Effects of urethrography on prostate position: considerations for radiotherapy treatment planning of prostate carcinoma

The Utility of Penile Bulb Contouring to Localise the Prostate Apex as Compared to Urethrography

PURPOSE

High-precision radiotherapy relies on accurate anatomic localisation. Urethrography is often used to localise the prostatic apex. However, urethrography is an invasive localisation procedure and may introduce a systemic error. The penile bulb (PB) is contoured to minimise the risk of erectile dysfunction. The purpose of this study is to assess the value of using the PB, as an alternative to urethrography, to localise the prostate.

METHODS AND MATERIALS

The PB was localised on 10 patients treated with simplified intensity-modulated arc radiotherapy at computed tomography simulation during treatment weeks 1 and 7. All patients underwent placement of fiducial markers. Urethrography was used only at simulation. Distances from the superior PB contour to the inferior prostate contour, the apex fiducial marker, and to the inferior prostate contour were obtained as well. The PB was contoured by two observers independently. Agreement coefficients and analysis of variance were used to assess reliability between rates and consistency of measurements over time.

RESULTS

The PB-apex distance was greater than or equal to the urethrogram-apex distance in 24/30 (80%) measurements, and the median difference was 3 mm and was consistent between raters. The greatest variation in PB-IM distance between weeks was 6 mm, the median was 3 mm, and the agreements of measurements between weeks for raters 1 and 2 were 0.79 and 0.69, respectively. These differences were not statistically different and were consistent with the computed tomography slice thickness.

CONCLUSIONS

The PB can be used to identify the prostate apex and can be reliably contoured between observers. Measurements are consistent between patients and through the duration of treatment. The PB distance measurements support studies indicating that urethrography causes a shift of the prostate superiorly. The distance from the PB to prostate apex remains stable during treatment for individual patients but varies between patients.

Target volume definition for post prostatectomy radiotherapy: Do the consensus guidelines correctly define the inferior border of the CTV?

AIM

We compare urethrogram delineation of the caudal aspect of the anastomosis to the recommended guidelines of post prostatectomy radiotherapy.

BACKGROUND

Level one evidence has established the indications for, and importance of, adjuvant radiotherapy following radical prostatectomy. Several guidelines have recently addressed delineation of the prostate bed target volume including identification of the vesico-urethral anastomosis, taken as the first CT slice caudal to visible urine in the bladder neck. The inferior border of clinical target volume is then variably defined 5-12 mm below this anastomosis or 15 mm cranial to the penile bulb.

METHODS AND MATERIALS

Thirty-three patients who received adjuvant radiotherapy following radical prostatectomy were reviewed. All underwent planning CT with urethrogram. The authors (MM, JC) independently identified the CT slice caudal to the last slice showing urine in the bladder neck (called the CT Reference Slice), and measured the distance between this and the tip of the urethrogram cone. Five patients also had a diagnostic MRI at the time of CT planning to better visualize the anatomy.

RESULTS

Sixty-six readings were obtained. The mean distance between the Bladder CT Reference Slice and the most cranial urethrogram contrast slice was 16.1 mm (MM 16.4 mm, JC 15.8 mm), range: 6.8-34.2 mm. The mean distance between the urethrogram tip and the ischial tuberosities was 19.9 mm (range 12.5-29.8 mm). The mean distance between the CT Reference Slice and the ischial tuberosities was 36.9 mm (range 28.3-52.4 mm).

CONCLUSIONS

Guidelines for prostate bed radiation post prostatectomy have been developed after publication of the trials proving benefit of such treatment, and are thus untested. The anastomosis is a frequent site of local relapse but is variably defined by the existing guidelines, none of which take into account anatomic patient variation and all of which are at variance with urethrogram data. We recommend the use of planning urethrogram to better delineate the vesico-urethral junction and minimize the potential for geographic misses.

