Palliative radiotherapy for thoracic spine metastases: Dosimetric advantage of three-dimensional conformal plans

Abstract

Abstract. The aim of the present study was to investigate the dosimetric advantages of three-dimensional conformal radiation therapy (3DCRT) for thoracic spine metastases and compare it with conventional two-dimensional (2D) plans. Radiation therapy (RT) planning data of 10 patients with mid-to-low thoracic spine metastases were analyzed. Computed tomography simulation was performed and the planning target volume (PTV), heart, esophagus, lung and spinal cord were contoured. The 3DCRT plan comprised one posteroanterior (PA) field and two posterior oblique fields. The 2D plans used a single PA field or opposed anteroposterior (AP)/PA fields. The prescription dose of radiation was 30 Gy in 10 fractions. All comparisons of the maximum or mean doses to the organs at risk or the PTV, between two of the three RT plans, demonstrated statistically significant differences (P<0.05), with the exception of the mean esophageal doses between the single PA vs. AP/PA (P=0.285) plans. The mean heart doses were 15.0±3.1 Gy in single PA, 17.3±4.3 Gy in AP/PA and 8.5±1.7 Gy using 3DCRT. The median reduction rates using 3DCRT were 38.9% compared with single PA (range, 29.4-58.5%) or 47.5% relative to AP/PA (range, 34.5-67.1%). The mean esophageal doses were 17.9±2.3 Gy in single PA, 18.2±2.2 Gy in AP/PA and 15.3±1.9 Gy in 3DCRT. The median reduction rate using 3DCRT was 12.8% compared with single PA or 15.6% relative to AP/PA. Compared with the single PA or AP/PA 2D plan, 3DCRT reduced the median dose by 13.7 or 1.9% of the maximum spinal cord dose, respectively, and 14.7 or 2.9% of the maximum PTV dose, respectively. The mean lung doses were 2.7±0.7 Gy in single PA, 2.6±0.7 Gy in AP/PA and 5.1±1.0 Gy in 3DCRT. In conclusion, 3DCRT for mid-to-low thoracic spine metastases demonstrated significant dosimetric advantages by reducing the unnecessary irradiation of critical organs, particularly the heart, and by achieving a homogeneous target dose.

The impact of radiation treatment planning technique on unplanned hospital admissions

“… 19 , 20 This dosimetric advantage of radiation delivery has been demonstrated in the 3-dimensional palliation of thoracic and lumbar metastases, where less dose is delivered to the heart and kidneys, respectively. 9 , 10 Nonconformal (2-dimensional) treatment planning may still be preferable in some circumstances given its availability, simplicity in planning, and lower cost. When utilized in anatomic areas where sensitive tissues are not nearby (eg, during palliation of metastases involving extremities), nonconformal treatment planning is particularly useful.…”

“… 8 The dose to surrounding normal structures is often higher with conventional nonconformal (2-dimensional) techniques compared with more conformal planning techniques. 9 , 10 , 11 Yet, given the scarcity of compelling data supporting the advantages of 3-dimensional or other highly conformal planning for limiting toxicity during treatment of bone metastases, 12 conformal planning is often not reimbursed by payers.…”

A method of respiratory phase optimization for better dose sparing of organs at risks: A validation study in patients with lung cancer

“…The contour of esophagus was performed on outer esophageal wall from its most cranial appearance to the esophageal hiatus [ 11 - 12 ]. The heart was defined with outer peri-cardial sac from the level of the inferior aspect of the pulmonary artery to the apex of the heart [ 22 ]. Spinal cord was contoured over the complete superior-inferior direction.…”

Treatment of spine metastases in cancer: a review

“…55,65 To improve radiation therapy, three-dimensional conformal radiation therapy was developed. 55 This technique is based on CT simulation, so there is a better dose-volume calculation that reduces unnecessary irradiation to adjacent organs and provides a more homogeneous irradiation of the target tumour, but the dosage can still not be high enough even with this technique. 55 With the advancement of radiation therapy technology, radiosurgery that can provide pain relief and improve neurological function has been developed.…”

“…55 This technique is based on CT simulation, so there is a better dose-volume calculation that reduces unnecessary irradiation to adjacent organs and provides a more homogeneous irradiation of the target tumour, but the dosage can still not be high enough even with this technique. 55 With the advancement of radiation therapy technology, radiosurgery that can provide pain relief and improve neurological function has been developed. For example, stereotactic radiosurgery with the help of an image-guidance system can provide a precise high dosage of radiation on the target vertebra while sparing the neighbouring vertebrae and normal tissue especially the spinal cord.…”