Clinical implications of the ISC technique for breast cancer radiotherapy and comparison with clinical recommendations.

PURPOSE The present project studied the implications of using the irregular surface compensator (ISC) technique in comparison to three-dimensional conformal radiation therapy (3D-CRT) for breast cancer treatment. ISC is an electronic compensation algorithm that modulates the fluence across the radiation fields to compensate for irregularly-shaped surfaces and deliver a homogeneous dose to a compensation plane. PATIENTS AND METHODS Ten breast cancer patients (five left- and five right-sided) were planned with both techniques. The planning was done for 50 Gy in 25 fractions with 2 Gy per fraction in all patients. Physical parameters such as doses to the clinical target volume (CTV-T) and the planned target volume (PTV), heterogeneity index and doses to lung and heart were determined and compared for the treatment plans. RESULTS The ISC technique led to significantly better coverage of the CTV-T and PTV in almost all patients with statistically significant better homogeneity of the dose distribution. The contralateral lung and the heart receive the same dose with both ISC and 3D-CRT plans. However, ISC showed a trend towards decreasing the volumes of the ipsilateral lung irradiated with high doses. CONCLUSION The ISC technique leads to an improvement of the target coverage and the radiation burden of the ipsilateral lung thus allowing better compliance with the national recommendations for breast radiotherapy and increasing the potential for improved quality of life for breast cancer patients. It should therefore be preferred over 3D-CRT for breast cases with difficult dose homogeneity to the PTV or CTV-T.