Akkineni Naga Prasanthi1
BACKGROUND
Intensity modulated radiation therapy (IMRT) has become the standard treatment
in head & neck cancer (HNC). Anatomic changes during IMRT can have impact on
dose coverage and organs at risk (OAR) doses. These changes can be
compensated by modifying the plan during treatment. The purpose of this study
is to evaluate the impact of anatomical variations during IMRT on target volumes,
OAR and dose volume histogram (DVH) in locally advanced HNC patients.
METHODS
Twenty-four HNC patients undergoing definitive chemoradiotherapy were planned
with initial plan. Repeated computerised tomography (CT) scans were performed
at 2nd week (repeat CT1) and 4th week (repeat CT2). Previous plan was transferred
to new CT for dosimetric analysis. Patient received remaining fractions with
adaptive plan if needed based on triggers (1. more than 5 % deviation in OAR
doses 2. If PTV dose did not conform to ICRU83). Plan 1 was generated by replanning
on repeat CT and plan 2 was by superimposition of previous plan. DVH
of both plans were compared for volumetric and dosimetric parameters in patients
who required re-planning.
RESULTS
Fifty-eight percent of patients required adaptive plan. Seventy-one percent
required re-plan at the end of 4th week and 28.5 % at 2nd week. Parotid glands
and gross tumour volume (GTV) node reduction were significant in patients who
required re-plan compared to patients who did not require re-plan. Patients with
significant GTV node reduction experienced grade III/IV mucositis. Patients with
significant GTV node and parotid glands reduction experienced grade III/IV
dermatitis.
CONCLUSIONS
More than half of HNC patients required re-planning. Most of them required replanning
at 4th week. GTV node and parotid glands reduction can predict the
requirement of re-plan, risk of grade III/IV dermatitis. GTV node reduction can
predict the risk of grade III/IV mucositis.
