External Beam Radiation Therapy For Cancer Research Articles

Improving normal tissue sparing using scripting in endometrial cancer radiation therapy planning.

The aim of this study was to improve the protection of organs at risk (OARs), decrease the total planning time and maintain sufficient target doses using scripting endometrial cancer external beam radiation therapy (EBRT) planning. Computed tomography (CT) data of 14 endometrial cancer patients were included in this study. Manual and automatic planning with scripting were performed for each CT. Scripts were created in the RayStation™ (RaySearch Laboratories AB, Stockholm, Sweden) planning system using a Python code. In scripting, seven additional contours were automatically created to reduce the OAR doses. The scripted and manual plans were compared to each other in terms of planning time, dose-volume histogram (DVH) parameters, and total monitor unit (MU) values. While the mean total planning time for manual planning was 368 ± 8s, it was only 55 ± 2s for the automatic planning with scripting (p < 0.001). The mean doses of OARs decreased with automatic planning (p < 0.001). In addition, the maximum doses (D2% and D1%) for bilateral femoral heads and the rectum were significantly reduced. It was observed that the total MU value increased from 1146 ± 126 (manual planning) to 1369 ± 95 (scripted planning). It is concluded that scripted planning has significant time and dosimetric advantages over manual planning for endometrial cancer EBRT planning.

The effect of lower urinary tract substructure doses on side effects of cervical cancer image-guided adaptive brachytherapy.

Image-Guided Adaptive Brachytherapy (IGABT) provides a survival advantage in locally advanced cervical cancer (LACC). Although side effects are seen less with this technique, dose parameters that cause urinary side effects are still questionable. We aim to investigate whether the radiotherapy doses of the lower urinary tract substructures (LUSS) affect the urinary system side effects (USSE) of cervical cancer external beam radiotherapy (EBRT) and the IGABT. LUSS (bladder, trigone, bladder neck, and urethra) doses were calculated in 40 patients diagnosed with LACC and receiving primary EBRT, IGABT, and concomitant chemotherapy. D0.1cc, D2cc, and D50% values were examined by contouring the bladder, trigone, bladder neck, and urethra from the intracavitary BT planning computed tomography (CT) images taken every 4 BT fractions, retrospectively. Besides, late USSE (urgency, dysuria (recurrent), frequency, obstruction, incontinence, hematuria, fistula, cystitis) were queried and categorized according to Common Toxicity Criteria for Adverse Events version 5.0. The Chi-square and Fisher's exact tests, Mann-Whitney U-test. For the whole study population, for both incontinence and dysuria, trigone (D50%), urethra (D50%, D0.1cc,), and bladder neck (D50%, D0.1cc, D2cc) volume and hot spot doses remained significant. For cystitis, urethra (D50%, D0.1cc,) and bladder neck doses (D0.1cc, D50%, D2cc) are worth investigating. Although USSE is less common in the intensity-modulated radiation therapy and IGABT era, it may be meaningful to take the doses of LUSS into account when planning IGABT. In addition, delineation of LUSS using only CT seems feasible. More proof is needed to determine delineation technique and dose constraints for LUSS for IGABT.

Overview of breast cancer external beam radiation therapy in Ghana: Towards the establishment of a national standardized treatment guidelines for improved patient care

