ESTRO 2022 - Abstract Book

S1469

Abstract book

ESTRO 2022

dose respectively. Plot c) and d) shows Bland-Altman plots for the same OAR. A good correlation was observed with R- squared values of 0.93 and 0.96 for heart and ipsilateral lung respectively.

Figure 1: a) and b) shows scatterplot of the actual dose versus the predicted dose for the mean heart dose and mean ipsilateral lung dose. c) and d) shows Bland-Altman plots for the same OAR, where the dashed lines indicate the limits of agreements (95% confidence interval). Conclusion PlanIQ shows to be useful to use as a quick prediction of doses to heart and ipsilateral lung in breast cancer radiotherapy. This could allow for early clinical decision-making on potential target compromises to keep doses to organs at risk below specific levels. In addition, an early detection of patients that could be candidates to proton therapy due to high dose to heart or lung would be possible with PlanIQ.

PO-1671 Total Marrow and Lymphoid Irradiation via Arc IMRT and Helical Tomotherapy

G. Kavak Eren 1 , F. Ertan 2 , S. Ş ahin 1 , E. Atasever Akkas 1 , E. Karakaya 1

1 Dr. Abdurrahman Yurtaslan Ankara Oncology Hospital, Radiation Oncology, Ankara, Turkey; 2 Dr. Abdurrahman Yurtaslan Ankara Oncology Hospital, Radiation oncology, Ankara, Turkey Purpose or Objective Total body irradiation (TBI) is a radiotherapy technique that has been used for over a century in various benign and malignant diseases. Opposed lateral irradiation technic via linear accelerator is applied to patients who will be using TBI in the hematological stem cell transplantation preparation regimen in our clinic. This TBI technique often results in high dose heterogeneity in patients and also does not preserve OARs other than the lungs. So the toxicity of treatment especially in combination with chemotherapy is high. The concepts of Total marrow irradiation (TMI) and Total marrow and lymphoid irradiation (TMLI) come into play in order to challenge this situation. It is known that with TMI/TMLI methods, the target tissue and organs at risk (OARs) are contoured and it is possible to protect more effectively OARs while giving more homogeneous doses to target volumes. Our aim in this study is TMLI planning via Arc IMRT and Helical Tomotherapy methods as an alternative to the old conventional techniques, also to compare these two planning techniques. Materials and Methods Two CTs were taken with 5 mm cross-section intervals, phased upper and lower, in 7 patients with ALL. The patients were fixed with a C pillow, thermoplastic head-neck mask and vacuum bed. After the upper CT, the lower CT was taken by turning the coach board without getting up the patient. Whole body bones (excluding mandible, hands and feet), all lymphoid structures (head and neck, waldeyer lymphatic ring, axilla, mediastinum, abdomen, pelvic lymphatics), brain, scrotum and spleen were targeted as PTV. Critical structures in the whole body were also delineated. The mean contouring time for one patient was 5.5 hours. Arc IMRT and Helical Tomotherapy planning were performed for each patient (In the attached picture, a section from both physics plans is shown). Arc IMRT plannings were done 4 isocenters for the upper body. Helical Tomotherapy planning parameters were taken as pitch factor 0,397, modulation factor 2-2,3, field width 5 cm.