Image-guided Radiotherapy For Prostate Cancer Research Articles

Infection after prostatic transrectal fiducial marker implantation for image guided radiation therapy

PurposeThe aim of this retrospective study is to assess the risk of infection after transrectal ultrasound-guided fiducial marker insertion for image-guided radiotherapy of prostate cancer. Material and methodsBetween January 2016 and December 2020, 829 patients scheduled for intensity-modulated radiotherapy for prostate cancer had an intraprostatic fiducial marker transrectal implantation under ultrasound guidance by radiation-oncologists specialized in brachytherapy. Patients received standard oral prophylactic antibiotic with quinolone. If Gram negative bacteria resistant to quinolone were detected at the time of the prostate cancer biopsies, the antibioprophylaxis regimen was modified accordingly. The resistance to quinolone screening test was not repeated before fiducial marker insertion. Infectious complications were assessed with questionnaires at the time of CT-planning and medical record reviewed. Toxicity was evaluated according to CTCAE v5.0. ResultsThe median time between fiducial marker implantation and evaluation was 10 days (range: 0–165 days). Four patients (0.48%) developed urinary tract infection related to the procedure, mostly with Gram-negative bacteria resistant to quinolone (75%). Three had a grade 2 infection, and one patient experienced a grade 3 urosepsis. The quinolone-resistance status was known for two patients (one positive and one negative) and was unknown for the other two patients prior to fiducial marker implantation. ConclusionIntraprostatic transrectal fiducial marker implantation for image-guided radiotherapy is well tolerated with a low rate of infection. With such a low rate of infection, there is no need to repeat the search of Gram-negative bacteria resistant to quinolone before fiducial marker implantation if it was done at the time of prostate biopsies. Optimal antibioprophylaxis should be adapted to the known status of Gram-negative bacteria resistant to quinolone.

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

To compare the reliability and the required time for two cone-beam CT (CBCT) registration methods for prostate irradiation (PI) and prostate bed irradiation (PBI). Two-hundred treatment fractions (in 10 PI and 10 PBI patients) were reanalyzed, using two CBCT registration methods: (1) a combination of an automated chamfer matching (CM) with manual matching (MM), and (2) the automated XVI dual registration tool (DRT). Bland-Altman 95% Limits of Agreement (LoA) were used to assess agreement with manual registration by Radiation Oncologists. All 95% LoA for CM+MM were≤0.33cm. For DRT, several 95% LoA were notably larger than the predefined clinical threshold of 0.3cm: -0.47 to +0.25cm (PI) and -0.36 to +0.23cm (PBI) for the superior-inferior direction and -0.52 to +0.24cm (PI) and -0.38 to +0.31cm (PBI) for the anterior-posterior direction.For PI, the average time required was 33s with CM+MM versus only 18s with DRT (p=0.002). For PBI, this was 13 versus 19s, respectively (p=0.16). For PI, DRT was significantly faster than CM+MM, but the accuracy is insufficient to use without manual verification. Therefore, manual verification is still warranted, but could offset the time benefit. For PBI, the CM+MM method was faster and more accurate.

Joint Registration and Segmentation via Multi-Task Learning for Adaptive Radiotherapy of Prostate Cancer

