Int. J. Radiation Oncology Biol. Phys., Vol. 78, No. 2, pp. 435–441, 2010Copyright � 2010 Elsevier Inc.

Printed in the USA. All rights reserved0360-3016/$–see front matter

jrobp.2009.08.023

doi:10.1016/j.i

CLINICAL INVESTIGATION Prostate

TOXICITY ANALYSIS OF POSTOPERATIVE IMAGE-GUIDED INTENSITY-MODULATED RADIOTHERAPY FOR PROSTATE CANCER

SAMEER K. NATH, B.A.,*z AJAY P. SANDHU, M.D.,* BRENT S. ROSE, B.S.,*z DANIEL R. SIMPSON, B.S.,*z

POLLY D. NOBIENSKY, R.N.,* JIA-ZHU WANG, PH.D.,* FRED MILLARD, M.D.,y

CHRISTOPHER J. KANE, M.D.,y J. KELLOGG PARSONS, M.D.,y AND ARNO J. MUNDT, M.D.*z

Departments of *Radiation Oncology and ySurgery, Division of Urology, and zCenter for Advanced Radiotherapy Technologies,Rebecca and John Moores Comprehensive Cancer Center, University of California –San Diego, La Jolla, CA

Reprintion OncoDrive #08(858) 822

This re

Purpose: To report on the acute and late gastrointestinal (GI) and genitourinary (GU) toxicity associated witha unique technique of image-guided radiotherapy (IGRT) in patients undergoing postprostatectomy irradiation.Methods and Materials: Fifty patients were treated with intensity-modulated radiation therapy (IMRT) after rad-ical prostatectomy. Daily image guidance was performed to localize the prostate bed using kilovoltage imaging orcone-beam computed tomography. The median prescription dose was 68 Gy (range, 62–68 Gy). Toxicity wasgraded every 3 to 6 months according to the Common Terminology Criteria for Adverse Events version 3.0.Results: The median follow-up was 24 months (range, 13–38 months). Grade 2 acute GI and GU events occurred in4 patients (8%) and 7 patients (14%), respectively. No Grade 3 or higher acute GI or GU toxicities were observed.Late Grade 2 GI and GU events occurred in 1 patient (2%) and 8 patients (16%), respectively. Only a single (2%)Grade 3 or higher late toxicity was observed.Conclusions: Image-guided IMRT in the postprostatectomy setting is associated with a low frequency of acute andlate GI/GU toxicity. These results compare more favorably to radiotherapy techniques that do not use in-room im-age-guidance, suggesting that daily prostate bed localization may reduce the incidence of adverse events in patientsundergoing postprostatectomy irradiation. � 2010 Elsevier Inc.

Image-guided radiotherapy, Intensity-modulated radiation therapy (IMRT), Prostate cancer, Adjuvant, Salvage.

INTRODUCTION

Radiotherapy is often recommended for the management of

postprostatectomy patients with prostate cancer (1–8). Two

recent randomized trials have demonstrated that adjuvant

and salvage therapy after radical prostatectomy (RP) improves

progression-free survival in select patients with high-risk

pathological features or rising prostate-specific antigen after

RP (2, 3). These results were also substantiated by the South-

west Oncology group(SWOG) 8794 study, which found that

the predominant treatment failure pattern in post-RP patients

is local (9). Furthermore, a recent report on the long-term fol-

low-up from this trial has shown that adjuvant radiotherapy af-

ter RP significantly increases survival and reduces the risk of

metastasis in patients with pT3N0M0 disease (10).