Background and purposeThis paper reports on results from the foremost national survey on external beam radiation therapy (EBRT) treatment practice at the three radiotherapy (RT) facilities in Ghana. It is to survey the current EBRT treatment protocols and its resources available in the country for breast cancer treatment. Results are intended to form the foundation for future clinical research into developing standardized institutional and/or National breast cancer treatment planning guidelines. This will introduce uniformity into EBRT protocols across the three facilities in the country for their breast cancer patients. Materials and methodsThe survey was conducted with two online-based questionnaires; a general questionnaire that targeted radiation oncology professionals working in the three RT facilities in Ghana and a follow-up specifically for the radiation oncologists. The first survey was rolled out from 21st August 2020 to 31st December 2020. The second survey was conducted from 15th February 2021 to 31st March 2021 after the initial analysis of the responses from the first survey. The first questionnaire had 54 general EBRT breast cancer treatment questions. The second questionnaire had 14 questions focusing on dose fractionation regimens, definition of treatment targets and organs at risk (OAR) delineation. ResultsThe Google web-based questionnaires had in total 11 responses from the targeted radiation oncologists, medical physicists, and radiation therapists working in the three radiotherapy facilities in the country. The facility response rate was 100% for the survey as there were participation from all three RT facilities. CT-based breast planning was considered standard and used in all three facilities. Reference markers to aid patient positioning and target delineations were employed during simulations. Majority of the relevant OAR associated with breast EBRT were very well defined. 3 dimensional conformal radiotherapy (3DCRT) planning with forward-planning field-in-field (FP-FIF) technique has become the preferred planning of choice. From this survey, there were three medical linear accelerators (Linacs) and two Cobalt-60 (Co-60) treatment units used in treating an average of 750 breast cancer patients annually. ConclusionResults from the survey gave an in-depth overview of the current state of EBRT resources available in the treatment and management of breast cancer in Ghana. Minor protocol variations amongst the facilities were observed. However, there were strong consensus amongst the facilities regarding majority of their current existing protocols and possible future techniques/technology implementation.

Online MR evaluation of inter- and intra-fraction uterus motions and bladder volume changes during cervical cancer external beam radiotherapy

Purpose/objective(s)The purpose of the study was to assess the uterus motions and bladder volume changes of fractional movements in cervical sites throughout the external beam radiotherapy (EBRT) treatment.Materials/methodsA prospective online MR imaging tracking study was conducted in EBRT 43 patients with at least 4 scans during each treatment (before: ultrasound scan, MRI scan, CBCT scan, after: MRI scan) were included. In order to improve the treatment repeatability, each patient was instructed to empty the bladder and drink 500 ml water 1 h before CT simulation and each treatment. If the ultrasound scan result reached the CT simulation volume of bladder, the treatment began. Bladder was outlined on the T2 weighted axial sequence and CBCT image by the two observers to avoid the influence of contouring. The data of bladder volume and scanning time were accurately recorded. The bladder volumes, filling rates and uterus motion were retrospectively analyzed by MIM software.ResultsInter-fraction variation of the bladder volume was significant (p < 0.0001). Intra-fraction mean increase of the bladder volume was modest (30 cc) but significant (p < 0.001). Both inter- and intra-fraction of the uterus motion were significant. The average time between the pre-and post-fraction MRI scans was 27.82 ± 7.12 min (range 10–55 min) for IMRT plans and 24.14 ± 5.86 min (range7-38 min) for VMAT plan. Average bladder filling rate was 3.43 ml/min. The bladder filling rate did not change significantly with the course of treatment, but the bladder was more intolerant.ConclusionThis is the most detailed assessment of intra-fraction and inter-fraction motion during EBRT for cervical cancer. Finally, this study will inform appropriate treatment margins for online adaptive radiotherapy. We suggest that at least one image scan is needed before the EBRT. The portable US scanner provides a quick but unreliable measurement of the bladder volume. There is a significant statistical difference between the results of ultrasonic scanning and that of image scanning.

Impact of dosimetric differences between CT and MRI derived target volumes for external beam cervical cancer radiotherapy.