Medical image registration and segmentation are two of the most frequent tasks in medical image analysis. As these tasks are complementary and correlated, it would be beneficial to apply them simultaneously in a joint manner. In this paper, we formulate registration and segmentation as a joint problem via a Multi-Task Learning (MTL) setting, allowing these tasks to leverage their strengths and mitigate their weaknesses through the sharing of beneficial information. We propose to merge these tasks not only on the loss level, but on the architectural level as well. We studied this approach in the context of adaptive image-guided radiotherapy for prostate cancer, where planning and follow-up CT images as well as their corresponding contours are available for training. At testing time the contours of the follow-up scans are not available, which is a common scenario in adaptive radiotherapy. The study involves two datasets from different manufacturers and institutes. The first dataset was divided into training (12 patients) and validation (6 patients), and was used to optimize and validate the methodology, while the second dataset (14 patients) was used as an independent test set. We carried out an extensive quantitative comparison between the quality of the automatically generated contours from different network architectures as well as loss weighting methods. Moreover, we evaluated the quality of the generated deformation vector field (DVF). We show that MTL algorithms outperform their Single-Task Learning (STL) counterparts and achieve better generalization on the independent test set. The best algorithm achieved a mean surface distance of 1.06 ± 0.3 mm, 1.27 ± 0.4 mm, 0.91 ± 0.4 mm, and 1.76 ± 0.8 mm on the validation set for the prostate, seminal vesicles, bladder, and rectum, respectively. The high accuracy of the proposed method combined with the fast inference speed, makes it a promising method for automatic re-contouring of follow-up scans for adaptive radiotherapy, potentially reducing treatment related complications and therefore improving patients quality-of-life after treatment. The source code is available at https://github.com/moelmahdy/JRS-MTL .

Ultrasound-guided transrectal implantation of fiducial markers for image-guided radiotherapy of prostate cancer without local anesthesia: Patient-reported gastrointestinal-genitourinary system complications and pain.

The present study evaluates procedure-associated pain and side effects in the gastrointestinal-genitourinary system in patients with early-stage prostate cancer who were treated with image-guided radiotherapy (IGRT), accompanied by an ultrasound-guided transrectal implantation of fiducial markers, without local anesthesia. A total of 46 patients who referred to our clinics between 2012 and 2017 with a diagnosis of early-stage prostate cancer were included in the study. Before undergoing radiotherapy, all patients were implanted with three intraprostatic fiducial markers through the ultrasound-guided transrectal approach without local anesthesia. The patients underwent radiotherapy after the clinical target volumes were established, in accordance with the respective risk groups, and localization of the markers was confirmed before each therapy session. The levels of procedure-associated pain and side effects were graded immediately after the procedure through the use of a patient-based scoring system. The faces pain scale - revised version was used for the measurement of the severity of procedure-associated pain. Of the total study sample, the facial expressions of 38 patients (35%) corresponded to level 0 in the study, seven (15%) to level 2, and a single patient (2%) to level 4. None of the facial expressions of the patients corresponded to levels 6, 8, or 10. The evaluation of procedure-related genitourinary and gastrointestinal system side effects indicated that nine patients (20%) experienced side effects, while no side effects were reported in 37 patients (80%). The reported side effects included rectal bleeding in two patients (4%), dysuria in three patients (6%), hematuria in five patients (11%), and frequent urination in five patients (11%). None of the patients experienced fever or hematospermia. All side effects were reported by the respondents as "a little," while only one patient answered positively to the question on the frequency of urination. Among the patients who answered "yes" and "a little" to the questions evaluating genitourinary and gastrointestinal system side effects, the severity of these events was reported as Grade 1, corresponding to mild adverse, in only 9 (20%) patients. None of the patients experienced a Grade 2 or higher severe adverse event. In the comparison of the severity of pain of the patients during the fiducial marker procedure without local anesthesia with the severity of pain during the biopsy, 24 patients (80%) reported "lower" levels of pain, while five patients (20%) reported "equal" levels of pain. None of the patients stated that they had experienced "more" pain. IGRT accompanied by an ultrasound-guided implantation of fiducial markers without local anesthesia can be considered a safe method, given the associated acceptable levels of pain, low side effect profiles, and high prostate-specific antigen control rates.

Feasibility of image quality improvement for high-speed CBCT imaging using deep convolutional neural network for image-guided radiotherapy in prostate cancer.

