[en] Treatment delivery verification has always been a topic of interest in radiation therapy resulting in some commercial products which can be externally fitted to the conventional C-arm therapy machine and monitor the planned and exit fluence through gantry. Since Halcyon has ring gantry it demands a different approach. Halcyon is equipped with an in-built EPID system which is in line with the beam and continuously acquires exit fluence with full field coverage during patient treatment without user interaction. These images can be retrieved and analyzed to monitor the delivery of planned treatment throughout and can be used as a decision making criteria for adaptive planning or rescan and replan as per the department protocol for the changed anatomy

[en] The aim of the study is to assess CTV to PTV margin for Head and Neck Cancer cases based on daily KVCBCT imaging over the course of treatment in Halcyon machine and compare this with PTV margins obtained by MVCBCT of Oncor impression Plus machine. Radiotherapy for Head and Neck Cancer has been evolving greatly especially in terms of imaging while treatment. Hence, we have to ensure that the errors while patient positioning remains as low as possible. This can be achieved by having good imaging modality and calculating the systematic and random errors effectively. Forty Head and Neck Cancer were taken who were treated by Rapid Arc method between the periods of February 2021 to June 2021 in Halcyon machine. All the patients had CTV to PTV margin of 5 mm while treatment planning. Daily KVCBCT based matching was chosen as the reference method. Based on the shifts obtained, the systematic and random errors were calculated in the three directions X, Y and Z respectively using the Van Herk formula. These margins were then compared with the margins that were previously obtained with MVCBCT imaging. The study included forty patients with Head and Neck Cancer treated by Rapid Arc method. 400 CBCT images were obtained and taken for the study. The margins obtained were as given in the tabular column below. It is seen that as the image quality has improved from MVCBCT to KVCBCT, the PTV margins that has to be added has come down by a millimeter. This study is an on-going project in which more population and samples can be added so that the PTV margins can be calculated and taken as a standard margin value for Head and Neck Cancer cases which would be treated in Halcyon Machine

[en] The purpose of the study is to find the relation between the composite and individual beam fluence gamma passing rate in a patient specific IMRT QA. IMRT has been implemented in most of the centers across the country. The proximity of the critical structure to the tumor leads to a very complex dose distribution with steep dose gradient justifying IMRT QA. The 3% dose and 3 mm distance to agreement is the most widely used criteria for accepting the IMRT QA. But not always this passing criteria is full filled and some plans fail with a very bad %gamma and it usually leads to repeating the QA. In this study gamma analysis for each beam is done separately and we tried to find whether or not the gamma passing of individual beam plays some role in composite gamma passing rate

[en] Stereotactic treatments has been in vogue for more than 3 decades and efforts were always made to reduce the errors in delivery by introducing a good number of quality assurance methods. The introduction of volumetric imaging before treatment delivery facilitated frameless stereotactic treatments. But, correcting for rotational errors required 6D couch. However, there are publications which show that 6D couch is an expensive technology and it is one among the many factors that contribute to the accuracy and its absence is not a major factor. In our setup, we have been performing stereotactic treatments with couches which has only translational movements. After introducing volumetric imaging and performing frameless stereotactic treatments, we found that rotational errors also need to be addressed. Out of the three rotational errors such as pitch, yaw and roll, we found that pitch is a rotational correction which is a dominant systemic error, has a significant role and it is addressed in our work