ht. @

0

1. Radiation

Oncology

Biol. Phys..

Vol. 5, pp. 289-294

0360-3016/79/02014289/$0280/0

PergamonPressInc., 1979. Printed in the U.S.A.

Technical

Innovation

and Note

A COMPARATIVE STUDY OF COMPUTERIZED TOMOGRAPHY ULTRASOUND IMAGING FOR TREATMENT PLANNING OF PROSTATIC CARCINOMA-f

AND

FREDERICK R. PAQUETTE, M.D., AVTAR S. AHUJA, Ph.D.,* PAUL L. CARSON, Ph.D., LAWRENCE A. MACK, M.D., GEOFFREY S. IBBOTT and MICHAEL L. JOHNSON, M.D. Department of Radiology, University of Colorado Medical Center, 4200 East Ninth Avenue, Denver, CO 80262, U.S.A. Both computerized tomography (CT) and ultrasound have the advantages over cystography of supplying more information without the need for catheterization. Statistical analysis of a small sample indicates that dimensions obtained from both ultrasound and computerized tomography images are about equally reproducible. In all patients adequate CT images were obtained, but in a significant number of patients, ultrasound images were felt to he inadequate for interpretation. Dosimetry,

Prostatic carcinoma,

Ultrasound,

Computerized

INTRODUCTION

patients the diagnosis was made at time of a transurethral resection; in 5 it was made by needle biopsy. Two of the patients had undergone pelvic node biopsy as part of a staging procedure prior to referral for radiation therapy. Each of the patients was studied by both ultrasound and CT. Ultrasound imaging was performed with either of two compound scanners.0 Usually, a 13-mm diameter, 3.5 mHz, 7-cm focal length transducer was used: but focused, 19-mm diameter transducers of 3.5 and 2.2 mHz also were employed. The basic ultrasound scanning technique employed has been described previously.5 The patient was asked to arrive at the department with a moderately full bladder; if this was accomplished the patient was scanned in the supine position with legs flat and spread apart slightly. Several images were obtained at 0.5 cm increments on either side of a midsagittal plane and in the midsagittal plane. These images were constructed from compound scanning of the abdominal wall and the perineal surface. Since this compound scanning depressed the skin, the images were completed by scanning gently along the skin to outline the patient contour. Care was taken to image the boundaries of the pubic bone as well as

Tumor localization is a major challenge in radiation therapy. Nowhere is this more critical than in the definitive treatment of carcinoma of the prostate, where a relatively high dose of radiation must be delivered to a tumor which is juxtaposed between two relatively radiosensitive structures, i.e. the urinary bladder and rectum. The traditional cystogram with barium in the rectum2 gives information from the midsagittal plane only and has the disadvantage of requiring catheterization in a patient who is going to receive significant doses of radiation to the bladder. The use of ultrasound has been reported for prostate localization;‘,5 it has definite advantages over the cystogram technique. X-ray computerized tomography (CT) scanning would appear to have similar advantages.3 This report discusses the relative merits of the two tomographic imaging modalities.

METHODS

tomography.

AND MATERIALS

The patient sample consisted of 8 individuals referred for definitive radiation therapy for carcinoma of the prostate. Their average age was 63 years. In 3

Research in Ophthalmology, 639 Wearn Research Building, 2065 Adelbert Road, Cleveland, OH 44106, U.S.A. 9Unirad Model Sonograph II or Sonograph III. Reprint requests to: Frederick R. Paquette, M.D. Accepted for publication 29 August 1978.

tThis investigation was supported by grant number 5T32 CA 09073, awarded by the National Cancer Institute, Depts

of Health, Education and Welfare. Presented at the annual meeting of the American Society of Therapeutic Radiologists, Denver, 2 November 1977. *Present address: Lorand V. Johnson Laboratory for 289

Radiation Oncology 0 Biology 0 Physics

February

1979,

Volume 5, Number 2

Fig. 1. Representative CT images moving cephalocaudad from the upper left to the lower right with (A) contrast agent in the defect resulting from a previous transurethral resection; (C) catheter in the rectum; (E) reflux into ejaculatory ducts; (M) bulbocavernous muscle, which has the same density as the prostate and gives an indistinct caudad margin of the prostate; and ( f ) prostate margins. possible in addition to those of the prostate, rectum and seminal vesicles. Transverse scans also were obtained with caudal angulation to avoid obstruction of the prostate image by the symphysis pubis. These angulated transverse scans were obtained at 1.0 or 0.5 cm increments as needed to determine the maximum lateral dimension of the prostate. A final scan was obtained in the transverse plane at the center of the prostate to provide an accurate contour for treatment planning. The entire process often required 2 hr. The CT images were obtained on a second generation scanner? which required a scanning time of approximately 2.5 min for each slice. Slice thickness of either 8 or 13 mm was employed in most studies; the earliest ones were done at 13 mm thickness. The patients received 50 ml of renografin 60 intravenously and an inflatable barium enema tip was introduced into the rectum prior to scanning. All of our studies were performed on equipment with flat tables for easy conversion to a flat treatment table. The CT scans and the ultrasound scans were both interpreted by 5 individual readers. A sixth reader read only the CT scans. The CT and ultrasound studies were interpreted on different days by each of

