Dados do Trabalho

Título

Whole Lung Irradiation in children - Volumetric Modulated Arc Therapy sparing heart and breasts

Introdução

The whole lung irradiation is frequently adopted as treatment of metastatic solid pediatric cancer, most international protocols concerning Wilms tumor, Rabdomyosarcoma and Ewing’s sarcoma include such technique. The concern of restricting radiation dosage to the heart is increasing as we see more survivors of cancer in the childhood. Cardiotoxic drugs (ex: Anthracicline) are included in chemotherapy of these patients, and the leading cause of death on those who survive the disease is cardiovascular events in younger ages than general population. In young women and girls there is another undesirable possible toxicity which is breast hypoplasia, that can contribute to detriment in quality of life. Futhermore, breast is a common site of radioinduced seccond malignancy. Newer technologies and techniques could aim to prevent, at least in part, those consequences.

Objetivo

Evaluate the use of VMAT (volumetric modulated arc therapy) to spare heart and breasts while maintaining PTV coverage.

Método

Female patient, 13 years old, in puberty, was diagnosed with metastatic Wilms tumor, whose treatment was planned using beam of photons with 6 MV, Wing Board and Vac-Lock accessories during a 2mm slices CT scan, conventionally(3D) and in 4D. ITV (internal target volume) was generated from the maximum and minimum pulmonary expansion CT. CTV (clinical target volume) was contoured on CT without breath control. PTV1 = CTV + 1cm and PTV2 = ITV + 0,5cm. Dose prescription was 12 Gy in 8 fractions. We used constraints for the heart D20%: 11,8 Gy; D40%: 11 Gy, D60%: 10Gy; D80%: 8 Gy e o D100%: 4,5Gy. Dmax on spinal cord, heart and liver were <107%, <110% e <110% respectively. Median dose to breast <10 Gy. The goal was that >95% of the PTV should receive >95% of the prescribed dose. Conformity and homogenity index were also evaluated.

Resultados

Histogram dose volume for 4D planning shows OAR: Heart D20%: 11,5 Gy; D40%: 8,5 Gy, D60%: 5,3 Gy; D80%: 3,4 Gy, D100%: 2,24 Gy and a median dose of 7,2 Gy. The maximum doses to the spinal cord, heart and liver were 102%, 106% e 110%, respectively. Breast received median dose 6,6 Gy, maximum dose 12,9 Gy and D5%: 11,1Gy. Conformity index = 0,77 and Homogenity index = 0,14
The PTV coverage was similar in both plans, 3D or 4D.

Conclusão

Although this case shows less than optimal gradient of dose in the PTV our treatment was capable of reducing the dose to the heart and breasts, thus contributing to lower rate of seccond malignancy and smaller rates of late toxicities on a pediatric population that, even when metastatic have a fair possibility of cure.