Endorectal Balloon Research Articles

Rectal wall sparing effect of three different endorectal balloons in 3D conformal and IMRT prostate radiotherapy

To investigate the dosimetric consequences and rectal wall (Rwall) sparing effect of three different endorectal balloons (ERBs) for three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) for prostate cancer. In 20 patients, 4 planning computed tomography scans were made: 1 without ERB and 3 with ERB1, ERB2, or ERB3 inserted. Two different planning target volumes were defined: prostate only, and prostate plus seminal vesicles. The 3D-CRT and IMRT planning techniques were used, and the prescription dose was 78 Gy. In 284 treatment plans, the Rwall mean dose, the Rwall normal tissue complication probability, and the absolute Rwall volumes exposed to > or =50 Gy (V(50)) and > or =70 Gy (V(70)) were calculated. For spatial dose distribution analysis, inner rectal wall dose maps and dose surface histograms were generated. Each ERB was tolerated well. In the case of 3D-CRT, each ERB showed a statistically significant reduction of all the measured parameters. ERB2 and ERB3 performed better than ERB1. In IMRT, a statistically significant reduction in the Rwall dose parameters could not be demonstrated for any of the ERBs. For 3D-CRT and IMRT, as a result of the rectal dilation, ranging from 8 to 20 cm in circumference, the ERBs resulted in a reduction of the relative inner Rwall surface exposed to intermediate and high doses. In 3D-CRT, any ERB showed a significant rectal wall sparing effect. ERB2 and ERB3 were superior to ERB1. For both 3D-CRT and IMRT, a reduction of the relative inner Rwall surface exposed to intermediate and high doses was found, which may lead to reduced late rectal toxicity. Development of user- and patient-friendly ERBs is warranted to increase their acceptability.

TU‐EE‐A4‐04: Inter‐Fraction Shape Change When Using An Endorectal Balloon for Radiation Therapy of the Prostate

Purpose: To investigate inter‐fraction shape change when using an air‐filled endorectal balloon (ERB) to localize and immobilize the prostate. Method and Materials: Under an IRB‐approved treatment protocol to evaluate the use of endorectal balloons, patients have port films acquired before delivery of the treatment fields. Position adjustments in the AP direction are made based on the comparison of lateral portal images with planning DRRs. After treatment, a left lateral portal image is taken to evaluate setup. Currently an ERB is used for 15 fractions (27Gy) of the total treatment. The anterior wall of the ERB in the left lateral portal images for five patients was contoured, and the results used to estimate inter‐fraction shape change. Results: The mean position of the ERB wall was within 2mm of its position in the treatment plan for all patients, with a standard deviation of 1.2 – 2.3mm at central axis (CAX). Since the ERB minimizes intrafraction rectum/prostate motion, most of this can be attributed to setup uncertainties or patient motion. The standard deviation of the ERB wall at a point 3cm superior to CAX, corresponding to the superior end of the prostate, was larger at 2.1 – 4.3mm. The total range in the position of the ERB wall (i.e. difference in most anterior and most posterior positions) at CAX and 3cm superior to CAX was 4–6mm and 6–13mm, respectively. These differences indicate some significant inter‐fraction shape change. Conclusions: Interfraction shape change of the ERB appears to be negligible (s.d. 3cm superior of CAX<3mm) for three patients, but more important (>3mm) for two patients, indicating that some form of image‐guided or adaptive radiation therapy may be useful for some patients. Results for more patients will be presented at the meeting.

SU-FF-T-291: Monte Carlo Calculation of Rectal Dose When Using An Endorectal Balloon During Prostate Radiation Therapy

Purpose: Air‐filled intrarectal balloons can be used to localize and immobilize the prostate for radiation therapy. This project investigates how well the Eclipse treatment planning system (Varian Inc.) includes the effect of this potentially significant heterogeneity on doses to the rectum. Method and Materials: The BEAMnrc/DOSXYZnrc Monte Carlo(MC) codes were used to simulate a 4‐field conformal therapy treatment for patients who have been treated for prostate cancer under an IRB‐approved protocol which includes a 27Gy cone‐down using a rectal balloon. The rectal doses calculated using MC were compared with those from Eclipse using isodose curves, dose‐volume histograms, and wall‐volume histograms. Results: The MC results showed that, for a 27Gy prescription to the 95% isodose line, Eclipse over‐estimates the volume of the rectum receiving more than 26 Gy by 2–10cc and the volume of the rectum receiving between 12–15 Gy by 10–20cc. Conclusion: The differences in the rectal dose calculated by Eclipse and MC are consistent and can be predicted. They can be explained by the scattering behavior of the PA and lateral fields inside the balloon: For each field, the lack of electronic equilibrium reduces the high dose region while the increased electron range widens the low dose region beyond the penumbra. The combined effect of the four fields divides the DVH into two major regions, corresponding to the AP‐PA and lateral fields, and four subregions, corresponding to the scattering behavior of electrons in air.

