Comparison of the Dosimetry of Spinal Fields in Craniospinal Irradiation using Two Dimensional, Three Dimensional and Intensity Modulated Radiation Therapy Planning Techniques

Abstract

Purpose/Objective(s)Craniospinal irradiation (CSI) is a technically difficult and time consuming radiation therapy technique. Dose inhomogeneity and long-term sequelae, especially in the pediatric population, from CSI is of concern. There has been an evolution from two dimensional (2D) to three dimensional (3D) and now Intensity Modulated Radiation Therapy (IMRT) planning for the spinal fields. Our goal was to investigate the dosimetric outcomes for target coverage and organs at risk (OAR) using these 3 different techniques for treatment planning as well as to look at the total time spent planning.Materials/MethodsThe CT-based treatment planning was performed for the CSI volume using lateral cranial fields with a matched posterior single spine field. The prescription dose was 36 Gy to the CS axis delivered with 4 junction shifts. Target delineations were as follows: 2D plan field edge was placed 1 cm lateral to vertebral bodies; 3D plan had 1 cm expansion from the spinal canal for clinical target volume (CTV) for adults (0.5 cm for children) and an additional 0.7 cm to field edge for planning target volume (PTV). For IMRT plan, CTV was equal to PTV without additional expansion. To improve target coverage, a field in field technique was used for both 2D and 3D plans to act as compensators. The OAR evaluated included heart, thyroid, liver, lung, kidney, and small bowel. Dose volume histograms were used to assess the plans and time spent per plan was recorded.ResultsThe CT scans of 10 consecutive patients (4 pediatric and 6 adult) treated at our institution with CSI from 2004-2007 were selected. There was no statistical difference in PTV coverage when looking at the mean, minimum, maximum, and median doses and the percent volume covered by 95% and 107% of the dose. Mean dose to OAR were all decreased when comparing IMRT to 3D as follows: heart 11.3%, liver 12%, thyroid 2%, kidneys 22%, bowel 8% (p < 0.05). Mean dose to OAR were all decreased when comparing 3D to 2D as follows: heart 5%, liver 13.5%, kidneys 31%, lungs 16.3% , bowel 28% (p < 0.05). Total time spent planning (not including contouring) for each plan was approximately 4 hours per IMRT plan and 6-7 hours per 3D and 2D plans.ConclusionsOptimal treatment planning using either 2D or 3D plans with field in field technique results in similar PTV coverage when compared to IMRT plans. However, IMRT plans were superior to either 2D or 3D when looking at mean dose to most OAR. The IMRT planning took significantly less amount of time for treatment planning. These results make IMRT treatment planning more desirable in clinical practice. Purpose/Objective(s)Craniospinal irradiation (CSI) is a technically difficult and time consuming radiation therapy technique. Dose inhomogeneity and long-term sequelae, especially in the pediatric population, from CSI is of concern. There has been an evolution from two dimensional (2D) to three dimensional (3D) and now Intensity Modulated Radiation Therapy (IMRT) planning for the spinal fields. Our goal was to investigate the dosimetric outcomes for target coverage and organs at risk (OAR) using these 3 different techniques for treatment planning as well as to look at the total time spent planning. Craniospinal irradiation (CSI) is a technically difficult and time consuming radiation therapy technique. Dose inhomogeneity and long-term sequelae, especially in the pediatric population, from CSI is of concern. There has been an evolution from two dimensional (2D) to three dimensional (3D) and now Intensity Modulated Radiation Therapy (IMRT) planning for the spinal fields. Our goal was to investigate the dosimetric outcomes for target coverage and organs at risk (OAR) using these 3 different techniques for treatment planning as well as to look at the total time spent planning. Materials/MethodsThe CT-based treatment planning was performed for the CSI volume using lateral cranial fields with a matched posterior single spine field. The prescription dose was 36 Gy to the CS axis delivered with 4 junction shifts. Target delineations were as follows: 2D plan field edge was placed 1 cm lateral to vertebral bodies; 3D plan had 1 cm expansion from the spinal canal for clinical target volume (CTV) for adults (0.5 cm for children) and an additional 0.7 cm to field edge for planning target volume (PTV). For IMRT plan, CTV was equal to PTV without additional expansion. To improve target coverage, a field in field technique was used for both 2D and 3D plans to act as compensators. The OAR evaluated included heart, thyroid, liver, lung, kidney, and small bowel. Dose volume histograms were used to assess the plans and time spent per plan was recorded. The CT-based treatment planning was performed for the CSI volume using lateral cranial fields with a matched posterior single spine field. The prescription dose was 36 Gy to the CS axis delivered with 4 junction shifts. Target delineations were as follows: 2D plan field edge was placed 1 cm lateral to vertebral bodies; 3D plan had 1 cm expansion from the spinal canal for clinical target volume (CTV) for adults (0.5 cm for children) and an additional 0.7 cm to field edge for planning target volume (PTV). For IMRT plan, CTV was equal to PTV without additional expansion. To improve target coverage, a field in field technique was used for both 2D and 3D plans to act as compensators. The OAR evaluated included heart, thyroid, liver, lung, kidney, and small bowel. Dose volume histograms were used to assess the plans and time spent per plan was recorded. ResultsThe CT scans of 10 consecutive patients (4 pediatric and 6 adult) treated at our institution with CSI from 2004-2007 were selected. There was no statistical difference in PTV coverage when looking at the mean, minimum, maximum, and median doses and the percent volume covered by 95% and 107% of the dose. Mean dose to OAR were all decreased when comparing IMRT to 3D as follows: heart 11.3%, liver 12%, thyroid 2%, kidneys 22%, bowel 8% (p < 0.05). Mean dose to OAR were all decreased when comparing 3D to 2D as follows: heart 5%, liver 13.5%, kidneys 31%, lungs 16.3% , bowel 28% (p < 0.05). Total time spent planning (not including contouring) for each plan was approximately 4 hours per IMRT plan and 6-7 hours per 3D and 2D plans. The CT scans of 10 consecutive patients (4 pediatric and 6 adult) treated at our institution with CSI from 2004-2007 were selected. There was no statistical difference in PTV coverage when looking at the mean, minimum, maximum, and median doses and the percent volume covered by 95% and 107% of the dose. Mean dose to OAR were all decreased when comparing IMRT to 3D as follows: heart 11.3%, liver 12%, thyroid 2%, kidneys 22%, bowel 8% (p < 0.05). Mean dose to OAR were all decreased when comparing 3D to 2D as follows: heart 5%, liver 13.5%, kidneys 31%, lungs 16.3% , bowel 28% (p < 0.05). Total time spent planning (not including contouring) for each plan was approximately 4 hours per IMRT plan and 6-7 hours per 3D and 2D plans. ConclusionsOptimal treatment planning using either 2D or 3D plans with field in field technique results in similar PTV coverage when compared to IMRT plans. However, IMRT plans were superior to either 2D or 3D when looking at mean dose to most OAR. The IMRT planning took significantly less amount of time for treatment planning. These results make IMRT treatment planning more desirable in clinical practice. Optimal treatment planning using either 2D or 3D plans with field in field technique results in similar PTV coverage when compared to IMRT plans. However, IMRT plans were superior to either 2D or 3D when looking at mean dose to most OAR. The IMRT planning took significantly less amount of time for treatment planning. These results make IMRT treatment planning more desirable in clinical practice.