The use of MRI is becoming more prevalent in cervical cancer external beam radiotherapy (RT). The aim of this study was to investigate the impact of dosimetric differences between CT and MRI-derived target volumes for cervical cancer external beam RT. An automated planning technique for volumetric modulated arc therapy was developed. Two automated planning plans were generated for 18 cervical cancer patients where planning target volumes (PTVs) were generated based on CT or MRI data alone. Dose metrics for planning target volumes and organs at risk (OARs) were compared to analyse any differences based on imaging modality. All treatment plans were clinically acceptable. Bladder doses (V40) were lower in MRI-based plans (p = 0.04, 53.6 ± 17.2 % vs 60.3 ± 13.1 % for MRI vs CT, respectively). The maximum dose for left iliac crest showed lower doses in CT-based plans (p = 0.02, 47.8 ± 0.7 Gy vs 47.4 ± 0.4 Gy MRI vs CT, respectively). No significant differences were seen for other OARs. The dosimetric differences of CT- and MRI-based contouring variability for this study was small. CT remains the standard imaging modality for volume delineation for these patients. This is the first study to evaluate the dosimetric implications of imaging modality on target and OAR doses in cervical cancer external beam RT.

SpaceOAR© hydrogel rectal dose reduction prediction model: a decision support tool.

Prostate cancer external beam radiation therapy can result in toxicity due to organ at risk (OAR) dose, potentially impairing quality of life. A polyethylene glycol‐based spacer, SpaceOAR© hydrogel (SOH), implanted between prostate gland and rectum may significantly reduce dose received by the rectum and hence risk of rectal toxicity. SOH implant is not equally effective in all patients. Determining patients in which the implant will offer most benefit, in terms of rectal dose reduction, allows for effective management of SOH resources. Several factors have been shown to be correlated with reduction in rectal dose including distance between rectum and planning treatment volume (PTV), volume of rectum in the PTV, and change in rectum volume pre‐ to post‐SOH. Several of these factors along with other pre‐SOH CT metrics were able to predict reduction in rectal dose associated with SOH implant. Rectal V55Gy metric, was selected as the dose level of interest in the context of 60 Gy in 20 fraction treatment plans. Models were produced to predict change in RV55Gy and pre‐SOH hydrogel RV55Gy. These models offered R‐squared between 0.81 and 0.88 with statistical significance in each model. Applying an ω1 = 3% lower limit of pre‐SOH RV55 Gy and an ω2 = 3.5% lower limit on change in RV55 Gy, retained 60% of patients experiencing the largest rectal dose reduction from the hydrogel. This may offer a clinically useful tool in deciding which patients should receive SOH implant given limited resources. Predictive models, nomograms, and a workflow diagram were produced for clinical management of SOH implant.

Variation in Interinstitutional Plan Quality When Adopting a Hypofractionated Protocol for Prostate Cancer External Beam Radiation Therapy

This study quantified plan quality differences across the 4 cancer centers in Alberta, Canada for plans that followed the PROstate Fractionated Irradiation Trial protocol. Prostate plans of 235 patients were retrospectively reviewed. Interinstitutional plan quality comparisons were made based on distributions of protocol-specified parameters using 1-way analysis of variance with Games-Howell post hoc analysis. Dosimetrically representative cases were selected from each center using k-medoid clustering, enabling side-by-side comparison of dose-volume histograms and dose distributions. Fourteen anatomic features were investigated to explore interinstitutional patient population differences. Anatomically representative cases were selected from each center to explore differences in planning practices. Tumor control probability (TCP), as well as rectal wall and bladder wall normal tissue complication probabilities (NTCPs), were calculated to quantify the clinical effect of the differences in plan quality. Comparing the mean value of each center to the other 3, statistically significant differences were observed for bladder wall D30% and D50%, left and right femoral heads D5%, planning target volume D99% and D1cc, and clinical target volume D99%. Dosimetrically representative cases demonstrated consistent results. Although anatomic differences were observed between the center-specific populations, an analysis using anatomically similar cases demonstrated consistent trends in the dosimetric differences, suggesting the dosimetric variation is not exclusively due to anatomic differences. Minimal differences (<1%) among the 4 centers were noted for TCP and NTCPs, suggesting the reported differences in plan quality may not have any clinical significance. Despite common guidelines, statistically significant differences in plan quality metrics occurred among the 4 investigated centers. The differences are due at least in part to variation in local planning practices. TCP and NTCP calculations suggest that the clinical significance of the differences is minimal. These results can serve as a reference for the degree of variation among centers that can be accepted when a common protocol is adopted.