Anatomic-based three-dimensional planning precludes use of catheter-delivered contrast for treatment of prostate cancer

PURPOSE

Retrograde urethrography is a standard method to identify the prostatic apex during planning for prostate cancer radiotherapy. This is an invasive and uncomfortable procedure. With modern three-dimensional computed tomography planning, we explored whether retrograde urethrography was still necessary to accurately identify the prostatic apex.

METHODS AND MATERIALS

Fifteen patients underwent computed tomography simulation with and without bladder, urethral, and rectal contrast. The prostatic base and apex were identified on both scans, using contrast and anatomy, respectively. The anatomic location of the prostatic apex as defined by these methods was confirmed in another 57 patients with postbrachytherapy imaging.

RESULTS

The prostatic base and apex were within a mean of 3.8 mm between the two scans. In every case, the beak of the retrograde urethrogram abutted the line drawn parallel to, and bisecting, the pubic bone on the lateral films. With these anatomic relationships defined, in the postbrachytherapy patients, the distance from the prostatic apex to the point at which the urethra traversed the pelvic floor was an average of 11.7 mm. On lateral films, we found that the urethra exited the pelvis an average of 16.6 mm below the posterior-most fusion of the pubic symphysis. On axial images, this occurred at a mean separation of the ischia of about 25 mm.

CONCLUSION

With a knowledge of the anatomic relationships and modern three-dimensional computed tomography planning equipment, the prostatic apex can be easily and consistently identified, obviating the need to subject patients to retrograde urethrography.

Qualitative estimation of pelvic organ interactions and their consequences on prostate motion: Study on a deceased person

In an attempt to have better targeting of the prostate during radiotherapy it is necessary to understand the mechanical interactions between bladder, rectum, and prostate and estimate their consequences on prostate motion. For this, the volumes of bladder, rectum, and lungs were modified concomitantly on a deceased person. A CT acquisition was performed for each of these different pelvic configurations (36 acquisitions). An increase in the volume of the bladder or lungs induces a compression of tissues of the pelvic area from its supero-anterior (S-A) to infero-posterior (I-P) side. Conversely, an increase of rectum volume induces a compression from the I-P to the S-A side of the pelvic region. These compressive actions can be added or subtracted from each other, depending on their amplitudes and directions. Prostate motion occurs when a movement of the rectum is observed (this movement depends, itself, on lungs and bladder volume). The maximum movement of prostate is 9 mm considering maximal bladder or rectal action, and 11 mm considering maximum lung action. In some other cases, opposition of compressive effects can lead to stasis of the prostate. Based on the volumes of bladder, rectum, and lungs, it is possible to qualitatively estimate the movement of organs of the pelvic area. The best way to reduce prostate movement is to recommend the patient to have an empty rectum, with either full bladder and/or full lungs.

Déplacements de la prostate et des vésicules séminales suite à l'uréthrographie : une étude par tomographie axiale

PURPOSE

It has been suggested that urethrography used for localization of the prostate apex may cause a systematic cranial displacement of the organ. Our objective was to use CT-CT image registration to identify if a clinically relevant systematic shift occurs in the position of the prostate and seminal vesicles following retrograde urethrography.

PATIENTS AND METHODS

Patients were scanned twice at the time of simulation. They were imaged supine, bladder empty. Scan resolution was 512x512 with 5 mm cuts. After the first CT sequence, with the patient still on the CT couch, an urethrogram was performed. The patients were then re-scanned. The image sets were registered through the use of external skin fiducials. A single author reviewed x, y and z-axis displacement. Z-axis motion of the prostate was also assessed by having three blinded radiation oncologists mark the cranial limit of the prostate on all 104 image sets.

RESULTS

Fifty-two pairs of CT scans were analyzed for post-urethrogram organ displacement. The mean x axis displacement of the prostate was 0.016 mm (P=0.8), the mean y-axis displacement was 1.3 mm anterior (P<0.001). Mean z-axis displacement of the prostate, using the blinded assessments, was a 1.35 mm cranial shift (P<0.0001). Analogous shifts were identified for the seminal vesicles.

