Calcifications are potential surrogates for prostate localization in image-guided radiotherapy

Prostatic calcifications: Quantifying occurrence, radiodensity, and spatial distribution in prostate cancer patients

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Intraprostatic calcifications are under-recognized and under-reported in imaging.

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Intraprostatic calcifications are common in patients with prostate cancer.

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They commonly occur within tumors or in the vicinity of tumors.

Background

To evaluate the prevalence, density, and distribution of prostate calcification in patients with prostate cancer.

Methods

Patients who underwent both Gallium-68 PSMA PET/CT and MRI of the prostate over the course of a year were selected for analysis. The CT images with visible calcifications within the prostate were included and calcifications automatically isolated using a threshold of 130 HU. The corresponding multiparametric MRI was assessed and the peripheral zone, transition zone, MRI-visible tumor, and urethra manually contoured. The contoured MRI and CT images were registered using rigid registration, and calcifications mapped automatically to the MRI contours.

Results

A total of 85 men (age range 50–88, mean 69 years, standard deviation 7.2 years) were assessed. The mean serum Prostate Specific Antigen PSA was 16.7, range 0.12 to 94.4. Most patients had intermediate-risk disease (68%; Gleason grade group 2 and 3), 26% had high-risk disease (Gleason grade group 4 and 5), and 6% had low-risk disease (Gleason grade group 1). Forty-six patients out of 85 (54%) had intraprostatic calcification. Calcification occurred more in transition zone than the peripheral zone (65% vs. 35%). The mean density of the calcification was 227 HU (min 133, max 1,966 HU). In 12 patients, the calcification was within an MRI-visible tumor, in 24 patients, there were calcifications within a 9 mm distance of the tumor border, and in 9 patients, there were calcifications located between the urethra and tumor.

Conclusions

Calcifications are common in patients with prostate cancer. Their density and location may make them a significant consideration when planning treatment or retreatment with some types of minimally invasive therapy.

Multiparametric prostate MRI-based intensity-modulated radiation therapy guided by prostatic calcifications

OBJECTIVES

The optimal technique to administer image-guided radiation therapy for prostate cancer remains poorly defined. This study assessed outcomes after multiparametric prostate MRI-based planning was delivered with image-guided radiation therapy using prostatic calculi observed on cone beam CT (CBCT).

METHODS

Between January 2015 and December 2017, 94 consecutive patients were treated with CBCT-based image-guided radiation therapy (IGRT) without fiducial markers. MRI was routinely incorporated for target delineation and intraprostatic tumor nodules were boosted to allow reduced doses to normal appearing prostate. The primary endpoint was the prevalence of prostatic calcifications while toxicity and biochemical control were secondary endpoints.

RESULTS

Median follow-up was 39.7 months with 82% NCCN intermediate to very high risk. Intraprostatic calculi were noted in 68% of patients. The 3-year biochemical control, late grade ≥2 rectal toxicity and late grade ≥2 urinary toxicity rates were 96%, 3 and 7%, respectively. Biochemical control and toxicity were not significantly impacted by the presence of prostatic calculi.

CONCLUSION

Prostatic calcifications can serve as natural fiducial markers to allow for non-invasive IGRT for prostate cancer with promising early disease control and toxicity outcomes.

ADVANCES IN KNOWLEDGE

Prostate calcification-guided IGRT is technically feasible.

Automatic matching using intraprostatic calcifications as a volume of interest in CBCT images during prostate radiotherapy: a comparative study

Aim:

The study aimed to assess the clinical feasibility of employing an automatic match during cone beam computed tomography (CBCT) imaging using prostatic calcifications within the 95% isodose set as the region of interest.

Materials and methods:

CBCT images were analysed on the 5th fraction in 34 patients evaluating the difference between standard manual soft tissue anatomy matching versus auto calcification matching. An assessment of the clinical feasibility of using prostatic calcifications during matching alongside considering the effect a more automated matching process has been conducted on interobserver variability.

Results:

The standard deviation values of the difference between the soft tissue match (baseline) versus automatic calcification matches fluctuated around 1 mm in all three axes for all of the matches carried out. The interobserver variability observed between the two radiographers was 0·055, 0·065 and 0·045 cm in the vertical, longitudinal and lateral axes, respectively.

Findings:

The clarity of the calcifications on the CBCT images might explain the low interobserver variability displayed by the two matching radiographers. A calcification provides a clear starting point for image matching before commencing a check of volumetric coverage, if the matching process begins in the same place, it can allow for a standardisation of matching technique between radiographers.

