March 14, 2013

Today, we will discuss some terms for treatment volumes of cancer, prostate cancer aspects, and urinary bladder.

• Terms

1.      Gross Tumor Volume (GTV):  palpable or visible extent of tumor.

2.      Clinical Target Volume (CTV):  GTV plus local margins for subclinical disease or regions or presumed microscopic disease.

3.      Planning Target Volume (PTV):  CTV plus margins for treatment reproducibility factors such as patient and organ movement, respiration, and daily setup; excludes margin for beam penumbra.

4.      Treated Volume:  volume enclosed by an isodose surface (e.g. 95% isodose), selected and specified by radiation oncologist as being appropriate to achieve the purpose of treatment.

5.      Irradiated Volume:  tissue volume which receives a dose that is considered significant in relation to normal tissue tolerance.

6.      Organs at risk:  normal tissues whose radiation sensitivity may significantly influence treatment planning and/or prescribed dose.

• Clinical presentation of prostate cancer:  decreased urinary stream, frequency, difficulty in starting urination, dysuria, and infrequently hematuria.
• Most malignant tumors of the prostate are adenocarcinomas.  Several types of cells are found in the prostate, but almost all prostate cancers develop from the gland cells.  Gland cells make the prostate fluid that is added to the semen.  The medical term for a cancer that starts in gland cells is adenocarcinoma.
• External radiation

1.      Decision must be made about the treatment volume and whether seminal vesicles and/or pelvic lymph nodes will be irradiated.

2.      Radiation of seminal vesicles and pelvic lymph nodes is controversial.

3.      There are no study results that document improved outcome by including the seminal vesicles, and lymph node irradiation has mixed results.

• Simulation for prostate cancer

1.      Refer to setup notes from RDTP 230.

2.      Isocenter is set from CT scan, is marked anteriorly and laterally (L and R) with BBs, and is tattooed on the patient at the three points.

• Conformal 3D treatment planning & delivery

1.      In general, required margins on the clinical target volume (CTV) to achieve the planning target volume (PTV) are usually in the range of 0.55-1.0cm for conformal and IMRT techniques when daily pre-prostate localization is carried out.

2.      Beam designs vary, but a common technique is six fields consisting of a right and left lateral pair and two parallel-opposed oblique pairs 45º off lateral, or a four field box followed by the six field approach.

3.      To shape each field, blocks or MLC settings are applied as specified by the computer plan

4.      Prostate doses typically range from 72-80Gy at 1.8-2.0Gy/day.

5.      It is only with IMRT that doses of 80Gy or more can be delivered to the prostate due to the very specific field shaping of MLC in multiple fields.

6.      Care should be taken to define the prescription point – isocenter, CTV or PTV.

7.      Acute GI side effects include diarrhea, abdominal cramping, rectal discomfort, and occasionally rectal bleeding.

• Site-specific instructions

1.      Patients should be treated with a full bladder to minimize the amount of bladder in the treatment portals.

2.      Since the prostate can be in a slightly different position each day due to bladder and rectal filling, accurate prostate targeting must be assured.

• Urinary bladder cancer

1.      Occurs about four times more often in men than in women.

2.      Usually presents with painless hematuria.

3.      Epithelial transitional cell carcinoma.

• Staging of urinary bladder cancer (The tumor extent and depth of muscle invasion are important factors affecting the tumor’s behavior and outcome of therapy).

1.      Stage 0:  Cancer cells found on the inner surface of the bladder.

2.      Stage I:  Cancer cells have pentrated the inner lining of the bladder but not the muscle.

3.      Stage II:  Cancer cells have spread into the muscle layer.

4.      Stage III:  Cancer cells have spread beyond the bladder muscle and into the outer layer.

5.      Stage IV:  Cancer cells have spread towards the abdominal or pelvic wall.

• Initial target volume

1.      Portals should include the total bladder and tumor volume, prostate and prostatic urethra, and pelvic lymph nodes.

2.      Typically, a four-field (AP/PA and laterals) pelvic technique is used.

3.      High energy beams (10-20MV) are most suitable.

4.      Portals are usually at least 12x12cm to include the empty bladder.

• Field borders

1.      Superior:  between S1 and S2.

2.      Inferior:   bottom of the obturator foramen.

3.      Lateral:  one to two centimeters beyond the bony pelvic side walls (usually around femurs).

4.      Anterior:  at least 1cm anterior to the most anterior portion of the bladder mucosa or 1cm anterior to the tip of the symphysis, whichever is more anterior.

5.      Posterior:   at least 2cm posterior to the bladder and tumor mass if it is present on the CT.

• Doses

1.      The larger pelvic field to include the bladder and pelvic lymphatics is generally treated to a dose of 45-50Gy at 180cGy/day which requires 5-5.5 weeks of treatment.

2.      A smaller boost dose is taken to 65Gy, or possibly 70Gy, if radiation is being used alone.

3.      Bladder boosts should be treated with a full bladder.

• Site-specific instructions

1.      Patients should be treated with an empty bladder when the entire bladder is being treated to reduce the size of the treatment volume and maintain an adequate margin.

2.      During a boost field, a full bladder will reduce the amount of bladder treated to the boost dose.

Reflections: 
In the notes it says that prostate patients should be simulated with full bladders and then they should be give treatment with full bladders so that the treatment is received in the correct place.  Having the full bladder helps keep the small intestines pushed up and out of the prostate fields as well as reducing the bladder's irradiated volume.
Urinary bladder cancer is different that you want the bladder to be empty when treating it except during the boost if there is one.  I assume the distention of the bladder will cause less of the bladder to be in the boost field, thus decreasing the dose to the bladder.