Breast boost: are we missing the target?

BACKGROUND: Randomized trials have shown improved local control with the use of a breast boost for patients given breast-conserving treatment for breast carcinoma. Although the use of a breast boost is routine practice, no standard technique has been established. The authors compared the commonly used clinical technique with a technique based on computed tomography (CT) imaging of surgical clips in the tumor bed. METHODS: Thirty patients underwent CT simulation for postoperative radiation treatment planning as part of breast conservation therapy. During simulation, a CT-compatible wire was placed on the patient's skin, outlining the intended electron boost field; an electron boost volume (EBV) was generated by contouring the tissue underlying the wire. Also contoured was a CT-based clinical target volume (CTV) using surgical clips and postsurgical changes in the tumor bed as a guide. A planning target volume (PTV) was generated using a 1 cm margin around the CTV. An electron beam treatment plan was generated for each technique using the FOCUS three-dimensional treatment planning system. Dose-volume histograms (DVH) were generated to determine the fraction of the PTV receiving 90% of the prescribed dose if treatment was delivered using the EBV. In addition, DVH analysis was done to determine the volume of normal tissue unnecessarily irradiated when using the EBV. RESULTS: Although the electron cone size remained unchanged in most patients for both EBV and PTV, the isocenter differed more than 1 cm in the medial-lateral direction in 5 patients and in the cephalocaudal direction in 12 patients. The en face gantry angle differed for most patients. On average, only 51% (range, 27-79%) of the PTV received 90% or more of the prescribed dose when the electron plan was generated using the EBV (P < 0.0001). Ten patients received the prescription dose to less than 50% of the PTV. Mean volume of normal tissue receiving more than 50% of prescribed dose was 64.5 cm(3) (range, 24-119 cm(3)). CONCLUSIONS: Clinical delineation of the tumor bed not only carries a significant risk of missing the target, but unnecessarily treats breast tissue that may otherwise be spared. Better delineation of the tumor bed, which optimizes coverage of the target volume and spares normal breast tissue, has the potential to improve both local control and cosmetic outcome. The authors recommend the use of surgical clips to delineate the target volume, followed by CT-based treatment planning, accounting for not only microscopic disease, but also organ motion and daily setup error.

Radiation exposure to the corporeal bodies during 3-dimensional conformal radiation therapy for prostate cancer.

PURPOSE: Radiation therapy for prostate cancer is associated with the development of post-treatment erectile dysfunction. Use of 3-dimensional (D) conformal delivery techniques has reduced delivery of radiation to periprostatic tissues. However, the exact magnitude of radiation that the corporeal bodies are exposed to using this delivery technique is currently unknown. This study was undertaken to calculate the radiation dose delivered to the corporeal bodies during 3-D conformal radiotherapy. MATERIALS AND METHODS: Ten patients with proven prostate adenocarcinoma who underwent pre-therapy computerized tomography simulation and radiation delivery planning had the proximal corporeal bodies outlined on axial computerized tomography. The dose to the proximal penile tissues was then calculated using computer modeling. RESULTS: The total dose of radiation administered to the prostate and seminal vesicles was 73.8 Gy. Mean radiation delivered to the most proximal 2 cm. of the corporeal bodies was 31 +/- 12.8 Gy., equating to 43% of the total dose of radiation delivered to the prostate and seminal vesicles. CONCLUSIONS: These data indicate that large doses of radiation are being delivered to erectile tissue in the proximal penis despite careful pretreatment planning for 3-D conformal radiation therapy for prostate cancer. These data should encourage the development of radiation delivery strategies that minimize corporeal tissue exposure.