Comparison of therapeutic dosimetric data from passively scattered proton and photon craniospinal irradiations for medulloblastoma.

Rebecca M Howell,Wendi Koontz-Raisig,Annelise Giebeler,Anthony M D’Amelio,Kenneth L Homann,Anita Mahajan,Carol J Etzel,Wayne D Newhauser

doi:10.1186/1748-717x-7-116

Abstract

BackgroundFor many decades, the standard of care radiotherapy regimen for medulloblastoma has been photon (megavoltage x-rays) craniospinal irradiation (CSI). The late effects associated with CSI are well-documented in the literature and are in-part attributed to unwanted dose to healthy tissue. Recently, there is growing interest in using proton therapy for CSI in pediatric and adolescent patients to reduce this undesirable dose. Previous comparisons of dose to target and non-target organs from conventional photon CSI and passively scattered proton CSI have been limited to small populations (n ≤ 3) and have not considered the use of age-dependent target volumes in proton CSI.MethodsStandard of care treatment plans were developed for both photon and proton CSI for 18 patients. This cohort included both male and female medulloblastoma patients whose ages, heights, and weights spanned a clinically relevant and representative spectrum (age 2–16, BMI 16.4–37.9 kg/m2). Differences in plans were evaluated using Wilcoxon signed rank tests for various dosimetric parameters for the target volumes and normal tissue.ResultsProton CSI improved normal tissue sparing while also providing more homogeneous target coverage than photon CSI for patients across a wide age and BMI spectrum. Of the 24 parameters (V5, V10, V15, and V20 in the esophagus, heart, liver, thyroid, kidneys, and lungs) Wilcoxon signed rank test results indicated 20 were significantly higher for photon CSI compared to proton CSI (p ≤ 0.05) . Specifically, V15 and V20 in all six organs and V5, V10 in the esophagus, heart, liver, and thyroid were significantly higher with photon CSI.ConclusionsOur patient cohort is the largest, to date, in which CSI with proton and photon therapies have been compared. This work adds to the body of literature that proton CSI reduces dose to normal tissue compared to photon CSI for pediatric patients who are at substantial risk for developing radiogenic late effects. Although the present study focused on medulloblastoma, our findings are generally applicable to other tumors that are treated with CSI.

Highlights

For many decades, the standard of care radiotherapy regimen for medulloblastoma has been photon craniospinal irradiation (CSI)
The qualitative observations for this older patient were similar to those for the younger patient, except that the normal tissue sparing in the proton plan was even greater for this patient because the sharp dose fall-off began at the anterior end of the spinal canal rather than at the anterior end of the vertebral bodies
The dose distributions and dose volume histogram (DVH) for these two representative patients highlight the differences in photon and proton dose distributions that result from age-specific treatment volumes

Summary

Introduction

The standard of care radiotherapy regimen for medulloblastoma has been photon (megavoltage x-rays) craniospinal irradiation (CSI). There is growing interest in using proton therapy for CSI in pediatric and adolescent patients to reduce this undesirable dose. Treatment for medulloblastoma often includes chemotherapy and craniospinal irradiation (CSI) [7,8,9], including a boost to the posterior fossa or the surgical bed with a margin. The standard of care radiotherapy regimen for CSI has been photon (megavoltave x-rays) therapy that included opposed lateral cranial fields and either single or multiple posterior spinal fields [29]. There is growing interest in using proton therapy for CSI in pediatric and adolescent patients

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Discussion

Conclusion