Measured and Calculated Dose to the Junction between Supraclavicular Field and Tangential Fields Using Different Techniques in Post-Mastectomy Radiotherapy.

Unlabelled: 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 junctional area was both measured using film dosimetry, and calculated using CT planning (Precise plan).

Results: Simple abutment of fields resulted in a significant junctional overdose in both measured (125%) and calculated (171% to 20% of junctional 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 junctional volume. Technique II and IV resulted in 120%, 120% measured dose and 128%, 138% calculated dose to 20% of volume of junctional 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 junctional overlap in the sitting of post-mastectomy radiotherapy for breast cancer in case of absence of CT-based treatment planning and conformal radiotherapy.

Key Words: Radiotherapy - Postmastectomy - Supraclavicular field - Tangential field.