Abstract book - ESTRO meets Asia

S25 ESTRO meets Asia 2018

H. Cha 1 , H. Cho 2 1 Samsung Medical Center- Sungkyunkwan University Scho ol of Medicine, Radiation Oncology, Seoul, Korea Republic of 2 Samsung Advanced Institute for Health Science & Techn ology- Sungkyunkwan University, Medical Device Management and Research, Seoul, Korea Republic of Purpose or Objective Electron bolus provides energy modulation compensating for the surface irregularity and the varying target depth. However, several challenges related to the use of boluse such as hot and cold spots as well as air gap effect remain unsolved. As an effort to find a better compensator for postmastectomy electron radiotherapy (RT), we investigated skin dose dosimetry of postmastectomy electron RT with the use of patient-tailored three- dimensional printed bolus (3DPTB) and Pinnacle 3D electron beam calculation. Material and Methods 3DPTB design was performed base on the patients’ computed tomography (CT) images acquired for treatment planning purposes. The optimal energy and bolus contour was determined using Pinnacle 3D electron beam calculation algorithm. 3D bolus contour was converted into the Stereolithography file format, and boluses were printed out using Fused deposition manufacturing 3D printer. Polylactic acid (PLA) was used as bolus material. Both in-vivo patient study and phantom measurements were performed to investigate the dosimetric parameters and percent depth dose (PDD) with the use of 3DPTB. For the in-vivo study, 20 patients were enrolled and 3DPTB was designed for each patient based on the CT simulation image (Figure 1a). The skin dose was measured using EBT3 film (Figure 1b), and was compared to the treatment planning system (TPS) calculated dose for each measurement. We sought to minimize the discrepancy between calculated dose and measured dose, by applying gel between the skin and 3DPTB. Effect of gel in skin dosimetry was measured and investigated. For the Phantom study, we used torso phantom and EBT3 film. PDD curves for the measured dose and TPS calculated dose by energy (6 MeV vs. 9 MeV) and by bolus thickness (0 cm, 0.5 cm, 1 cm, 1.5 cm and 2 cm) were generated to evaluate the difference.

Conclusion Current study shows that postmastectomy electron RT using 3DPTB with PLA bolus material and Pinnacle TPS can be applied to clinical practice when accepting approximately 8 % of discrepancy between planned dose and actual dose delivered to the skin in selected patients. This discrepancy can be decreased to approximately 5 % with the use of gel. To minimize the discrepancy between planned and measured skin dose, bolus thickness of < 1 cm is recommended for the electron energy of 6 MeV, while thickness of ≥ 1.5 cm is recommended to be used with 9 MeV. SP-062 ESTRO-HERO: Introduction and background B. Slotman 1 1 VU University Medical Center, Department of Radiation Oncology, Amsterdam, The Netherlands Abstract text The provision of radiotherapy shows considerably variation among the European countries and even between regions within countries. In the ESTRO QUARTS (QUAntification of Radiation Therapy infrastructure and Staffing needs) project, partly funded by the EU, the availability and content of guidelines on radiotherapy infrastructure and staffing were evaluated and it was suggested to have one linear accelerator per 450 patients, one radiation oncologist per 200–250 patients and one physicist per 450– 500 patients (or one per MV-machine). However, there are large variations in demographics and cancer incidence between the European countries. In order to obtain adequate and equitable access to radiotherapy in all countries, attempts were made to derive evidence-based estimates of the radiotherapy needs. The model developed in the QUARTS project establishes a direct relationship between epidemiological data and radiotherapy needs. Comparison of the estimates of this model with the levels of infrastructure in 2005 revealed major inequalities in provision of RT in the European countries. In the following ESTRO project on Health Economics in Radiation Oncology (HERO), an improvement in radiotherapy infrastructure was noted, but still significant heterogeneity in access to radiotherapy was seen. In high- income countries, especially in North-Western Europe (Scandinavian countries, BeNeLux, Austria and Switzerland), there is a good provision of radiotherapy with modern equipment. In these countries, around 90% of the machines was capable of delivering IMRT and the Symposium: HERO

Results In in-vivo patient measurements, the average of the % difference was -2.3 % (range, -16.5 % - 8.5 %) (Figure 2a) and was decreased to -0.8 % (range, -12.0 %- 14.8 %) with the use of gel between chest wall and bolus (Figure 2b). In general, the increase in bolus thickness was associated with greater discrepancy between the measured vs. calculated dose. In the phantom study, PDD curves showed that, when using 6MeV energy, boluses with thickness and ≥ 1 cm was related with greater discrepancy between calculated and measured dose, whereas thickness < 1.5 cm was related with greater discrepancy when using 9MeV energy.