Quantification of fiducial marker visibility for MRI-only prostate radiotherapy simulation

To objectively compare the suitability of MRI pulse sequences and commercially available fiducial markers (FMs) for MRI-only prostate radiotherapy simulation. Most FMs appear as small signal voids in MRI images making them difficult to differentiate from tissue heterogeneities such as calcifications. In this study we use quantitative metrics to objectively evaluate the visibility of FMs in 27 patients and an anthropomorphic phantom with a variety of standard clinical MRI pulse sequences and commercially available FMs. FM visibility was quantified using the local contrast-to-noise-ratio (lCNR), the difference between the 80th and 20th percentile iso-intensity FM volumes (V _fall) and the largest iso-intensity volume that can be distinguished from background: apparent-marker-volume (AMV). A larger lCNR and AMV, and smaller V _fall represents a more easily identifiable FM. The number of non-marker objects visualized by each pulse sequence was calculated using FM-derived template-matching. The FM-based target-registration-error (TRE) between each MRI and the planning-CT image was calculated. Fiducial marker visibility was rated by two medical physicists with over three years of experience examining MRI-only prostate simulation images. The rater's classification accuracy was quantified using the F ₁ score, which is the harmonic mean of the rater's precision and recall. These quantitative metrics and human observer ratings were used to evaluate FM identifiability in images from nine subtypes of T ₁-weighted, T ₂-weighted and gradient echo (GRE) pulse sequences in a 27-patient study. A phantom study was conducted to quantify the visibility of 8 commercially available FMs. In the patient study, the largest mean lCNR and AMV and, smallest normalized V _fall were produced by the 3.0 T multiple-echo GRE pulse sequence (T ₁-VIBE, 2° flip angle, 1.23 ms and 2.45 ms echo-times). This pulse sequence produced no false marker detections and TREs less than 2 mm in the left-right, anterior-posterior and cranial-caudal directions, respectively. Human observers rated the 1.23 ms echo-time GRE images with the best average marker visibility score of 100% and an F ₁ score of 1. In the phantom study, the Gold-Anchor GA-200X-20-B (deployed in a folded configuration) produced the largest sequence averaged lCNR and AMV measurements at 16.1 and 16.7 mm³, respectively. Using quantitative visibility and distinguishability metrics and human observer ratings, the patient study demonstrated that multiple-echo GRE images produced the best gold FM visibility and distinguishability. The phantom study demonstrated that markers manufactured from platinum or iron-doped gold quantitatively produced superior visibility compared to their pure gold counterparts.

Moderate versus extreme hypofractionated radiotherapy: a toxicity comparative analysis in low- and favorable intermediate-risk prostate cancer patients

PURPOSE

External beam radiotherapy (EBRT) is an effective treatment option for low- and favorable intermediate-risk prostate cancer (PCa) and it is usually delivered in conventional fractionation or with moderate hypofractionation (hRT), with comparable results. In the last years, a new treatment approach with stereotactic body radiotherapy (SBRT) has shown promising results. The aim of the present study was to directly compare the toxicity and outcome between hRT and SBRT in low and favorable intermediate PCa patients.

MATERIALS AND METHODS

The hRT schedules were: 71.4 Gy or 74.2 Gy in 28 fractions for low- or favorable intermediate-risk PCa, respectively, while the SBRT schedules were: 35 Gy or 37.5 Gy in five fractions, for low or favorable intermediate risk, respectively. Toxicity assessment was performed according to CTCAE v5.0 grading. The International Prostatic Symptoms Score (IPSS) was also recorded.

RESULTS

One hundred forty-nine patients were analyzed, overall 81 (54.36%) patients were low risk and 68 (45.64%) were favorable intermediate risk. Sixty-nine (46.3%) patients were treated with hypo-RT and 80 (53.7%) with SBRT. Median follow-up was 33 months (range 11-58 months). The actuarial survival rate was 98.66%. The 3-years BFS rates were 95.5% and 100% for hRT and SBRT, respectively (p = 0.051). One case (0.6%) of acute grade 3 urinary toxicity occurred in a patient with favorable intermediate risk treated with hRT. He initially suffered gross hematuria and acute urinary retention not treatable with urinary catheter, therefore a suprapubic catheter was placed and steroids were administered. No differences in acute, late or severe toxicity were detected.

CONCLUSION

Stereotactic body radiotherapy reported a good clinical outcome and safe toxicity profile. Results are comparable to hRT, but a longer follow-up is needed to assess the late effectiveness and toxicity.

Observed high incidence of prostatic calculi with the potential to act as natural fiducials for prostate image guided radiotherapy

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Prostatic calculi are a frequent radiological finding and may aid prostate IGRT.

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Incidence of prostatic calculi in a population of radiotherapy patients is reported.

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Significant proportion of patients have calculi detectable on radiotherapy images.

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Prostatic calculi may reduce the need for surgically implanted markers.

Purpose

This study aims to quantify the incidence and distribution of prostatic calculi in a population of prostate radiotherapy patients and assess their potential role in prostate image guided radiotherapy (IGRT).

Methods & materials

A retrospective analysis of trans-rectal ultrasound (TRUS), computed tomography (CT) planning and treatment verification cone beam CT (CBCT) scans from radical prostate radiotherapy patients (external beam and brachytherapy) between 2012 and 2014 was undertaken by a single experienced observer. An internationally validated schema from the Prostate Imaging Reporting and Data system (PIRADS) was used to map the location of calculi. The association of calculi with patient and disease characteristics was explored. Data was analysed using SPSS (IBM version 22.0) using descriptive statistical methods and logistic binary regression analysis.