IMRT versus conventional 3DCRT on prostate and normal tissue dosimetry using an endorectal balloon for prostate immobilization

This study was undertaken to compare prostate and normal tissue dosimetry in prostate cancer patients treated with intensity-modulated radiation therapy (IMRT) and conventional 3-dimensional conformal radiotherapy (3DCRT) using an endorectal balloon for prostate immobilization. Ten prostate cancer patients were studied using both IMRT and conventional 3DCRT at Houston Veterans Affairs Medical Center. For IMRT, the prescription was 70 Gy at 2 Gy/fraction at the 83.4% isodose line, allowing no more than 15% of the rectum and 33% of the bladder to receive above 68 and 65 Gy, respectively. For conventional 3DCRT, a 6-field arrangement with lateral and oblique fields was used to deliver 76 Gy at 2Gy/fraction, ensuring complete tumor coverage by the 72-Gy isodose line. Mean doses for prostate and seminal vesicles were 75.10 and 75.11 Gy, respectively, for IMRT and 75.40 and 75.02 Gy, respectively, for 3DCRT ( p > 0.218). 3DCRT delivered significantly higher doses to 33%, 50%, and 66% volumes of rectum by 3.55, 6.64, and 10.18 Gy, respectively ( p < 0.002), and upper rectum by 7.26, 9.86, and 9.16 Gy, respectively ( p < 0.007). 3DCRT also delivered higher doses to femur volumes of 33% and 50% by 9.38 and 10.19 Gy, respectively, ( p < 0.001). Insignificant differences in tumor control probability (TCP) values between IMRT and 3DCRT were calculated for prostate ( p = 0.320) and seminal vesicles ( p = 0.289). Compared to 3DCRT, IMRT resulted in significantly reduced normal tissue complication probability (NTCP) only for upper rectum ( p = 0.025) and femurs ( p = 0.021). This study demonstrates that IMRT achieves superior normal tissue avoidance, especially for rectum and femurs compared to 3DCRT, with comparable target dose escalation.

Impact of setup uncertainty in the dosimetry of prostate and surrounding tissues in prostate cancer patients treated with Peacock/IMRT

The purpose of this paper was to assess the effect of setup uncertainty on dosimetry of prostate, seminal vesicles, bladder, rectum, and colon in prostate cancer patients treated with Peacock intensity-modulated radiation therapy (IMRT). Ten patients underwent computed tomography (CT) scans using the “prostate box” for external, and an “endorectal balloon” for target immobilization devices, and treatment plans were generated (T1). A maximum of ± 5-mm setup error was chosen to model dosimetric effects. Isodose lines from the T1 treatment plan were then superimposed on each patient’s CT anatomy shifted by 5 mm toward the cephalad and caudal direction, generating 2 more dosimetric plans (H1 and H2, respectively). Average mean doses ranged from 74.5 to 74.92 Gy for prostate and 73.65 to 74.94 Gy for seminal vesicles. Average percent target volume below 70 Gy increased significantly for seminal vesicles, from 0.53% to 6.26%, but minimally for prostate, from 2.08% to 4.4%. Dose statistics adhered to prescription limits for normal tissues. Setup uncertainty had minimum impact on target dose escalation and normal tissue dosing. The impact of target dose inhomogeneity is currently evaluated in clinical studies.

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

Daily prostate deformation hinders accurate calculation of dose, especially to intraprostatic targets. We implemented a three-dimensional deformable registration algorithm to aid dose tracking for targeted prostate radiotherapy. The algorithm registers two computed tomography (CT) scans by iteratively minimizing their differences in image intensity. For validation, we measured the accuracy in registering (a) a pelvic CT set to its mathematically deformed counterpart, (b) CT scans of a deformable pelvic phantom with and without an endorectal balloon inflated, to simulate intraprostatic targets, 23 CT-opaque seeds were embedded in the prostate, and (c) two pelvic CT scans of a patient obtained on 2 separate days. The mean (SD) error in registering the pelvic CT set to its transformed set was 0.5 mm (1.5), with correlation coefficient improvement from 0.626 to 0.991. Using the deformable pelvic phantom, the correlation coefficient improved from 0.543 to 0.816 after registration. The mean (SD) error in tracking the intraprostatic seeds was 0.8 mm (0.5). The correlation coefficient improved from 0.610 to 0.944 after registration of the two patient CT sets. The algorithm had an accuracy of about 1 mm. It could be used for optimizing dose calculation and delivery for prostate radiotherapy.