‘IOhio Nuclear Delta Scan 50.

the readers to minimize direct comparison between the two studies. Figures l-4 are representative illustrations of the two techniques. The measurements analyzed were the three dimensions of a box created to encompass the volume of the prostate and the distance from the center of that box to the overlying anterior skin surface. The longitudinal dimension on the CT scan was obtained by determining the distance between the most cephlad cut and caudad cut showing the prostate. With the intention that arc therapy would be used, it was essential that the cephalocaudad axis and the anterior and posterior surfaces of the box be parallel to the treatment table. In addition to the four measurements which were evaluated mathematically, other measurements were easily obtained by CT and ultrasound. The position of the center of the prostate box in relation to an external landmark was obtained and is very helpful in treatment set-up. The maximum AP and lateral dimensions of the patient contour through the center of the prostate were measured as a check on accuracy of contours. In ultrasound and CT significant errors can occur in the patient images, contour unless careful calibrations and quality control are performed regularly with physical test objects.’

A

comparative study of prostatic carcinoma 0 F. R. PAQUETTE et al

Fig. 2. Lateral and transverse,

with caudad angulation, ultrasound images. Illustrated bladder, (R) rectum and (S) symphysis pubis.

Image distortion on television monitors is a particular problem. With accurate scanning arm registration adjustments and use of vertical and horizontal marker dots, the position of the skin at any point can be obtained to +5 mm accuracy with ultrasound. With the CT unit employed in this study, only a horizontal distance scale was given on the image, so contours were obtained from the line printer, rather than film, and an accuracy of at least +5 mm was achieved. One of the authors (G.S.I.) has obtained accurate contours more consistently by interfacing the ultrasound scanning arm position signals directly to a therapy treatment planning computer system.

RESULTS

291

are: (P) prostate,

(B)

AND DISCUSSION

The statistical formulas employed to analyze the patient data are included in the Appendix. Table 1 provides the average dimension of the four distances measured for each patient. These figures compare favorably with the estimated size of the prostate at rectal examination. The CT scans average approximately 8% larger than ultrasound. A similar finding has been reported recently by Sukov et al., although measurement criteria were considerably different in the two studies. Although all readers felt subjectively that the CT image is more reliable and easier to read, Table 1

292

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Oncology

0 Biology 0 Physics

Fig. 3. CT scan showing

Fig. 4. Caudally

(V) seminal

vesicles

angulated

ultrasound

February 1979, Volume 5, Number 2

posterior

showing

to the contrast

( t ) seminal

filled bladder.

vesicles.

A

Table 1. Average dimensions Skin to center of prostate box Patient No.

in individual

Transverse dim. of box

cases for all readers? Longitudinal dim. of box

Anterior-Posterior of box

dim.

USS (cm)

CT (cm)

US (cm)

CT (cm)

US (cm)

CT (cm)

US (cm)

CT (cm)

9.8 ? 0.98 11.022.1 10.2 2 1.1 8.9 2 0.7 10.1 + 0.4 8.9 2 0.3 8.6 * 1.3 9.8 -c 0.6

10.1 * 0.9 12.3 4 1.2 11.oa0.3 9.6 r 0.4 10.1 kO.7 9.3 * 1.2 7.9 2 0.8 9.4 * 0.3

6.2 2 1.5 5.2 + 1.2 4.8 2 0.8 5.6? 0.6 4.6 c 2.0 5.5 2 0.7 4.7 4 0.5 4.5 + 0.5

7.2 + 1.2 5.4 * 0.3 5.6 +-0.6 6.0 -+0.6 6.6 2 0.9 5.120.3 5.1 + 1.6 6.3 ? 0.9

4.9 2 0.9 6.1 22.3 5.622.1 4.7 2 0.5 5.4-c 1.9 4.4 -e 0.3 3.9 2 0.9 4.5 -+0.9

4.6 4 0.6 4.920.9 5.3 * 1.1 6.3? 1.1 5.2 ? 0.9 4.820.1 5.2 ? 0.8 4.1 kO.8

4.3 r 0.7 4.8? 0.9 5.2 & 0.7 4.94 1.0 5.3 * 2.0 4.7 f 0.7 3.8 2 1.3 3.8 2 0.7

5.5 f 0.9 4.92 1.5 4.8? 1.1 5.1 20.9 5.4kO.9 3.9 2 0.4 5.022.2 4.4 -c 1.0

tNo. of readers = 5 for US and 6 for CT. SUS = ultrasound; CT = computed tomography. §The ? values given are the standard deviation

Table 2. Average dimensions Skin to center of box

Av. dim. ?s, (cm) Av. fsctional std. dev. S, (%)

s, defined in the appendix.

and fractional

standard

deviations

for all readers and all patients?