High-speed cone-beam computed tomography (CBCT) scan for image-guided radiotherapy (IGRT) can reduce both the scan time and the exposure dose. However, it causes noise and artifacts in the reconstructed images due to the lower number of acquired projection data. The purpose of this study is to improve the image quality of high-speed CBCT using a deep convolutional neural network (DCNN). CBCT images of 36 prostate cancer patients were selected. The CBCT images acquired at normal scan speed were defined as CBCT100%. Simulated high-speed CBCT images acquired at twofold and fourfold scan speed were created, which were defined as CBCT50% and CBCT25%, respectively. The image quality of the CBCT50% was treated as the requirement for IGRT in this study because previous studies reported that its image is sufficient with respect to IGRT. The DCNN model was trained to learn direct mapping from CBCT25% to the corresponding CBCT100%. The performance of the DCNN model was evaluated using the sixfold cross-validation method. CBCT images generated by DCNN (CBCT25%+DCNN) were evaluated for voxel value accuracy and image quality. The DCNN model can process CBCT25% of a new patient within 0.06s/slice. The CBCT25%+DCNN was comparable to the CBCT50% in terms of both voxel value accuracy and image quality. We developed a DCNN model to remove noise and artifacts from high-speed CBCT. We emphasize that it is possible to reduce exposure to one quarter and to increase the CBCT scan speed by a factor of four.

Patient-based low dose cone beam CT acquisition settings for prostate image-guided radiotherapy treatments on a Varian TrueBeam linear accelerator.

To evaluate the performance of low dose cone beam CT (CBCT) acquisition protocols for image-guided radiotherapy of prostate cancer. CBCT images of patients undergoing prostate cancer radiotherapy were acquired with the settings currently used in our department and two low dose settings at 50% and 63% lower exposure. Four experienced radiation oncologists and two radiation therapy technologists graded the images on five image quality characteristics. The scores were analysed through Visual Grading Regression, using the acquisition settings and the patient size as covariates. The low dose acquisition settings have no impact on the image quality for patients with body profile length at hip level below 100 cm. A reduction of about 60% of the dose is feasible for patients with size below 100 cm. The visibility of low contrast features can be compromised if using the low dose acquisition settings for patients with hip size above 100 cm. Low dose CBCT acquisition protocols for the pelvis, based on subjective evaluation of patient images.

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

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). 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. 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. 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. Prostate calcification-guided IGRT is technically feasible.

Adaptive radiotherapy and the dosimetric impact of inter- and intrafractional motion on the planning target volume for prostate cancer patients

PurposeTo investigate the dosimetric influence of daily interfractional (inter) setup errors and intrafractional (intra) target motion on the planning target volume (PTV) and the possibility of an offline adaptive radiotherapy (ART) method to correct larger patient positioning uncertainties in image-guided radiotherapy for prostate cancer (PCa).Materials and methodsA CTV (clinical target volume)-to-PTV margin ranging from 15 mm in LR (left-right) and SI (superior-inferior) and 5–10 mm in AP (anterior-posterior) direction was applied to all patients. The dosimetric influence of this margin was retrospectively calculated by analysing systematic and random components of inter and intra errors of 31 consecutive intermediate- and high-risk localized PCa patients using daily cone beam computed tomography and kV/kV (kilo-Voltage) imaging. For each patient inter variation was assessed by observing the first 4 treatment days, which led to an offline ART-based treatment plan in case of larger variations.Results:Systematic inter uncertainties were larger (1.12 in LR, 2.28 in SI and 1.48 mm in AP) than intra systematic errors (0.44 in LR, 0.69 in SI and 0.80 mm in AP). Same findings for the random error in SI direction with 3.19 (inter) and 2.30 mm (intra), whereas in LR and AP results were alike with 1.89 (inter) and 1.91 mm (intra) and 2.10 (inter) and 2.27 mm (intra), respectively. The calculated margin revealed dimensions of 4–5 mm in LR, 8–9 mm in SI and 6–7 mm in AP direction. Treatment plans which had to be adapted showed smaller variations with 1.12 (LR) and 1.72 mm (SI) for Σ and 4.17 (LR) and 3.75 mm (SI) for σ compared to initial plans with 1.77 and 2.62 mm for Σ and 4.46 and 5.39 mm for σ in LR and SI, respectively.ConclusionThe currently clinically used margin of 15 mm in LR and SI and 5–10 mm in AP direction includes inter and intra uncertainties. The results show that offline ART is feasible which becomes a necessity with further reductions in PTV margins.