Results

389 scan sets from 254 patients were included in the analysis. The overall incidence of calculi was 85% (n = 218) of which 79% (n = 201) were intra-prostatic calculi. The mean number of intra-prostatic calculi was 2 (range 1–10) and the mean size of calculi was 3.7 mm (range 0.5–15 mm). Calculi were most frequently observed in the posterior of the mid-gland (PI-RADs 3p, 9p) and posterior of the apex (PI-RADs 5p, 11p). 99% (n = 135) of CT planning scans with a corresponding CBCT had calculi in the same PIRADs location and all calculi were visible at the last fraction. There was no statistically significant association of calculi and N stage, M stage or Gleason score.

Conclusions

A significant proportion of prostate radiotherapy patients have prostatic calculi detectable on pre radiotherapy imaging. Calculi observed on CT were also detectable on CBCT in 99% of cases and remain visible at the end of treatment. These findings add to the growing evidence base supporting the potential of calculi as an alternative to fiducial markers to aid prostate IGRT.

Improving fiducial and prostate capsule visualization for radiotherapy planning using MRI

BACKGROUND AND PURPOSE

Intraprostatic fiducial markers (FM) improve the accuracy of radiotherapy (RT) delivery. Here we assess geometric integrity and contouring consistency using a T2*-weighted (T2*W) sequence alone, which allows visualization of the FM.

MATERIAL AND METHODS

Ten patients scanned within the Prostate Advances in Comparative Evidence (PACE) trial (NCT01584258) had prostate images acquired with computed tomography (CT) and Magnetic Resonance (MR) Imaging: T2-weighted (T2W) and T2*W sequences. The prostate was contoured independently on each imaging dataset by three clinicians. Interobserver variability was assessed using comparison indices with Monaco ADMIRE (research version 2.0, Elekta AB) and examined for statistical differences between imaging sets. CT and MR images of two test objects were acquired to assess geometric distortion and accuracy of marker positioning. The first was a linear test object comprising straight tubes in three orthogonal directions, the second was a smaller test object with markers suspended in gel.

RESULTS

Interobserver variability for prostate contouring was lower for both T2W and T2*W compared to CT, this was statistically significant when comparing CT and T2*W images. All markers are visible in T2*W images with 29/30 correctly identified, only 3/30 are visible in T2W images. Assessment of geometric distortion revealed in-plane displacements were under 0.375 mm in MRI, and through plane displacements could not be detected. The signal loss in the MR images is symmetric in relation to the true marker position shown in CT images.

CONCLUSION

Prostate T2*W images are geometrically accurate, and yield consistent prostate contours. This single sequence can be used to identify FM and for prostate delineation in a mixed MR-CT workflow.

Calcium Phosphate Cement Paste Injection as a Fiducial Marker of Cervical Cancer

BACKGROUND/AIM

Calcium phosphate cement (CPC) is used to fill bone voids in dental, orthopedic, and craniofacial applications. This study evaluated CPC marker as an injectable non-metallic fiducial marker.

MATERIALS AND METHODS

Six patients received 3-5 injections of CPC paste placed at a depth of 10 mm into tumors of the cervix before treatment planning CT (TPCT). Patients were treated with external-beam radiotherapy (EBRT) and high-dose rate brachytherapy (BT). We investigated marker visibility on cone-beam CT (CBCT), T2-weighted MRI, and interfraction of the marker motion for cervical cancer patients.

RESULTS

Of a total of 22 visible CPC markers at TPCT, 17 CPC markers were visible on the first CBCT. Excluding one patient, all markers were visible on CBCT during EBRT. Of 16 visible CPC markers on CBCT, 13 CPC markers were visible on the magnetic resonance imaging (MRI) obtained before BT. For CPC marker centroid movement, the mean-of-means/systematic variation/random variation were 0.2/0.4/1.4, -1.6/5.1/4.1, and -3.4/2.1/2.8 mm for the left-right, dorsal-ventral, and cranial-caudal directions, respectively.

CONCLUSION

This is the first report of a CPC marker injected into tumors of the cervix. It can be visualized on CBCT and MRI with reductions in marker loss and artifacts.

Mask-Adapted Background Field Removal for Artifact Reduction in Quantitative Susceptibility Mapping of the Prostate

We propose an alternative processing method for quantitative susceptibility mapping of the prostate that reduces artifacts and enables better visibility and quantification of calcifications and other lesions. Three-dimensional gradient-echo magnetic resonance data were obtained from 26 patients at 3 T who previously received a planning computed tomography of the prostate. Phase images were unwrapped using Laplacian-based phase unwrapping. The background field was removed with the V-SHARP method using tissue masks for the entire abdomen (Method 1) and masks that excluded bone and the rectum (Method 2). Susceptibility maps were calculated with the iLSQR method. The quality of susceptibility maps was assessed by one radiologist and two physicists who rated the data for visibility of lesions and data quality on a scale from 1 (poor) to 4 (good). The readers rated susceptibility maps computed with Method 2 to be, on average, better for visibility of lesions with a score of 2.9 ± 1.1 and image quality with a score of 2.8 ± 0.8 compared with maps computed with Method 1 (2.4 ± 1.2/2.3 ± 1.0). Regarding strong artifacts, these could be removed using adapted masks, and the susceptibility values seemed less biased by the artifacts. Thus, using an adapted mask for background field removal when calculating susceptibility maps of the prostate from phase data reduces artifacts and improves visibility of lesions.