Comparison between Conventional IMRT Planning and a Novel Real-Time Adaptive Planning Strategy in Hypofractionated Regimes for Prostate Cancer: A Proof-of-Concept Planning Study.

In prostate cancer external beam radiation therapy (EBRT), intra-fraction prostate drifts may compromise the treatment efficacy by underdosing the target and/or overdosing the organs at risk. In this study, a recently developed real-time adaptive planning strategy for intensity-modulated radiation therapy (IMRT) for prostate cancer was evaluated in hypofractionated regimes against traditional treatment planning based on a treatment volume margin expansion. The proposed workflow makes use of a “library of plans” corresponding to possible intra-fraction prostate positions. During delivery, at each beam end, the plan prepared for the position of the prostate closest to the current one is selected and the corresponding beam delivered. This adaptive planning strategy was compared with the traditional approach on a clinical prostate cancer case where different prostate shift magnitudes were considered. Five, six and fifteen fraction hypofractionated schemes were considered for each of these scenarios. When shifts larger than the treatment margin were present, using the traditional approach the seminal vesicles were underdosed by 3–4% of the prescribed dose. The adaptive approach instead allowed for correct target dose coverage and lowered the dose on the rectum for each dosimetric endpoint on average by 3–4% in all the fractionation schemes. Standard intensity-modulated radiation therapy planning did not always guarantee a correct dose distribution on the seminal vesicles and the rectum. The adaptive planning strategy proposed resulted insensitive to the intra-fraction prostate drifts, produced a dose distribution in agreement with the dosimetric requirements in every case analysed and significantly lowered the dose on the rectum.

PV-087: A comparison for pelvic cancer external beam Radiotherapy with and without immobilization devices

PV-087: A comparison for pelvic cancer external beam Radiotherapy with and without immobilization devices

Implementation of Dietary Education Within a Multidisciplinary Team Approach to Improve Treatment Accuracy and Efficiency in Prostate Cancer External Beam Radiation Therapy

Prostate cancer is the most common cancer in the Veterans Health Administration. Radiation is an important treatment option for prostate cancer patients. Imaging is done before each daily radiation treatment to ensure the radiation beam is aimed accurately. Imaging can be inaccurate due to excess gas or stool in the rectum, which alters the treatment field and leads to delays in the daily treatment schedule, increased radiation exposure due to re-imaging, repetitive staff treatment delivery interventions, and an unsatisfactory veteran experience. A quality improvement project utilizing A3.9 Box Process Improvement Methodology (problem solving template) was undertaken to address identified gastrointestinal concerns hindering daily treatment. A dietitian integrated services into the Radiation Oncology clinic by providing dietary education and counseling to avoid gas-producing foods and manage bowel regularity for prostate cancer patients. Daily images were reviewed for accuracy. For 3 months prior to intervention, we examined daily treatment images and documented any interruption in treatment delivery from gas or stool in the rectum as a nutrition-related defect. Baseline data analysis revealed that 72 of 208 (34.62%) daily treatment deliveries experienced nutrition-related defects. As a result of changing the radiation therapy process to include dietary education to patients, we experienced a 45.84% reduction rate in nutrition-related defects (from 34.62% to 18.75%). Calculated cost avoidance showed an annual savings of $21,252 with implementation of a multidisciplinary approach. An estimate of approximately 132 daily treatment visits and 99 patient treatment hours can be saved annually with this approach. This project improved overall clinic function by implementing a multidisciplinary approach to prostate cancer radiation oncology care, increased patient’s satisfaction, reduced excess radiation exposure, and improved department efficiency.