Prostate Fiducial Marker Placement in Patients on Anticoagulation: Feasibility Prior to Prostate SBRT.

Background and Purpose: Fiducial marker placement is required in patients undergoing robotic-based Stereotactic Body Radiotherapy (SBRT) or image-guided radiation therapy (IGRT) for prostate cancer. Many patients take antiplatelet or anticoagulant medication due to other medical comorbidities. They are often required to temporarily discontinue these medications prior to invasive medical procedures as they are prone to bleed. Some patients are unable to discontinue therapy due to an elevated risk of thromboembolic events. The purpose of this study is to report this institution's experience placing fiducial markers in prostate cancer patients who are on chronic antiplatelet or anticoagulant medication.Materials and Methods: From August 2015–March 2019 57 patients on chronic antiplatelet or anticoagulation therapy who were not cleared to stop these medications underwent transrectal ultrasound guided (TRUS) fiducial marker placement for SBRT/IGRT. All patients were monitored by a registered nurse during the procedure for prolonged bleeding that required staff to hold pressure to the area with a 4 × 4 gauze until it resolved. All patients were also called the following day to assess for ongoing bleeding events. Treatment planning CT scan confirmed the ideal geometry of the marker placement.Results: All 57 patients on antiplatelet or anticoagulant medication who underwent fiducial marker placement were discharged home the same day of the procedure. Four patients experienced persistent bleeding that required a nurse to hold prolonged pressure to the area. No patient experienced significant bleeding the following day or any untoward cardiovascular event.Conclusions: This series suggests the use of antiplatelet or anticoagulant medication is not an absolute contraindication to fiducial marker placement in patients undergoing SBRT or IGRT for prostate cancer. These patients should be closely monitored after the procedure for bleeding complications. Practitioners may consider the patient's medical comorbidities, risk factors for thromboembolism, and overall functional status as there is no standardized protocol for discontinuing anticoagulant or antiplatelet therapy for fiducial marker placement.

A study on prostate movement and dosimetric variation because of bladder and rectum volumes changes during the course of image-guided radiotherapy in prostate cancer.

AimTo study the impact of bladder and rectum volume changes on prostate positioning and the dosimetric parameters.BackgroundProstate is a moving organ, and its position is also affected by bladder and rectum volumes. Image-guided radiotherapy (IGRT) is being practiced widely for the treatment of prostate carcinoma (Ca). So, it is important to accurately study the effect of bladder and rectum volume changes in treatment.Materials and methodsThirty patients with Ca prostate were included in this study, and all were treated with 50 Gray (Gy) in 25 fractions for the first phase of treatment. A total of 750 cone-beam computed tomography (CBCT) sessions were performed. Prostate position w.r.t. its day one position was noted, and the bladder and rectum volumes were compared with their volumes on day one. Also, repeat CT was done for five patients after 10 fractions. The initial plan was imported as it was on the repeat CT images, and a hybrid plan was prepared by putting the plan isocenter at the relative anatomical reference point in repeat CT images as it was in primary CT images. The multileaf collimators (MLC) fluence was put as it is, and the dose was calculated using the monitoring units (MU), which were in the initial plan. Doses to bladder, rectum, and the target were analyzed.ResultsThe mean prostate motion in lateral and anterior-posterior direction was found to be 0.71 (±0.69) centimeter cm) and 0.77 (±0.57) cm, respectively. The mean change in bladder and rectum volumes as compared to that in day one CT images was found to be 110.51 (±84.25) cubic centimeters (cc) and 10.89 (±10.17) cc, respectively. No significant variation was observed in the doses to bladder, rectum, and the target volume in a hybrid plan, as compared to that in actual initial plan.ConclusionsBladder and rectum volume affects the position of prostate, rather the dosimetric parameters, and therefore, it can be concluded that daily CBCT should be done for accurate IGRT delivery to the prostate cancer.

Observer uncertainties of soft tissue-based patient positioning in IGRT.

