Localized paediatric orbital rhabdomyosarcoma: influence of imaging on treatment

Imaging and diagnostic strategy of soft tissue tumors in children

The diagnosis of a soft tissue mass in children is a common clinical situation. Most of the lesions are benign and can be treated conservatively or by non-mutilating surgery. Nevertheless, the possibility of a malignant soft tissue tumor must be systematically considered. The most frequent benign soft tissue lesions in children are vascular lesions, fibrous and fibrohistiocytic tumors and pseudotumors, whereas rhabdomyosarcomas account for 50% of all soft tissue sarcomas. A child presenting an atypical soft tissue mass should be managed by a multidisciplinary centre, and primary resection must be proscribed until a definite diagnosis has been established. The role of imaging is essential either to confirm the benign nature of the mass or to give arguments to perform a diagnostic biopsy. Clinical examination, conventional radiography and ultrasound with Doppler represent the first-line examinations and are sometimes sufficient to assess a diagnosis. In all other situations, MRI is mandatory to establish the probable nature of the lesion and to assess local extension.

Importance of protocol target definition on the ability to spare normal tissue: An IMRT and 3D-CRT planning comparison for intraorbital tumors

PURPOSE

We selected five intraorbital tumor sites that are frequently found in clinical practice in children diagnosed with orbital rhabdomyosarcoma and performed three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated photon radiotherapy (IMRT) planning. Results of target coverage and doses to critical structures were compared. The goal of this study was to evaluate and to document realistic expectations as to organ-sparing capabilities of modern radiation therapy planning technologies with a focus on lens-sparing irradiation. Furthermore, we investigated potential added benefits of IMRT compared with 3D-CRT and the influence of protocol volume criteria definitions on the ability to obtain normal tissue dose sparing using the orbit as an example of a complex anatomic site.

METHODS AND MATERIALS

The five intraorbital tumor sites were placed retrobulbar, temporal, nasal, in the upper inner and upper outer quadrant, the latter two more complex in shape. Gross tumor volume (GTV), clinical target volume (CTV), and planning target volume (PTV) were defined in image-fused computed tomography and magnetic resonance data sets. 3D-CRT and IMRT photon plans, using equal beam angles and collimation for direct comparison, were designed to 45 Gy prescription dose according to Intergroup Rhabdomyosarcoma Study Group-D9602 (IRSG-D9602) protocol (Intergroup Rhabdomyosarcoma Study V [IRS-V] protocol) for Stage I, Clinical Group 3 orbital rhabdomyosarcoma. To compare the impact of changed target definitions in IMRT planning, additional IMRT plans were generated using modified volume and dose coverage criteria. The minimum dose constraint (95%) of the PTV was substituted by a required minimum volume coverage (95%) with the prescribed dose. Dose-volume histograms (DVHs) were obtained, including target volumes, lens, optic nerves, optic chiasm, lacrimal gland, bony orbit, pituitary gland, frontal and temporal lobes.

RESULTS

Protocol target volume coverage criteria were fulfilled in all cases (5/5) with 3D-CRT and IMRT. Using the protocol criteria, lens sparing was achieved only for two tumor sites (retrobulbar and lateral position) with either planning technique. Mean lens doses were 8.5 and 10.4 Gy for 3D-CRT and 7.5 and 13.2 Gy for IMRT, respectively. The mean lens doses for the other three tumor locations averaged 26.8 Gy. IMRT plans reduced the lens dose in four of five cases by an average of 2.6 Gy compared with 3D-CRT. Modified target protocol prescription markedly reduced mean lens doses by 23-50% and by as much as 18 Gy. Recorded mean lens doses after protocol modification were 26% lower using IMRT plans compared with 3D-CRT. The cold spot as a result of the relaxed volume coverage requirements was within 2% of the original protocol criteria and located at the edge of the PTV, outside the CTV. Compared with 3D-CRT, IMRT resulted in an increase of brain volume receiving 10% (V10) and 20% (V20) of the prescribed dose.

CONCLUSION

Strict adherence to IRS-V protocol criteria prohibits at present lens sparing within compliance criteria for the majority of intraorbital tumor locations because of protocol-specific CTV and PTV target definitions. Changing protocol definitions by prescribing to the volume rather than to a dose constraint, IMRT planning significantly reduced lens doses. This was not accomplished to the same degree with 3D-CRT. Our study underlines the importance of appropriate selection of planning objectives to maximize the specific capabilities and advantages of IMRT in terms of sufficient target coverage and simultaneous sparing of critical structures. Our results can add to the ongoing discussion in the design of future 3D-CRT/IMRT protocols.

Les hémangiomes palpébraux du nourisson : apport de l’IRM

OBJECTIVES

To describe the MR imaging features and patterns of local extension of hemangiomas of the eyelid in correlation with the clinical presentation.

PATIENTS AND METHODS

Retrospective study including 21 MRI (GE, 1.5T, T1 +/- Gadolinium, T2 +/- fat saturation, 3 planes) examinations performed for eyelid hemangiomas with occlusion>50% and/or ocular deviation. All examinations were reviewed by two observers using a standardized list of criteria.

RESULTS

All hemangiomas had a heterogeneous signal described as "salt and pepper" on T2W sequences. The extension was extra-orbital in 8 cases, intra-orbital in 13 cases, extra-conal in 9 cases, intra-conal in 4 cases. The "fat sat T2" sequence provided the best anatomical details. There was a strong correlation between ocular deviation at clinical examination and intra-orbital extension, but no correlation between the extent of eyelid involvement and orbital location of the hemangioma. Dysplastic cerebellum anomalies related to the PHACES syndrome were present in 3 patients.

CONCLUSION

MRI of the brain and orbits provides information that appears essential for optimal management of infants with hemangioma of the eyelid.