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Conformal orbit sparing radiation therapy: a treatment option for advanced skin cancer of the parotid and ear region

View Article: PubMed Central - PubMed

ABSTRACT

Introduction: New surgical methods have enabled resection of previously in‐operable tumours in the region of the parotid gland and ear. This has translated to deeper target volumes being treated with adjuvant radiotherapy. Due to the limitations of existing conformal techniques, alternative planning approaches are required to cover the target volume with appropriate sparing of adjacent critical structures. Although intensity modulated radiation therapy (IMRT) may be able to achieve these goals compared with the existing conformal method, a new orbital sparing radiation therapy (OSRaT) technique was evaluated as an alternative conformal planning process. The study objective was to evaluate the dosimetry of three planning methods: pre‐existing conformal, IMRT and OSRaT techniques.

Methods: Ten patients were planned retrospectively using the existing three‐dimensional conformal radiotherapy (3DCRT), IMRT and OSRaT techniques. Dosimetry was analysed using the homogeneity index (HI), conformity index (CI), the volume of planning target volumes (PTV) under and over treated by the 95% isodose and dose to critical structures.

Results: OSRaT achieved superior 95% coverage of the high‐dose PTV while delivering HI similar to IMRT for intermediate and high‐dose PTVs. The CI for the high‐dose PTV was comparable between the three techniques, however IMRT was statistically better for the low‐ and intermediate dose PTVs. All three techniques showed adequate orbital sparing, however OSRaT and IMRT achieved this with less under dosing of the PTVs.

Conclusion: For the treatment of patients with advanced skin cancer of the parotid and ear, both IMRT and the OSRaT techniques are viable options.

No MeSH data available.


Transverse slice through skull base illustrating target volumes and their proximity to critical structures. Blue, clinical target volume; red, high target volume; purple, intermediate target volume; brown, brainstem; orange, ipsilateral orbit; yellow, brain structures.
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jmrs161-fig-0001: Transverse slice through skull base illustrating target volumes and their proximity to critical structures. Blue, clinical target volume; red, high target volume; purple, intermediate target volume; brown, brainstem; orange, ipsilateral orbit; yellow, brain structures.

Mentions: This increase in target volume depth inherently presented challenges for the existing radiation therapy techniques commonly used. Deeper planning target volume (PTV) coverage was required within close proximity to adjacent organs at risk (OAR) as depicted in Figure 1. The previous treatment method included three‚Äźdimensional conformal radiotherapy (3DCRT) with an electron junction to limit dose to the optic structures. The issue with this technique was its inability to provide adequate dose coverage to the increased depth of the PTV in the temporal region. The electron field could not simply be replaced by extending the photon fields in this area due to the proximity to the surrounding optic structures, temporal lobe and cerebellum. As a result, PTV coverage was compromised or OAR dose was increased at the discretion of the consulting radiation oncologist. Intensity modulated radiation therapy (IMRT) may be able to achieve PTV coverage and organ sparing, however its use may be restricted to departmental resources. Hence, a new radiotherapy treatment technique needed to be developed to achieve adequate PTV coverage while minimising dose to surrounding OAR.


Conformal orbit sparing radiation therapy: a treatment option for advanced skin cancer of the parotid and ear region
Transverse slice through skull base illustrating target volumes and their proximity to critical structures. Blue, clinical target volume; red, high target volume; purple, intermediate target volume; brown, brainstem; orange, ipsilateral orbit; yellow, brain structures.
© Copyright Policy - creativeCommonsBy-nc-nd
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5016620&req=5

jmrs161-fig-0001: Transverse slice through skull base illustrating target volumes and their proximity to critical structures. Blue, clinical target volume; red, high target volume; purple, intermediate target volume; brown, brainstem; orange, ipsilateral orbit; yellow, brain structures.
Mentions: This increase in target volume depth inherently presented challenges for the existing radiation therapy techniques commonly used. Deeper planning target volume (PTV) coverage was required within close proximity to adjacent organs at risk (OAR) as depicted in Figure 1. The previous treatment method included three‚Äźdimensional conformal radiotherapy (3DCRT) with an electron junction to limit dose to the optic structures. The issue with this technique was its inability to provide adequate dose coverage to the increased depth of the PTV in the temporal region. The electron field could not simply be replaced by extending the photon fields in this area due to the proximity to the surrounding optic structures, temporal lobe and cerebellum. As a result, PTV coverage was compromised or OAR dose was increased at the discretion of the consulting radiation oncologist. Intensity modulated radiation therapy (IMRT) may be able to achieve PTV coverage and organ sparing, however its use may be restricted to departmental resources. Hence, a new radiotherapy treatment technique needed to be developed to achieve adequate PTV coverage while minimising dose to surrounding OAR.

View Article: PubMed Central - PubMed

ABSTRACT

Introduction: New surgical methods have enabled resection of previously in‐operable tumours in the region of the parotid gland and ear. This has translated to deeper target volumes being treated with adjuvant radiotherapy. Due to the limitations of existing conformal techniques, alternative planning approaches are required to cover the target volume with appropriate sparing of adjacent critical structures. Although intensity modulated radiation therapy (IMRT) may be able to achieve these goals compared with the existing conformal method, a new orbital sparing radiation therapy (OSRaT) technique was evaluated as an alternative conformal planning process. The study objective was to evaluate the dosimetry of three planning methods: pre‐existing conformal, IMRT and OSRaT techniques.

Methods: Ten patients were planned retrospectively using the existing three‐dimensional conformal radiotherapy (3DCRT), IMRT and OSRaT techniques. Dosimetry was analysed using the homogeneity index (HI), conformity index (CI), the volume of planning target volumes (PTV) under and over treated by the 95% isodose and dose to critical structures.

Results: OSRaT achieved superior 95% coverage of the high‐dose PTV while delivering HI similar to IMRT for intermediate and high‐dose PTVs. The CI for the high‐dose PTV was comparable between the three techniques, however IMRT was statistically better for the low‐ and intermediate dose PTVs. All three techniques showed adequate orbital sparing, however OSRaT and IMRT achieved this with less under dosing of the PTVs.

Conclusion: For the treatment of patients with advanced skin cancer of the parotid and ear, both IMRT and the OSRaT techniques are viable options.

No MeSH data available.