Although the use of intensity-modulated radiation therapy

(IMRT) in the definitive radiotherapy setting for localized

prostate cancer has been extensively studied (11–21), data

in the postoperative setting are more limited (22–29). In

part, this has been due to concerns regarding the cumulative

ts request to: Ajay P. Sandhu, M.D., Department of Radia-logy, UCSD Moores Cancer Center, 3855 Health Sciences43, La Jolla, CA 92093-0843. Tel: (858) 822-5036; Fax:-5568; E-mail: apsandhu@ucsd.edusearch will be presented in part at the 51st Annual Meeting

435

toxicity from any form of postoperative radiotherapy. How-

ever, IMRT has the potential to improve the therapeutic ratio

by allowing higher doses to be delivered to the target volume

while simultaneously limiting the irradiation of normal tis-

sues. Research on IMRT in the postprostatectomy setting

has furthermore shown improved toxicity profiles in compar-

ison to conventional radiotherapy techniques (22–26).

An important concern regarding the use of IMRT is organ

motion. As IMRT involves steep dose gradients, small

changes in organ position can have large dosimetric implica-

tions. Research on organ motion after RP suggests that inter-

fractional movement of the prostate bed, rectum, and bladder

is of clinical significance (25, 30–34). Accordingly, shifting

of the bladder and rectum into higher-dose fields may be re-

sponsible for added toxicity, especially given the mounting

evidence that the dose to critical organs during post-RP irra-

diation is predictive of toxicity (35).

To account for organ motion during IMRT after RP, we

have devised a unique system of imaged-guided radiotherapy

of the American Society for Therapeutic Radiology and Oncology,November 1–5, 2009, Chicago, IL.

Conflict of interest: none.Received May 26, 2009, and in revised form Aug 6, 2009.

Accepted for publication Aug 7, 2009.

Table 1. Patient characteristics

Characteristic No. (%)

Age (y)Range 52–77Median 63

Gleason scoreMedian 7Range 6–96 8 (16)7 22 (44)8 6 (12)9 14 (28)

Pathological stage*T1c 1 (2)T2a 2 (4)T2b 3 (6)T2c 15 (30)T3a 13 (26)T3b 14 (28)T4 1 (2)

Surgical margins*Postive 31 (62)Negative 18 (36)

PSA before RP< 5 ng/ml 45 (90)$ 5 ng/ml 5 (10)

PSA after RP< 0.2 ng/ml 40 (80)$ 0.2 ng/ml 10 (20)

Treatment settingAdjuvant 13 (26)Salvage 37 (74)

Androgen deprivationYes 14 (28)No 36 (72)

Abbreviations: PSA = prostate-specific antigen; RP = radicalprostatectomy.

* Unavailable in 1 patient.

436 I. J. Radiation Oncology d Biology d Physics Volume 78, Number 2, 2010

(IGRT) in which prostate-bed localization via planar kilovolt-

age (kV) imaging is performed on a daily basis using existing

surgical clips as a surrogate for the prostate bed. We have

previously reported on the use of this technique primarily to

define prostate bed motion and patient setup errors in 26 pa-

tients (25). In this study, we now report on the acute and

late gastrointestinal (GI) and genitourinary (GU) toxicity after

image-guided adjuvant or salvage radiotherapy. In addition,

we describe the use of kV cone-beam computed tomography

(CBCT) as an alternative means of image guidance in a minor-

ity of patients for whom surgical clips were not readily visu-

alized. To the authors’ knowledge, this is the first study

evaluating clinical outcomes from postprostatectomy patients

receiving IMRT with daily kV-based image-guidance.

METHODS AND MATERIALS

Institutional Review Board approval was obtained before initiat-

ing this study. Between December 2005 and February 2008, 50 pa-

tients were treated with adjuvant or salvage radiotherapy after

radical retropubic or robot-assisted prostatectomy for localized pros-

tate adenocarcinoma at our institution. The clinical characteristics of

the 50 consecutive patients treated with postprostatectomy imaged-

guided IMRT are listed in Table 1. Adjuvant therapy was used for

select patients with positive margins, seminal vesicle invasion, or

extraprostatic extension (pathological T3 disease). The median

time from RP to adjuvant therapy was 3.0 months (range, 1.8–8.4

months). Salvage therapy was used for men with rising PSA after

RP. The median time from RP to salvage radiotherapy was 31.8

months (range, 3.4–167.6 months). Before, during, or after treat-

ment, 28% of patients received androgen deprivation for a median

of 24 months (range, 3–73 months).

