Measured and Calculated Dose to the Junction between Supraclavicular Field and Tangential Fields Using Different Techniques in Post-Mastectomy Radiotherapy.
Appropriately delivered post-operative radiotherapy is an integral part in the multidisciplinary approach for the treatment of invasive breast cancer.


OBJECTIVE
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.


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.


CONCLUSIONS
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.


BACKGROUND
Radiotherapy - Postmastectomy - Supraclavicular field - Tangential field.
The Department of Radiotherapy, National Cancer Institute, Cairo University, Egypt.
Magda
M
El-Mongy
Gerges A
GA
Mehany
Aida R
AR
Tolba