The effect of an endorectal balloon and off-line correction on the interfraction systematic and random prostate position variations: A comparative study

To investigate the effect of an endorectal balloon (ERB) and an off-line correction protocol on the day-to-day, interfraction prostate gland motion, in patients receiving external beam radiotherapy for prostate cancer. In 22 patients, irradiated with an ERB in situ (ERB group) and in 30 patients without an ERB (No-ERB group), prostate displacements were measured daily in three orthogonal directions with portal images. Implanted gold markers and an off-line electronic portal imaging correction protocol were used for prostate position verification and correction. Movie loops were analyzed to evaluate prostate motion and rectal filling variations. The off-line correction protocol reduced the systematic prostate displacements, equally for the ERB and No-ERB group, to 1.3-1.8 mm (1 SD). The mean 3D displacement was reduced to 2.8 mm and 2.4 mm for the ERB and No-ERB group, respectively. The random interfraction displacements, relative to the treatment isocenter, were not reduced by the ERB and remained nearly unchanged in all three directions: 3.1 mm (1 SD) left-right, 2.6 mm (1 SD) superior-inferior, and 4.7 mm (1 SD) for the anterior-posterior direction. These day-to-day prostate position variations can be explained by the presence of gas and stool beside the ERB. The off-line corrections on the fiducial markers are effective in reducing the systematic prostate displacements. The investigated ERB does not reduce the interfraction prostate motion. Although the overall mean displacement is low, the day-to-day interfraction motion, especially in anterior-posterior direction, remains high compared with the systematic displacements.

490 oral Rectal wall sparing effect of 3 different endorectal balloons in 3D-CRT and IMRT of the prostate: a comparative planning study

490 oral Rectal wall sparing effect of 3 different endorectal balloons in 3D-CRT and IMRT of the prostate: a comparative planning study

489 oral Correlation of rectal wall dose surface maps with endoscopic scoring of rectal toxicity after prostate irradiation with and without an endorectal balloon

489 oral Correlation of rectal wall dose surface maps with endoscopic scoring of rectal toxicity after prostate irradiation with and without an endorectal balloon

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

Deformable image registration for the use of magnetic resonance spectroscopy in prostate treatment planning

Purpose There is now convincing evidence that prostate cancer cells lack the ability to produce and accumulate citrate. Using magnetic resonance spectroscopy imaging (MRSI), regions of absent or low citrate concentration in the prostate can be visualized at a resolution of a few mm. This new advancement provides not only a tool for early diagnosis and screening but also the opportunity for preferential targeting of radiation to regions of high tumor burden in the prostate. The differences in the shape and location of the prostate between MRSI imaging and treatment have been the major obstacle in integrating MRSI in radiation therapy treatment planning. The purpose of this study is to develop a reliable method for deforming the prostate and surrounding regions from the geometry of MRSI imaging to the geometry of treatment planning, so that the regions of high tumor burden identified by the MRSI study can be faithfully transferred to the images used for treatment planning. Methods and materials Magnetic resonance spectroscopy imaging studies have been performed on 2 prostate cancer patients using a commercial MRSI system with an endorectal coil and coupling balloon. At the end of each study, we also acquired the MRI of the pelvic region at both the deformed state where the prostate is distorted by the endorectal balloon and the resting state with the endorectal balloon deflated and removed. The task is to find a three-dimensional matrix of transformation vectors for all volume elements that links the two image sets. We have implemented an optimization method to iteratively optimize the transformation vectors using a Newton-Ralphson algorithm. The objective function is based on the mutual information. The distorted images using the transformation vectors are compared with the images acquired at the resting conditions. Results and discussion The algorithm is capable of performing the registration automatically without the need for intervention. It does not require manual contouring of the organs. By applying the algorithm to multiple image sets of different patients, we found a good agreement between the images transformed from those acquired at the deformed state and those acquired at resting conditions. The computation time required for achieving the registration is in the range of a half-hour (for image size: 256 pixels × 256 pixels × 25 slices). However, the space of registration can be restricted to speed up the process. Conclusion In this article, we described a three-dimensional deformable image registration method to automatically transform images from the deformed imaging state to resting state. Our examples show that this method is feasible and useful to the treatment planning system.

