phoenix5 logo This is an archived copy of an original page from The Prostate Cancer InfoLink site that went off-line in February, 2001. It is reproduced at Phoenix5 with the permission of Vox Medica.
More Prostate Cancer Pages at Phoenix5             About this archive

prostate cancer info link
click here to go to Where To Begin? click here to go to Diagnosis men click here to go to Treatment menu click here to go to Support & Help menu click here to go to Home menu
The information which follows is the opinion of the named author(s).
It does not necessarily constitute the opinion of The Prostate Cancer InfoLink or of CoMed Communications, Inc.

Three-Dimensional Conformal Radiation Therapy (3DCRT) for Prostate Cancer

Part 2 of 2
[divided only to help load time - go to Part 1]

Jeff M. Michalski, MD, Carlos A. Perez, MD, and James A. Purdy, PhD
Radiation Oncology Center, Mallinckrodt Institute of Radiology,
Washington University Medical Center, St. Louis, Missouri

Originally Received July 6, 1996; Last Revised July 8, 1996

Introduction | What is 3DCRT? | How is 3DCRT planned? | How is 3DRCT delivered? | What are the side effects of radiation therapy? | Is 3DCRT better than conventional radiation therapy? | What studies are currently ongoing investigating 3DCRT for prostate cancer? | What will the future hold for 3DCRT and the treatment of prostate cancer? | References | Editorial comment

[Continuing from Part 1]

Step 4: Virtual simulation in 3D treatment planning

Virtual simulation is a process in which the physician uses the digital CT data to define normal tissue and target volume contours to reconstruct the patient in three dimensions on a video display terminal. The physician and medical dosimetrist can interactively manipulate the view of the patient and his anatomy to find an optimal arrangement of radiation beams that will minimize radiation of adjacent normal tissues. Computer software tools, such as beam's-eye-view (BEV) and room view (RV) displays, help in selecting the best radiation beam geometry.

Figure 7. A beam's-eye-view (BEV) display allows the physician to appreciate the tumor containing target from the same perspective as the radiation treatment source. This view allows the radiation oncologist to shape the radiation field to the contour of the target's silhouette. In this example, the stair step edges of the field are a computer simulation of a multi-leaf collimator (MLC). This stair step has little effect inside the patient. The radiation scatter and additive effects of multiple radiation beams smoothes the radiation dose around the prostate tumor.

As implied, the BEV allows the clinician to look down the radiation beam and see the target from the same perspective as the radiation energy source. The RV display is helpful to see the position of multiple beams and how they are oriented relative to the patient. After the optimal beam projections are chosen, the physician shapes the beam to the contour of the target with the BEV display and a radiation dose is assigned to each beam. The computer then sums the radiation dose delivered from each projection and the physician and dosimetrist can view the dose distribution with the RV tools.

Figure 8. A room-view display allows the radiation oncologist to evaluate the relationship of multiple radiation beams relative to the patient's anatomy and the target volume. In this case six beams criss-cross and intersect within the prostate (red), behind the bladder (yellow), and in front of the rectum (brown).

(a) 9(b)
Figure 9 The room-view display allows the physician to evaluate the adequacy of radiation dose coverage of the target volume. In Figure 9(a) the seminal vesicles were not treated to the prescribed dose of 5580 cGy as illustrated by the "birdcage" display. This distribution was based on a two-dimensional treatment plan. Despite this inadequate tumor coverage the rectum and bladder are receiving a large dose. Figure 9(b) demonstrates the effects of a conformal treatment plan. The prostate and seminal vesicles received 5580 cGy but large portions of the rectum and bladder are spared. The treatment plan for this patient included an additional "boost" to the prostate for a total dose of 7380 cGy (not shown).

Another software feature that is helpful for 3DCRT, although not mandatory, is the digital reconstructive radiograph (DRR). This DRR tool computes a "virtual radiograph" from the planning CT data. The DRR looks like a plain X-ray but has the advantage of displaying the target volumes and normal tissues contoured from the CT scan data. This is very important for treatment verification and quality assurance. The DRR can have the radiation portal shape superimposed upon it. The DRR is used to verify that treatment delivery is being done as planned.

Figure 10. The digitally reconstructed radiograph (DRR) is computed from the CT data. This has a similar appearance to a plain X-ray but allows concurrent display of a patient's internal anatomy and radiation target. The physician can use this DRR to verify the adequacy of treatment delivery.

Another helpful tool in the evaluation of 3D radiation therapy plans is the dose volume histogram (DVH). DVHs are graphical display tools that allow a physician to quickly estimate the dose of radiation delivered to normal tissues and target volumes. They are extremely valuable when comparing different radiation therapy techniques.

Figure 11. A dose-volume histogram allows the physician to compare the quality of various treatment plans. These tools allow a radiation oncologist to select a treatment plan that maximizes radiation coverage of the tumor while minimizing radiation dose to the normal tissues. In this display the red curve demonstrates a completely 3D conformal plan, the green curve a "partially" 3D conformal plan, and the blue curve a traditional, two-dimensional plan. For the normal tissues the vertical bar represents a conservative estimate of the expected organ tolerance. Those estimates were based on historical experiences with inexact data from traditional, two-dimensional therapies. The vertical bar on the target volume curve represents the intended radiation dose prescription. Each plan adequately covers the target volumes but the most conformal plan (red) delivers substantially lower doses of radiation to the normal tissue volumes.