Implementation of Dietary Education Within a Multidisciplinary Team Approach to Improve Treatment Accuracy and Efficiency in Prostate Cancer External Beam Radiation Therapy

Implementation of Dietary Education Within a Multidisciplinary Team Approach to Improve Treatment Accuracy and Efficiency in Prostate Cancer External Beam Radiation Therapy

Implementation of dietary education within a multidisciplinary team approach to improve treatment accuracy and efficiency in prostate cancer external beam radiation therapy.

6599Background: Prostate cancer is the most common cancer in the Veterans Health Administration. Radiation is an important treatment option for prostate cancer patients. Imaging is done before each...

The risk of second primary cancers due to peripheral photon and neutron doses received during prostate cancer external beam radiation therapy

BackgroundOut-of-field organs can be affected by secondary radiations originating from high energy linear accelerators, leading to an increased risk of carcinogenesis. The aim of this work was to determine the risk of second primary cancers (SPC) in the organs distal to the prostate during 3D conformal radiotherapy. Materials and methodsBased on previously measured peripheral photon and neutron doses in a Rando phantom using an 18MV photon beam, SPC risks in the out-of-field organs were estimated using the linear-no-threshold and the competitive risk models. Whole body as well as organ specific risk coefficients were used to calculate the SPC risks in order to estimate upper and lower risk limits, given the uncertainties associated with the coefficients. ResultsThe corresponding estimated average SPC risks ranged from 1.5±0.3% for thyroid to 4.5±4.2% for colon using whole body risk coefficients and 0.12±0.03% and 1.45±1.34%, respectively, using organ specific risk coefficients. The linear-no-threshold and the competitive risk models resulted in the same risk estimates (within the estimated errors) in the dose range received by out-of-field organs (≤1Gy). Distally located organs such as lungs, oesophagus, and thyroid received higher neutron versus photon dose. ConclusionsThe findings have important radiation protection implications when using high energy linear accelerators, as radiation protective measures could be employed to minimize the secondary out-of-field radiation for patients undergoing high energy external beam irradiation of the prostate.

MRI to CT Prostate Registration for Improved Targeting in Cancer External Beam Radiotherapy.

External radiotherapy is a major clinical treatment for localized prostate cancer. Currently, computed tomography (CT) is used to delineate the prostate and to plan the radiotherapy treatment. However, CT images suffer from a poor soft-tissue contrast and do not allow an accurate organ delineation. On the contrary, magnetic resonance imaging (MRI) provides rich details and high soft-tissue contrast, allowing tumor detection. Thus, the intraindividual propagation of MRI delineations toward the planning CT may improve tumor targeting. In this paper, we introduce a new method to propagate MRI prostate delineations to the planning CT. In the first step, a random forest classification is performed to coarsely detect the prostate in the CT images, yielding a prostate probability membership for each voxel and a prostate hard segmentation. Then, the registration is performed using a new similarity metric which maximizes the probability and the collinearity between the normals of the manual registration (MR) existing contour and the contour resulting from the CT classification. The first study on synthetic data was performed to analyze the influence of the metric parameters with different levels of noise. Then, the method was also evaluated on real MR-CT data using manual alignments and intraprostatic fiducial markers and compared to a classically used mutual information (MI) approach. The proposed metric outperformed MI by 7% in terms of Dice score coefficient, by 3.14 mm the Hausdorff distance, and 2.13 mm the markers position errors. Finally, the impact of registration uncertainties on the treatment planning was evaluated, demonstrating the potential advantage of the proposed approach in a clinical setup to define a precise target.