Radiation techniqueOur radiation technique has been described in a previous publica-

tion (25). All patients were treated with IMRT encompassing the

prostate bed and underwent planning simulation in the supine posi-

tion after immobilization with a Vac-Loc (Civco Medical Instru-

ments, Kalona, IA) cushion. The axial computed tomography

(CT) images of the pelvis were obtained with 2.5 mm spacing.

Patients were instructed to keep their bladder full (by drinking 12

oz. of water) and rectum empty (by means of an enema) during

the planning session and subsequently at the time of treatment to

ensure reproducibility of daily positioning and to minimize the influ-

ence of bowel/bladder motion.

The clinical target volume (CTV) was contoured based on the

location of surgical clips, preoperative imaging when available,

operative findings, and additional information from surgical pathol-

ogy. The anatomical boundaries of the CTV included the posterior

portion of bladder and posterior aspect of symphysis pubis anteri-

orly, the anterior rectal wall posteriorly, the top of penile bulb infe-

riorly, periprostatic tissues, and surgical anastomoses with

surrounding surgical clips. Superiorly, the target was extended to in-

clude surgical clips and remnant seminal vesicles only if patholog-

ically involved. The planning target volume (PTV) was generated

with an 8- to 10-mm margin except posteriorly where the margin

was reduced to 5 mm. The superior margin was also tightened to

minimize the volume of small bowel receiving high doses.

An IMRT plan was generated using a seven-field technique with

Eclipse planning software (Varian Medical Systems, Palo Alto,

CA). The median prescribed dose was 68 Gy (range, 62–68 Gy)

at 1.8 to 2.0 Gy per fraction for all patients. Adjuvant therapy

patients received a lower median prescribed dose in comparison to

salvage therapy patients (66 vs. 68 Gy). The dose for margin-posi-

tive disease was determined by treatment type (adjuvant vs. sal-

vage). Normal tissues contoured included the rectum, bladder, and

femoral heads. The small bowel and penile bulb were not included

as avoidance structures during inverse planning. The goals of treat-

ment planning included at least 95% of the PTV to receive the com-

plete prescription dose. In addition, normal tissue constraints

included coverage of 65 Gy and 35 Gy not to exceed 25% and

60% of rectum and bladder volumes, respectively. The rectal dose

constraints were given precedence over bladder doses. Finally, the

dose to each femoral head was not to exceed 50 Gy.

Imaged-guided radiation techniqueOur image-guided technique has also been described in a previous

publication (25). Patients undergoing planar kV-based image-guid-

ance had orthogonal digitally reconstructed radiographs (DRRs) that

were generated from the planning CT. Surgical clips were contoured

and projected onto the DRRs to be used for comparison with the po-

sition of the surgical clips on orthogonal kilovoltage (kV) images

performed daily to localize the prostate bed. Multiple clips per

patient were contoured to reduce the influence of clip migration.

Table 2. Acute toxicity in study subjects

Grade

Side effects* I (%) II (%) III (%) IV (%) V (%)

GenitourinaryFrequency/

urgency19 (38) – – – –

Obstruction 1 (2) 3 (6) – – –Dysuriay 13 (26) 2 (4) – – –

Toxicity analysis of postoperative image-guided IMRT d S. K. NATH et al. 437

In 5 patients (10%), the position of the surgical clips was not readily

observed by kV imaging, and kV CBCT was instead used to visual-

ize the position of the prostate bed. For these patients, the position-

ing of soft-tissue anatomy between the daily CBCT and the original

planning CT was compared. Image guidance was achieved by using

the On-board Imaging (OBI) system on a Varian Trilogy linear

accelerator (Varian Medical Systems, Palo Alto, CA). Surgical clips

on planar kV films or soft-tissue anatomy on CBCT images were

aligned to their position on planning DRRs or the planning CT, re-

spectively, by automatic isocenter shifting to reposition the patient.