Evaluation of acute GI and GU toxicity with postprostatectomy intensity-modulated radiation therapy (IMRT) with endorectal balloon immobilization

Evaluation of acute GI and GU toxicity with postprostatectomy intensity-modulated radiation therapy (IMRT) with endorectal balloon immobilization

82 oral Controlling geometry in prostate irradiation: implanted markers and endorectal balloons

82 oral Controlling geometry in prostate irradiation: implanted markers and endorectal balloons

Rectal dose sparing with a balloon catheter and ultrasound localization in conformal radiation therapy for prostate cancer.

To compare the rectal wall and bladder volume in the high dose region with or without the use of a balloon catheter with both three-dimensional (3D)-conformal and intensity modulated radiation therapy (CRT, IMRT) approaches in the treatment of prostate cancer. Five patients with a wide range of prostate volumes and treated with primary external beam radiation therapy for localized prostate cancer were selected for analysis. Pinnacle treatment plans were generated utilizing a 3D conformal six-field design and an IMRT seven coplanar-field plan with a novel, three-step optimization and with ultrasound localization. Separate plans were devised with a rectal balloon deflated or air inflated with and without inclusion of the seminal vesicles (SV) in the target volume. The prescription dose was 76Gy in 38 fractions of 2Gy each. Cumulative dose-volume histograms (DVHs) were analyzed for the planning target volume (PTV), rectal wall, and bladder with an inflated (60cc air) or deflated balloon with and without SV included. The volumes of rectal wall and bladder above 60, 65, and 70Gy with each treatment approach were evaluated. Daily balloon placement was well-tolerated with good patient positional reproducibility. Inflation of the rectal balloon in all cases resulted in a significant decrease in the absolute volume of rectal wall receiving greater than 60, 65, or 70Gy. The rectal sparing ratio (RSR), consisting of a structure's high dose volume with the catheter inflated, divided by the volume with the catheter deflated, was calculated for each patient with and without seminal vesicle inclusion for 3D-CRT and IMRT. For 3D-CRT, RSRs with SV included were 0.59, 0.59, and 0.56 and with SV excluded were 0.60, 0.58, and 0.54 at doses of greater than 60, 65, and 70Gy, respectively. Similarly, for IMRT, the mean RSRs were 0.59, 0.59, and 0.63 including SV and 0.71, 0.66, and 0.67 excluding SV at these same dose levels, respectively. Averaged over all conditions, inflation of the rectal balloon resulted in a significant reduction in rectal volume receiving > or =65Gy to a mean ratio of 0.61 (P=0.01) or, in other words, a mean fractional high dose rectal sparing of 39%. There was a slight overall increase to 1.13 in the relative volume of bladder receiving at least 65Gy; however, this was not significant (P=0.6). Use of an endorectal balloon with a non-image-guided 3D-CRT plan produced about as much rectal dose sparing as a highly conformal, image-guided IMRT approach without a balloon. However, inclusion of a balloon with IMRT produced further rectal sparing still. These results indicate that use of a rectal balloon with a 3D-CRT plan incorporating typical treatment margins will produce significant high dose rectal sparing that is comparable to that achieved by a highly conformal IMRT with ultrasound localization. Further sparing is achieved with the inclusion of a balloon catheter in an IMRT plan. Thus, in addition to a previously reported advantage of prostate immobilization, the use of a rectal displacement balloon during daily treatment results in high dose rectal wall sparing during both modestly and highly conformal radiotherapy. Such sparing could assist in controlling and limiting rectal toxicity during increasingly aggressive dose escalation.

81 poster Application of an endorectal balloon to reduce brachytherapy induced proctitis

81 poster Application of an endorectal balloon to reduce brachytherapy induced proctitis

Towards integrating functional imaging in the treatment of prostate cancer with radiation: the registration of the MR spectroscopy imaging to ultrasound/CT images and its implementation in treatment planning

