ESTRO 37 Abstract book

ESTRO 37

S602

shown. Abbreviations: HI = (D2% - D98%) / D50%, CI= V PTV95% 2 / (V PTV* V 95% ) Dosimetry QA for the automated plans are all within the gamma-criteria 3%/3mm. Conclusion The plan quality has been improved for the automated plans compared to the original manual optimized VMAT plans. Actual hands on time to make the plans can be reduced from 2 hours to 30 minutes. This automated planning technique can be safely introduced in the clinic. PO-1071 Dosimetric quality and delivery time of Dynamic Jaw Mode in TomoTherapy® for Breast Cancer Patients S.T. Chiu 1 , P.M. Wu 2 , K.F. Cheng 1 , P.H. Fok 1 , G. Chiu 1 1 Hong Kong Sanatorium & Hospital, Department of Radiotherapy, Happy Valley, Hong Kong SAR China 2 Hong Kong Sanatorium & Hospital, Medical Physics & Research Department, Happy Valley, Hong Kong SAR China Purpose or Objective Dynamic Jaw (DJ) Mode in Helical TomoTherapy® (HT) allows the jaws to move continuously and to adapt the field width (FW) dynamically at the cranial and caudal edges of a target to reduce the cranio-caudal dose penumbra during treatment. Few studies claimed that it can improve the cranio-caudal dose distribution without prolonging the treatment time in treating different types of cancer. Also, studies suggested that DJ with a wider 5 cm FW can replace fixed jaws (FJ) with 2.5 cm FW, which can sustain the plan quality and reduce the treatment delivery time. Yet, the study on breast cancer with supraclavicular fossa (SCF) nodal involvement using DJ Mode in HT is limited. This study aims to evaluate the DJ Mode retrospectively by comparing their dosimetric quality with Normal Tissue Complication Probability (NTCP) of OARs and treatment delivery time with FJ Mode on treating left-side breast with SCF nodal involvement. The best choice of mode will be advised to maximize the patient’s benefit. Material and Methods All post-mastectomy patients, who had been irradiated for left-side breast with SCF nodal involvement and planned under HT using DJ Mode with 2.5 cm FW (DJ2.5), from November 2014 to August 2016 at Hong Kong Sanatorium & Hospital, were selected retrospectively in this study. With the same dose constraint and prescription as the treated DJ2.5 plan, 2 extra plans using DJ Mode with 5cm FW (DJ5.0) and FJ mode with 2.5 cm FW (FJ2.5) were computed for plan comparison. Homogeneity index (HI) and ICRU-recommended dose- volume specifications (e.g. D95) of PTV for chestwall (CW) and SCF, dose-volume specifications with clinical value of OARs, NTCP of heart and lung, treatment delivery time and actual modulation factor (MF) were used for comparison.

Table 1. Settings for the developed automated planning technique.

Plan quality was evaluated by comparing the conformity index (CI), homogeneity index (HI), PTV coverage and dose to the OARs. Furthermore, scorecards are used to check if the automated plan fulfils all dose criteria. Results All automated plans offered similar PTV coverage as the original clinical plans. For 11 of the 22 automated plans, the plans were ready after Auto-Planning and an extra warm restart had been done. For the remaining 11 plans, the scorecard showed that an extra warm restart with adaption of an objective weight or value for some OAR had to be done before the plan was clinical acceptable. A typical example of the dose distribution for the original clinical (upper left panel) and automated plan (upper right panel) of a patient plan is shown in Figure 1. Plan quality of all plans were compared and the results are shown in Figure 1. The PTV coverage and CI were comparable for manual and automated plans, the homogeneity index was significantly improved. For the OARs the max dose to the spinal cord, the volume of the oesophagus V35Gy/V50Gy and V20Gy of the lung and the mean dose to heart and lung were significantly improved.

Figure 1: Upper panels show an example of the dose distribution for the original clinical (upper left panel) and automated plan (upper right panel). In the lower panels, the plan quality is evaluated for all plans comparing the manual (light blue) with the automated plans (dark blue). In the lower left panel, the plan quality criteria for PTV are plotted and scaled (if necessary) for visualisation: V95% (divided by 100), HI (multiplied with factor 10) and CI. In the lower right panel, the dose to the OARs are