Comparison of two different rectal spacers in prostate cancer external beam radiotherapy in terms of rectal sparing and volume consistency

Background and purposeIn external beam radiation (EBRT) of the prostate, the rectum is the dose-limiting organ at risk, and sparing of the anterior rectal wall is a prerequisite for safe delivery of doses beyond 70Gy. Spatial sparing of the rectum can be achieved by introducing a spacer material into the retroprostatic space, thus separating the anterior rectal wall from the PTV. Materials and methodsTwo spacer technologies, Spacer OAR, a polyethylene glycol gel and ProSpace, a saline inflated balloon, were compared in terms of spacer volume, stability, and dose reduction to the anterior rectum wall in 78 patients. ResultsBoth spacer systems significantly reduced the rectum surface encompassed by the 95% isodose (gel: −35%, p<0.01; balloon −63.4%, p<0.001) compared to a control group. The balloon spacer was superior in reducing rectum dose (−27.7%, p=0.034), but exhibited an average volume loss of >50% during the full course of treatment of 37–40 fractions, while the volume of gel spacers remained fairly constant. ConclusionsIn choosing between the two spacer technologies, the advantageous dose reduction of the balloon needs to be weighed up against the better volume consistency of the gel spacer with respect to the duration of hypofractionated vs normofractionated regimens.

Hypofractioned radiotherapy in prostate cancer: is it the next step?

There are many available options for prostate cancer treatment, including active surveillance, surgery, brachytherapy and external beam radiotherapy. Based on a radiobiological rationale, which considers the prostate tumor as a low α/β tumor, the use of higher and fewer fractions to prostate cancer external beam radiotherapy treatment has been proposed. Instead of the traditional fractions of 1.8–2.0 Gy per day, fractions higher than 2 Gy per day were the subject of a number of studies. In addition, new technologies such as intensity-modulated radiation therapy, image-guided radiation therapy, volumetric-modulated arch therapy and others have emerged as background for changing paradigms. Meanwhile, moderate and ultra-hypofractionation have been the subject of studies in recent years. Some moderate hypofractionation data from randomized controlled trials are ready to use, though other non-inferiority data are still lacking. The data on ultra-hypofractionation are still very new and require further evaluation to determine its long-term safety and efficacy.

Modeling positioning uncertainties of prostate cancer external beam radiation therapy using pre-treatment data

PurposeTo investigate the influence of treatment plan data and image guidance (IG) on positioning uncertainty during prostate cancer (PCa) radiotherapy (RT). MethodsBody mass index (BMI), planning target volume (PTV), bladder volume (BV), and rectal cross section area (RCS) were collected for 267 consecutive PCa patients undergoing daily IGRT. Radiographic isocenter corrections to intra-prostatic fiducials for 12,490 treatment fractions were used to derive random (RE) and systematic (SE) inter-fraction uncertainties for the cardinal axes. These data were used to simulate RE and SE for weekly IG and Action Level (AL)-IG treatment protocols. ResultsSE and RE were 2–5 and 3–4mm in the cardinal axes, respectively, during simulation of no IG. Without IG, positive correlations (p<0.01) were noted for (1) anterior-posterior RE vs. RCS and BV and (2) cranio–caudal RE vs. RCS, BV and BMI. The RE increase was 3mm for the highest quartile of RCS, BV and BMI. Daily IGRT eliminated this relationship. 3D IG corrections of 1cm or more occured in 27% of treatment fractions and in 97% of patients. ConclusionPCa patients with elevated pre-treatment BV, RCS and BMI have increased inter-fractionation positioning uncertainty and appear the primary candidates for daily IGRT.

SU‐E‐J‐134: Effect of Reproducibility of the Deep Inspiration Breath Hold in Left Breast Cancer Radiotherapy