CONCLUSION

Our results suggest a small cranial and anterior displacement of the prostate and seminal vesicles following retrograde urethrography.

Australian and New Zealand three-dimensional conformal radiation therapy consensus guidelines for prostate cancer

Three-dimensional conformal radiation therapy (3DCRT) has been shown to reduce normal tissue toxicity and allow dose escalation in the curative treatment of prostate cancer. The Faculty of Radiation Oncology Genito-Urinary Group initiated a consensus process to generate evidence-based guidelines for the safe and effective implementation of 3DCRT. All radiation oncology departments in Australia and New Zealand were invited to complete a survey of their prostate practice and to send representatives to a consensus workshop. After a review of the evidence, key issues were identified and debated. If agreement was not reached, working parties were formed to make recommendations. Draft guidelines were circulated to workshop participants for approval prior to publication. Where possible, evidence-based recommendations have been made with regard to patient selection, risk stratification, simulation, planning, treatment delivery and toxicity reporting. This is the first time a group of radiation therapists, physicists and oncologists representing professional radiotherapy practice across Australia and New Zealand have worked together to develop best-practice guidelines. These guidelines should serve as a baseline for prospective clinical trials, outcome research and quality assurance.

Intensity Modulated Radiation Therapy (IMRT) in the Management of Prostate Cancer

Intensity modulated radiation therapy (IMRT) is gaining widespread use in the radiation therapy community. Prostate cancer is the ideal target for IMRT due to the growing body of literature supporting dose escalation and normal tissue limitations. The need for dose escalation and the limits of conventional radiation therapy necessitate precise patient and prostate localization as well as advanced treatment delivery. The treatment of prostate cancer has been dramatically altered by the introduction of technology that can focus on the target while avoiding normal tissue. IMRT is evolving as the treatment of the future for prostate cancer.

Prostate movement during simulation resulting from retrograde urethrogram compared with “natural” prostate movement

PURPOSE

Retrograde urethrography (UG) is commonly used at the time of simulation to assist in defining the prostate apex. Some investigators have reported that performing the UG introduces error by causing prostate displacement. We investigate the movement of the prostate caused by the retrograde UG.

METHODS AND MATERIALS

Twenty-four patients treated with three-dimensional conformal radiotherapy for prostate cancer who had gold marker seeds placed into their prostates were studied. Marker seed locations at the time of simulation and on the portal images acquired just before the treatment were compared with the locations on digitally reconstructed radiographs (DRR). Movement in the superior-inferior and anteroposterior directions as seen on lateral images was measured from 402 portal images by offline customized imaging software and evaluated using analysis of variance methods for continuous variables and chi-square statistics for categoric variables.

RESULTS

"Natural" nonrandom movement of the prostate around an "origin" as defined by markers on DRR was observed. This movement tends to be in a superior and anterior direction, with the average shift being 1 mm and 0.82 mm, respectively. The magnitude of movement in the superior direction averaged 2.88 mm compared with 1.64 mm in the inferior direction (p = 0.04). There was slightly greater movement after the UG compared with mean "natural" movement but the difference was less than 3 mm in either direction on average (difference: superior-inferior = 2.64 mm, p = 0.004; anteroposterior = 2.24, p = 0.035).

CONCLUSIONS

Use of the UG induces a small but clinically insignificant displacement of the prostate when "natural" movement is taken into account.

An Evaluation of Beam Cath®in the Verification Process for Prostate Cancer Radiotherapy

AIMS

As the trend towards more conformal treatment continues, the accuracy of treatment delivery becomes more important. Conventionally, treatment set-up for prostate cancer patients is verified in relation to the bony anatomy. However, there can be prostate movement independent of bony anatomy. This study tested the feasibility of using Beam cath to enable online correction of treatment set-up in relation to the prostate position, and to assess inter-fraction and intra-fraction prostate movement.

