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Skin-Sparing Intensity-Modulated Radiotherapy of the Breast

Martin Luther University Halle-Wittenberg, Halle/Saale, Germany

To the Editor:

I read with great interest the recent article by Pignol et al¹ on the effect of intensity-modulated radiotherapy (IMRT), compared with standard wedge radiotherapy, on dose distribution within the conserved breast and consequential skin toxicity. In their randomized trial, the authors found that a rather simple approach to modulate the dose by adding about five subsegment fields— instead of a wedge—to each tangential irradiation field resulted in a significant homogenization of dose distribution within the target volume and concomitant reduction of a more severe form of acute skin reaction: moist desquamation.

While this resulting toxicity reduction appears to speak for itself, it is not totally clear if target volume definition and dose prescription in the two treatment arms were identical. The authors state that the total dose (50 Gy) was prescribed to a point in a specific anatomic location and the clinical target volume (CTV) was defined by the 95% isodose level.¹ The crucial question is how the CTV—and also the associated planning target volume (PTV), if defined, which incorporates uncertainties caused by patient setup error and organ motion—relate to the skin itself. In standard breast radiotherapy after breast-conserving surgery, the PTV has traditionally contained the whole breast (including the skin). At the same time, a standard radiotherapy plan containing two opposing wedged fields of a typical energy of 5 or 6 MV was known to deliver less than the actual prescribed dose to the skin surface.² Therefore, with standard technique, the radiation oncologist underdosed the skin "knowingly but unintentionally." Furthermore, differences in dose prescription policy (to a point, to a volume, or to a given isodose level) between investigators accounted for variations in total dose, despite identical nominal doses, frequently of 10% or higher.³

Advanced radiotherapy planning and delivery techniques, such as IMRT, often require more precise definitions of PTVs as radiation dose distributions unachievable with standard plans can be obtained. If the skin surface in the treated breast is to be part of the PTV (eg, due to the certainly low risk of tumor cell dissimination within the lumpectomy scar), then it should also be treated with the prescribed dose and skin sparing could be associated with a reduction in in-breast tumor control. If this risk is to be neglected, then a skin/subcutaneous tissue layer of a thickness to be specified can possibly be excluded from the PTV and spared, using the approach described by Pignol et al or alternative strategies. For a widespread application of tangential-beam IMRT in breast-conserving therapy, the CTVs and PTVs should be clearly defined with regard to the skin as an organ at risk in the radiotherapy planning procedure.

AUTHOR'S DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST

The author(s) indicated no potential conflicts of interest.

REFERENCES

1. Pignol JP, Olivotto I, Rakovitch E, et al: A multicenter randomized trial of breast intensity-modulated radiation therapy to reduce acute radiation dermatitis. J Clin Oncol 26:2085-2092, 2008[Abstract/Free Full Text]

2. Yagamuchi S, Karasawa K, Furuya T, et al: Comparison of 4 MV photon surface dose among Varian, Siemens, and Elekta linear accelerators for tangential breast treatment: A phantom study. Radiat Med 25:8-13, 2007[CrossRef][Medline]

3. Kantorowitz DA: The impact of dose specification policies upon nominal radiation dose received by breast tissue in the conservation treatment of breast cancer. Int J Radiat Oncol Biol Phys 47:841-848, 2000[CrossRef][Medline]

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  Jean-Philippe Pignol, Eileen Rakovitch, and Ivo Olivotto
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