How is 3D conformal radiation treatment delivered?

As in conventional radiation therapy, 3DCRT delivery is fractionated. A course of radiation therapy is generally given over several weeks in small daily fractions. Radiation fractions are typically administered for 5 days/week for as many as 6.5-8 weeks for curative prostate cancer therapy. A small daily fraction, 1.8-2.0 Gy/d (1 Gy = 100 rad), allows the normal tissues to recover between treatments whereas tumor cells are less efficient at repairing radiation damage.

There are several acceptable methods for delivery of the radiation treatments. Some institutions use four conformally shaped fields directed at the prostate; two from the sides and two angled from the front of the patients' feet. Others use six to eight fields all directed from a single plane rotating about the pelvis. Methods used by each institution are selected based upon linear accelerator machine characteristics. It is not clear that any one method is physically superior to another. At the Mallinckrodt Institute of Radiology we have been using a six- or seven-field coplanar method for several years with good reliability and clinical results. As the number of fields used to treat the prostate increases, it is convenient to use automatic field shaping devices in the head of the treatment linear accelerator. A multi-leaf collimator (MLC) allows automatic reshaping of the treatment field from outside the room while the patient is being treated. The ease and speed of automatic field shaping makes the delivery of complex multiple field arrangements more efficient. It also eliminates the hazards of handling heavy lead alloy blocks by the radiation therapist.

Figure 12. A multi-leaf collimator (MLC) assists in the shaping of the radiation beam. In this photograph the MLC is removed from the head of the treatment delivery machine (a linear accelerator). Data from the 3D treatment plan is used to shape the radiation fields with the MLC. This device allows the physician to use multiple radiation beams to treat a patient in less time than it generally takes to treat him with lead alloy blocks. This added efficiency allows the radiation oncologist to use more treatment fields to shape the radiation dose inside the patient. In the future this device will be used to modulate the intensity of radiation beams and create even more conformal treatment plans with increased protection of the normal tissues and more intensive treatment of the tumor.

What are the side effects of radiation therapy?

Generally, few if any side effects accompany the first few weeks of radiation therapy. X-rays are not felt or seen as the linear accelerator moves about the patient delivering X-rays. Gradually, after 2-3 weeks of therapy, side effects may begin to develop. They are generally confined to the treatment area. Bladder and rectal irritation can occur, giving the patient an urge to urinate more frequently, especially at night, or to have more frequent bowel movements. Sometimes a burning or stinging sensation accompanies bowel movements or bladder emptying. There can be loose stools or diarrhea.

In general, most of the side effects associated with radiation therapy are mild, especially when administered with 3DCRT techniques. If they do occur they can often be managed with medications or dietary modifications. Some men may have diarrhea precipitated by high fiber foods, dairy products, or high fat foods. Changing to a low residue, lactose-free, or low-fat diet may help identify the aggravating dietary factor.

In most men the acute side effects resolve within 4-6 weeks after radiation therapy is completed. Some men may need to use hemorrhoidal preparations or sitz baths to alleviate anal/rectal discomfort for longer than that. Occasionally, food intolerances are identified during treatment that may linger on for a few months or more. Serious rectal/bladder injury is fortunately an uncommon event. It is extremely rare to require surgery or long-term medical management to treat chronic radiation effects to normal tissues. It is expected that the lower dose of radiation that the bladder and rectum receive as a consequence of the use of 3DCRT will result in even fewer long-term deleterious effects.

Is 3D conformal radiation therapy better than conventional radiation therapy?

3DCRT is a relatively new technology and until recently has been available at only a few academic institutions [5]. Data on long-term effectiveness are sparse, but early data have convincingly demonstrated that the volume of normal bladder and rectum receiving a high dose of radiation therapy is substantially reduced. Some institutions have demonstrated that early acute side effects are reduced with the use of 3DCRT [6]. Others have demonstrated that equal side effects are seen in patients treated with 3DCRT compared to conventional radiotherapy despite being treated with higher radiation doses using 3DCRT [7].

A recent report from by the Fox Chase Cancer Center in Pennsylvania has demonstrated an improved outcome as measured by disease-free survival based on PSA data (PSA < 1.5 ng/ml and not rising after treatment). These encouraging results were reported with 3DCRT using standard, non-escalated radiation therapy doses [8].

What studies are currently ongoing investigating 3DCRT for prostate cancer?

One of the theoretical advantages of 3DCRT is that the smaller volumes of normal tissue receiving a high dose will allow more safe escalation of radiation therapy dose to the prostate cancer. Mature studies have demonstrated that the likelihood of controlling prostate cancer with radiation therapy is dependent on the amount of radiation delivered [3, 4]. Higher doses appear more effective at controlling more cancers.

