Script-based automated placement of gantry angles for tangential beams of breast cancer / 中华放射医学与防护杂志

ABSTRACT

Objective To reduce the dose to organ at risk ( OAR) by script-based optimizing the gantry angles of tangential beams for forward-planned intensity-modulated breast radiotherapy ( fIMRT ) plans. Methods A total of 46 patients with breast cancer (26 in left and 20 in right) after conservative surgery who were treated with manually planned fIMRT were retrospectively re-planned using a script to place the tangential beams automatically. The script program was developed using Pinnacle3 scripting language as imbedded in the Pinnacle3 treatment planning system, and the Python scripting language. Dosimetric indices, including V20 of the ipsilateral lung, D1 of the contralateral breast and V10 of the heart were extracted by the script for plans of different gantry angles. Then the optimal tangential angles were selected by a penalty function. Results For the 26 left breast cancer cases, V20 of the ipsilateral lung for manual and script were (18.2 ±3.4)% and (18.1 ±3.4)%, respectively(P>0.05), while D1 of the contra-lateral breast(249. 2 ± 88. 4) cGy and (230. 4 ± 80. 2) cGy, respectively( t=2. 27, P<0. 05), V10 of the heart (13. 7 ± 5. 7)% and (13. 1 ± 5. 7)%(t=2. 82, P<0. 05). The V20 of the ipsilateral lung of the 20 right breast cancer cases were (19. 8 ± 3. 8)% and (19. 8 ± 3. 9)%, respectively(P>0. 05). The script plans achieved better V10 of the heart[(298. 0 ± 239. 7) cGy] than the manual plans[(340. 0 ± 286. 2) cGy] (t =2. 53, P <0. 05). Conclusions Compared with the manualmethod, the script can assess of the impact of tangential beam angles on the OAR dose, patient-specifically and quantitatively, hence make better trade-offs and improve the plan quality.