Advanced nasopharyngeal carcinoma radiotherapy with volumetric modulated arcs and the potential role of flattening filter-free beams

Abstract

PurposeThe purpose of this study is to investigate the dosimetric characteristics of volumetric modulated arc therapy (VMAT) with flattening filter-free (FFF) beams and assess the role of VMAT in the treatment of advanced nasopharyngeal carcinoma (NPC).MethodsTen cases of CT data were randomly selected from advanced NPC patients. Three treatment plans were optimized for each patient, RapidArc with FFF beams (RA-FFF), conventional beams (RA) and static gantry intensity-modulated radiation therapy (IMRT). The doses to the planning target volumes (PTVs), organs at risk (OARs), skin and normal tissue were compared. All the plans were delivered on a Varian TrueBeam linear accelerator and verified using the Delta4 phantom. Technical delivery parameters including the mean gamma score, treatment delivery time and monitor units (MUs) were also analyzed.ResultsAll the techniques delivered adequate doses to the PTVs. RA-FFF gave the highest D1% (dose received by 1% of the volume), but the poorest conformity index (CI) and homogeneity index (HI) among the PTVs except for the planning target volume of involved regional lymph nodes (PTV66) CI, which showed no significant difference among three techniques. For the planning target volume of the primary nasopharyngeal tumor (PTV70), RA-FFF provided for higher mean dose than other techniques. For the planning target volume receiving 60 Gy (PTV60) and PTV66, RA delivered the lowest mean doses whereas IMRT delivered the highest mean doses. IMRT demonstrated the highest percentage of target coverage and D99% for PTV60. RA-FFF provided for the highest doses to the brain stem, skin and oral cavity. RA gave the highest D1% to the right optic nerve among three techniques while no significant differences were found between each other. IMRT delivered the highest mean doses to the parotid glands and larynx while RA delivered the lowest mean doses. Gamma analysis showed an excellent agreement for all the techniques at 3%/3mm. Significant differences in the MUs were observed among the three techniques (p < 0.001). Delivery times for RA-FFF and RA were 152 ± 7s and 153 ± 7s, respectively, nearly 70% lower than the 493 ± 24s mean time for IMRT.ConclusionsAll treatment plans met the planning objectives. The dose measurements also showed good agreement with computed doses. RapidArc technique can treat patients with advanced NPC effectively, with good target coverage and sparing of critical structures. RA has a greater dosimetric superiority than RA-FFF.

A dosimetric evaluation of flattening filter-free volumetric modulated arc therapy in nasopharyngeal carcinoma

“…[11121524] All the results reported could well meet the clinical criteria. From all these investigations, it could be extrapolated that dose calculation accuracy in state-of-the-art TPS will certainly not be impaired when removing the FF.…”

Dosimetric Comparison and Evaluation of Three Radiotherapy Techniques for Use after Modified Radical Mastectomy for Locally Advanced Left-sided Breast Cancer

“…Precise radiotherapy techniques, including IMRT and VMAT, have been clinically implemented in head and neck tumors, such as nasopharyngeal carcinoma 33 . However, the utilization of such precise technology in thoracic targets inevitably creates the problems of set up and respiration motion uncertainties.…”

Dosimetric comparison between jaw tracking and static jaw techniques in intensity-modulated radiotherapy

“…Thirdly, the performance of flattening filter-free (FFF) module combined with the jaw tracking technique of TrueBeam accelerator is still uncertain. There were several reports [ 14 - 19 ] about the clinical usage of FFF beams, indicating more potential of reducing the doses to OARs with comparable target dose coverage. The potential benefit of applying jaw tracking technique in FFF beams will be further studied in the future work.…”