Longitudinal dim. of box

Transverse dim. of box

Anterior-Posterior of box

dim.

uss

CT

us

CT

us

CT

us

CT

9.65

9.%

5.14

5.90

4.92

5.05

4.58

4.87

9.4

7.2

19.0

13.4

24.0

tNo. of readers = 5 for US and 6 for CT: there were 8 patients SUS = ultrasound; CT = computed tomography.

Table 3. Comparison Advantages

293

comparative study of prostatic carcinoma 0 F. R. PAQUETTE et al.

of ultrasound

1. Readily available in most institutions 2. Intravenous contrast material is not required 3. Cost is relatively low

of ultrasound Advantages

and CT of CT

Technique is simple and fast A larger fraction of the patients can be imaged successfully Bone is delineated for more accurate treatment planning 4. Images are interpreted more easily 5. The procedure is more comfortable for the patient

illustrates that the two techniques give quite comparable dimensions. The f limits listed after each average dimension give the per cent standard deviation of the values determined for that dimension by the readers. These figures and the average fractional standard deviations in Table 2 indicate that the readers were essentially as consistent in reading the dimension by ultrasound as they were by CT. Table 2 summarizes our results. Tables 1 and 2 do

17.8

21.5

22.4

for both US and CT.

not show that of the possible 40 separate interpretations of the eight ultrasound studies by the five reviewers, there were seven instances in which a reader felt that a particular ultrasound study was inadequate for his evaluation. These failures occurred in spite of a considerably greater time investment in obtaining the ultrasound images. Three of the seven failures were in patients who had had a staging laparotomy prior to the study. The other failures were in patients who could not tolerate a full bladder or who were obese. In no case was a CT scan considered to be inadequate for evaluation. All readers considered the cephalocaudad dimension of the prostate to be the most difficult dimension to measure. This is the result of a lack of distinct margins at the prostate-seminal vesicle and the prostate-urogenital diaphragm interfaces. These areas are illustrated in Figs. 1 and 2. For localization of the prostate, both CT and ultrasound have the aforementioned advantages over the traditional cystogram with barium in the rectum. Table 3 compares the relative advantages of CT and ultrasound as indicated by this preliminary study.

Radiation

294

Oncology

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February

1979, Volume

5, Number

2

REFERENCES Carson, P.L., Wenzel, W.W., Avery, P., Hendee, W.R.: Sukov, R.J., Scardino, P.T., Sample, W.F., Winter, J., Ultrasound imaging as an aid to cancer therapy. Znt. .Z. Confer, D.J.: Computed tomography and transabdominal Radiat. Oncol. Biol. Phys. 1: 119-132, 1975; 335-343, ultrasound in the evaluation of the prostate. .Z. Comput. 1976. Assist. Tomogr. 1: 281-289, 1977. Fletcher, G.H.: Textbook of Radiotherapy, Philadelphia, Wenzel, W.W., Carson, P.L., Johnson, F.B.: Prostate Lea & Febiger, 1973, pp. 755-762. localization using ultrasound B-mode scanning. In Jelden, G.L. et al.: Further progress in CT scanning and Ultrasound in Medicine-Z, New York, Plenum Press, computerized radiation therapy treatment planning. Am. 1975, pp. 149-157. J. Roentgenol. 127: 179-185, 1976.

APPENDIX Statistical formulas

Let x be one of the dimensions for a patient, np be the number of patients, and n, be the number of readers. Then for any dimension of a patient, the reader average is:

readers for a given dimension of a patient. Reader averages for individual patients, f, + s, are included in Table 1. The average dimension for all readers and patients from equation (Al) is: XT

and the standard deviation of the readings of that dimension x is:

sr=[&($~2-$($~)T)111*

=-J-$ _fr,

(A3)

and the average fractional standard deviation expressed as a per cent for all readers and patients from equations (Al) and (A2) is:

642)

100 X s,/ff, is defined as the per cent standard deviation for all

The average dimensions

.& and $

are included in Table 2.