PurposeThere remain uncertainties due to inter‐ and intraobserver variability in soft‐tissue‐based patient positioning even with the use of image‐guided radiation therapy (IGRT). This study aimed to reveal observer uncertainties of soft‐tissue‐based patient positioning on cone‐beam computed tomography (CBCT) images for prostate cancer IGRT.MethodsTwenty‐six patients (7–8 fractions/patient, total number of 204 fractions) who underwent IGRT for prostate cancer were selected. Six radiation therapists retrospectively measured prostate cancer location errors (PCLEs) of soft‐tissue‐based patient positioning between planning CT (pCT) and pretreatment CBCT (pre‐CBCT) images after automatic bone‐based registration. Observer uncertainties were evaluated based on residual errors, which denoted the differences between soft‐tissue and reference positioning errors. Reference positioning errors were obtained as PCLEs of contour‐based patient positioning between pCT and pre‐CBCT images. Intraobserver variations were obtained from the difference between the first and second soft‐tissue‐based patient positioning repeated by the same observer for each fraction. Systematic and random errors of inter‐ and intraobserver variations were calculated in anterior–posterior (AP), superior–inferior (SI), and left–right (LR) directions. Finally, clinical target volume (CTV)‐to‐planning target volume (PTV) margins were obtained from systematic and random errors of inter‐ and intraobserver variations in AP, SI, and LR directions.ResultsInterobserver variations in AP, SI, and LR directions were 0.9, 0.9, and 0.5 mm, respectively, for the systematic error, and 1.8, 2.2, and 1.1 mm, respectively, for random error. Intraobserver variations were <0.2 mm in all directions. CTV‐to‐PTV margins in AP, SI, and LR directions were 3.5, 3.8, and 2.1 mm, respectively.ConclusionIntraobserver variability was sufficiently small and would be negligible. However, uncertainties due to interobserver variability for soft‐tissue‐based patient positioning using CBCT images should be considered in CTV‐to‐PTV margins.

Fiducial markers in prostate cancer image-guided radiotherapy

Fiducial markers in prostate cancer image-guided radiotherapy

Fiducial markers in prostate cancer image-guided radiotherapy.

Background: Image-guided radiotherapy (IGRT) is recommended to reduce the risk of geometrical miss when modern radiotherapy technologies with high grades of conformity are used. The purpose of this study was to evaluate the efficacy of fiducial markers (FMs) for electronic portal imaging in prostate cancer radiotherapy in term of evaluating the complications associated with FMs implantation, quantifying inter-fraction prostate motion, and determination of optimal planning target volume (PTV) margins. Methods: In this single institution, prospective, consecutive study, 27 patients underwent implantation of three-gold seed FMs into the prostate gland before prostate radiotherapy. Prior to computed tomography planning, all patients were asked to report any complication associated with FMs implantation that have experienced to date. Daily pre-treatment electronic portal images were captured, and prostate position errors were corrected if they were greater than 2 mm along three translational directions. Optimal PTV expansions were computed using van Herk formula [PTV-margin= 2.5Σ + 0.7σ]. Results: FMs implantation was successful with an acceptable toxicity profile in all patients. Without IGRT, margins of 5.4 mm, 5.8 mm and 5.5 mm, in vertical, longitudinal and lateral directions, respectively, are needed for a 95% confidence level of complete clinical target volume (CTV) coverage in each treatment session. The PTV margins of 3.0 mm, 3.3 mm and 4.0 mm in corresponding directions were calculated when FMs based electronic portal imaging was applied. Conclusion: FMs based electronic portal imaging is an effective tool for prostate cancer IGRT.

Analyses of the factors influencing the accuracy of three-dimensional ultrasound in comparison with cone-beam CT in image-guided radiotherapy for prostate cancer with or without pelvic lymph node irradiation