Stenosis/

stricture– 2 (4) – – –

Incontinence 2 (4) – – – –Hematuriaz 1 (2) – – – –

GastrointestinalDiarrhea 18 (36) 4 (8) – – –Proctitis 7 (14) – – – –Abdominal

painx6 (12) – – – –

Bleedingk 5 (10) – – – –Incontinence 1 (2) – – – –Nausea 3 (6) – – – –Vomiting 2 (4) – – – –

OtherFatigue 22 (44) – – – –

* Multiple events in a single patient are presented as separateevents.y Common Terminology Criteria short name: pain, GU-bladder.z Common Terminology Criteria short name: hemorrhage, GU.x Common Terminology Criteria short name: pain, adbomen

NOS.k Common Terminology Criteria short name: hemorrhage, GI.

Follow-up and toxicity assessmentRoutine follow-up occurred every 3 to 6 months with a radiation

oncologist or urologist and consisted of clinical and laboratory

evaluation. Patient records both before and during radiotherapy, as

well as all other electronically available records after completion

of treatment, were reviewed for toxicity assessment. In addition,

patients not seen within the last 3 months were contacted by phone

and interviewed for specific GI and GU symptoms. Toxicity was

graded on a scale of 1 to 5 according to the National Cancer Insti-

tute’s Common Terminology Criteria for Adverse Events, version

3.0 (http://www.cancer.gov). Acute toxicities were defined as events

occurring during treatment or within 90 days of the initiation of

radiotherapy. Late toxicities were new or persisting events occurring

>90 days from the start of treatment. Toxicity was reported as the

highest toxicity in each patient. In addition, the number of individual

adverse events (e.g., dysuria, hematuria) were also determined, with

multiple events in a single patient reported as separate events to

present the entire toxicity profile. Symptoms present before radia-

tion therapy were not included in this dataset unless those symptoms

became more severe during the surveillance period. The cumulative

incidence of late toxicity was estimated by the Kaplan-Meier

method. A forward conditional multivariate analysis was performed

using Cox regression modeling to assess factors predictive of late

toxicity, as per other reports (36). All statistical analyses were

performed using NCSS version 7.1.13 (NCSS, Kaysville, UT).

RESULTS

The median follow-up for all 50 patients was 24 months

(range, 13–38 months). At the time of analysis, 3 patients

(6%) were no longer living and had been followed for 13,

22, and 24 months before death.

Acute toxicityOf the 50 patients included in this study, 46 (92%) experi-

enced acute side effects. In all, 35 patients (70%) had GU

symptoms, and 34 patients (68%) had GI symptoms. Regard-

ing the severity of acute toxicity, 35 patients (70%) experi-

enced Grade 1 symptoms, while 11 (22%) experienced

Grade 2 toxicity. No Grade 3 or higher acute events were

observed. In addition, no patients required treatment interrup-

tions because of radiation effects.

For GU toxicity, Grade 1 and 2 events occurred in 28

(56%) and 7 (14%) patients, respectively. All toxicities,

including multiple events in a single patient, are listed in

Table 1. The most common GU radiation effect was

frequency/urgency (Table 1). Three patients required tempo-

rary catheter placements for urinary obstruction or stricture.

For GI toxicity, Grade 1 and 2 events occurred in 30 (60%)

and 4 (8%) patients, respectively. The most common acute GI

radiation effect was diarrhea (Table 2).

Late toxicityEighteen patients (36%) experienced late radiation effects.

Thirteen patients (26%) experienced chronic GU symptoms.

Five patients (10%) experienced chronic GI symptoms.

Regarding the severity of late toxicity, 8 patients (16%) expe-

rienced Grade 1 toxicity and 10 (20%) experienced Grade 2

or higher toxicity.

For GU toxicity, Grade 1 and 2 events occurred in 4 (10%)

and 8 (16%) patients, respectively. A single late Grade 3 GU

toxicity was observed and consisted of macroscopic hematu-

ria requiring cauterization in a patient on Coumadin. The 2-

year cumulative incidence of Grade 2 or higher and Grade

3 or higher late GU toxicity was 16% (95% confidence inter-

val [CI] 9–30) and 2% (95% CI, 0.3–14), respectively

(Fig. 1). No Grade 4 or higher GU events were observed.

