External Beam Radiotherapy for prostate cancer

Tomotherapy MachineCurative external beam radiotherapy for prostate cancer is the therapy choice for all patients with intermediate risk or higher risk early prostate cancer (in conjunction with anti-hormonal downstaging in the higher risk patients: e.g. those with capsular breach on their pelvic staging MRI scan). External beam radiotherapy is also treatment of choice in the elderly, as it is the least invasive method of curing the cancer and has equivalent cure chance.

Modern external beam radiotherapy to the prostate relies on intensity modulated technologies (IMRT), technology that can alter the “fluence” across the radiation field during treatment, thereby allowing the most exact deposition to the contours of an individual’s prostate (bespoke conformity), at the edge of which the dose gradient gives a sharp “fall-off” in dose. Where the rectum is intruding into the prostate volume, IMRT allows a concavity in the high dose volume to the prostate to minimise collateral damage to the rectum.

IMRT

Isodosimetry by conventional radiotherapy (left) compared to isodosimetry by IMRT (right)

Perhaps the most sensitive current form of IMRT is tomotherapy where a fine radiation beam (6MV energy) spirals helically through the treatment volume with on/off phases during the spiral to alter the overall fluence and effect the bespoke modelling of dose, including “scalloping” of dose around high risk adjacent structures. Tomotherapy has been used for all prostate radiotherapy treatments at the BUPA Cromwell Hospital for the last eight years.

CT scanning is used to plan the treatment and daily CT verification scan (low dose scan) ensures accuracy of patient positioning.

Unlike most other IMRT techniques, Tomotherapy accuracy does not depend and does not require implanted fiducials into the prostate, giving it a real advantage over other IMRT techniques.

Axial CT scan through pelvis with an IMRT isodosimetric plan superimposed and the high dose regions dose-washed in turquoise and red. Note the ability of the IMRT technique to cause a concavity in the high dose region such that the rectum (pink) is spared from the high dose radiotherapy.

Axial CT scan through pelvis with an IMRT isodosimetric plan superimposed and the high dose regions dose-washed in turquoise and red. Note the ability of the IMRT technique to cause a concavity in the high dose region such that the rectum (pink) is spared from the high dose radiotherapy.

The radical (curative) radiotherapy course lasts up to 7.5 weeks, treating every weekday. The patient lies on the treatment couch, the position is verified by CT and then treatment delivered. The treatment is not “sensed” by the body and after the treatment is over (10 minutes)the patient departs hospital unaware of any therapy related effects. However, towards the end of the 7.5 weeks, urinary frequency and slowing occur and often some tiredness and increased call to stool. Alpha blocking drugs may help improve a slow urinary stream.

There is no risk of incontinence following radiotherapy and two thirds of men maintain potency (but not fertility).

Elderly patients and those with capsular breach (T3 disease) are usually advised to receive this therapy. Those with T3 disease, usually have anti-hormone therapy first (for 1-3 months) to shrink the tumour back inside the gland prior to radiotherapy and often continue the anti-hormone therapy after radiotherapy for two years.