BackgroundThree-dimensional ultrasound (3DUS) is an attractive option in image-guided radiotherapy (IGRT) for prostate cancer (PCa) patients. However, the potential factors influencing the accuracy of 3DUS in comparison with cone-beam CT (CBCT) in IGRT for PCa patients haven’t been clearly identified.MethodsThe differences between US/US and CBCT/CT registrations were analyzed over 586 and 580 sessions for 24 and 25 PCa patients treated with or without pelvic lymph node irradiation, respectively. The clinical factors that may influence registration differences were also evaluated.ResultsThe average discrepancies between US/US and CBCT/CT registrations were − 0.28 ± 5.28 mm, − 0.16 ± 3.48 mm, and − 0.47 ± 4.31 mm in the superior-inferior (SI), left-right (LR), and anterior-posterior (AP) directions, respectively. The discrepancies were respectively less than 5 mm longitudinally, laterally, and vertically in 64.4 and 70.1%, 84.9 and 89.2%, and 75.9 and 79.1% of the patients treated with or without pelvic lymph node irradiation, respectively. The registration differences were significantly smaller at least in one direction in patients younger than 70 years, without pelvic lymph node irradiation, guided by transperineal ultrasonography and had a bladder volume smaller than 300 mL.ConclusionsAge, irradiated regions, 3DUS modality, and bladder volume are important factors that may influence the differences between US/US and CBCT/CT registrations. 3DUS guidance is more feasible for younger PCa patients with a better control of bladder volume during the treatment and those who did not undergo pelvic lymph node irradiation.

Image-guided radiotherapy for prostate cancer.

Intensity-modulated radiotherapy (IMRT) has become the standard radiotherapy technology utilized for the treatment of prostate cancer, as it permits the delivery of highly conformal radiation dose distributions. Image-guided radiotherapy (IGRT) is an essential companion to IMRT that allows the treatment team to account for daily changes in target anatomy and positioning. In the present review, we will discuss the different sources of geometric uncertainty and review the rationale behind using IGRT in the treatment of prostate cancer. We will then describe commonly employed IGRT techniques and review their benefits and drawbacks. Additionally, we will review the evidence suggesting a potential clinical benefit to utilizing IGRT.

OC-0538: Daily versus weekly prostate cancer image-guided radiotherapy: A Phase 3 randomized trial

OC-0538: Daily versus weekly prostate cancer image-guided radiotherapy: A Phase 3 randomized trial

Daily versus weekly prostate cancer image-guided radiotherapy: A phase 3, multicenter, randomized trial.

4 Background: The optimal frequency of prostate cancer image-guided radiation therapy (IGRT) has not yet been clearly identified. This study sought to compare the safety and efficacy of daily versus weekly IGRT. Methods: This Phase III randomized trial recruited 470 patients with N0 localized prostate cancer, from 21 centers between June 2007 and November 2012. Total IGRT doses ranged from 70 to 80 Gy. Patients were randomly assigned (1:1) to two prostate IGRT control frequency groups: daily or weekly (Days 1, 2, and 3, then weekly). The primary outcome was 5-year recurrence-free survival (RFS). Secondary outcomes included overall survival (OS) and toxicity (CTCAE V.3.0). Post-hoc analyses included biochemical progression-free interval (BPFI), clinical progression-free interval (CPFI) and second cancer-free interval (SCFI). Results: Median follow-up was 4.1 years (Q1 – Q3 = 3.1 – 5.1).There was no statistically-significant difference in RFS between the groups (hazard ratio [HR] = 0.81 [95% CI: 0.52 – 1.25]; p = 0.330). OS was worse in the daily control group versus the weekly control group (HR = 2.12 [95% CI: 1.03 – 4.37]; p = 0.042). Late rectal toxicity (Grade ≥1) incidence was significantly lower in the daily control group (HR = 0.71 [95% CI: 0.53 – 0.96]; p = 0.027). BPFI was better in the daily control group versus the weekly control group (HR = 0.45 [95% CI: 0.25 – 0.80]; p = 0.007). CPFI was better in the daily control group (HR = 0.50 [95% CI: 0.24 – 1.02]; p = 0.057). SCFI was worse in the daily control group versus the weekly control group (HR = 2.21 [95% CI: 1.10 – 4.44]; p = 0.026). Conclusions: Compared to weekly control, daily IGRT control in prostate cancer significantly decreases the risks of recurrence and late rectal toxicity but is associated with an increased risk of second cancer. Clinical trial information: NCT00433706.