MATERIALS AND METHODS

Beam cath is a urethral catheter containing radio-opaque markers, which can be seen on electronic portal imaging, enabling verification of prostate rather than bony anatomy position. The Beam cath was used for planning and treatment of a boost phase of 10 Gy in 5 fractions, delivered before the conventional conformal plan of 60 Gy in 30 fractions. Patients were scanned by computed tomgography (CT), with and without the catheter, and a radio-opaque marker in the catheter was used as the isocentre of the boost phase to enable accurate and rapid pre-treatment isocentre adjustment. The set-up errors between the Beam Cath and bony images were compared to identify the magnitude of prostate movement, independent of bony anatomy. Post-treatment portal images were taken to assess intra-fraction prostate movement.

RESULTS

Of 29 patients approached to take part in the study, 18 patients gave informed consent, but only five completed the intended 5 fractions of the boost phase using Beam cath. Pre- and post-treatment portal images were obtained for a total of 29 fractions in six patients. Inter-fraction prostate movement, independent of bony anatomy, was identified. The mean movements were 0.2 mm (standard deviation [SD] 1.2 mm), 2.9 mm (SD 3.1 mm) and 0.7 mm (SD 2.3 mm) in the right left (RL), cranio-caudal (CC) and anterior posterior (AP) direction, respectively. The mean intra-fraction movement was 0.2 mm (SD 1.2 mm), 2.9 mm (SD 3.1 mm) and 0.7 mm (SD 2.3 mm) in the RL, CC and AP direction, respectively.

CONCLUSION

Although independent prostate movement was identified, the use of Beam cath was poorly tolerated. Alternative methods of identifying and correcting for prostate movement should be investigated.

CT slice index and thickness: impact on organ contouring in radiation treatment planning for prostate cancer

Objective: To assess the impact of CT slice index and thickness (3 mm versus 5 mm) on (i) prostate volume, dimensions, and isocenter coordinates, (ii) bladder and rectal volumes, and (iii) DRR quality, in the treatment of prostate cancer. Methods: 16 patients with prostate cancer underwent two planning CT‐scans using 3 and 5 mm slice index/thickness. Prostate, bladder, and rectum were outlined on all scans. Prostate isocenter coordinates, maximum dimensions, and volumes were compared along with bladder and rectal volumes. Bladder volumes and maximum diameters were further investigated using a second observer. A comparative analysis of DRR quality was conducted as well as a dosimetric analysis using DVH. Results: The differences in measurements of prostate volume, isocenter coordinates and maximum dimensions between the 3 and 5 mm scans, were small and not statistically significant. Similar finding was seen for rectal volume. However, bladder volume was always larger on the 3 mm scan (mean difference=27.9 cc;  SE=4.8 cc;  95% CI:  17.7−38.2 cc;  p<0.001) and the findings were reproduced with the second observer (mean difference=31.9 cc;  SE=4.7 cc;  95% CI:  21.9−41.9 cc;  p<0.001). The differences in volume are caused by a slight increase in (1) the measurement of the longitudinal dimensions on the 3 mm scans, and (2) the slice by slice measured bladder area on the 3 mm scans. The latter is due to partial volume effect. The 3 mm DRR were slightly better than the 5 mm DRR. The bladder DVH differed significantly in some patients. Conclusion: Bladder volume is significantly larger on the 3 mm scans. Differences in contoured areas may be accounted for, in part, by the partial volume effect.

PACS number(s): 87.57.–s, 87.53.–j

Predictors of Extracapsular Extension and Its Radial Distance in Prostate Cancer

PURPOSE

Tightly constricted isodose lines are generated using brachytherapy or intensity-modulated radiation therapy (IMRT) treatment planning systems for prostate cancer. Definition of margins that encompass subclinical disease extension is important to maximize dose escalation while attemptingto adhere to normal tissue dose tolerances. In this study, we attempted to find predictors of extracapsular extension (ECE) and its radial distance.

