Measurement of skin and target dose in post-mastectomy radiotherapy using 4 and 6 MV photon beams.
BACKGROUND
For patients with high risk breast cancer and mastectomy, radiotherapy is the treatment of choice to improve survival and local control. Target dose is mainly limited due to skin reactions. The feasibility of using 4 MV beams for chest wall treatment was studied and compared to standard 6 MV bolus radiotherapy.


METHODS
Post-mastectomy IMRT was planned on an Alderson-phantom using 4 and 6 MV photon beams without/with a 0.5 cm thick bolus. Dose was measured using TLDs placed at 8 locations in 1 and 3 mm depth to represent skin and superficial target dose, respectively.


RESULTS
4 MV and 6 MV beams with bolus perform equally regarding target coverage. The minimum and mean superficial target dose for the 6 MV and 4 MV were 93.0% and 94.7%, and 93.1% and 94.4%, respectively. Regarding skin dose the 4 MV photon beam was advantageous. The minimum and mean skin dose for the 6 MV and 4 MV was 76.7% and 81.6%, and 69.4% and 72.9%, respectively. The TPS was able to predict dose in the build-up region with a precision of around 5%.


CONCLUSIONS
The use of 4 MV photon beams are a good alternative for treating the thoracic wall without the need to place a bolus on the patient. The main limitation of 4 MV beams is the limited dose rate.
Melanie
M
Fischbach
Roger A
RA
Hälg
Matthias
M
Hartmann
Jürgen
J
Besserer
Günther
G
Gruber
Medical Physics, Radiotherapy Hirslanden, Witellikerstrasse 40, Zürich, CH-8032, Switzerland. uwe.schneider@uzh.ch.
Uwe
U
Schneider
D001943:Breast Neoplasms / Q000532:radiotherapy* / Q000601:surgery*; D004867:Equipment Design; D005260:Female; D006801:Humans; D008408:Mastectomy / Q000379:methods*; D019047:Phantoms, Imaging; D017785:Photons / Q000627:therapeutic use*; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012867:Skin / Q000528:radiation effects*; D035441:Thoracic Wall / Q000528:radiation effects; D016896:Treatment Outcome