A phase I/II study piloting accelerated partial breast irradiation using CT-guided intensity modulated radiation therapy in the prone position.
OBJECTIVE
External beam accelerated partial breast irradiation (EB-aPBI) is noninvasive with broader potential applicability than aPBI using brachytherapy. However, it has inherent challenges in daily reproducibility. Image-guide radiotherapy (IGRT) can improve daily reproducibility, allowing smaller treatment margins. Our institution proposed IG-IMRT in the prone position to evaluate dose homogeneity, conformality, normal tissue avoidance, and reliable targeting for EB-aPBI. We report preliminary results and toxicity from a phase I/II study evaluating the feasibility of EB-aPBI in the prone position using IG-IMRT.


METHODS
Twenty post-menopausal women with node-negative breast cancer, excised tumors <3.0 cm, negative sentinel lymph node biopsy, and surgical clips demarcating the lumpectomy cavity underwent prone EB-aPBI using IG-IMRT on an IRB-approved phase I/II study. All patients underwent CT planning in the prone position. The lumpectomy cavity PTV represented a 2.0 cm expansion. 38.5 Gy was delivered in 10 fractions over 5 days, such that 95% of the prescribed dose covered >99% of the PTV. Dose constraints for the whole breast, lungs and heart were met.


RESULTS
The median patient age was 61.5. Mean tumor size was 1.0 cm. 35% of patients had DCIS. Median PTV was 243 cc (108-530) and median breast reference volume was 1698 cc (647-3627). Average daily shifts for IGRT were (0.6, -4.6, 1.7 mm) with standard deviations of (6.3, 6.5, 6.4mm). Acute toxicity was G1 erythema in 80%, and G2 erythema, G2 fatigue, and G2 breast pain each occurred in 1 patient. With a median follow-up of 18.9 months (12-35), 40% of patients have G1 fibrosis and 30% have G1 hyperpigmentation. 95% of patients have good to excellent cosmesis. There have been no recurrences.


CONCLUSIONS
These data demonstrate that EB-aPBI in the prone position using IG-IMRT is well tolerated, yields good dosimetric conformality, and results in promising early toxicity profiles.
Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, USA.
Carmen
C
Bergom
Phillip
P
Prior
Kristofer
K
Kainz
Natalya V
NV
Morrow
Ergun E
EE
Ahunbay
Alonzo
A
Walker
X
X
Allen Li
Julia
J
White
D000367:Age Factors; D000368:Aged; D001943:Breast Neoplasms / Q000401:mortality / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D018572:Disease-Free Survival; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015412:Mastectomy, Segmental / Q000379:methods; D008875:Middle Aged; D009361:Neoplasm Invasiveness / Q000473:pathology; D009364:Neoplasm Recurrence, Local / Q000401:mortality / Q000473:pathology* / Q000628:therapy; D009367:Neoplasm Staging; D056888:Patient Positioning / Q000379:methods; D061214:Patient Safety; D010865:Pilot Projects; D017698:Postmenopause / Q000502:physiology; D011379:Prognosis; D016684:Prone Position; D011446:Prospective Studies; D011832:Radiation Injuries / Q000175:diagnosis / Q000453:epidemiology; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects / Q000379:methods*; D018570:Risk Assessment; D016019:Survival Analysis; D014057:Tomography, X-Ray Computed / Q000379:methods; D016896:Treatment Outcome
Accelerated partial breast irradiation; Breast cancer; CT guidance; Image-guided radiation therapy; Intensity modulated radiation therapy; Prone