ESTRO meets Asia 2024 - Abstract Book

S42

Invited Speaker

ESTRO meets Asia 2024

State of the art target volume delineation

ANUSHEEL MUNSHI

RADIATION ONCOLOGY, MANIPAL HOSPITAL, DELHI, India

Abstract

Contouring of any site remains an ever-evolving phenomenon. With increasing inputs and advancements from diagnostic radiology, nuclear imaging, pathology and molecular oncology, the target volumes for NSCLC have undergone continuous refinements.

The process for correct target delineation begins with correct patient positioning and use of appropriate patient immobilisation. Typically Spiral CT scans are preferable over single-slice axial CT scans for target volume definition

Target volumes in Lung Cancer

• Gross tumour volume (GTV): Primary and Nodal disease as per Clinico-radiological findings • Clinical target volume (CTV): GTV + margins for subclinical disease • Planning target volume (PTV): CTV + Margins for Set up error and Organ motion ( Internal + External)

Optimal window setting need to be used for target delineation for lung parenchyma/mediastinal area. It is now well accepted that there is a negligible role for elective nodal irradiation in NSCLC.

PET- CT is now being increasingly adopted for better delineation of GTV target volume. It is has approximately 80 TO 90 % accuracy in detecting nodal mets. It is also superior to CT to distinguish between tumour, atelectasis, collapse and consolidation.

CTV margin in NSCLC depends upon histological type and tumour volume. Range for CTV margin for primary and node can vary from 5 – 10 mm.

A challenging situation can be delineation of Post operative CTV in indicated cases. This can involve inclusion of resected involved anatomical mediastinal lymph node regions, bronchial stump and Ipsilateral hilum and nodal stations 4 and 7. Optionally, other structures may be contoured: e.g. brachial plexus if superior sulcus tumour and if the GTV is adjacent to or abuts the upper thoracic inlet. The trachea, proximal bronchial tree, great vessels and chest wall do not need to be defined for conventionally fractionated or moderately hypo-fractionated RT. PTV is defined by adding margin to CTV. This is typically based on institutional experience. In addition, the PTV margins would be governed by the use (or not) of 4 D simulation process

Adaptive RT/Replanning should be done on a case-to-case basis, especially in cases where CBCT/other imaging reveals shrinkage/shifts

Precision in contouring is crucial for effective treatment and minimizing side effects. Collaboration among radiation oncologists, radiologists, medical physicists, and dosimetrists ensures the highest level of accuracy and safety in lung cancer radiation therapy