4–52 Initial Dosimetric Experience Using Simple Three-dimensional Conformal External-Beam Accelerated Partial-Breast Irradiation

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this noninvasive approach may increase the availability of APBI to patients with early-stage breast cancer.

Initial Dosimetric Experience Using Simple Threedimensional Conformal External-Beam Accelerated Partial-Breast Irradiation Taghian AG, Kozak KR, Doppke KP, et al (Massachusetts Gen Hosp, Boston; Boston Med Ctr; Beth Israel Deaconess Med Ctr, Boston) Int J Radiat Oncol Biol Phys 64:1092-1099, 2006

Purpose.—Several accelerated partial-breast irradiation (APBI) techniques are being investigated in patients with early-stage breast cancer. We present our initial experience using threedimensional conformal radiation therapy (3D-CRT). Methods and Materials.—Sixty-one patients with tumors of 2 cm or less and negative axillary nodes were treated with 3D-CRT accelerated partial-breast irradiation (APBI) between August 2003 and March 2005. The prescribed radiation dose was 32 Gy in 4-Gy fractions given twice daily. Efforts were made to minimize the number of beams required to achieve adequate planning target volume (PTV) coverage. Results.—A combination of photons and electrons was used in 85% of patients. A three-field technique that consisted of opposed, conformal tangential photons and enface electrons was employed in 43 patients (70%). Nine patients (15%) were treated with a four-field arrangement, which consisted of three photon fields and enface electrons. Mean PTV volumes that received 100%, 95%, and 90% of the prescribed dose were 93% ± 7%, 97% ± 4%, and 98% ± 2%, respectively. Dose inhomogeneity exceeded 10% in only 7 patients (11%). Mean doses to the ipsilateral lung and heart were 1.8 Gy and 0.8 Gy, respectively. Conclusions.—Simple 3D-CRT techniques of APBI can achieve appropriate PTV coverage while offering significant normal-tissue sparing. Therefore,

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The emergence of APBI as an alternative to standard whole-breast irradiation offers the potential for preserving local control rates while reducing the burden of care and possibly toxic effects for women who have undergone lumpectomy for early-stage breast cancer. This article adds to the growing body of evidence supporting the feasibility of APBI with external-beam methods. It emphasized the incorporation of electrons into the treatment with the intention of simplifying the field design and improving the accessibility of APBI to all radiation oncology departments. The field arrangement for most (70%) of the 61 patients in this prospective study was a 3-field technique of conformal “minitangents” and en face electrons. A combination of photons and electrons was used in 85% of cases. This method successfully delivered the prescription dose of 32 Gy in 4-Gy fractions given twice a day to an average 95% of the PTV. This PTV coverage is comparable to that of the other 2 methods described so far for external-beam APBI, one of which uses 4 to 6 non-coplanar photon fields with 3D-CRT1 and the other minitangents with the patient treated in the prone position.2 The limitation of this trial is the absence of defined dose-volume constraints on normal tissue in the treatment plan. On average, the prescription dose was delivered to 28% (median, 28%) of the non-PTV ipsilateral breast, but values as high as 50% were observed. Similarly, despite reasonable averages of 44% (median, 46%) and 52% (median, 52%) of the ipsilateral breast receiving 75% and 50% of the prescription dose, respectively, the maximum values were 70% and 86%, respectively. As a point of comparison, in the currently accruing National Surgical Adjuvant Breast and Bowel Project B-39-

Breast Diseases: A Year Book Quarterly Vol 17 No 4 2007

Radiation Therapy Oncology Group 0413 trial evaluating APBI vs wholebreast irradiation for patients with earlystage breast cancer, the maximum volume of ipsilateral breast that can receive the prescription dose is 30%, and 60% of the ipsilateral breast can receive 50% of the prescription dose. Long-term followup of all patients undergoing externalbeam APBI will be necessary to determine the implications for late toxicity-particularly the rate of fibrosis, given the combined influences of hypofractionation and the breast volume irradiated. Many questions remain unanswered about external-beam methods for APBI in particular and the ideal use of APBI in general after lumpectomy for earlystage breast cancer. This work will help to better define the efficacy and toxicity of external-beam APBI, particularly when electrons are used. Finally, the traditional thinking in breast-cancer radiation is to define a simple method that is then broadly applied to all clinical scenarios and patients. It may be time to break from this tradition and move instead toward clearly defining the targets and normal tissue constraints for optimal breast-cancer radiation and maximize the therapeutic ratio by using the best delivery method for each individual patient. J. White, MD

References 1. Vicini F, Remouchamps V, Wallace M, et al: Ongoing clinical experience utilizing 3D conformal external beam radiotherapy to deliver partial-breast irradiation in patients with early-stage breast cancer treated with breast conserving therapy. Int J Radiat Oncol Biol Phys 57:1247-1253, 2003. 2. Formenti SC, Truong MT, Goldberg JD, et al: Prone accelerated partial breast irradiation after breastconserving surgery: Preliminary clinical results and dose-volume histogram analysis. Int J Radiat Oncol Biol Phys 60:493-504, 2004.