Primary external radiation therapy for prostate cancerMedical editor Oslo University Hospital
External radiation therapy to the prostate is completed as 4-field conformal (organ configured) radiation therapy.
Conformal radiation therapy distinguishes itself from conventional radiation therapy by delivering a higher dose toward a reduced target volume. This provides a reduced toxicity to the neighboring structures (rectum, bladder, nerves).
It can be appropriate to give hormone treatment in addition to radiation treatment in patients where:
- Volume of the prostate is great (> 60 cc)
- The tumor has grown through the capsule (T3) and/or PSA > 20 and/or Gleason score ≥ 8
- T1/T2 pN0, PSA ≤ 20
- T1/T2 pN0, Gleasonscore ≥ 8
- T2 pN0, 20 < PSA < 70
- T3 pN0, PSA < 70
|Target volume definitions from ICRU
(International Commission on Radiation Units and Measurements)
GTV (= Gross 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)
Volume containing CTV and one inner margin taking into account inner movements and revisions of CTV.
PTV (= Planning Target Volume)
Geometric volume containing ITV and one Setup margin taking into account patient movement, variation in patient positioning, and field modeling.
In addition to clarification with biopsy, measurement of PSA and possible gland staging, the following is normally performed:
- Bone scan: A bone scan is usually done before radiation therapy to map possible metastases to the bone. If the bone scan shows an increase in radioactive uptake, it can be necessary to supplement with x-ray, most often of the spine, pelvis, and hips.
- X-ray thorax
In some instances, it be also be necessary with MR investigations and supplementary biopsies.
Neoadjuvant androgen blockade
For large prostates (>60 cc), hormone treatment before radiation therapy can be appropriate. The prostate can shrink 40-50% after 3-6 months with LH-RH agonist. Cytoreduction of target volume provides less toxicity and better possibility for dose escalating.
At Rikshospitalet HF, 6 month neoadjuvant therapy is administered for:
- T1/T2 with Gleason ≥ 8
- T2 with PSA > 20
Preparation for patients before external radiation therapy
- Empty rectum one week before CT dosage plan and during entire treatment period.
- Empty bladder before 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 with 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 (canbe two hours in difficult cases). The simulator is an X-ray apparatus with a radiation apparatus set-up and dimension. 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.
Currently, 37 radiation doses are usually given as one treatment daily, 5 days per week.
The first series includes 25 treatments with a daily dose of 2 Gy toward the prostate and seminal vesicles. If the tumor does not include the seminal vesicles, the remaining 12 treatments are administered toward a smaller radiation field. It should also be considered whether larger parts of the rectum and bladder should be protected.
- T1-T3a: 2 Gy x 25 to the prostate and seminal vesicles. Thereafter, boost to the prostate 2 Gy x 12. Total dose is 74 Gy.
- T3b: 2 Gy x 37 to prostate and seminal vesicles
The adjustment of target volume must take into consideration multiple factors including:
- Demonstrated macro tumor
- Assumed microscopic disease
- Variations in positioning of the patient (systematic and coincidental)
- Inner movements (systematic and coincidental) of target volume and organs at risk.
Details relating to the practical use of different target volumes and the margins between them are being revised.
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 the opening of the symphysis.
- 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
- Postoperative fever
- Cystitis symptoms
- Dysuria can be treated with alfa-blocker and anti-inflammatory drugs
- Local soreness
- Sphincter disturbances
Related to total dose, radiated volume, fractioning, and patient related factors (diabetes, inflammatory bowel disease, previous pelvic operation)
- Up to 50% (30-60%), depending on age
- It is important to resume sex life early after external radiation therapy before fibrosis worsens the condition
- Chronic cystitis (4-8%), possibly with hematuria and bladder shrinkage
- Urethra strictures (3-6%, increased risk by indwelling catheter
- Chronic proctitis (1-4%)
- Incontinence (0.5%-1.5%)
Follow-up after 3, 6, 12, 18, 24, and 26 months. Thereafter, yearly for 5 years.
Additionally the patient should be seen by the referring physician at local hospital when appropriate.