ICHNO-ECHNO 2022 - Abstract Book

S15

ICHNO-ECHNO 2022

Herlev, Department of Oncology, Copenhagen, Denmark; 6 Zealand University Hospital, Naestved, Department of Oncology, Copenhagen, Denmark; 7 Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark; 8 Aarhus University Hosputal, Department of Experimental Clinical Oncology, , Aarhus, Denmark; 9 Aarhus University Hospital, Department of Experimental Clinical Oncology, , Aarhus, Denmark; 10 University of Southern Denmark, Department of Clinical Research, Odense, Denmark Purpose or Objective The clinical target volume consists of macroscopic tumour volume and a margin accounting for microscopic disease, and varies across different treatment centres despite the fact that risk of acute and late morbidity is related to the target volume. The risk of radiation-induced toxicities hinders further dose escalation and patient quality of life after treatment. In 2013, the Danish Head and Neck Cancer Group (DAHANCA) introduced consensuses guidelines that entailed a geometric 5 mm margin from Gross Tumour Volume (GTV) to the high dose Clinical Target Volume (CTV1) and additional 5 mm to the intermediate CTV2. This was a change from former guidelines where the margin varied from zero to 10 mm, or more. The new guidelines were intended to produce more consistent treatment volumes. The current study aimed to compare GTV- CTV1 margins in patients treated three years before (2010-2012) and three years after (2013-2015) the implementation of the 5+5 mm CTV margin guidelines in three DAHANCA centres. Materials and Methods The cohort consisted of patients with squamous cell carcinoma in the larynx (except T1 glottis), oropharynx, and hypopharynx receiving accelerated (66-68 Gy/33-34fx, 6 fx/week) or hyperfractionated (76 Gy/56fx, 10 fx/week) radiotherapy in three centres. 1,712 treatment planning CTs (pCT) were collected using a national treatment plan bank. A total of 760 and 952 patients received treatment in 2010-2012 and 2013-2015, respectively. The structure-naming of target volumes was identified using MatLab to locate all volumes. The patient-specific GTV-CTV1 margin was estimated as the median of all shortest distances from the GTV surface to the CTV1 surface. GTV, CTV1, and PTV1 (planning treatment volume) were calculated for all patients. Results he median GTV was 18.7 cm 3 (IQR 7.8-34.5) and 18.3 cm 3 (IQR 8.8-34.2) for 2010-2012 and 2013-2015, respectively. The median CTV1s ranged between 51.7 cm 3 (IQR 30.6-85.5) and 58.6 cm 3 (IQR 35.5-96.5) and were more consistent across the three centres in 2013-2015 (Figure 1). The median GTV-CTV1 margins decreased from 9.2 mm in 2010-2012 to 4.9 mm in 2013-2015 (Figure 2). The change was from median 9.6, 0.0, 4.5 mm in Centre 1, 2 and 3, respectively in 2010-2012, to median 4.5, 5.4, and 4.6 mm in 2013-2015. The median PTV1 increased from 108 cm 3 (IQR 73-164) in 2010-2012 to 130 cm 3 (IQR 84-199) in 2013-2015.

Conclusion DAHANCA radiotherapy guidelines, based on geometrically generated isotropic CTV1 margin and implemented in 2013, led to a decrease of variation in treatment volumes and reduce variance between centers compared to previous guidelines where more heterogeneous margins were used. There were no changes in GTV definition, however, PTVs increased following changes in CTV1.

OC-0028 Patient selection in the DAHANCA35 RCT of protons vs photons for H&N cancer

C.R. Hansen 1,2 , J. Friborg 2,3 , P. Skyt 2 , B. Smulders 2,4 , P. Sibolt 5 , M.S. Nielsen 6 , E. Samsøe 7 , A.I.S. Holm 8 , J. Johansen 1,2 , R. Zukauskaite 1 , E. Andersen 5 , M. Farhadi 7 , M. Andersen 6 , J.G. Eriksen 9 , J. Overgaard 10 , C. Grau 2,8 , K. Jensen 2 1 Odense University Hospital, Department of Oncology, Odense, Denmark; 2 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark; 3 Rigshospitalet, Department of Oncology, Copenhagen, Denmark; 4 Department of Oncology, Rigshospitalet, Copenhagen, Denmark; 5 Copenhagen University Hospital Herlev, Department of Oncology, Herlev, Denmark; 6 Aalborg University Hospital, Department of Oncology, Aalborg, Denmark; 7 Zealand University Hospital Næstved, Department of Oncology, Næstved, Denmark; 8 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 9 Department of Oncology, Department of Oncology, Aarhus, Denmark; 10 Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus, Denmark