Purpose: To evaluate the dosimetric impact of variable reproducibility of the Deep Inspiration Breath Hold (DIBH) level for left breast cancer external beam radiotherapy. Methods: Left breast cancer patients went through CT scans at FB and DIBH prior to external beam treatment. Deformable registration between the two data sets was performed using the demons algorithm on a GPU developed by Gu et al. PMB 55(1). With an in‐house program using Matlab, the vectors were verified for accuracy and applied to the FB image at 75%, 90% and 110% magnitude, in order to simulate fictional anatomical configurations with different breath hold levels . The new images were saved as DICOM files. These new images represent variable reproducibility of a patientsˈ DIBH level. The new DICOM Files were imported into the treatment planning system (TPS). The DIBH scan and the 75%, 90%, 110% fictitious scans were registered in the TPS based on the breast/chest surface. A treatment plan was created on the DIBH CT scan, and was copied to the registered breath hold images. Dose to the heart was calculated and compared for all the inspiration levels to determine the effect of the reproducibility of DIBH levels on the dose to the heart. Results: Preliminary results show that there is a significant effect on the location of the heart from FB to the various inspiration levels. Normal tissue complication probability decreases greatly from the FB to the breath hold scans, although it is patient dependent. Variation amongst the breath hold levels is less severe. Conclusions: We have developed a tool to quantify the effect of reproducibility of the DIBH level on dose to the heart in left breast cancer radiation treatments. Preliminary results show that the effect of DIBH reproducibility is less severe than the change from FB to DIBH.

Implementation and validation of a 3-dimensional deformable registration algorithm for targeted prostate cancer radiotherapy

The daily position and shape changes of the prostate pose an obstacle to reducing the safety margin and decreasing radiation to the surrounding normal tissues during prostate cancer external beam radiotherapy. The daily prostate deformation also complicates accurate dose tracking. The uncertainty in dosimetry is further accentuated when intraprostatic targets based on molecular imaging need to be treated to a desired dose. Against this background, we have implemented and validated a 3-dimensional deformable registration algorithm to aid targeted prostate radiotherapy. We implemented and enhanced a deformable 3-dimensional image registration algorithm. This algorithm performs registration between two computed tomography (CT) images based on iteratively minimizing the difference in their image intensities (CT numbers). We used three methods to quantify the accuracy of the algorithm. First, a deformed pelvic CT set was created using a mathematically transformed set of patient pelvic CT images that was obtained with an in-room CT scanner during a course of radiotherapy. The precise voxel-to-voxel correspondence was available from the known mathematical transformation. We measured the accuracy of the deformable registration algorithm in registering the original pelvic CT set to the deformed CT set. In the second test, a custom-made deformable pelvic phantom was used. The phantom contains bony structures, and deformable bladder, rectum and prostate. Two separate CT sets of the phantom were obtained with an endorectal balloon inserted into the rectum with or without inflation with 100 cc of air. To simulate intraprostatic targets, 23 CT-opaque seeds were embedded into the prostate. We measured the accuracy of the algorithm in registering the images of the phantom with and without deformation. Lastly, two sets of pelvic CT images of the same patient were obtained on two different days during the course of treatment. These CTs were 9 days apart. We tested the goodness of the registration. In each case, correlation coefficients that measure the similarity of CT image intensities of two CT data sets were computed for a 256 × 256 − 120 cubic mm region of interest around the prostate. Correlation coefficients were computed at each CT slice as well as globally. Based on point-to-point comparison between the mathematically transformed and the registered CT sets, we found the errors were as follows: in x (lateral) direction: −0.10 ± 0.52mm; y (anterior-posterior) direction: 0.10 ± 1.11mm; and z (superior-inferior) direction: −0.21 ± 1.10mm. The corresponding 3 dimensional error was 0.57 ± 1.56mm. The overall correlation coefficient improved from 0.971 to 0.997 with the deformable registration. Using the deformable pelvic phantom, the range of shifts of the intraprostatic seeds in space created by inflating the endorectal balloon with 100 cc of air was 4.69 mm to 9.54 mm. The corresponding mean (S.D.) shift due to deformation for the 23 seeds was 6.81(±1.33) mm. The range of error in registering the seeds was 0.23 mm to 3 mm. The corresponding mean (S.D.)error was 0.86 ± 0.53mm. The correlation coefficient improved from 0.979 to 0.993 with deformable registration. Using deformable registration on the two patient CT sets obtained on two separate CT sessions, the correlation coefficient improved from 0.945 to 0.972; discounting the top and bottom CT slices that did not have sufficient information for 3-D registration, the correlation coefficient improved from 0.945 to 0.989 for the remaining 38 CT slices. Our 3-dimensional deformable registration algorithm performs accurate registration between the reference pelvic images and its deformed counterparts. The absolute registration accuracy is in the order of 1mm. In particular, the algorithm tracked the intraprostatic seeds accurately. We argue that our algorithm may aid in optimizing dose calculation and delivery for prostate radiotherapy. It may also help to allow daily mapping of intraprostatic targets for prostate cancer radiotherapy

