Can IMRT reduce the risk of a SMN?

One of the oft-cited arguments against IMRT is that it can increase the chance of developing a second malignancy. However one of the articles in the articles in press section of the red journal brings a provocative finding to fore.

The article is Galloway TJ, Indelicato DJ, Amdur RJ, Morris CG, Swanson EL, Marcus RB. Analysis of Dose at the Site of Second Tumor Formation After Radiotherapy to the Central Nervous System. International Journal of Radiation Oncology*Biology*Physics [Internet]. [cited 21:21:10];In Press, Corrected Proof. Available from: http://www.sciencedirect.com/science/article/B6T7X-51Y2SRB-D/2/6a92762a3b61b3b630195ecc07b2342e

P.S. If you need the full text drop in an email to contact.isocentre at gmail dot com with the JC1 in subject line and we will tell you where to get the pdf from. Of course you have to be a member for that to happen.

The salient features of the article:

  1. 370 consecutive patients with median FU of 20.4 years (median age 8.9 months)
  2. 16 developed a Second brain tumor
  3. Only two tumors - one nasal sarcoma and one thyroid occured outside the brain
  4. Radiation details:
    1. 8 patients CSI
    2. 4 patients WBRT
    3. 4 patients partial brain RT
  5. SMN location:
    1. 2 occurred in volumes receiving dose > 45 Gy
    2. 1 occurred in volume receiving < 20 Gy
    3. Rest in region receiving moderate dose 20 - 36 Gy

While the study is limited by the number of patients and by the fact that the field descriptions of the patients who did not go on to develop a cancer (26% were treated for CSI / WBRT ALL or AML). So while the population with the cancer is primarily comprised of patients receiving WBRT and CSI it is difficult to make a comparison with the cohort who did not develop a SMN in terms of the brain dose.

However what is important nonetheless is in the whole cohort only one patient developed a tumor distant from the beam at thyroid. Excluding this patient all patients developed cancers at region receiving > 20 Gy. Even accounting for the fact that all these are brain tumor patients, it stands to reason that if we can reduce the volume of brain receiving 20 - 36 Gy we can expect a reduction in the risk of SMN. This coupled with the advantages of IMRT in terms of reduced morbidity and a potentially better control secondary to dose escalation can shift the balance in favour of IMRT. This is more so in limited brain tumor treatments where IMRT can certainly spare a larger volume of the brain from the moderate dose level w.r.t 3DCRT which is the standard treatment planning modality today (even better sparing will be achived if we are considering a parallel opposed configuration as standard).

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