There are several studies that follow.

This is a very interesting study that talks about the movement of the prostate in the body and why this is so important in external bream radiation of any kind. In this case they were treating the patient with 3dEBRT. CT simulation was performed at the beginning and at 5 weeks into the treatment. The 3d was broken down into the following:

1. The first 46 Gy was administered with a 2.0-cm margin around the prostate.

2. An additional 10 Gy was given with a 1.5-cm margin

3. The next 16 Gy was given with a 1.0-cm margin.

All of this was for a total of 72 Gy of 2Gy fractions.

In the final section they gave daily CT scans and ultrasound while still on the table to locate the prostate so that the radiation could be set to treat the prostate for up to three days for each patient. This was an additional 4 Gy for a grand total of 76 Gy. Does-escalation studies has shown simply that the higher the dose of radiation the better the results. This is what made seed implants popular - the fact that they can deliver 125 Gy directly into the gland with few side effects when done by an "artist" with an additional 45 to 50 Gy of EBRT. A total of 170 Gy in comparison of the total 76 Gy in this study - more than double the amount of radiation. With seeds the implanted seeds move with the gland.

The shifts in the gland itself was reported as follows. "The magnitude of difference between the CT and ultrasound localization ranged from 0 to 7.0 mm in the anterior/posterior, 0 to 6.4 mm in the lateral, and 0 to 6.7 mm in the superior/inferior dimension."

The movement of the gland itself is important from the standpoint that the closer that they can get for outlining only the gland and no surrounding tissue the more radiation they can push into the confines of the gland. One thing you must always remember is that where the radiation goes in - it has to go straight through and out thus exposing what ever is on the opposite side to radiation.

In a sense it makes little difference, in prostate radiation, when you are giving a margin of up to 2.0-cm whether you do it with tight conformal EBRT, 3dEBRT or even IMRT as the target is movable and one has to allow for that movement.

ABSTRACT

Ultrasound-based stereotactic guidance of precision conformal external beam radiation therapy in clinically localized prostate cancer

Joseph Lattanzi a,b a,bA, Shawn McNeeley b, Alexandra Hanlon b, Timothy E. Schultheiss b and Gerald E. Hanks b [a]Department of Radiation Oncology, Community Medical Center, Toms River, New Jersey, USA[b]Department of Radiation Oncology, Fox Chase Cancer Center, Philadelphia, Pennsylvania, USA A Reprint requests: Joseph Lattanzi, M.D., Department of Radiation Oncology, Community Medical Center, 99 Highway 37 West, Toms River, NJ 08755-6423 Manuscript received 21 June 1999 Revised 12 August 1999 Accepted 12 August 1999;

Objectives. Use of external beam radiation fields that conform to the shape of the target improves biochemical control in prostate cancer by facilitating dose escalation through increased sparing of normal tissue. By correcting potential organ motion and setup errors, ultrasound-directed stereotactic localization is a method that may improve the accuracy and effectiveness of current conformal technology. The purpose of this study was to quantify the precision of the transabdominal ultrasound-based approach using computed tomography (CT) as a standard.

Methods. Thirty-five consecutive men participated in a prospective comparison of daily CT and ultrasound-guided localization at Fox Chase Cancer Center. Daily CT prostate localization was completed before the delivery of each final boost field. In the CT simulation suite, transabdominal ultrasound-based stereotactic localization was also performed. The main outcome measure was a three-dimensional comparison of prostate position as determined by CT versus ultrasound.

Results. Sixty-nine daily CT and ultrasound prostate position shifts were recorded for 35 patients. The magnitude of difference between the CT and ultrasound localization ranged from 0 to 7.0 mm in the anterior/posterior, 0 to 6.4 mm in the lateral, and 0 to 6.7 mm in the superior/inferior dimension. The corresponding directed average disagreements were extremely small: anterior/posterior, -0.09 ± 2.8 mm SD; lateral, -0.16 ± 2.4 mm SD; and superior/inferior, -0.03 ± 2.3 mm SD). Analysis of the paired CT-ultrasound shifts revealed a high correlation between the two modalities in all three dimensions (anterior/posterior r = 0.88; lateral r = 0.91; and superior/inferior r = 0.87).

Conclusions. Ultrasound-directed stereotactic localization is safe and as accurate as CT scanning in targeting the prostate for conformal external beam radiation therapy. The application of this technology to current conformal techniques will allow the reduction of treatment margins in all dimensions. This should diminish treatment-related morbidity and facilitate further dose escalation, resulting in improved cancer control.

The abstract below is interesting in terms of extra capsular penetration (ECP). It came from the examination of 265 prostates removed by surgery. In this they found that 35% of them had ECP. They found that in these specimens, the extent of the penetration was within 4mm in 90% of the cases. (If you use this as a treatment margin you would be under treating 10% of the ECP in those patients.