Purpose: Dose-escalation to intraprostatic tumor deposits detected by magnetic resonance spectroscopy (MRS) is an example of tumor-targeted radiation therapy. Because treatment planning for prostate brachytherapy is performed based on ultrasound (US)/computed tomography (CT) images, a sine qua non of this technique is the ability to map MRS-positive volumes (obtained in a gland deformed by the endorectal balloon coil) to the US/CT images. An empirical algorithm designed to perform this function, and its validation, are described.Methods and Materials: Mathematically, the problem of mapping points between the MR and US/CT domains comes to: (a) ascertaining that the position of any point in the interior of the prostate is uniquely determined by the shape of the gland, and (b) finding an algorithm that describes this relationship. The image registration algorithm described here is based on the assumption that points within the gland maintain the same relative position with respect to both the axial contours of the prostate and the center of the prostate along the superior-inferior direction. Relative positions of MRS-positive voxels are calculated with this method in both MR and US/CT space. For a particular voxel in the MR space, one obtains first the z coordinate in the US/CT space, that is, along the superior-inferior direction. This determines the axial slice in the US/CT frame of reference where the other two coordinates (x, y) will be calculated. The validity of this algorithm was examined with the aid of a pelvic phantom built to simulate realistically the prostate and its surrounding bony and tissue structures and with CT scans of implanted patients obtained, at several weeks’ intervals, as part of an edema-resolution study. Seventy-five “dummy” seeds were placed in the phantom, within the simulated prostate gland, in a quasi-regular pattern. The coordinates of these seeds were determined and thus served as markers of prostate deformation when an inflated rectal probe was introduced in the phantom. CT images of this phantom were taken for different volumes of the MR rectal probe and in each case the prostate outlines were contoured and seed coordinates calculated. Using these data, the predictions of the mapping algorithm could be directly verified.Results: Absolute values of the 3D-positional errors in this algorithm were 2.2 mm ± 1.2 mm (average ± SD). Only 6 of 75 seeds had positional displacement of 4 mm or more. Similar results were obtained in the patient analysis.Conclusions: In comparison to the MRS voxel size (6.25 × 6.25 × 3.0 mm3), the present algorithm achieves the desired clinical accuracy. As well, with this 3D algorithm seed positions are reconstructed with an uncertainty that, along the z direction, is less than half the thickness of the typical US slice (0.5 cm).

On-line correction of beam portals in the treatment of prostate cancer using an endorectal balloon device

Background: Reproducible target volume assessment is required in order to optimize portal field margins in the treatment of prostate cancer. The benefits of an endorectal balloon on target volume assessment remain unclear. Material and methods: Nine patients were treated with a daily placed air filled rectal balloon. Portal films and computer-associated tomography during the treatment were used to determine the position of the structures of interest. Comparative planning with or without a balloon was performed in order to determine rectal wall exposure to radiation. Results: The range of movements during treatment predicting the position of the prostate in relation to the symphysis was 0.05–0.59 cm in the lateral direction, 0.27–2.2 cm in the antero-posterior direction, and 0.33–1.8 cm in the crano-caudal direction, as compared to the position of the prostate predicted by the balloon ranging from 0.18 to 0.76 cm in the lateral direction, 0.22–1.68 cm in the antero-posterior direction, and 0.58–2.99 cm in the crano-caudal direction. Planning target volumes (PTV) margins as defined by the position of the balloon were 10 mm in the antero-posterior direction, 6 mm in the lateral direction, and 16 mm in the crano-caudal direction. The volume of rectal wall exposed to radiation was reduced from 40 (±12%) to 25% (±19%) with an endorectal balloon ( P<0.05). Conclusions: Daily online correction with portal vision for external beam set-up is improved by an endorectal balloon device, leading to improved PTV margins and reduced radiation exposure of the rectal wall.

The use of an endorectal balloon catheter and ultrasound localization in conformal radiation therapy for prostate cancer: a DVH analysis of rectal dose-sparing with 3D-CRT, IMRT, and helical tomotherapy

Materials/Methods: 5 patients treated with radiation therapy for prostate cancer were selected for analysis. PinnacleTM treatment plans were generated utilizing 3D-conformal 6-field and IMRT 7-coplanar field designs with a novel, three-step optimization and with ultrasound (U/S) localization. Helical Tomotherapy, a form of IMRT that integrates radiotherapy and helical-CT, can provide inherent image guidance and exquisitely conformal therapy. Tomotherapy treatment plans were also compared. Separate plans were devised with a rectal balloon deflated or inflated with and without inclusion of the seminal vesicles (SV) in the target volume. PTV was defined by GTV 5mm margin. The prescription dose was 76Gy (38 fx) such that the 95% isodose line encompassed 95% of the PTV. Cumulative dose-volume histograms (DVHs) were analyzed for the PTV, rectal wall, and bladder for an inflated or deflated endorectal balloon SV. The volumes of rectal wall and bladder receiving 60Gy, 65Gy, and 70Gy with each treatment approach were evaluated.

Analysis of biochemical control following definitive intensity-modulated radiation therapy (IMRT) alone with endorectal balloon immobilization and dose escalation for localized prostate cancer

Analysis of biochemical control following definitive intensity-modulated radiation therapy (IMRT) alone with endorectal balloon immobilization and dose escalation for localized prostate cancer

322 Oral Rectal wall dose reduction by an endorectal balloon during prostate radiotherapy

322 Oral Rectal wall dose reduction by an endorectal balloon during prostate radiotherapy