Prior to the availability of 3DCRT, radiation oncologists were restricted to moderately high doses because of the risks of bladder and rectal toxicity. The radiation oncologist could not give the prostate an extremely high dose because he/she was limited by what the bladder and rectum would tolerate. Now, with the use of 3DCRT, several institutions are conducting trials of escalated doses of radiation therapy for prostate and other cancers. Once the safest high dose of radiation therapy is determined, it is expected that a randomized study will be conducted comparing high dose 3DCRT to standard dose radiation therapy to determine whether or not the higher dose of radiation therapy is truly more effective.

Currently, a nationwide dose escalation study is being conducted jointly by the 3D Oncology Group and the Radiation Therapy Oncology Group. An initial cohort of patients were treated at doses of 68.4 Gy and patient accrual is currently ongoing at a dose of 73.8 Gy. If no serious side effects are encountered at this level (and none have been to date), then patients will be treated at doses of 79.2 Gy. Some institutions have already used 3DCRT to treat patients with doses as high as 81 Gy with no increase in severe late complication rates [9]. Administering this level of radiation dose would not have been safe without the use of 3DCRT planning.

What will the future hold for 3DCRT and the treatment of prostate cancer?

Even as patients are currently being treated with 3DCRT, technological developments are further improving the ways in which radiation therapy will be delivered in the future.

Research is being conducted to minimize the effects of internal organ motion on treatment delivery. If prostate movement and daily setup variations can be minimized, then even more tightly shaped conformal dose distributions will be possible.

Some technology, such as proton beam therapy, may benefit from improved target localization. Eventually, the use of radiation beam intensity modifiers, such as a dynamic multi-leaf collimator, will be used while the radiation beam is delivering dose and "sculpt" conformal radiation therapy dose distributions tightly to levels similar to that seen with proton beam therapy. This process of beam intensity modulation is currently being used by some radiation therapy clinics in tumor sites other than the prostate. It will not be too long before it is used in high dose radiation therapy for prostate cancer.


1. Ten Haken RK, Perez-Tamayo C, Tesser RJ, et al: Boost treatment of the prostate using shaped fixed fields. Int J Radiat Oncol Biol Phys 1989; 6: 193.

2. Sandler HM, McShan DL, Lichter AS: Potential improvement in the results of irradiation for prostate carcinoma using improved dose distribution. Int J Radiat Oncol Biol Phys 1991; 22: 361.

3. Hanks GE, Martz KL, Diamond JJ: The effect of dose on local control of prostate cancer. Int J Radiat Oncol Biol Phys 1988; 15: 1299.

4. Perez CA, Pilepich MV, Zivnuska F: Tumor control in definitive irradiation of localized carcinoma of the prostate. Int J Radiat Oncol Biol Phys 1986; 12: 523.

5. Meyer JL, Purdy JA (eds): 3-D Conformal Radiotherapy (Frontiers in Radiation Therapy and Oncolology, vol 29) Basel, Karger, 1996.

6. Soffen EM, Hanks G, Hunt MA, et al.: Conformal static field radiation therapy treatment of early prostate cancer versus non-conformal techniques: A reduction in acute morbidity. Int J Radiat Oncol Biol Phys 1992; 24: 485.

7. Pollack A, Zagars GK, Starkschall G, et al: Conventional vs. conformal radiotherapy for prostate cancer: Preliminary results of dosimetry and acute toxicity. Int J Radiat Oncol Biol Phys 1996; 34: 555.

8. Hanks G, Lee WR, Schultheiss TE: Clinical and biochemical evidence of control of prostate cancer at 5 years after external beam radiation. J Urol 1995; 154: 456.

9. Zelfefsky MJ, Leibel SA, Kutcher GJ, et al: The feasibility of dose escalation with three-dimensional conformal radiotherapy in patients with prostatic carcinoma. Cancer J Sci Am 1995; 1: 142.

Editorial comment

This article offers a useful introduction to three-dimensional conformal radiation therapy for the interested patient. As the authors note, it is not a detailed scientific review. 3DCRT is a form of therapy that is in a stage of rapid evolution as more radiation oncologists and radiation therapists are exposed to this technique. It is certain that the ability to maximize quality of outcome depends upon the experience and expertise of the radiotherapy team. Thus, patients may wish to consider this experience and expertise in deciding whether to seek 3DCRT at specific medical centers.

In the long term, The Prostate Cancer InfoLink expects 3DCRT to lead to lower levels of adverse reaction with better survival than has been the case in the past for prostate cancer patients undergoing radiation therapy. However, the ability of radiation therapy to cure prostate cancer is still dependent upon the ability to actually
kill all of the viable prostate cancer cells. Whether 3DCRT is actually able to significantly improve on this ability compared to conventional, standard radiotherapy is still an unanswered question.

[This editorial comment was part of the original page.]

Where to Begin?    |    Diagnosis    |    Treatment    |    Support    |    Home Page

The content in this section of the Phoenix 5 site was originally developed by CoMed Communications (a Vox Medica company) as part of The Prostate Cancer InfoLink. It is reproduced here with the permission of Vox Medica.

Go to Phoenix5 Main Menu