The most common late GU radiation effect was obstruction

(Table 3). Three patients developed bladder neck contrac-

tures, including one that started during treatment and

persisted, and 2 patients developed urethral strictures.

For GI toxicity, Grade 1 and 2 events occurred in 4 (8%)

and 1 (2%) patients, respectively. No Grade 3 or higher late

GI toxicity was observed. The 2-year cumulative incidence

of Grade 2 or higher late GI toxicity was 2% (95% CI, 0.3–

0.00

0.25

0.50

0.75

1.00

0 10 20 30 4

Cumulative Incidence of Late GU Toxicity

Months

Cu

mu

la

tiv

e In

cid

en

ce

o

f T

ox

ic

ity

0

Fig. 1. Cumulative incidence of late Grade 2 or higher genitouri-nary toxicity.

Table 3. Late toxicity

Grade

Side effects* I (%) II (%) III (%) IV (%) V (%)

GenitourinaryFrequency/urgency 1 (2) – – – –Obstruction – 3 (6) – – –Dysuriay 1 (2) – – – –Stenosis/stricture – 2 (4) – – –Incontinence 2 (4) 1 (2) – – –Cystitis – 2 (4) 1 (2)k – –

GastrointestinalDiarrhea 1 (2) – – – –Proctitis – – – – –Abdominal painz – – – – –Bleedingx 2 (4) 1 (2) – – –Incontinence 1 (2) – – – –Nausea – – – – –Vomiting – – – – –

Abbreviations: GI = gastrointestinal; GU = genitourinary; NOS =not otherwise specified.

* Multiple events in a single patient are presented as separateevents.y Common Terminology Criteria short name: pain, GU-bladder.z Common Terminology Criteria short name: pain, adbomen

NOS.x Common Terminology Criteria short name: hemorrhage, GI.k Patient on Coumadin.

438 I. J. Radiation Oncology d Biology d Physics Volume 78, Number 2, 2010

14) (Fig. 2). The most common late GI radiation effect was

mild bleeding (Table 3). One patient required minor cauter-

ization for hemostasis.

Multivariate analysis was performed to identify factors

predictive of late Grade 2 or higher GI or GU toxicity, includ-

ing prescription dose, androgen deprivation, and stage

(<pT3b vs. $pT3b). No factors were found to significantly

predict the incidence of late toxicity (prescription dose,

p = 0.45; androgen deprivation, p = 0.84; stage, p = 0.24).

0.00

0.25

0.50

0.75

1.00

0 10 20 30 4

Cumulative Incidence of Late GI Toxicity

Months

Cu

mu

la

tiv

e In

cid

en

ce

o

f T

ox

ic

ity

0

Fig. 2. Cumulative incidence of late Grade 2 or higher gastrointes-tinal toxicity.

DISCUSSION

Although IMRT is a well-established technique for intact

prostate cancer management, its use in the postprostatectomy

setting has been limited. Moreover, research providing clin-

ical outcomes from the use of daily image guidance in post-

prostatectomy IMRT patients is sparse (26, 29). Accordingly,

the objective of this study was to report clinical data on the

acute and late GI and GU toxicity associated with image-

guided postoperative irradiation. Overall, our results demon-

strate a favorable toxicity profile.

A comparison of normal-tissue radiation effect between

studies is complicated by the use of a variety of toxicity

scales, as well as differences in radiation technique, treatment

indication, prescribed dose, field margins, and patient demo-

graphics. For instance, complications from the SWOG 8794

trial were reported but not graded, making comparisons dif-

ficult to perform (2). In addition, among the limited number

of clinical studies on postprostatectomy IMRT, one study

does not report data on toxicity (28), and others present com-

bined outcomes with primary prostate cancer patients, mak-

ing comparisons problematic (23, 27).

