The influence of patient geometry on the selection of chest wall irradiation techniques in post-mastectomy breast cancer patients.
OBJECTIVE
To evaluate three chest wall (CW) irradiation techniques: wide tangential photon beams, direct appositional electron field and electron arc therapy with regards to target coverage and normal tissue tolerance.


METHODS
Thirty-two post-mastectomy breast cancer patients were planned using three CW irradiation techniques. Computed tomography (CT) simulation was done on all patients and clinical target, heart and lung volumes were contoured. For each technique, dose distributions and dose-volume histograms (DVH) were calculated. Pass/fail criteria were applied based on volumetric target and critical structure dose coverage. Passing criteria for target was 95% of target receiving 95% of dose using a standard dose of 50 Gy/25 fractions, for heart </=10% volume receiving 50% dose (i.e. 25 Gy) and for lung </=25% volume ipsilateral lung receiving 50% dose (i.e. 25 Gy).


RESULTS
The number of patients optimally treated by each technique were as follows: wide tangential photon beams 23/32 (72%), direct appositional electron field 1/32 (3%), electron arc 4/32 (12.5%) and in 4/32 (12.5%) no technique was optimal. Geometric predictors for technique suitability include CW thickness, medial to lateral CW curvature, uniformity of superior to inferior CW curvature and length of mastectomy scar.


CONCLUSIONS
This study confirms the utility of CT planning and DVH analysis for treatment planning of breast cancer. Patient factors that predict for treatment technique suitability and aid in technique selection can be identified. In a small subset of patients, none of the currently studied techniques were optimal and more novel methods of chest wall irradiation are required.
Ung
Y C
YC
Toronto-Sunnybrook Regional Cancer Centre, 2075 Bayview Ave., ON M4N 3M5, Toronto, Canada.
Sixel
K E
KE
Bell
C
C
D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000601:surgery; D015331:Cohort Studies; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008408:Mastectomy; D008875:Middle Aged; D011446:Prospective Studies; D011832:Radiation Injuries / Q000517:prevention & control; D011836:Radiation Tolerance; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000379:methods*; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013909:Thorax / Q000528:radiation effects*; D014057:Tomography, X-Ray Computed