Prostate deformation from inflatable rectal probe cover and dosimetric effects in prostate seed implant brachytherapy

PURPOSE

Prostate brachytherapy is an important treatment technique for patients with localized prostate cancer. An inflatable rectal ultrasound probe cover is frequently utilized during the procedure to adjust for unfavorable prostate position relative to the implant grid. However, the inflated cover causes prostate deformation, which is not accounted for during dosimetric planning. Most of the therapeutic dose is delivered after the procedure when the prostate and surrounding organs-at-risk are less deformed. The aim of this study is to quantify the potential dosimetry changes between the initial plan (prostate deformed) and the more realistic dosimetry when the prostate is less deformed without the cover.

METHODS

The authors prospectively collected the ultrasound images of the prostate immediately preceding and just after inflation of the rectal probe cover from thirty-four consecutive patients undergoing real-time planning of I-125 permanent seed implant. Manual segmentations of the deformed and undeformed images from each case were used as the input for model training to generate the initial transformation of a testing patient. During registration, the pixel-to-pixel transformation was further optimized to maximize the mutual information between the transferred deformed image and the undeformed images. The accuracy of image registration was evaluated by comparing the displacement of the urethra and calcification landmarks and by determining the Dice index between the registered and manual prostate contours. After registration, using the optimized transformation, the implanted seeds were mapped from the deformed prostate onto the undeformed prostate. The dose distribution of the undeformed anatomy, calculated using the VariSeed treatment planning system, was then analyzed and compared with that of the deformed prostate.

RESULTS

The accuracy of image registration was 1.5 ± 1.0 mm when evaluated by the displacement of calcification landmarks, 1.9 ± 1.1 mm when characterized by the displacement of the centroid of the urethra, and 0.86 ± 0.05 from the determination of the Dice index of prostate contours. The magnitude of dosimetric changes was associated with the degree of prostate deformation. The prostate coverage V100% dropped from 96.6 ± 1.7% on prostate-deformed plans to 92.6 ± 3.8% (p < 0.01) on undeformed plans, and the rectum V100% decreased from 0.48 ± 0.39 to 0.06 ± 0.14 cm³ (p < 0.01). The dose to the urethra increased, with the V150% increasing from 0.02 ± 0.06 to 0.11 ± 0.10 cm³ (p < 0.01) and D1% changing from 203.5 ± 22.7 to 239.5 ± 25.6 Gy (p < 0.01).

CONCLUSIONS

Prostate deformation from the inflation of an ultrasound rectal probe cover can significantly alter brachytherapy dosimetry. The authors have developed a deformable image registration method that allows for the characterization of dose with the undeformed anatomy. This may be used to more accurately reflect the dosimetry when the prostate is not deformed by the probe cover.

Fiducial marker guided prostate radiotherapy: a review

Image-guided radiotherapy (IGRT) is an essential tool in the accurate delivery of modern radiotherapy techniques. Prostate radiotherapy positioned using skin marks or bony anatomy may be adequate for delivering a relatively homogeneous whole-pelvic radiotherapy dose, but these surrogates are not reliable when using reduced margins, dose escalation or hypofractionated stereotactic radiotherapy. Fiducial markers (FMs) for prostate IGRT have been in use since the 1990s. They require surgical implantation and provide a surrogate for the position of the prostate gland. A variety of FMs are available and they can be used in a number of ways. This review aimed to establish the evidence for using prostate FMs in terms of feasibility, implantation procedures, types of FMs used, FM migration, imaging modalities used and the clinical impact of FMs. A search strategy was defined and a literature search was carried out in Medline. Inclusion and exclusion criteria were applied, which resulted in 50 articles being included in this review. The evidence demonstrates that FMs provide a more accurate surrogate for the position of the prostate than either external skin marks or bony anatomy. A combination of FM alignment and soft-tissue analysis is currently the most effective and widely available approach to ensuring accuracy in prostate IGRT. FM implantation is safe and well tolerated. FM migration is possible but minimal. Standardization of all techniques and procedures in relation to the use of prostate FMs is required. Finally, a clinical trial investigating a non-surgical alternative to prostate FMs is introduced.

Potential of quantitative susceptibility mapping for detection of prostatic calcifications

PURPOSE

To evaluate whether quantitative susceptibility (QSM) may be used as an alternative to computed tomography (CT) to detect calcification in prostate cancer patients.

