Proceedings of the 50th Annual ASTRO Meeting S525

showed a large amount of dose variation from faction to fraction, which was considered to be because of geometric variation.Therefore, it may be useful to monitor skin dose through the whole treatment, especially for patients with a shallow thickness be-tween the balloon surface and the skin.

Author Disclosure: S. Kim, MT&T (Medical Tool and Technology, LLC), E. Ownership Interest; S. Oh, None; A. Gale, None;L.A. Vallow, None.

2796 Comparison of Displacement of the Silver Clips in the Cavity Determined by KV-plain Film and Cone-

beam Computed Tomography for the Breast Cancer Patients Treated by Three-dimensional ConformalExternal-beam Partial Breast Irradiation Assisted by Active Breathing Control

C. Liu, J. Li, J. Xing, C. Liang, S. Tian, T. Fan, M. Xu

Shan dong Tumor Hospital, Jinan, China

Purpose/Objective(s): To compare the margins of CTV extended to PTV depending on the displacement of the silver clips in thecavity determined by KV-plain film and cone-beam computed tomography (CBCT) for the breast cancer patients treated by three-dimensional conformal external-beam partial breast irradiation (EB-PBI) assisted by active breathing control (ABC).

Materials/Methods: Ten patients consistent with the condition of external-beam partial breast irradiation were enrolled the study.The patients received CT simulated positioning assisted by ABC to get the CT image sets based on the respiratory condition ofmoderate deep inspiration breath hold (mDIBH), and the clips located at the cephal, pedal, lateral border and bottom of the cavitywere delineated respectively. Before each irradiation, twice CBCT and KV-plain film were received assisted by ABC device in thesequence of CBCT/KV-plain film/CBCT/KV-plain film, and then 3D-3D registration based on pixel between the CBCTimage and the planning CT image and 2D-2D registration based on pixel between KV-plain film and the planning digitally recon-structed radiograph (DRR) were finished, and the shifts of the marked clips on LAT, LNG ,VRT directions were recorded. Themean of the shifts and the margins of CTV to PTV on LAT, LNG ,VRT direction were calculated , and then the margins determinedby KV-plain film and CBCT were compared to observe the significance of difference.

Results: By comparison, the displacement of the marked clips determined by KV-plain film and CBCT on every directions had nosignificant difference (p . 0.05), the margins from CTV to PTV calculated by the marked clips displacement determined by KV-plain film on LAT, LNG,VRT directions were 5.0, 7.8, and 9.3 mm of on the cephal clip , 4.4, 6.4, 6.7 mm of the pedal clip, 5.0, 8.6,and 10.5 of the lateral clip and 5.4, 8.5, and 10.8 of the bottom clip. The margins from CTV to PTV calculated by the marked clipsdisplacement determined by CBCT were 5.7, 8.0, and 9.8 mm of the cephal clip, 5.0, 7.1, and 7.8 mm of the pedal clip, 5.3, 12.8,and 10.6 mm of the lateral clip and 5.3, 7.5, and 10.9 mm of the bottom clip . By comparison, the margins from CTV to PTV de-termined respectively by CBCT and KV-plain in the same clip and the same direction had no significant difference (p . 0.05).

Conclusions: Silver clips in the cavity can be clearly discovered on the KV-plain film and CBCT image ; CBCT and KV-plain areall the ideal image-guided methods to determine the displacement of silver clips for EB-PBI, comparably KV-plain film is a morefeasible method.

Author Disclosure: C. Liu, None; J. Li, None; J. Xing, None; C. Liang, None; S. Tian, None; T. Fan, None; M. Xu, None.

2797 Inverse IMRT Planning for Breast Cancer with ‘‘Limited Regional Metastatic Cancer’’ Involving the

Ipsilateral Anterior Mediastinal Nodes

S. Yoo, J. Boyd, S. Das, F. Yin, E. Jones, K. Light, L. Marks

Duke University Medical Center, Durham, NC

Purpose/Objective(s): With the increasing use of PET imaging, we are seeing more patients with ‘‘limited regional metastaticcancer’’ involving the ipsilateral anterior mediastinal nodes. The design of conformal RT plan is extremely difficult in these cases.We herein report the dosimetric results of IMRT planning for a series of such patients, and suggest a ‘‘class solution’’.

Materials/Methods: Five patients with regionally-extensive nodal disease were treated in the last year (1 right-, 4 left-sided). All 5patients underwent concurrent chemotherapy with Xeloda or Navelbine. All underwent CT scanning; 2 of the left-sided patientswith deep inspiration breath-hold to maximize the separation between the heart and chest wall. GTVs, CTVs, and PTVs were de-fined by the physician to include the breast/chest-wall, IMN, supraclavicular (Scv) and mediastinal nodes. The targets were large,with the average depth of the mediastinal nodes 10 cm from the anterior chest (range, 7-13 cm). Prescribed doses were typically 45-50 Gy to the CTV, 53-60 Gy to the GTV in Scv and 60-66 to the GTV in the mediastinum; usually in 30-33 fractions. IMRT plansinclude 8-9 6MV photon beams: 2 ‘‘AP/PA type’’ beams were set to cover Scv area only, 2-3 ‘‘lateral-tangential type’’ beams tocover breast CTV only, 2-3 ‘‘medial-tangential type’’ beams and 1-2 ‘‘enface type’’ beams to cover IMN, breast, and mediastinalCTVs. Beams had collimator rotation and their jaws fixed to minimize lungs and heart exposure. Beam intensity maps were op-timized to satisfy physician-defined dose constraints.

Results: The use of 8-9 IMRT beams provided reasonably good coverage of the targets: Average D95% (% of the prescribed dose toa 95% of target) were 99.1 ± 3.6% for the breast CTV, 96.3 ± 3.9% for the Scv CTV, 99.9 ± 4.5% for the mediastinum CTV, and101.0 ± 3.8% for the GTVs. The average dose homogeneity index (% of target volume getting between 95% and 110% of pre-scribed dose) was 90.3 ± 0.1% for breast CTV. Average V20 and mean dose to entire lung were 21.4. ± 8.3% and 13.4 ± 3.7Gy. Average V30 and mean dose to heart were 12.9 ± 16.5% and 12.5 ± 9.6 Gy. Average maximum cord dose was 26.5 ± 7.8Gy. One patient had acute symptomatic pneumonitis at 20 Gy requiring treatment interruption although the dose to the lung forthis patient was not higher than other patients. The remaining 4 patients tolerated the treatment without acute complications.We found no reported late complications, although follow-up is short.

Conclusions: Inverse IMRT planning using multiple beams with fixed jaws/collimator rotation is proposed as a ‘‘class solution’’for patients with breast cancer and metastases to the ipsilateral mediastinal nodes. Reasonably good target coverage was achievedand doses to the adjacent critical normal tissues generally appeared acceptable.

Author Disclosure: S. Yoo, None; J. Boyd, None; S. Das, None; F. Yin, None; E. Jones, None; K. Light, None; L. Marks, None.