Measured and calculated dose to the junction between supraclavicular field and tangential fields using different techniques in post-mastectomy radiotherapy

Abstract EN

Appropriately delivered post-operative radiotherapy is an integral part in the multidisciplinary approach for the treatment of invasive breast cancer.

The Aim of the Work : Is to find the most effective simple way to achieve homogeneous dose distribution to the junction of the supraclavicular beam and tangential beams, in absence of CT planning facilities, through measurement / calculation of dose using different techniques.

Material and Methods : Alderson human phantom was planned and irradiated through 4 different techniques.

Technique I, simple abutment of fields ; technique II, table rotation in tangential fields; technique III, table rotation in tangential beams and half beam block in supraclavicular field; and technique IV, simple triangular block in supraclavicular field.

Dose to the functional area was both measured using film dosimeter, and calculated using CT planning (Precise plan Results: Simple abutment of fields resulted in a significant functional overdose in both measured 125 %)) and calculated (171 % to 20 % of functional volume) dose.

Best results were seen in technique III (table rotation and half beam block) where the measured dose was 89 % and calculated dose was 89 % to 20 % of functional volume.

Technique II and IV resulted in 120 %, 120 % measured dose and 128 %, 138 % calculated dose to 20% of volume of functional area, respectively.

Conclusion : Table rotation in tangential beams and half beam block in supraclavicular beam seems to be an effective and simple method to prevent functional overlap in the sitting of post-mastectomy radiotherapy for breast Cancer in case of absence of CT-based treatment planning and conformal radiotherapy.