This is importance, in the treatment of the prostate when using radiation, is because you have to have a margin around the prostate to cover this ECP. In addition the movement of the prostate has to be taken into consideration (see http://www.prostate-help.org/cartmov.htm) If you have too tight of a margin then you may have some of the gland outside the field of radiation. If you have too large of a radiation field then you do more damage to the surrounding area. You have to reach a happy medium to cover the gland, any ECP and any anticipated movement of the prostate. Since the movement of the gland is a daily occurrence on a second by second basis, and it may change in size and shape because of the radiation, one must have some way to measure the size and location on a daily basis (see http://www.prostate-help.org/carcog.htm).

Now when they give the older method of radiation therapy, still practiced in the majority of places across the nation, they make no attempt to see the movement and usually treat the whole area from above, below and both sides with a minimum amount of radiation 6200 to 6500 cGy. This is where the major damage is caused and the nightmare morbidities come from this method. Now as we become more expert in the giving of the radiation we are able to control where the radiation is delivered through three primary methods, conformal EBRT, 3DEBRT and IMRT all of which use the same radiation beam on the same machine but controlled by more sophisticated controls and software.

BUT regardless of what is used one must consider that there has to be a margin around the prostate to cover the ECP, movement, and a full/empty bladder, full/empty rectum and or gas in the system. You can control the bladder by having the patient go pee immediately before the procedure, no so easy to control the bowel movement and impossible to control the amount of gas in the location where the rectum wall is against the prostate gland.

Therefore in my view there is no difference in the use of conformal EBRT, 3DEBRT or IMRT in the treatment of the prostate gland. All have to allow the same margins and allowances so the more expensive treatment has no advantage over the lower cost conformal EBRT. This is assuming you have equal expertise for all modalities.

All treat the moving target the same - none has any inherent advantage.

Urology 2000 Mar;55(3):382-6

Extent of extracapsular extension in localized prostate cancer.

Sohayda C, Kupelian PA, Levin HS, Klein EA Department of Radiation Oncology, Cleveland Clinic Foundation, Cleveland, Ohio, USA.

Objectives. To measure the radial extent of extracapsular penetration by tumor cells, thereby providing estimates of the margins needed around target volumes. New radiotherapeutic techniques, like brachytherapy and conformal radiotherapy, irradiate small volumes and reduce the dose to periprostatic tissues. Even in the early stages of localized prostate cancer, extracapsular extension (ECE) is commonly seen.

Methods. Two hundred sixty-five consecutive radical prostatectomy specimens were analyzed for the presence of ECE. ECE was found in 92 of all cases (35%); measurements were performed in 79 of the 92 cases. A total of 98 ECE sites were evaluated in the 79 cases. The distance of tumor outside the capsule was measured in millimeters. Extension less than 0.1 mm was considered as "focal."

Results. The site of ECE was posterolateral in 53% of cases, lateral in 24%, posterior in 13%, and at the base in 10%. The median amount of ECE at all sites was 1. 1 mm (mean 1.7). However, the range was wide; the minimum measurable extent was 0.1 mm and the maximum 10.0 mm. The extent was within 3.8 mm for 90% of all cases. By stratifying cases with favorable and unfavorable tumors, the 90th percentiles of ECE were as follows: 3.3 mm for favorable tumors (clinical Stage T1-2, initial prostate-specific antigen 10 ng/mL or less, and biopsy Gleason score 6 or less) and 3.9 mm for unfavorable tumors (clinical Stage T3, initial prostate-specific antigen greater than 10 ng/mL, or biopsy Gleason score 7 or greater).

Conclusions. Most of the ECE was at posterolateral sites. The extent of disease outside the prostate was within 4 mm in 90% of cases. Since ECE was observed in 30% to 60% of all patients with clinical Stage T1-2 prostate cancer, only 3% to 7% of all such cases would have disease extent exceeding 4 mm. The present study provides useful estimates of the amount of ECE. These estimates could be potentially used in planning the target volumes for treatment of prostate cancer with either conformal radiotherapy or brachytherapy.

To All

This is another indication of how the prostate moves even when you are immobilized in thermoplastic shells. It would indicate, at least for respiration, that shells may be a detriment instead of a plus. Then you would have to take other things into consideration - but all in all they show about the same movement.

This is a confirmation of one of the many forces that play on the movement of the prostate and requires that when the prostate is treated by conformal EBRT - a wide margin must be made around the prostate. Because of this I see no inherent advantage of 3D conformal or IMRT over a well trained Doc using conformal EBRT.

Int J Radiat Oncol Biol Phys 2000 Aug 1;48(1):105-9

Respiratory-induced prostate motion: quantification and characterization.

Malone S, Crook JM, Kendal WS, Szanto J

Department of Radiation Oncology, Ottawa Regional Cancer Centre, Ontario, Ottawa, Canada. smalone@cancercare.on.ca

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.