MATERIALS AND METHODS

Pathological assessment of ECE and its radial distance was performed on 712 radical prostatectomy specimens. Preoperative data (initial prostate-specific antigen, clinical stage, ultrasound volume, and biopsy Gleason score) were evaluated for their ability to predict the presence of ECE and its radial distance.

RESULTS

Measurable disease was noted outside the prostatic capsule in 185 of 712 (26.0%) specimens. All preoperative parameters except ultrasound volume were able to predict the presence of ECE. However, none of them was predictive of the radial ECE distance. In this group, the median and the range of the maximum depth of invasion (radial extension from the capsule) were 2.00 and 0.5-12.00 mm, respectively. The mean radial distance from the capsule was 2.93 mm, SD +/- 2.286 mm. All subgroups had some patients with radial extension ranging from 0-2 mm, 2-5 mm, to > 5 mm. Only patients with a prostate-specific antigen of 0-4 ng/mL had no extension > 5 mm.

CONCLUSIONS

This is the largest series in the literature thus far that quantitatively assesses radial extracapsular extension. Coverage of subclinical disease must be addressed carefully before successful implementation of intensity-modulated radiation therapy, brachytherapy, or prostatectomy in order to avoid geographical miss.

Bulb of penis as a marker for prostatic apex in external beam radiotherapy of prostate cancer

PURPOSE

To investigate the relationship between the bulb of the penis and the peak of the urethrogram, and to compare this measurement with the ischial tuberosities (ITs) to peak distance.

METHODS AND MATERIALS

Pelvic CT scans from 50 consecutive patients with localized prostate cancer were analyzed to identify the penile bulb. Each patient was required to undergo retrograde urethrography during CT-based treatment planning with 3-mm slices. The peak of the urethrogram was defined as the last CT slice in which the contrast dye in the urethra could be visualized. Measurements were taken from the slice containing the most superior aspect of the penile bulb to the last slice of the urethrogram peak. The superior aspect of the penile bulb was defined as the CT slice nearest the peak that contained a bulbous structure at the base of the penis. This distance was defined as the bulb-peak distance. Similarly, the IT-peak distance was recorded for comparison.

RESULTS

The mean bulb-peak and IT-peak distances were calculated for 47 of 50 patients. The peak of the urethrogram was unable to be evaluated in 3 patients. The mean, median, and range bulb-peak distance was 2.4 mm (SD 1.8), 3 mm, and 0-6 mm, respectively. The mean, median, and range IT-peak distance was 20.1 mm (SD 6.6), 21 mm, and 6-33 mm, respectively. No patient had the bulb located above the apex of the urethrogram.

CONCLUSION

The bulb of the penis is a relatively consistent soft-tissue landmark compared with the ITs and is located an average of 3 mm below the peak of the urethrogram. Therefore, the bulb of the penis is another landmark for the identification of the prostatic apex and is less invasive than retrograde urethrography.

IMRT for prostate cancer: defining target volume based on correlated pathologic volume of disease

PURPOSE

The intensity-modulated radiation therapy (IMRT) treatment planning system generates tightly constricted isodose lines. It is very important to define the margins that are acceptable in the treatment of prostate cancer to maximize the dose escalation and normal tissue avoidance advantages offered by IMRT. It is necessary to take into account subclinical disease and the potential for extracapsular spread. Organ and patient motion as well as setup errors are variables that must be minimized and defined to avoid underdosing the tumor or overdosing the normal tissues. We have addressed these issues previously. The purpose of the study was twofold: to quantify the radial distance of extracapsular extension in the prostatectomy specimens, and to quantify differences between the pathologic prostate volume (PPV), CT-based gross tumor volume (GTV), and planning target volume (PTV).

MATERIALS AND METHODS

Two related studies were undertaken. A total of 712 patients underwent prostatectomy between August 1983 and September 1995. Pathologic assessment of the radial distance of extracapsular extension was performed. Shrinkage associated with fixation was accounted for with a linear shrinkage factor. Ten patients had preoperative staging studies including a CT scan of the pelvis. The GTV was outlined and volume determined from these CT scans. The PTV, defined as GTV with a 5-mm margin in all dimensions, was then calculated. The Peacock inverse planning system (NOMOS Corp., Sewickley, PA) was used. The PPV, GTV, and PTV were compared for differences and evaluated for correlation.

