A dosimetric analysis of 6MV versus 15MV photon energy plans for intensity modulated radiation therapy (IMRT) of carcinoma of cervix

Abstract

Background

Intensity modulated radiotherapy (IMRT) is being used to treat carcinoma of cervix (Ca Cx). Integral dose to normal tissue and increased leakage are the concern about IMRT. 6[[ce:hsp sp="0.25"/]]MV photon beam is a good choice of energy for Ca Cx IMRT treatment.

Aim

The objective of this study was to compare intensity modulated radiotherapy (IMRT) plans generated by 6[[ce:hsp sp="0.25"/]]MV and 15[[ce:hsp sp="0.25"/]]MV photon energies for carcinoma of cervix (Ca Cx) with regards to dosimetric parameters of planning target volume (PTV) and organs at risk (OAR), homogeneity index (HI), conformity index at 98% level (CI 98%), integral dose to normal tissue (NTID) and total number of monitor units (MUs).

Material and methods

A cohort of 16 patients was selected for this study. All patients were to receive a dose of 50[[ce:hsp sp="0.25"/]]Gy in 25 fractions. IMRT plans were generated for both energies using same dose–volume constraints.

Results

Our results show a comparable coverage of planning target volume (PTV) for both energies. Volume of PTV receiving a prescription dose is 97.8[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.5% and 98.8[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.4% for the 6[[ce:hsp sp="0.25"/]]MV and the 15[[ce:hsp sp="0.25"/]]MV plans. Volume of PTV receiving a dose of 107% is 4.4[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]7.8% and 16.1[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]22.2%. Bladder and rectum mean doses for the 6[[ce:hsp sp="0.25"/]]MV and the 15[[ce:hsp sp="0.25"/]]MV photon plans were 39.8[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]3.0[[ce:hsp sp="0.25"/]]Gy and 40.0[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]3.2[[ce:hsp sp="0.25"/]]Gy, and 35.8[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]3.1[[ce:hsp sp="0.25"/]]Gy and 36.0[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]3.1[[ce:hsp sp="0.25"/]]Gy, respectively. Homogeneity index (HI) for both energies was 1.04. The conformity indices at 98% isodose (CI 98%) were 1.3[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.1 and 1.4[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.1 for 6[[ce:hsp sp="0.25"/]]MV and 15[[ce:hsp sp="0.25"/]]MV photon plans, respectively.

Conclusions

We conclude that a 6[[ce:hsp sp="0.25"/]]MV photon is a good choice for Ca Cx IMRT as it produces a highly conformal, homogeneous plan with superior target coverage and better OAR sparing.