Can we predict plan quality for external beam partial breast irradiation: results of a multicenter feasibility study (Trans Tasman Radiation Oncology Group Study 06.02).
OBJECTIVE
Partial breast irradiation (PBI) after lumpectomy may be an option for selected patients with early breast cancer. A feasibility study of accelerated PBI delivered using external beam 3-dimensional conformal radiation therapy (RT) was undertaken at 8 Australasian centers. The present study evaluated the impact of patient, tumor, and RT technique-related factors on the quality of RT plans as determined by the dose-volume parameters of organs at risk.


METHODS
Forty-eight patients were enrolled in the study. All RT plans were centrally reviewed using predefined dosimetric criteria before commencement and after completion of protocol therapy. The RT plans of 47 patients met the dose-volume constraints, and all 47 patients received PBI to a prescribed dose of 38.5 Gy in 10 fractions. The RT plan quality was determined by volumes of the ipsilateral whole breast, lung, and heart that received 50% and 95%; 30%; and 5% of the prescribed dose, respectively. Patient, tumor, and RT technique-related factors were investigated for association with the parameters of RT plan quality.


RESULTS
The ratio of the planning target volume to the ipsilateral whole-breast volume was significantly associated with the ipsilateral breast doses on multiple variable analyses. The distance of the postlumpectomy surgical cavity from the heart and lung were predictive for heart and lung doses, respectively. A distance between surgical cavity and heart of >4 cm typically resulted in <1% of the heart volume receiving 5 Gy or less. It was more difficult to meet the heart dose constraint for left-sided and medially located tumors.


CONCLUSIONS
Partial breast irradiation using 3-dimensional conformal RT was feasible within the study constraints. The ratio of planning target volume to ipsilateral whole-breast volume and the distance of surgical cavity from the heart were significant predictors of the quality of treatment plan for external beam PBI.
Peter MacCallum Cancer Centre, Departments of Radiation Oncology, Physical Sciences and Radiation Therapy, Melbourne, Victoria, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, Victoria, Australia; School of Science, Engineering and Technology, Royal Melbourne Institute of Technology University, Melbourne, Victoria, Australia. Electronic address: Tomas.Kron@petermac.org.
Tomas
T
Kron
David
D
Willis
Emma
E
Link
Margot
M
Lehman
Gillian
G
Campbell
Peter
P
O'Brien
Boon
B
Chua
D000368:Aged; D001315:Australia; D001940:Breast / Q000528:radiation effects; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D005240:Feasibility Studies; D005260:Female; D006321:Heart / Q000000981:diagnostic imaging / Q000528:radiation effects; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000528:radiation effects; D008327:Mammography / Q000379:methods; D015412:Mastectomy, Segmental; D008875:Middle Aged; D009520:New Zealand; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects*; D011446:Prospective Studies; D058996:Quality Improvement / Q000592:standards; D011829:Radiation Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods / Q000592:standards*; D020266:Radiotherapy, Conformal / Q000379:methods / Q000592:standards*; D047368:Tumor Burden