Despite these difficulties, it is certain that acute toxicity as-

sociated with prostate bed irradiation can be significant and

might lead to major interventions or treatment interruptions.

In the European Organisation for Research and Treatment of

Cancer (EORTC) 22911 trial, acute radiation toxicity follow-

ing conventional radiotherapy was severe enough to warrant

treatment interruption in 3% of patients (3). Furthermore,

Grade 3 or higher GI and GU toxicity occurred in 5% and

5% of patients, respectively. In contrast, our patients experi-

enced no severe acute toxicities or treatment interruptions re-

sulting from radiation effect, and low-grade acute adverse

events occurred less often than in other contemporary series

in which image guidance was not used (Table 4).

It is likely that some of the differences in acute toxicities

between our study and others can also be attributed to varying

fields and the use of IMRT in place of conventional radiother-

apy, as well as the use of daily prostate-bed localization.

Table 4. Comparison of Grade 2 or higher gastrointestinal or genitourinary toxicity among studies on adjuvant and salvage prostate-bedirradiation stratified by radiation technique

Gastrointestinal (%) Genitourinary (%)

Acute Late Acute Late

Study/First author (Ref) Patients (n) Dose (Gy)* Margin (mm) 2 $3 2 $3 2 $3 2 $3

Conventional RTEORTC 22911 (3)y 457 60 NR 18 5 NR 3z 28 5 NR 3z

Choo (38) 76 60 10 17 1 8 0 16 0 15 4Feng (37) 959 64 NR NR NR 4 < 1 NR NR 10 2Pearse (39) 75 66 10 15 3 8 1 9 3 24 6

IMRTTeh (22) 40 64 5 NR NR NR NR 18 0 NR NRDe Meerleer (24) 135 75 7 15 0 13 3 28 3 31 3

Image-guided IMRTCheng (29)x 70 69 3–6 41 0 NR NR 36 0 NR NRWong (26) 50 65k 5–7 2 0 4 0 8 0 4 0Present series 50 68 5–10 8 0 2 0 14 0 16 2

Abbreviations: IMRT = intensity-modulated radiotherapy; Ref = reference; RT = radiotherapy.* Median or mean prescribed dose.y Non–three-dimensional planning.z Cumulative incidence of all late events.x Helical tomotherapy.k Hypofractionated radiotherapy with daily ultrasound-based image guidance.

Toxicity analysis of postoperative image-guided IMRT d S. K. NATH et al. 439

However, in comparison to other series reporting on non–im-

age-guided post-RP IMRT, our toxicity data were either

lower or were equivalent with a higher median prescribed

dose delivered to our patients (Table 4). Of note, De Meerleer

et al. recently reported on the use of high-dose IMRT without

daily image guidance in 135 post-RP patients. Their results

showed higher acute Grade 2 or higher GI and GU toxicity

of 15% and 31% in comparison to 8% and 14% in our pa-

tients, respectively (24). Although prescribed doses were

higher in their study, PTV expansions were larger for our pa-

tients (Table 4). Teh et al. reported on acute GU toxicity

alone in a group of patients treated with postoperative

IMRT. Using smaller margins and a lower median prescribed

dose, they also report a higher Grade 2 toxicity rate of 18%

after radiotherapy (Table 4). Finally, Wong et al. recently re-

ported on a series of postprostatectomy patients treated with

salvage hypofractionated IMRT and daily ultrasound-based

image guidance (26). Their study also found minimal toxicity

associated with daily prostate bed localization (Table 4).

Late toxicity from postoperative radiotherapy can also be

severe and can substantially affect the quality of patients’

lives after radiotherapy. Similar to our acute toxicity data,

high-grade chronic GI and GU adverse events were also in-

frequent in this study. In addition, when compared with stud-

ies in which daily image guidance was not used, our late

toxicity profile was either lower or was equivalent with

a higher median prescribed dose delivered to our patients

(Table 4). Again, in regard to the De Meerleer et al. study

on salvage IMRT, Grade 2 or higher late GI and GU events

occurred in 16% and 34% of patients, respectively. Using im-

age-guided postprostatectomy irradiation, we found a marked

reduction in late Grade 2 or higher adverse events, consisting

of 2% and 18% for late GI and GU toxicities, respectively.

