionCTV and OAR automatic delineation had little influence on dosimetric characteristics. Software developments are ongoing to enable routine use and interobserver evaluation is needed.     

Diagnostic performance of imaging techniques for detecting of local recurrence after prostate brachytherapy

PurposeThe purpose of this study was to evaluate MRI and fluorocholine PET/CT diagnostic performances for the detection of local recurrence following prostate brachytherapy for localised prostate cancer.Material and methodsIn this single-centre study, we retrospectively reviewed data from 21 patients treated by brachytherapy for localised prostate cancer and diagnosed with biochemical recurrence according to Phoenix Criteria, who underwent MRI and fluorocholine PET/CT. We included patients with local relapse suspicion according to imaging exams, with biopsy for the final assessment of local recurrence. Patient analysis data were supplemented by segment analysis using an 8-segment model.ResultsThe fluorocholine PET/CT was positive for 81% and negative for 19% of patients. The sensitivity and specificity were 92% and 33% with diagnosis accuracy of 67%. The MRI was positive for 57% and negative for 43% of patients. The sensitivity and specificity were 67% and 56% with diagnosis accuracy of 62%. There was no statistically significant difference between fluorocholine PET/CT and MRI accuracy (P = 0.63). On a segment-based analysis, the sensitivity and specificity were 44% and 82% for fluorocholine PET/CT with diagnosis accuracy of 78%. For MRI, specificity was 91% diagnosis accuracy was 82%.ConclusionBoth MRI and fluorocholine PET/CT permit to highlight local recurrence sites after prostate brachytherapy. Confirmation biopsies are, however, necessary since this accuracy is insufficient.     

Inter-observer Variability of Prostate Delineation on Cone Beam Computerised Tomography Images

AimTo determine the inter-observer variability of defining the prostate gland on cone beam computerised tomography images for the purposes of image-guided radiotherapy.Materials and methodsFive genitourinary oncologists contoured the prostate gland on five cone beam computerised tomography datasets. The variations in prostate boundary delineation and consequent isocentre placement between observers were measured. Variations in volume and centre of mass were calculated. The variation in boundary definition was determined with finite element modelling.ResultsThe average standard deviation for centre of mass displacements was small, measuring 0.7, 1.8 and 2.8 mm in the left–right, anterior–posterior and superior–inferior directions, respectively. The standard deviation for volume determination was 8.93 cm³ with large variability (3.98–19.00 cm³). The mean difference between the computerised tomography-derived volume and the mean cone beam-derived volume was 16% (range 0–23.7%). The mean standard deviations for left–right, anterior–posterior and superior–inferior boundary displacements were, respectively, 1.8, 2.1 and 3.6 mm. The maximum deviation seen was 9.7 mm in the superior direction.ConclusionExpert observers had difficulty agreeing upon the location of the prostate peri-prostatic interface on the images provided. The effect on the centre of mass determination was small, and inter-observer variability for prostate detection on cone beam computerised tomography images is not prohibitive to the use of soft tissue guidance protocols. Potential exists for significant systematic matching errors, and points to the need for rigorous therapist image recognition training and development of guidance protocols before clinical implementation of soft tissue cone beam image guidance.     

Rectal Filling at Planning Does Not Predict Stability of the Prostate Gland during a Course of Radical Radiotherapy if Patients with Large Rectal Filling are Re-imaged

AimsIt has been suggested that large rectal filling is associated with an increased risk of prostate motion in radiotherapy. The aim of the present study was to determine if there is a correlation between rectal distension on planning computed tomography and the intrafraction and interfraction stability of the prostate gland during a course of radical radiotherapy for prostate cancer if a protocol was used to rescan patients with excessive rectal diameter during planning.Materials and methodsThe computed tomography planning scans of 89 patients with adenocarcinoma of the prostate treated with conformal radiotherapy were reviewed. All patients had three gold seed fiducial markers implanted into the prostate before planning computed tomography. About one in five patients had repeat computed tomography because their rectum was judged to be too large at the time of the first planning computed tomography. Rectal distension was assessed on planning computed tomography using outlines following European Organization for Research and Treatment of Cancer guidelines by measuring the rectal volume, the average cross-sectional area and the mean anterior–posterior diameter of the rectum. Daily kV images were obtained before and after treatment delivery to determine positional matching of the fiducial markers in the superior–inferior, anterior–posterior and right–left dimensions.ResultsIn total, 2860 pre- and post-treatment daily kV image pairs were obtained of 89 patients (average 32.1 image pairs per patient). The median rectal cross-sectional area was 7.3 cm² (range 2.8–17.1), the median rectal volume was 54.8 cm³ (range 20.9–128.2), and the median anterior–posterior rectal diameter was 3.03 cm (range 1.58–8.30). Unifactor linear regression models showed no statistically significant relationship between intra- and interfraction prostate stability and rectal volume on planning computed tomography.ConclusionsNo statistically significant relationship between rectal distension on planning computed tomography and the intra- and interfraction stability of the prostate gland was identified if patients with a large rectal volume were rescanned for planning.