RESULTS

Extracapsular extension (ECE) (i.e., prostatic capsular invasion level 3 [both focal and established]) was found in 299 of 712 patients (42.0%). Measurable disease extending radially outside the prostatic capsule (i.e., ECE level 3 established) was noted in 185 of 712 (26.0%). The median radial extension was 2.0 mm (range 0.50-12.00 mm) outside the prostatic capsule. As a group, 20 of 712 (2.8%) had extracapsular extension of more than 5 mm. In the volumetric comparison and correlation study of the GTV and PTV to the PPV, the average GTV was 2 times larger than the PPV. The average PTV was 4.1 times larger than the PPV.

CONCLUSIONS

This is the largest series in the literature quantitatively assessing prostatic capsular invasion (i.e., the radial extracapsular extension). It is the first report of a comparison of PPV to CT-planned GTV and PTV. Using patient and prostate immobilization, 5 mm of margin to the GTV in this study provided sufficient coverage of the tumor volume based on data gathered from 712 patients. In the absence of prostate immobilization, additional margins of differing amounts depending on the technique employed would have to be placed to account for target, patient, and setup uncertainties. The large mean difference between CT-based estimates of the tumor volume and target volume (GTV+PTV) and PPV added further evidence for adequacy of tumor coverage. Target immobilization, setup error, and coverage of subclinical disease must be addressed carefully before successful implementation of IMRT to maximize its ability to escalate dose and to spare normal tissue simultaneously and safely.

[Target-volume and critical-organ delineation for conformal radiotherapy of prostate cancer: experience of French dose-escalation trials]

The delineation of target volume and organs at risk depends on the organs definition, and on the modalities for the CT-scan acquisition. Inter-observer variability in the delineation may be large, especially when patient's anatomy is unusual. During the two french multicentric studies of conformal radiotherapy for localized prostate cancer, it was made an effort to harmonize the delineation of the target volumes and organs at risk. Two cases were proposed for delineation during two workshops. In the first case, the mean prostate volume was 46.5 mL (extreme: 31.7-61.3), the mean prostate and seminal vesicles volume was 74.7 mL (extreme: 59.6-80.3), the rectal and bladder walls varied respectively in proportion from 1 to 1.45 and from 1 to 1.16; in the second case, the mean prostate volume was 53.1 mL (extreme: 40.8-73.1), the volume of prostate plus seminal vesicles was 65.1 mL (extreme: 53.2-89), the rectal wall varied proportionally from 1 to 1, 24 and the vesical wall varied from 1 to 1.67. For participating centers to the french studies of dose escalation, a quality control of contours was performed to decrease the inter-observer variability. The ways to reduce the discrepancies of volumes delineation, between different observers, are discussed. A better quality of the CT images, use of urethral opacification, and consensual definition of clinical target volumes and organs at risk may contribute to that improvement.

Computed tomography determination of prostate volume and maximum dimensions: a study of interobserver variability

OBJECTIVE

(1) To evaluate the reproducibility of prostate volume, maximum dimensions and geometrical center coordinates determination using computed tomography (CT) and (2) to identify patterns of interobserver variability.

MATERIALS AND METHODS

Forty patients, suitable for our brachytherapy program, were selected for the study. All patients underwent CT scanning and the prostate volumes were determined by three radiation oncologists. Measurements of geometrical center coordinates, maximum organ dimensions in the anterior-posterior (AP), lateral (Lat) and longitudinal (Long) axes as well as prostate volumes were recorded. This yielded 840 measurements of seven variables for analysis. The means and corresponding standard deviations (SD) of each variable were calculated for each patient. The SDs were then averaged and presented as indices of dispersion. Average variations from the mean were also calculated for each observer along with the SDs.

