Proton versus conventional radiotherapy for pediatric salivary gland tumors: Acute toxicity and dosimetric characteristics

PURPOSE

We evaluated acute toxicity profiles and dosimetric data for children with salivary gland tumors treated with adjuvant photon/electron-based radiation therapy (X/E RT) or proton therapy (PRT).

METHODS AND MATERIALS

We identified 24 patients who had received adjuvant radiotherapy for salivary gland tumors. Data were extracted from the medical records and the treatment planning systems. Toxicity was scored according to the Common Terminology Criteria for Adverse Effects 4.0.

RESULTS

Eleven patients received X/E RT and 13 PRT, with a median prescribed dose of 60 Gy in each group. In the X/E RT group, 54% of patients developed acute grade II/III dermatitis, 27% grade II/III dysphagia, and 91% grade II/III mucositis, and the median weight loss was 5.3% with one patient requiring feeding tube placement. In the PRT group, 53% had acute grade II/III dermatitis, 0% grade II/III dysphagia, and 46% grade II/III mucositis, with a median weight gain of 1.2%. Additionally, PRT was associated with lower mean doses to several normal surrounding midline and contralateral structures.

CONCLUSION

In this retrospective study of pediatric salivary tumors, PRT was associated with a favorable acute toxicity and dosimetric profile. Continued follow-up is needed to identify long-term toxicity and survival data.

Patterns of failure, toxicity, and survival after extrapleural pneumonectomy and hemithoracic intensity-modulated radiation therapy for malignant pleural mesothelioma

INTRODUCTION

We investigated safety, efficacy, and recurrence after postoperative hemithoracic intensity-modulated radiation therapy (IMRT) in patients with malignant pleural mesothelioma treated with extrapleural pneumonectomy (EPP), during the past decade at a single institution.

METHODS

In 2001-2011, 136 consecutive patients with malignant pleural mesothelioma underwent EPP with planned adjuvant IMRT. Eighty-six patients (64%) underwent hemithoracic IMRT; the rest were not eligible because of postoperative complications, disease progression, or poor performance status. We assessed toxicity, survival, and patterns of failure in these 86 patients. Toxicity was scored with the Common Terminology Criteria for Adverse Events version 4.0; survival outcomes were estimated with the Kaplan-Meier method; and locoregional patterns of failure were classified as in-field, marginal, or out-of-field. Risk factors related to survival were identified by univariate and multivariate Cox regression analysis.

RESULTS

Median overall survival time for all 86 patients receiving IMRT was 14.7 months. Toxicity rates of grade of 3 or more were: skin 17%, lung 12%, heart 2.3%, and gastrointestinal toxicity 16%. Five patients experienced grade 5 pulmonary toxicity. Rates of locoregional recurrence-free survival, distant metastasis-free survival, and overall survival (OS) were 88%, 55%, and 55% at 1 year and 71%, 40%, and 32% at 2 years. On multivariate analysis, pretreatment forced expiratory volume in 1 second, nonepithelioid histology, and nodal status were associated with distant metastasis-free survival and OS.

CONCLUSION

IMRT after EPP is associated with low rates of locoregional recurrence, though some patients experience life-threatening lung toxicity. Tumor histology and nodal status can be helpful in identifying patients for this aggressive treatment.

Use of a deformable atlas to identify cryptic critical structures in the treatment of glioblastoma multiforme

Dose constraints for traditional neural critical structures (e.g. optic chiasm, brain stem) are a standard component of planning radiation therapy to the central nervous system. Increasingly, investigators are becoming interested in accounting for the dose delivered to other non-target neural structures (e.g. hippocampi), which are not easily identified on axial imaging. In this pilot study, a commercially available digital atlas was used to identify cryptic neural structures (hippocampus, optic radiations, and visual cortices) in 6 patients who received intensity modulated radiation therapy (IMRT) as part of multimodal management of glioblastoma multiforme (GBM). The patient's original IMRT plans were re-optimized, with avoidance parameters for the newly identified critical structures. Re-optimization was able to reduce both mean and maximum dose to the volumes of interest, with a more pronounced effect for contralateral structures. Mean dose was reduced by 11% and 3% to contralateral and ipsilateral structures, respectively, with comparable reduction in maximum dose of 10% and 2%, respectively. Importantly, target coverage was not compromised, with an average change in coverage of 0.2%. Overall, our results demonstrate the feasibility of incorporating tools for cryptic critical structure identification into the treatment planning process for GBM.