Although a multi-institutional analysis by Feng et al. recently

reported a lower incidence of Grade 2 or higher late GU tox-

icity (7% at 2 years, 12% at 5 years) in patients treated

between 1986 and 2004, half of their patients received total

doses between 50 and 64 Gy and field margins, as well as

radiation technique, were not described (37). Furthermore,

with only a single late Grade 3 or higher GI/GU adverse event

in our patient population, our high-grade late toxicity data

compared favorably to those in recent studies that did not

use daily image guidance (Table 4). Considering that this iso-

lated toxicity consisted of bleeding in a patient on Coumadin,

we suspect that even fewer late high-grade toxicities are to be

expected in patients without other comorbidities.

In a previous study, we quantified the average interfrac-

tional prostate bed motion in three directions, assuming sur-

gical clips to be a surrogate for the prostate bed (25). Based

on the expected degrees of interfractional prostate bed

motion, it should be possible to reduce treatment margins

by up to 2 mm from those currently used when aligning to

bony anatomy if surgical clips are used instead. As this

margin reduction was not yet applied to the current series

of patients, further improvements in toxicity profiles may

be possible.

Several techniques have been investigated for post-RP

IGRT. Ultrasound, electric portal imaging devices (EPID),

helical tomotherapy, and weekly CT scans to monitor inter-

fractional organ motion have all been evaluated (29–34);

however clinical data from patients treated with these tech-

niques sole6ly in the postoperative setting are limited

(26, 29). For EPID, gold seeds are implanted into the prostate

bed to aid in target localization. A significant advantage of

440 I. J. Radiation Oncology d Biology d Physics Volume 78, Number 2, 2010

our technique is the use of pre-existing surgical clips that re-

quire no additional invasive procedure for fiducial implanta-

tion. Furthermore, in contrast to other techniques for target

motion measurement, planar kV imaging is likely to be

more efficient, less time consuming, and subject to minimal

interuser variability. In addition, we have reported here on

the use of CBCT for patients in whom surgical clips are

not easily visualized. This provides another feasible means

of daily image guidance for improved target localization;

however a larger study is required before further conclusions

can be drawn.

Although the results of the present study are promising,

there are several limitations. First, our study is a retrospective

chart review and therefore subject to all of the inherent biases

and shortcomings of such analyses. In particular, some toxic-

ity may have been missed because of lack of documentation.

We have tried to account for this limitation by reviewing all

available electronic records and not limiting our review to

Radiation Oncology and Urology notes. Furthermore, the pri-

mary goal of this study was not to assess the efficacy of post-

prostatectomy irradiation as longer follow-up is still required.

As such, efficacy studies will have to be performed to ensure

that tumor control is not being compromised for a reduction

in normal-tissue toxicity. More than likely, however, treat-

ment efficacy should also improve with IGRT because of bet-

ter targeting of the prostate bed.

CONCLUSION

In conclusion, as the use of IMRT with dose escalation in

the postprostatectomy setting is becoming more common,

a concern for targeting inaccuracy and increased normal tis-

sue toxicity is raised by the possibility of significant interfrac-

tional prostate bed motion. In this study, we have described

the use of daily image guidance with post-RP IMRT in an ef-

fort to counteract the influence of organ motion. Overall, our

results indicate that the use of image-guided IMRT in the

postprostatectomy setting is associated with a low frequency

of acute and late gastrointestinal and genitourinary toxicity.

These results compared favorably to non–image-guided ra-

diotherapy approaches, suggesting that daily prostate-bed lo-

calization may reduce the incidence of radiation toxicity in

patient’s receiving postprostatectomy irradiation. Ultimately,

larger prospective studies with extended follow-up are

needed to define the true benefits and risks of this technique.

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