Intensity-modulated radiotherapy (IMRT) - KCE

Intensity-modulated radiotherapy (IMRT) - KCE

16 Intensity-modulated radiotherapy KCE reports 62

Hypofractionation (a larger dose per fraction, e.g. 3 Gy instead of 1.8 or 2 Gy, and less

number of fractions) is also being investigated using IMRT in good prognosis prostate

cancer patients. 40

The mean interfraction displacement of the prostate gland has been reported to range

between 3 and 7 mm. 40 Treatment margins are used to compensate for this uncertainty

but excessive margins need to be avoided. Image guidance can reduce set-up variability

and can be obtained using ultrasound, electronic portal imaging devices (e.g. using three

gold marker seeds, as technique does not provide internal soft-tissue verification), a kvcone-beam

CT, or a MV-CT scanner as part of the tomotherapy machine (also allowing

for transit dosimetry). In patients with hip replacement MV-CT produces less ‘scatter’

artefact compared with kv-cone beam.

In conclusion, IMRT or 3DCRT are recommended if high doses of external radiotherapy

are delivered for prostate cancer. The challenge is to precisely target the prostate with

or without the pelvic lymph nodes each session. The use of specific localisation

techniques such as imaging are expected to improve the efficacy and safety of high dose

external radiotherapy of the prostate. Breast cancer

Post-operative radiotherapy in patients with breast cancer has been shown to improve

locoregional disease-free survival and overall survival. Treatment to the whole breast

with standard tangential fields produces rather inhomogeneous dose distributions due

to the variations in thickness across the target volume, in particular in large breasted

women. Based on the opinion of the external expert group such patients constitute

about a quarter of all patients undergoing radiotherapy for breast cancer. Such dose

inhomogeneities, may lead to increased late skin toxicity (poor cosmesis, fibrosis, pain)

and increased cardiac and lung morbidity. 14

A 2006 technology assessment report from Blue Cross Blue Shield concluded available

data were insufficient to determine whether IMRT is superior to 3DCRT for improving

health outcomes of patients with breast cancer. 44

Two randomized trials (one abstract 10 , one full paper 31 ) and one retrospective

comparison 8 of IMRT with conventional radiotherapy confirm that IMRT reduces the

frequency of skin complications (table IC), which are more frequently seen in large

breasted patients. However no improvement in overall quality of life could be

demonstrated using standard techniques. 31

The risk of tumour induction in the contralateral breast has often led to a restriction of

the IMRT fields to two tangents. 45 Conventional radiotherapy plus physical wedges as a

compensation technique resulted in 2.4 to 3.3 times more total body exposure

compared with IMRT, because the physical wedges scattered a lot of the radiation. 46

IMRT is also being developed to treat the whole breast and thoracic wall with or

without irradiation of surrounding lymph node areas, including the internal mammary

nodes. When multiple field IMRT is used to also treat the chest wall and the nodal

areas, a higher mean dose to the contralateral lung (12 Gy) and breast (6 Gy) are

delivered compared with the standard technique. This limits the use of IMRT in this

indication. 45

In conclusion, use of IMRT may reduce skin complications in breast cancer external

radiotherapy. Long term studies are required to assess the risk of induction of a

secondary tumour in the contralateral breast after IMRT.

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