MATERIALS AND METHODS

Susceptibility map calculation was performed using 3D gradient echo magnetic resonance imaging (MRI) data from 26 patients measured at 3T who previously received a planning CT of the prostate. Phase images were unwrapped using Laplacian-based phase unwrapping, the background field was removed with the V-SHARP method, and susceptibility maps were calculated with the iLSQR method. Two blinded readers were asked to identify peri- and intraprostatic calcifications.

RESULTS

Average mean and minimum susceptibility values (referenced to iliopsoas muscle) of calcifications were -0.249 ± 0.179 ppm and -0.551 ± 0.323 ppm, and average mean and maximum intensities in CT images were 319 ± 164 HU and 679 ± 392 HU. Twenty-one and 17 out of 22 prostatic calcifications were identified using susceptibility maps and magnitude images, respectively, as well as more than half of periprostatic phleboliths depicted by CT. Calcifications in the prostate and its periphery were quantitatively differentiable from noncalcified prostate tissue in CT (mean values for calcifications / for noncalcified tissue: 71 to 649 / -1 to 83 HU) and in QSM (mean values for calcifications / for noncalcified tissue: -0.641 to 0.063 / -0.046 to 0.181 ppm). Moreover, there was a significant correlation between susceptibility values and CT image intensities for calcifications (P < 0.004).

CONCLUSION

Prostatic calcifications could be well identified with QSM. Susceptibility maps can be easily obtained from clinical prostate MR protocols that include a 3D gradient echo sequence, rendering it a promising technique for detection and quantification of intraprostatic calcifications.

LEVEL OF EVIDENCE

1 J. Magn. Reson. Imaging 2017;45:889-898.

High-quality Linac-based Stereotactic Body Radiation Therapy with Flattening Filter Free Beams and Volumetric Modulated Arc Therapy for Low-Intermediate Risk Prostate Cancer. A Mono-institutional Experience with 90 Patients

AIMS

The aim of this phase II study was to evaluate the efficacy and toxicity of stereotactic body radiotherapy in patients with low or intermediate risk prostate cancer.

MATERIALS AND METHODS

Biopsy-confirmed prostate cancer patients were enrolled, provided that they had the following characteristics: initial prostate-specific antigen (PSA) ≤ 20 ng/ml, Gleason Score < 7, International Prostate Symptom Score < 7. The treatment schedule was 35 Gy in five fractions, delivered with volumetric modulated arcs with flattening filter free beams. Toxicity was recorded according to CTCAE criteria v4.0. Biochemical failure was calculated according to the Phoenix definition. The Expanded Prostate Cancer Index Composite questionnaire was used to record health-related quality of life.

RESULTS

Between December 2011 and March 2015, 90 patients were enrolled (53 low risk, 37 intermediate risk). The median age was 71 years (range 48-82). In total, 58 (64.5%) of the patients had Gleason Score=6, the remaining had Gleason Score=7.The median initial PSA was 6.9 ng/ml (range 2.7-17.0). Acute toxicity was mild, with 32.2 patients presenting grade 1 urinary toxicity and 32.2% of patients presenting grade 2 urinary toxicity, mainly represented by urgency, dysuria and stranguria. Rectal grade 1 toxicity was found in 15.5% of patients, whereas grade 2 toxicity was recorded in 6.6% of patients. Regarding late toxicity, grade 1 proctitis was recorded in 11.1% of patients and grade 1 urinary in 38.8%; only two events of grade 2 urinary toxicity were observed (transient urethral stenosis, resolved by a 24 h catheterisation). At a median follow-up of 27 months (6-62 months) only two intermediate risk patients experienced a biochemical failure. Health-related quality of life revealed a slight worsening in all the domains during treatment, with a return to baseline 3 months after treatment.

CONCLUSIONS

Stereotactic body radiotherapy delivered using linac-based flattening filter free volumetric modulated arc radiotherapy in low and intermediate risk prostate cancer patients is associated with mild toxicity profiles and good patient-reported quality of life.

Consistency of Organ Geometries during Prostate Radiotherapy with Two Different Bladder and Bowel Regimens

BACKGROUND

The majority of Ontario cancer centres incorporate bladder and bowel preparation protocols for the treatment of prostate cancer with radical radiotherapy. Differing methods are used to achieve a full bladder and empty rectum for planning and treatment. We compared the effects of two different bladder and bowel preparation regimens on bladder, rectum, and prostate +/- seminal vesicle geometries through a course of radiotherapy. An optimal preparation would achieve reliable spatial arrangements and a high therapeutic ratio.