Treatment planning with protons for pediatric retinoblastoma, medulloblastoma, and pelvic sarcoma: How do protons compare with other conformal techniques?

PURPOSE

To calculate treatment plans and compare the dose distributions and dose-volume histograms (DVHs) for photon three-dimensional conformal radiation therapy (3D-CRT), electron therapy, intensity-modulated radiation therapy (IMRT), and standard (nonintensity modulated) proton therapy in three pediatric disease sites.

METHODS AND MATERIALS

The tumor volumes from 8 patients (3 retinoblastomas, 2 medulloblastomas, and 3 pelvic sarcomas) were studied retrospectively to compare DVHs from proton therapy with 3D-CRT, electron therapy, and IMRT. In retinoblastoma, several planning techniques were analyzed: A single electron appositional beam was compared with a single 3D-CRT lateral beam, a 3D-CRT anterior beam paired with a lateral beam, IMRT, and protons. In medulloblastoma, three posterior fossa irradiation techniques were analyzed: 3D-CRT, IMRT, and protons. Craniospinal irradiation (which consisted of composite plans of both the posterior fossa and craniospinal components) was also evaluated, primarily comparing spinal irradiation using 3D-CRT electrons, 3D-CRT photons, and protons. Lastly, in pelvic sarcoma, 3D-CRT, IMRT, and proton plans were assessed.

RESULTS

In retinoblastoma, protons resulted in the best target coverage combined with the most orbital bone sparing (10% was the mean orbital bone volume irradiated at > or =5 Gy for protons vs. 25% for 3D-CRT electrons, 69% for IMRT, 41% for a single 3D lateral beam, 51% for a 3D anterolateral beam with a lens block, and 65% for a 3D anterolateral beam without a lens block). A single appositional electron field was the next best technique followed by other planning approaches. In medulloblastoma, for posterior fossa and craniospinal irradiation, protons resulted in the least dose to the cochlea (for only posterior fossa irradiation at > or =20 Gy, 34% was the mean cochlear volume irradiated for protons, 87% for IMRT, 89% for 3D-CRT) and hypothalamus-pituitary axis (for only posterior fossa irradiation at > or =10 Gy, 21% was the mean hypothalamus-pituitary volume irradiated for protons, 81% for IMRT, 91% for 3D-CRT); additional dose reductions to the optic chiasm, eyes, vertebrae, mandible, thyroid, lung, kidneys, heart, and liver were seen. Intensity-modulated radiotherapy appeared to be the second best technique for posterior fossa irradiation. For spinal irradiation 3D-CRT electrons were better than 3D-CRT photons in sparing dose to the thyroid, heart, lung, kidney, and liver. With pelvic sarcoma, protons were superior in eliminating any dose to the ovaries (0% of mean ovarian volume was irradiated at > or =2 Gy with protons) and to some extent, the pelvic bones and vertebrae. Intensity-modulated radiotherapy did show more bladder dose reduction than the other techniques in pelvic sarcoma irradiation.

CONCLUSIONS

In the diseases studied, using various techniques of 3D-CRT, electrons, IMRT, and protons, protons are most optimal in treating retinoblastomas, medulloblastomas (posterior fossa and craniospinal), and pelvic sarcomas. Protons delivered superior target dose coverage and sparing of normal structures. As dose-volume parameters are expected to correlate with acute and late toxicity, proton therapy should receive serious consideration as the preferred technique for the treatment of pediatric tumors.