Dosimetric influence of filtered and flattening filter free photon beam on rapid arc (RA) radiotherapy planning in case of cervix carcinoma

Abstract

Aim

To investigate the dosimetric influence of filtered and flattening filter free (FFF) photon beam of 6 and 10[[ce:hsp sp="0.25"/]]MV energies on cervix RA radiotherapy planning and to find possibilities to develop the clinically acceptable RA plans with FFFB photon beam and explore their potential benefits to cervix cancer patients.

Background

FFF photon beams enhances the treatment delivery by increased dose rate which results in shorter treatment time, this shorter treatment time reduces intrafraction motion and enhance comfort to the patients.

Materials and methods

RA plans were generated for filtered and flattening filter free photon beams of 6 and 10[[ce:hsp sp="0.25"/]]MV energies using same dose–volumes constraints. RA plans were generated to deliver a dose of 50.4[[ce:hsp sp="0.25"/]]Gy in 28 fractions, for a cohort of eleven patients reported with cervix carcinoma. RA plans were evaluated in terms of PTV coverage, dose to OAR's, CI, HI, total no. of monitor units (MUs) and NTID and low dose volume of normal tissues.

Results

Clinically acceptable and similar plans were generated for filtered and flattening filter free photon beams. FFFB delivered slightly higher mean target dose (52.28[[ce:hsp sp="0.25"/]]Gy vs. 52.0[[ce:hsp sp="0.25"/]]Gy, p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.000 for 6[[ce:hsp sp="0.25"/]]MV and 52.42[[ce:hsp sp="0.25"/]]Gy vs. 52.0[[ce:hsp sp="0.25"/]]Gy, p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.000 for 10[[ce:hsp sp="0.25"/]]MV) less homogeneous (1.062 vs. 1.052, p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.000 for 6[[ce:hsp sp="0.25"/]]MV and 1.066 vs. 1.051, p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.000 for 10[[ce:hsp sp="0.25"/]]MV) and less conformal (1.007 vs. 1.004, p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.104 for 6[[ce:hsp sp="0.25"/]]MV and 1.012 vs. 1.003, p[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.010 for 10[[ce:hsp sp="0.25"/]]MV) RA plans compared to FB. FFFB delivered more doses to the bladder and rectum, also required more numbers of MUs in comparison to FB.

Conclusions

This study concludes that FB is more beneficial for cervix RA planning in comparison to FFFB, as FB generates more conformal and homogenous rapid arc plans and offers better OAR's sparing.