Contralateral breast doses following radiotherapy of the breast and regional lymph nodes: Measurements and treatment planning calculations.
OBJECTIVE
To measure the dose distribution in the contralateral breast (CB) following radiotherapy of the breast and regional lymph nodes by a 4-field technique, and to examine whether related treatment planning calculations of CB doses reproduce the measurements.


METHODS
CB doses were measured by thermoluminescence dosimetry on the surface of 8 patients and in an anthropomorphic phantom. Dose calculations at corresponding points of interest were performed by the treatment planning system Helax-TMS 6.1 using the pencil beam or the collapsed cone algorithm.


RESULTS
The measured CB doses were typically between 1% and 15% of the prescribed dose. The dose decreased significantly both in the medial-lateral and cranial-caudal direction. The average ratio of the measured to the calculated CB dose was about 0.7 and 0.9 for the pencil beam and the collapsed cone algorithm, respectively. One of the treatment fields aimed at the regional lymph nodes and some of the chest wall gave the highest contribution to the CB dose.


CONCLUSIONS
The dose distribution in the CB following locoregional radiotherapy of the breast and regional lymph nodes is quite inhomogeneous. The collapsed cone algorithm may be used for estimating doses to the CB. Some concern is raised regarding the current field arrangement and the consequences for the CB dose.
Johansen
Safora
S
Department of Radiation Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Oslo, Norway.
Olsen
Dag Rune
DR
Danielsen
Turi
T
Malinen
Eirik
E
D000465:Algorithms; D001943:Breast Neoplasms / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D008198:Lymph Nodes / Q000528:radiation effects; D009367:Neoplasm Staging; D009381:Neoplasms, Radiation-Induced / Q000517:prevention & control*; D019047:Phantoms, Imaging; D011835:Radiation Protection / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D013819:Thermoluminescent Dosimetry