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Adjuvant external radiation therapy for prostate cancer


Medical editor Oslo University Hospital

General

For patients with infiltration through the capsule (pT3) and microscopic involved margins after prostatectomy, it is additional radiation therapy is given. This is performed as external radiation.

This type of treatment is given to reduce the local relapse frequency, but has no definite effect on survival. Multiple studies are in progress to identify alternative methods of treatment for this patient group. It may also be an alternative for these patients to await the rise of the PSA-level in the serum postoperatively before radiation therapy is started. Preferably, this should be done before the level has increased above 1 ng/ml.

Indications

  • Previous prostatectomy
  • pT3 or involved resection margins
  • Rising serum PSA (< 1 ng/ml) after prostatectomy

Goal

  • Curative the disease

Definitions

Target Volume

 

Target volume definitions from ICRU
(International Commission on Radiation Units and Measurements)

GTV (= Gross Tumor Volume)

Tumor volume

Palpable or visible/demonstrative area of malignant growth.

CTV (= Clinical Target Volume)

Clinical target volume

Tissue volume which contains GTV and/or subclinical microscopic malignant disease.

ITV (= Internal Target Volume)

Target volume

Volume containing CTV and one inner margin taking into account inner movements and revisions of CTV. 

PTV (= Planning Target Volume)

Planning volume

Geometric volume containing ITV and one Setup margin taking into account patient movement, variation in patient positioning, and field modeling.

 

 


Preparation

In addition to clarifying with biopsy, measurement of PSA and possibly node staging, the following is normally performed:
  • Skeletal scintigraphy (bone scan): To map possible metastases to the bone, a bone scan is usually performed before radiation therapy. If the bone scan shows an increase in radioactive uptake, it may be necessary to supplement with x-ray, most often of the spine, pelvis, and hips.
  • X-ray of thorax

In some cases, it may also be necessary to do an MRI examination and supplementary biopsies.

Preparation for the patient

  • Empty the rectum from 1 week before the CT dosage plan and during the entire treatment period.
  • Empty the bladder before the CT dosage plan and before each treatment.

The CT for dosage planning is taken on the simulator apparatus at the radiation department. It is very important the patient is well medicated for pain and is able to lie still on their back for the required period of time. If appropriate, pre-medication of 1-2 g paracetamol can be administered. For patients already taking opiates, an extra dose may be necessary. The patient lies on a flat examination table with only a thin mattress. The patient obtains a standardized pillow under their knees and a large pillow under their head. This set-up is identical to that used on the treatment apparatus.

Intravenous contrast is used routinely. Patients using anti-diabetics of the metformin-type (“Metformin”, “Glucophage”) should not take these in the last 48 hours before CT dosage planning. 

The planning of the radiation field and marking, estimation of radiation field, necessary adjustments and checks, as well as preparation of documentation from the simulator, usually takes one week under normal routine.

The simulator setting is completed one week after the CT. Again, it is just as important to have the patient well medicated for pain and able to lie still. The simulator setting often takes one hour (can be two hours in difficult cases). The simulator is an X-ray apparatus with a set-up and dimension like a radiation apparatus. This provides the possibility of obtaining good control images of the field set up. This will be used to compare with the shade images of the radiated fields which can be obtained on the treatment apparatus.

After, the simulator transfers the final treatment plan to the radiation machines. This takes two working days under a normal routine.

Start of radiation treatment can then take around 10 days after the dosage plan CT.


Implementation

2 Gy x 35 is given, total 70 Gy

Target Volume

The setting of target volume must take into consideration multiple factors including:

  • Visible macro tumor
  • Assumed microscopic disease
  • Variations in positioning of the patient (systematic and coincidental)
  • Inner movements (systematic and coincidental) of target volume and risk organ

The details associated with the practical use of different target volumes and the margins between these are under revision.

Field Limits

Currently, 4 radiation fields are used with 2 cm margins around the prostate and seminal vesicles, except the side field toward the bowel, where the margin is 1-1.5 cm. The lower limit is 2 cm caudal to opening of symphysis.

Weighting

  • 100% to the front
  • 40% to the back
  • 60% from the sides
  • If there is no weighting: 0.5 Gy toward each of the fields

Follow-up

The same as in primary external radiation therapy.

Acute Complications

  • Urethra/bladder
    • Cystitis symptoms
    • Pollakisuria
    • Incontinence
    • Hematuria
    • Dysuria can be treated with alfa-blocker and anti-inflammatory drugs
  • Rectum:
    • Tenesmus
    • Local soreness
    • Sphincter disturbances

Chronic complications

These are related to total dose, radiated volume, fractioning, and patient related factors (diabetes, inflammatory bowel disease, previous pelvic operation).

  • Impotence
    • Up to 50% (30-60%), depending on age
    • I t is important to resume sexual relations early after external radiation therapy before fibrosis worsens status)
  • Chronic cystitis (4-8%), possibly with hematuria and bladder shrinkage
  • Urethra strictures (3-6%, increased risk for internal catheter
  • Chronic proctitis (1-4%)
  • Incontinence (0.5%-1.5%)
  • Osteoradionecrosis

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