RESULTS

Analysis of the geometrical center coordinates revealed acceptable variability amongst observers. For the AP, Lat and Long coordinates the SDs were 0.78, 0.89 and 1.72 mm, respectively. The corresponding values for the maximum organ dimensions were 2.54, 2.72 and 4.43 mm, respectively. While the volumes outlined by observer B were less than or equal to the mean in 95% of cases and those of observer C were greater than or equal to the mean in 93% of cases, the volumes of observer A were equally distributed above and below the mean (48% in both cases).

CONCLUSION

The determination of the geometrical center coordinates was reproducible amongst observers. The largest variations were seen with the Long axis. The volume determination is more variable. However, a characteristic trend was seen amongst observers when their volumes were compared to the mean volumes of the group.

The rush to judgment: Does the evidence support the enthusiasm over three-dimensional conformal radiation therapy and dose escalation in the treatment of prostate cancer?

PURPOSE

To discuss the assumptions behind and current clinical evidence on three-dimensional conformal radiation therapy (3D-CRT) and dose escalation in the treatment of prostate cancer.

METHODS

We first define 3D-CRT in comparison to standard radiation therapy and discuss the assumptions on which the technology of 3D-CRT and dose escalation are based. We then examine the evidence on the benefits and limitations from the current most commonly cited studies on dose-escalation trials to treat prostate cancer.

RESULTS

The assumption that 3D-CRT can provide a tighter margin around the tumor area to allow for dose escalation is not yet proven by studies that show continual difficulty in defining the planning treatment volume because of extrinsic and intrinsic difficulties, such as imaging variabilities and patient and organ movement. Current short-term dose-escalation studies on the use of 3D-CRT to treat prostate cancer are limited in their ability to prove that increasing dose improves survival and does not incur potential long-term complications to normal tissue.

CONCLUSION

Although 3D-CRT is a promising technology that many radiation oncologists and clinics are quickly adopting to treat such tumors as prostate cancer, the long-term evidence on the benefits and limitations of this technology is still lacking. Until we have solid long-term evidence on the true clinical potential of this new technology, let us not rush to judgment, but exercise caution, diligence, and thoughtfulness in using this new technology to treat our patients.

Treatment planning aids in prostate cancer: friend or foe?

BACKGROUND

Rectal barium is commonly used as a treatment planning aid for prostate cancer to delineate the anterior rectal wall. Previous research at the Ottawa Regional Cancer Centre demonstrated that retrograde urethrography results in a systematic shift of the prostate. We postulated that rectal barium could also cause prostate motion.

PURPOSE

The study was designed to evaluate the effects of rectal barium on prostate position.

METHODS AND MATERIALS

Thirty patients with cT1-T3 prostate cancer were evaluated. Three fiducial markers were placed in the prostate. During simulation, baseline posterior-anterior and lateral films were taken. Repeat films were taken after rectal barium opacification. The prostate position (identified by the fiducials) relative to bony landmarks was compared before and after rectal barium. Films were analyzed using PIPsPro software.

RESULTS

The rectal barium procedure resulted in a significant displacement of the prostate in the anterior and superior direction. The mean displacement of the prostate measured on the lateral films was 3.8 mm (SD: 4.4 mm) in the superior direction and 3.0 mm (SD: 3.1) in the anterior direction.

CONCLUSIONS

Rectal barium opacification results in a systematic shift of the prostate. This error could result in a geographic miss of the target; therefore, alternate methods of normal tissue definition should be used.

To move or not to move: measurements of prostate motion by urethrography using MRI

PURPOSE

Urethrography is commonly used to aid in definition of the prostate apex during CT simulation for prostate cancer. If the position of the prostate were altered by the urethrogram itself, then systematic error could be introduced into the patient's treatment. Sagittal MRI scans were acquired immediately before and after a localization urethrogram to determine the extent of displacement.

