ESTRO 2024 - Abstract Book

S3734

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

The planning goals included V17Gy < 35% and V20 Gy < 10% for the ipsilateral lung and heart respectively, and if possible D98 > 38 Gy for PTVp (breast) and D98 > 36 Gy for PTVn (level I-IV axillary nodes) and PTVn_IMN. Dose volume parameters for the OARs were compared between 3D-CRT and VMAT using the Wilcoxon signed-rank test.

The automated VMAT-script was finally run on a new set of 100 CT-studies, to evaluate the general performance on a wide specter of anatomies.

Results:

Figure 1 shows dose volume histograms for the PTVs, heart, lungs, contralateral breast and body for the 20 cases used for script development and benchmarking. While all VMAT plans met the required D98 for the PTVs, this was not achieved for all 3D-CRT plans in terms of PTVn_IMN. CTV-coverage was adequate for all plans. VMAT provided improved conformity with reduced volume at all doses levels above 12 Gy. The mean dose to the ipsilateral lung was significantly reduced from 12.8 Gy for 3D-CRT to 9.9 Gy for VMAT. The heart mean dose was reduced from 2.5 Gy (3D-CRT) to 2.1 Gy (VMAT). The same significant trend between 3D-CRT and VMAT was observed for V20 Gy to the heart and V17 Gy and V5 Gy to the ipsilateral lung. The mean dose to the contralateral lung increased significantly by 0.7 Gy for VMAT as compared to 3D-CRT, while no significant difference was found in the mean dose to the contralateral breast. The mean body dose was reduced by 5% by the use of VMAT as compared to 3D CRT. Figure 2 show box plots of dose metrics for the automated VMAT on 100 new patient cases, documenting the versatility of the method for a large specter of body shapes. For all cases, the V17 Gy and V5 Gy for the ipsilateral lung remained below 35% and 55%, respectively, while the mean dose was below 13.5 Gy. For the heart, the V20 Gy was below 1.2% for all cases, while the mean dose remained below 3 Gy. D98 was above 38 Gy for all PTVs and doses to the contralateral breast and lung, thyroid gland, trachea, oesophagus, humeral head and total body were monitored and found acceptable.