Dosimetric influence of photon beam energy and number of arcs on volumetric modulated arc therapy in carcinoma cervix: A planning study

Abstract

Aim

Aim of the present study was to compare the dosimetric impact of different photon beam energies and number of arcs in the treatment of carcinoma cervix.

Background

Carcinoma cervix is a common cancer in women worldwide with a high morbidity rate. Radiotherapy is used to treat such tumours. Volumetric Modulated Arc Therapy (VMAT) is considered superior to other techniques with multiple arcs and energies.

Materials and methods

Twenty patients with carcinoma cervix underwent radiotherapy in a prospective observation study conducted at our institute. Volumetric modulated arc plans with 6[[ce:hsp sp="0.25"/]]MV, 10[[ce:hsp sp="0.25"/]]MV and 15[[ce:hsp sp="0.25"/]]MV photon energies using single arc (SA) and dual arc (DA) were generated. Several physical indices for planning target volume (PTV) like V_95%, V_100%, V_110%, D_98%, D_50%, D_2% and total number of MUs were compared. Normal Tissue Integral Dose (NTID) and dose to a shell structure PHY_2.5 and PHY_5.0 were analyzed.

Results

Comparable dose coverage to PTV was observed for all the energies and arcs. CI for DA_6MV (1.095) was better than SA_6MV (1.127), SA_10MV (1.116) and SA_15MV (1.116). Evaluated parameters showed significant reduction in OAR doses. Mean bladder dose for DA_6MV (41.90[[ce:hsp sp="0.25"/]]Gy) was better than SA_6MV (42.48[[ce:hsp sp="0.25"/]]Gy), SA_10MV (42.08[[ce:hsp sp="0.25"/]]Gy) and SA_15MV (41.93[[ce:hsp sp="0.25"/]]Gy). Similarly, p-value for the mean rectal dose calculated was 0.001 (SA_{6 vs 15}), 0.013 (DA_{6 vs 10}) and 0.003 (DA_{6 vs 15}) and subsequently favoured DA_6MV. Difference in NTID was very small.

Conclusions

The study showed no greater advantage of higher energy, and DA VMAT plan with 6[[ce:hsp sp="0.25"/]]MV photon energy was a good choice of treatment for carcinoma cervix as it delivered a highly homogeneous and conformal plan with superior target coverage and better OAR sparing.