Intensity-modulated arc therapy with simultaneous integrated boost in the treatment of primary irresectable cervical cancer. Treatment planning, quality control, and clinical implementation.

PURPOSE

To report on the planning procedure, quality control, and clinical implementation of intensity-modulated arc therapy (IMAT) delivering a simultaneous integrated boost (SIB) in patients with primary irresectable cervix carcinoma.

PATIENTS AND METHODS

Six patients underwent PET-CT (positron emission tomography-computed tomography) and MRI (magnetic resonance imaging) before treatment planning. Prescription (25 fractions) was (1) a median dose (D(50)) of 62, 58 and 56 Gy to the primary tumor (GTV_cervix), primary clinical target volume (CTV_cervix) and its planning target volume (PTV_cervix), respectively; (2) a D(50) of 60 Gy to the PET-positive lymph nodes (GTV_nodes); (3) a minimal dose (D(98)) of 45 Gy to the planning target volume of the elective lymph nodes (PTV_nodes). IMAT plans were generated using an anatomy-based exclusion tool with the aid of weight and leaf position optimization. The dosimetric delivery of IMAT was validated preclinically using radiochromic film dosimetry.

RESULTS

Five to nine arcs were needed to create valid IMAT plans. Dose constraints on D(50) were not met in two patients (both GTV_cervix: 1 Gy and 3 Gy less). D(98) for PTV_nodes was not met in three patients (1 Gy each). Film dosimetry showed excellent gamma evaluation. There were no treatment interruptions.

CONCLUSION

IMAT allows delivering an SIB to the macroscopic tumor without compromising the dose to the elective lymph nodes or the organs at risk. The clinical implementation is feasible.