Comparison of bat system and a new 3D trans-abdominal ultrasound-based image-guided system for prostate daily localization during external beam radiotherapy

Combined with modern radiation treatment techniques, such as 3DCRT or IMRT, reduction of PTV margins in prostate cancer external beam radiotherapy [EBRT] reduces dose to nearby normal tissues and could potentially allow an increased radiation dose to the prostate. However, tight margins could lead to geographical misses due to daily prostate displacement. The purpose of this study was to compare 2 distinctly different image-guided verification methods for prostate alignment during daily radiotherapy. A prospective clinical trial was conducted whereas prostate displacements were measured in 40 patients undergoing daily EBRT for prostate cancer. Comparison was made between a two-dimensional trans-abdominal ultrasound-based system (BAT System, NOMOS, Pennsylvania) [BAT] and a three-dimensional trans-abdominal ultrasound-based system (RESTITU System, Resonant Medical, Montreal) [RES]. A total of 217 BAT and 217 RES displacements measurements were collected within a minute of each other with all patients in the supine position. For prostate alignment with the BAT, two nearly orthogonal 2D ultrasound images obtained immediately prior to treatment were compared to the position of the CT-designed treatment planning volumes (i.e., cross-modality calculation method, comparing ultrasound to CT data). The RES system compared 3D ultrasound images acquired immediately prior to the planning CT scan to those acquired immediately prior to the treatment (i.e., intra-modality calculation method, comparing ultrasound to ultrasound data). Since the RES system resides in the CT-simulation room as well, prostate displacements were also compared to those measured by CT scan, which is the gold standard since it is used for treatment planning. This comparison was done in 10 patients, who were rescanned 3 additional times, at bi-weekly intervals, during their treatment course. The prostate displacement between the planning CT and the subsequent CT scans was calculated with the AcQSim CT-Sim Software (Phillips Medical Systems, Massachusetts) and compared to the 3D-US data obtained just prior each of the CT scans. Analysis performed on the difference in the paired 217 BAT and RES prostate displacements shows a mean difference of 0.9 (95% C.I. 0.5, 1.3) mm in the lateral [LAT] direction (p < 0.0001), of 0.1 (95% C.I. -0.5, 0.7) mm in the anteroposterior [A/P] direction (p = 0.604), and 6.0 (95% C.I. 5.4, 6.6) mm in the superoinferior [S/I] direction (p < 0.0001). These trends in the difference results are similar to those determined by Langen et. al.1, who compared the BAT system and implanted radio-opaque markers. Analysis of the thirty CT-scan and RES measured prostate displacements shows mean values of 0.2 (95% C.I. -0.4, 0.8) mm in the LAT direction (p = 0.314), - 0.3 (95% C.I. -0.9, 0.3) mm in the A/P direction (p = 0.405), and 0.1 (95% C.I. -0.5, 0.7) mm in the S/I directions (p = 0.727). Our study indicates that a significant systematic difference exists between cross-modality (BAT) and intra-modality (RES) methods when assessing prostate alignment during daily EBRT. Since RES displacements are consistent with the CT displacements, a more accurate prostate alignment is obtained when the RES method is used, compared to the BAT method.