Prostate Movement and Deformation in Fractionated Prostate Radiotherapy

Aims: Despite image-guided radiotherapy for prostate cancer, there remain uncertainties regarding dose delivered to intended planning target volumes [1]. To reduce intra-fraction variability, daily bowel and bladder preparation are now incorporated in most protocols [2]. However, the impact of these on prostate movements (PM) and deformation (PD) is yet not completely understood to aid anisotropic margins [3]. Our aim is to assess the impact of differential rectal filling on PM and PD.

Intraprostatic Fiducials Compared with Bony Anatomy and Skin Marks for Image-Guided Radiation Therapy of Prostate Cancer.

PurposeProstate motion occurs during radiotherapy for localized prostate cancer. We evaluated the input of intraprostatic fiducials for image-guided radiation therapy and compared it with bony anatomy and skin marks.MethodsEleven patients were implanted with three fiducial markers in the prostate. Daily sets of orthogonal kV-kV images were compared with digitally reconstructed radiography. Data were recorded for skin marks, bony anatomy, and fiducial markers. The variations were analyzed along three principal axes (left-right: LR, superoinferior: SI, and anteroposterior: AP).ResultsA total of 2,417 measures were recorded over 38 fractions of radiotherapy (76 Gy). Fiducial marker movements from bony anatomy were ≤ 5 mm for 84.2% (confidence interval: CI 95%±1.5), 91.3% (CI 95%±1.1), and 99.5% (CI 95%±0.4) of the measures along the AP, SI, and LR axes, respectively. Ninety-five percent of the shifts between a fiducial marker and the bony anatomy were < 8 mm in the AP and SI axes, and < 3 mm in the LR axis. Fiducial marker movements from skin marks were ≤ 5 mm for 64.8% (CI 95%±1.9), 79.2% (CI 95%±1.6), and 87.2% (CI 95%±1.3) of the measures along the AP, SI, and LR axes, respectively. Bony anatomy movements from skin marks were ≤ 5 mm for 84% (CI 95%±1.4), 92% (CI 95%±1.1), and 87% (CI 95%±1.3) of the measurements along the AP, SI, and LR axes, respectively.ConclusionUsing fiducial markers provides better accuracy of repositioning of the prostate than using bony anatomy and skin marks for image-guided radiotherapy of prostate cancer.

Effect of imaging frequency on PTV margins and geographical miss during image guided radiation therapy for prostate cancer

BackgroundThe relationship between frequency of imaging during image guided radiation therapy (IGRT) and planning target volume (PTV) margin remains unclear. This issue is of practical significance given resource and time intensive nature of IGRT. The purpose of this study was to evaluate PTV margins with predefined and commonly used less-than-daily IGRT schedules using data obtained from patients treated with daily IGRT for prostate cancer. Methods and materialsDaily setup error and 3-dimensional daily alignment data for a total of 108 consecutive patients with prostate cancer treated with 2700 fractions of daily image guidance on tomotherapy were retrospectively analyzed. Five IGRT scenarios were simulated: alternate day, twice weekly, once weekly, first 3 days only, and no image guidance. The daily alignment data were modeled to simulate the 5 predefined scenarios by applying appropriate corrections to determine the PTV margin for each image guidance scenario. The data were also analyzed to predict possible geographical miss in any direction using 2 frequently used PTV margins of 7 and 5 mm for all the scenarios. ResultsDecreasing the frequency of image guidance increased the mean systematic error and the standard deviation of the systematic error. With decreased image guidance frequency, an increase in PTV margins was required to achieve adequate coverage of the clinical target volume. With reduction in image guidance from 50% to 12%, a gradual increase in percentage of fractions with predicted geographical miss using an isotropic PTV margin of 7 or 5 mm was seen. With every 15% decrease in imaging, a 5% increased risk of geographical miss was estimated. ConclusionsThe use of less-than-daily IGRT requires larger PTV margins for patients treated with intensity modulated radiation therapy for prostate cancer. With every 15% reduction, a 5% increased risk of geographical miss was estimated.