METHODS

This prospective longitudinal study involved 59 prostate cancer patients treated with radical radiotherapy, of which half followed cohort 1 (laxative cohort) and the other cohort 2 (consistent timing cohort) bladder and bowel preparation regimen. Participants were asked to maintain an empty rectum for both planning and daily treatment appointments in cohort 1 through a fleet enema the morning of the planning appointment, and intake milk of magnesium during daily treatments. No specific bowel preparation was provided to cohort 2 patients. Instead, their appointment times were aligned with their natural bowel habits. This information was collected through a prescreening tool before treatment booking. All cohort 1 and 2 participants were asked to drink 250 mL of water 1 hour before planning and daily treatment appointments. Cohort 2 participants who identified no pre-existing urinary conditions were also asked to drink 2 L of water within 24 hours before the planning session and to continue this during treatment trajectory unless unable to do so because of treatment-induced bladder toxicities later in the treatment. A total of 1,335 structures (bladder, rectum +/- gas, and prostate +/- seminal vesicles) were contoured on the cone beam computerized tomography scans by three radiotherapists. A stringent quality assurance process was performed to assure quality and consistency of contours. Organ volumes were measured and evaluated for consistency over time from planning to completion of radiotherapy. Data analysis included the Fischer exact test and mixed effect modelling for total and subvolumes for bladder, rectum, rectal gas, and prostate +/- seminal vesicles.

RESULTS

Baseline total volumes for bladder ranged from 132 mL to 501 mL with means of 325 mL and 315 mL in cohorts 1 and 2, respectively. Bladder volume declined 3.6 mL per fraction and 2.4 mL per fraction in cohorts 1 and 2, respectively. The volume of the bladder structure inside the planning target volume (PTV) on simulation showed no difference by cohort (P = .095) but there was an effect of time (linear P < .0005). Baseline total volumes for rectum ranged from 19.2 mL to 106.3 mL with means of 52.0 mL and 54.7 mL in cohorts 1 and 2, respectively. The volume of the rectum inside the PTV on simulation showed no difference by cohort (P = .12) or time (P = .30) during the treatment course. Volume of gas in the rectum did not vary by cohort (P = .6) or time (P = .08). Baseline total volumes for the clinical prostate +/- seminal vesicles target ranged from 37.1 mL to 167.5 mL with means of 76.2 mL and 66.0 mL in cohorts 1 and 2, respectively. The clinical target decreased by 3% in total volume during the course of radiotherapy in both cohorts, with similar rates of the target falling outside the planned PTV structure.

CONCLUSIONS

No significant difference was found between cohorts for rectal volume, gas volume, target coverage, and rectal and bladder volumes in the PTV. Hence, patients should be offered a choice between cohort 1 and 2 bowel preparation regimens to allow for patient preference customization. Cohort 2 bladder preparation regimen was shown to be superior for consistency with slightly larger volume over time.

Image-Guided Radiotherapy for Prostate Cancer using 3 Different Techniques: Localization Data of 186 Patients

Aims and Background

This study evaluates 3 different imaging modalities—ultrasound (US), stereoscopic X-ray imaging of implanted markers (Visicoils) (X-ray), and kV cone-beam computed tomography (CBCT)—to assess interfraction and intrafraction localization error during conformal radiation therapy of prostate cancer.

Methods and Study Design

The study population consisted of 186 consecutive prostate cancer patients treated with an image-guided radiotherapy (IGRT) hypofractionated protocol using 3 techniques: 32 with X-ray, 30 with CBCT, and 124 with US. Treatment dose of 70.2 Gy was delivered in 26 fractions with a conformal dynamic arcs technique. Interfraction prostate localization errors were determined for the 3 techniques. Moreover, interfraction and intrafraction prostate motion in terms of translations and rotations, as well as residual errors, were determined with X-ray.

Results

The systematic and random components of the prostate localization errors were as follows: ( 1 ) with X-ray 3.0 ± 3.4, 2.3 ± 2.7, 1.8 ± 2.3 mm in anterior-posterior (AP), superior-inferior (SI), and left-right (LR) directions and 1.8° ± 1.2°, 2.3° ± 1.5°, 2.7° ± 3.1°, for the yaw, roll, and pitch rotations; ( 2 ) with CBCT3.5 ± 4.2, 3.3 ± 3.3, 2.5 ± 3.1 mm in AP, SI, and LR directions; ( 3 ) with US 3.7 ± 4.7, 3.4 ± 4.3, 2.3 ± 3.5 mm in AP, SI, and LR directions. Residual errors with X-ray were less than 1 mm in all directions. Intrafraction prostate motion of less than 0.5 mm in LR and of the order of 1 mm in AP and SI directions was found. This led to a significant reduction of the margins, potentially important for dose escalation studies.

Conclusions

Daily on-line IGRT with stereoscopic X-ray imaging allowed a consistent PTV margin reduction considering residual interfraction prostate localization error and intrafraction motion. X-ray offers the best compromise among accuracy, reliability, dose to the patient, and time investment for daily IGRT treatment of prostate.

[Intraprostatic calcifications as natural fiducial markers in image-guided radiotherapy for prostate cancer]

PURPOSE

To establish whether intraprostatic calcifications can serve as natural fiducials for image-guided radiotherapy (IGRT), replacing the implantation of intraprostatic fiducial markers.

