Dose Constraints for Remaining Volume at Risk and its Clinical Significance in IMRT Planning of Head and Neck Cancers

Abstract

Modulated Radiotherapy (IMRT) have led to the delivery of
precision radiotherapy where lower doses to normal tissues
can be achieved which may otherwise cause more acute and
chronic radiotherapy induced toxicities. Radiotherapy toxicity
acute oral mucositis presents with pain, and difficulty in
swallowing, leading to decreased nutrition intake, weight loss,
treatment breaks and ultimately poor outcomes. To reduce
acute oral mucositis, it should be considered as an organ at
risk and dose constraints to be prescribed. ICRU 83 refers to
these regions as remaining volume at risk (RVR). The present
study evaluates whether acute mucositis can be decreased
clinically by delineating RVR in such patients.
Material and Methods: Fifty patients of head and neck
cancers presented to the department who were to be treated
with definitive concurrent chemoradiotherapy by IMRT were
selected. Patients were randomly assigned in a 1:1 ratio into
two groups (twenty-five each)- group 1 (RVR dose constraints
not prescribed) and group 2 (RVR dose constraints of Dmean
30 Gy prescribed). Both groups evaluated and compared the
dosimetric parameters of planning target volumes, OARs, and
RVR. The radiation toxicities of skin, parotid and RVR were also
assessed. The statistical analysis was done using an unpaired
t-test and chi-square test.
Results: The median age in both groups was 55 years with
male to female ratio 24:1. Dosimetric parameters of PTV, OARs
and RVR did not show any statistical difference. No grade
IV skin reactions or xerostomia were seen in either group,
though the severity of reactions was higher in group 1. During
radiotherapy, no grade IV mucositis was seen in group 2,
whereas the group had in 12% of patients. After radiotherapy,
in a follow-up of one month, grade III mucositis was persistent
in all patients of group 1 (44%) in comparison to group 2 where
none had grade III mucositis.
Conclusion: The delineation of RVR and prescribing dose
constraint decreased the severity of oral mucositis clinically
but a significant difference could not be seen in the dosimetric
parameters of RVR.