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 ofprecision radiotherapy where lower doses to normal tissuescan be achieved which may otherwise cause more acute andchronic radiotherapy induced toxicities. Radiotherapy toxicityacute oral mucositis presents with pain, and difficulty inswallowing, leading to decreased nutrition intake, weight loss,treatment breaks and ultimately poor outcomes. To reduceacute oral mucositis, it should be considered as an organ atrisk and dose constraints to be prescribed. ICRU 83 refers tothese regions as remaining volume at risk (RVR). The presentstudy evaluates whether acute mucositis can be decreasedclinically by delineating RVR in such patients.Material and Methods: Fifty patients of head and neckcancers presented to the department who were to be treatedwith definitive concurrent chemoradiotherapy by IMRT wereselected. Patients were randomly assigned in a 1:1 ratio intotwo groups (twenty-five each)- group 1 (RVR dose constraintsnot prescribed) and group 2 (RVR dose constraints of Dmean30 Gy prescribed). Both groups evaluated and compared thedosimetric parameters of planning target volumes, OARs, andRVR. The radiation toxicities of skin, parotid and RVR were alsoassessed. The statistical analysis was done using an unpairedt-test and chi-square test.Results: The median age in both groups was 55 years withmale to female ratio 24:1. Dosimetric parameters of PTV, OARsand RVR did not show any statistical difference. No gradeIV skin reactions or xerostomia were seen in either group,though the severity of reactions was higher in group 1. Duringradiotherapy, 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 persistentin all patients of group 1 (44%) in comparison to group 2 wherenone had grade III mucositis.Conclusion: The delineation of RVR and prescribing doseconstraint decreased the severity of oral mucositis clinicallybut a significant difference could not be seen in the dosimetricparameters of RVR.