PATIENTS AND METHODS

Patients with prostate cancer, having intraprostatic calcifications visible on CT scan were selected and underwent intensity-modulated radiotherapy/3D conformal radiotherapy with IGRT in the department of radiotherapy of Henri-Mondor Hospital. All cone-beam computed tomographies (CBCT) were repositioned on intraprostatic calcifications. For each acquired image, displacements of intraprostatic calcifications were calculated with reference to position on planning CT in three directions: lateral, longitudinal and vertical.

RESULTS

Between 2011 and 2013, nine patients had 183 CBCT. For each image, three displacements and space coordinates were calculated using a single reference (intraprostatic calcification). Mean lateral, longitudinal and vertical movements were 0.26±5.7 mm, -1±4.6 mm and 0.42±3.5 mm, respectively.

CONCLUSION

Studies exploring prostatic movements with fiducial markers as reference and ours with natural fiducials yield similar results. Our data confirm previous studies that have suggested that intraprostatic calcifications can be used as natural fiducials with potential reduction of iatrogenic risks and costs associated with the implantation of fiducial markers.

Detection of prostate calcification with megavoltage helical CT

RATIONALE AND OBJECTIVES

Prostate calcification is a noninvasive landmark for daily positioning of image-guided radiation therapy. However, detectability of prostate calcification with megavoltage helical computed tomography (MVCT) has not been evaluated. The purpose of this study was to evaluate the detectability of prostate calcification and to investigate how to predict detectability of calcification with MVCT.

MATERIALS AND METHODS

Thirty patients with prostate cancer who were scheduled for helical tomotherapy were included in this study. The detectability of prostate calcification on MVCT was evaluated by comparing against kilovoltage multidetector-row CT (KVCT) as the standard of reference. Maximum signal intensity (SImax), area (A) of calcification, and the product of both (SImax·A) were compared between undetectable and detectable calcifications. Then, the threshold values of SImax, A, and SImax·A were decided to achieve 100% sensitivity on MVCT.

RESULTS

KVCT identified 49 calcifications in 28 of 30 patients. MVCT detected 19 (39%) of 49 calcifications in 15 (50%) of 30 patients. The minimum threshold values of SImax, A, and SImax·A to detect prostate calcifications were 953 HU, 20.98 mm(2), and 7784 HU mm(2), respectively. Using the threshold values of SImax, A, and SImax·A, 20% (10/49), 18% (9/49), and 35% (17/49) of calcifications were in the detection range, respectively.

CONCLUSIONS

MVCT can depict about one-third of prostate calcifications detectable on KVCT. The product of maximum signal intensity and area of calcification is the most distinguishable index for predicting patients showing prostate calcifications on MVCT.

Assessment of interfractional prostate motion in patients immobilized in the prone position using a thermoplastic shell

The aim of this study was to evaluate the interfractional prostate motion of patients immobilized in the prone position using a thermoplastic shell. A total of 24 patients with prostate calcifications detectable using a kilo-voltage X-ray image-guidance system (ExacTrac X-ray system) were examined. Daily displacements of the calcification within the prostate relative to pelvic bony structures were calculated by the ExacTrac X-ray system. The average displacement and standard deviation (SD) in each of the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions were calculated for each patient. Based on the results of interfractional prostate motion, we also calculated planning target volume (PTV) margins using the van Herk formula and examined the validity of the PTV margin of our institute (a 9-mm margin everywhere except posteriorly, where a 6-mm margin was applied). In total, 899 data measurements from 24 patients were obtained. The average prostate displacements ± SD relative to bony structures were 2.8 ± 3.3, -2.0 ± 2.0 and 0.2 ± 0.4 mm, in the SI, AP and LR directions, respectively. The required PTV margins were 9.7, 6.1 and 1.4 mm in the SI, AP and LR directions, respectively. The clinical target volumes of 21 patients (87.5%) were located within the PTV for 90% or more of all treatment sessions. Interfractional prostate motion in the prone position with a thermoplastic shell was equivalent to that reported for the supine position. The PTV margin of our institute is considered appropriate for alignment, based on bony structures.

Linac based SBRT for prostate cancer in 5 fractions with VMAT and flattening filter free beams: preliminary report of a phase II study

Background

To evaluate the feasibility and early side effects of a short course hypo-fractionated SBRT programme with Volumetric Modulated Arc Therapy (VMAT) and Flattening Filter Free (FFF) beams.

Methods

A prospective phase I-II study, started on February 2012. Inclusion criteria were: age ≤ 80 years, WHO-PS ≤ 2, PSA ≤ 20 ng/ml, histologically proven prostate adenocarcinoma, T1-T2 stage, no distant metastases, no previous surgery other than TURP, no malignant tumours in the previous 5 years, IPSS 0–7. The schedule was 35 Gy in 5 alternative days. SBRT was delivered with RapidArc VMAT, with 10MV FFF photons. Toxicity assessment was performed according to CTCAE v4.0 scale. EPIC questionnaires assessed Quality-of-Life. Neo-adjuvant/concomitant hormonal-therapy was prescribed according to risk classification. SpaceOAR™ gel was optionally implanted to increase the separation space between the prostate and the rectal wall.