METHODS AND MATERIALS

Thirteen patients underwent sagittal T2-weighted fast spin echo MRI scans. Patients were scanned supine in an alpha cradle cast in the treatment position. The prostate was contoured by 3 different observers to determine the apex location on the central sagittal MRI section and the center of mass relative to an immobile bony landmark. Statistical multivariate analysis was performed to establish if there was a net displacement of the prostate (systematic error), and to determine the margin required to cover the random prostate position within a 95% confidence interval.

RESULTS

There was no significant systematic motion of either the prostate nor its apex in either the anterior-posterior or superior-inferior directions. The average motion of the prostate center of mass was 0.04 +/- 0.40 cm (1 SD) and 0.01 +/- 0.33 cm in the anterior-posterior and superior-inferior direction, respectively. The corresponding figures for location of the apex were 0.05 +/- 0.30 cm and 0.01 +/- 0.33 cm, respectively. The statistical analysis revealed that a margin of 2 mm is sufficient to cover any random motion of the prostate that could occur as a result of the urethrogram 95% of the time.

CONCLUSION

Urethrography during CT simulation for prostate cancer does not cause significant prostate displacement or systematic error in planning and delivering external-beam radiation.

Organ motion and its management

PURPOSE

To compile and review data on the topic of organ motion and its management.

METHODS AND MATERIALS

Data were classified into three categories: (a) patient position-related organ motion, (b) interfraction organ motion, and (c) intrafraction organ motion. Data on interfraction motion of gynecological tumors, the prostate, bladder, and rectum are reviewed. Literature pertaining to the intrafraction movement of the liver, diaphragm, kidneys, pancreas, lung tumors, and prostate is compiled. Methods for managing interfraction and intrafraction organ motion in radiation therapy are also reviewed.

Simulation for localized prostate cancer: a comparison of urethrography techniques

Forty-five patients having conventional fluoroscopic, or CT scan simulation of the prostate gland from January 1999 to June 1999 were studied. Patients were consecutively assigned (not randomized) in groups of 15 to 3 different urethrography techniques: air contrast alone (group 1), hypaque contrast alone (group 2), and xylocaine jelly and hypaque contrast (group 3). Outcome measures were pain scores, visualization of the apex (indicated by urethrogram tip), and frequency of corrections necessary on the basis of verification port films. Group 3 patients had the lowest mean pain score and required fewer lateral setup corrections at the time of portal imaging on the first day of treatment. A comparison of radiographs also revealed that group 2 and 3 patients (hypaque contrast) had better delineation of the prostatic anatomy than group 1 patients (air contrast). We found that of the 3 techniques tested, urethrography utilizing xylocaine jelly and hypaque was associated with the least amount of pain, least amount of corrective shifts, and best quality in defining the prostatic anatomy.

Respiratory-induced prostate motion: quantification and characterization

PURPOSE

The precise localization of the prostate is critical for dose-escalated conformal radiotherapy. This study identifies and characterizes a potential cause of inaccurate prostatic localization-respiratory-induced movement.

METHODS AND MATERIALS

Prostate movement during respiration was measured fluoroscopically using implanted gold fiducial markers. Twenty sequential patients with CT(1)-T(3) N(0) M(0) prostate carcinoma were evaluated prone, immobilized in customized thermoplastic shells. A second 20 patients were evaluated both prone (with and without their thermoplastic shells) and supine (without their shells).

RESULTS

When the patients were immobilized prone in thermoplastic shells, the prostate moved synchronously with respiration. In the study the prostate was displaced a mean distance of 3.3 +/- 1.8 (SD) mm (range, 1-10.2 mm), with 23% (9/40) of the displacements being 4 mm or greater. The respiratory-associated prostate movement decreased significantly when the thermoplastic shells were removed.

CONCLUSION

Significant prostate movement can be induced by respiration when patients are immobilized in thermoplastic shells. This movement presumably is related to transmitted intraabdominal pressure within the confined space of the shells. Careful attention to the details of immobilization and to the possibility of respiratory-induced prostate movements is important when employing small field margins in prostatic radiotherapy.