Results

Median follow-up was 11 months (range: 5–16); 40 patients were recruited in the protocol and treated. According to NCCN criteria, 26/40 patients were low-risk and 14/40 were intermediate risk. Median age was 70 years (56–80), median initial PSA was 6.25 ng/ml (0.50-13.43 ng/ml). Median Gleason score was 6 (6–7). All patients completed the treatment as programmed (median 11.8 days (9–22). Acute Toxicities were as follow: Rectum G0: 30/40 cases (75%); G1: 6/40 (15%); G2: 4/40 (10%). Genito-urinary: G0: 16/40 (40%); G1: 8/40 (20%); G2: 16/34 (40%). In two G2 urinary retention cases, intermittent catheter was needed. No acute G3 or greater toxicity was found. Median treatment time was 126 sec (120–136). SpaceOAR™ was implanted in 8 patients. PSA reduction from the pre-treatment value of the marker was documented in all patients.

Conclusions

Early findings suggest that SBRT with RapidArc and FFF beams for prostate cancer in 5 fractions is feasible and tolerated in acute setting. Longer follow-up is needed for assessment of late toxicity and outcome.

Role of intra- or periprostatic calcifications in image-guided radiotherapy for prostate cancer

PURPOSE

Image-guided radiotherapy (IGRT) allows more precise localization of the prostate, thus minimizing errors resulting from organ motion and set-up during treatment of prostate cancer. Using megavoltage cone-beam computed tomography (MVCBCT), references such as bones, the prostate itself or implanted fiducial markers can be used as surrogates to correct patient positioning immediately before each treatment fraction. However, the use of fiducials requires an invasive procedure and may increase costs. We aimed to assess whether intra- or periprostatic calcifications (IPC) could be used as natural fiducials.

METHODS AND MATERIALS

Data on patients treated with IGRT for prostate cancer with clearly visible IPC and implanted fiducials in both planning CT and MVCBCT images were reviewed. IPC were classified as central when inside the prostate and peripheral when within the planning target volume. Daily deviations in lateral, longitudinal, and vertical directions from baseline positioning using fiducials and using IPC were compared.

RESULTS

A total of 287 MVCBCT images were obtained and analyzed from 10 patients. The mean ± standard deviation daily deviation (mm) in the lateral, longitudinal, and vertical coordinates were 0.55 ± 3.11, 0.58 ± 3.45, and -0.54 ± 4.03, respectively, for fiducials, and 0.72 ± 3.22, 0.63 ± 3.58, and -0.69 ± 4.26, for IPC. The p values for comparisons (fiducials vs. IPC) were 0.003, 0.653, and 0.078 for lateral, longitudinal, and vertical coordinates, respectively. When cases with central IPC were analyzed (n = 7), no significant difference was found in such comparisons. Central IPC and fiducials exhibited a similar pattern of displacement during treatment, with equal values for daily displacements in the three directions for more than 90% of measurements.

CONCLUSIONS

Our data suggest that centrally located IPC may be used as natural fiducials for treatment positioning during IGRT for prostate cancer, with potential reductions in the risks and costs associated with fiducial implantation.

Clinical evaluation of soft tissue organ boundary visualization on cone-beam computed tomographic imaging

PURPOSE

Cone-beam computed tomographic images (CBCTs) are increasingly used for setup correction, soft tissue targeting, and image-guided adaptive radiotherapy. However, CBCT image quality is limited by low contrast and imaging artifacts. This analysis investigates the detectability of soft tissue boundaries in CBCT by performing a multiple-observer segmentation study.

METHODS AND MATERIALS

In four prostate cancer patients prostate, bladder and rectum were repeatedly delineated by five observers on CBCTs and fan-beam CTs (FBCTs). A volumetric analysis of contouring variations was performed by calculating coefficients of variation (COV: standard deviation/average volume). The topographical distribution of contouring variations was analyzed using an average surface mesh-based method.

RESULTS

Observer- and patient-averaged COVs for FBCT/CBCT were 0.09/0.19 for prostate, 0.05/0.08 for bladder, and 0.09/0.08 for rectum. Contouring variations on FBCT were significantly smaller than on CBCT for prostate (p < 0.03) and bladder (p < 0.04), but not for rectum (p < 0.37; intermodality differences). Intraobserver variations from repeated contouring of the same image set were not significant for either FBCT or CBCT (p < 0.05). Average standard deviations of individual observers' contour differences from average surface meshes on FBCT vs. CBCT were 1.5 vs. 2.1 mm for prostate, 0.7 vs. 1.4 mm for bladder, and 1.3 vs. 1.5 mm for rectum. The topographical distribution of contouring variations was similar for FBCT and CBCT.

CONCLUSION

Contouring variations were larger on CBCT than FBCT, except for rectum. Given the well-documented uncertainty in soft tissue contouring in the pelvis, improvement of CBCT image quality and establishment of well-defined soft tissue identification rules are desirable for image-guided radiotherapy.