Clinical investigation: head and neck
Treatment planning comparison of conventional, 3D conformal, and intensity-modulated photon (IMRT) and proton therapy for paranasal sinus carcinoma☆

https://doi.org/10.1016/S0360-3016(03)01452-4Get rights and content

Abstract

Purpose

To determine the potential improvements in patients with paranasal sinus carcinoma by comparing proton and intensity-modulated radiotherapy (IMRT) with conventional and conformal photon treatment planning techniques.

Methods and materials

In 5 patients, comparative treatment planning was performed by comparing proton plans and related conventional, conformal, and IMRT photon plans. The evaluations analyzed dose–volume histogram findings of the target volumes and organs at risk (OARs, i.e., pituitary gland, optical pathway structures, brain, nontarget tissue).

Results

The mean and maximal doses, dose inhomogeneities, and conformity indexes for the planning target volumes were comparable for all techniques. Photon plans resulted in greater volumes of irradiated nontarget tissues at the 10–70% dose level compared with the corresponding proton plans. The volumes thereby increased by a factor of 1.3–3.1 for conventional, 1.1–3.8 for conformal, and 1.1–3.7 for IMRT. Compared with conventional techniques, conformal and IMRT photon treatment planning options similarly reduced the mean dose to the OARs. The use of protons further reduced the mean dose to the OARs by up to 65% and 62% compared with the conformal and IMRT technique, respectively.

Conclusion

Compared with conventional treatment techniques, conformal RT and IMRT similarly enabled dose reductions to the OARs. Additional improvements were obtained using proton-based treatment planning modalities.

Introduction

Malignant neoplasms of the nasal cavity and paranasal sinuses are a problematic entity for treatment and cure (1). They are often diagnosed at locally advanced stages, with extensions through the bony walls of the paranasal sinus, orbit, sphenoid, and anterior skull base. The cure rates are poor, and most patients die of direct tumor invasion of vital organs or rapidly recurrent local disease (2). In a significant number of patients, the tumor volume is close to optic pathway structures, such as the optic nerves or optic chiasm. There has been considerable controversy about the respective roles of surgery, radiotherapy (RT), and chemotherapy 3, 4, 5. Tumor invasion of adjacent structures often makes complete resection impossible. During surgical tumor resection, enucleation of the eye or removal of head facial bones cannot be avoided and the related morbidity is substantial (2).

Radical megavoltage RT combined with surgery may prolong the survival of patients with advanced tumors of the paranasal sinuses, with chemotherapy optional (5). Conventional RT is typically given by an anterior and a lateral or bilateral wedged beam arrangement 6, 7 to a tumor prescription dose of 60–66 Gy in 30–33 fractions. The total dose delivered to the tumor bed is frequently limited by the tolerance of the different organs at risk (OARs), and the RT prescription dose typically exceeds the tolerance of the optic pathways. Blindness (uni- or bilateral) is a known side effect of the high doses to the eyes and optic pathways. Thus, conventional RT often involves the decision of which eye to sacrifice.

Efforts to reduce treatment-related side effects have centered on the use of multiple-field techniques with shaped fields and patient positioning (8). In addition, research in planning technology mainly has had the aim of improving the delivery methods such that the high-dose volume approaches the volume of the clinical target, thus reducing unnecessary dosage to healthy tissue (1).

Protons have a finite penetration range and the end of range can be spread out to deliver a uniform dose to the target volume. Tissues lying distal to the target volume receive no dose and those in the entrance region receive less dose than the target. This allows dose distributions to be contoured to tumor volumes, resulting in reduced normal tissue radiation. In daily routine practice, protons have been successfully used in the treatment of different tumor entities (e.g. uveal melanomas, prostate carcinoma); however, the role of proton-based RT in several other tumor entities is still not clearly defined 9, 10.

In the present study, comparative planning was performed to evaluate the differences in dose distribution for proton- and photon-based irradiation techniques in patients with carcinoma of the paranasal sinuses.

Section snippets

Methods and materials

Comparative treatment planning was performed for 5 patients receiving external beam RT for carcinoma of the maxillary sinuses. Patients were immobilized in the supine position in a thermoplastic mask. CT scans were performed specifically for treatment planning from the top of the skull to the lower part of the neck, with a 5-mm slice thickness.

Anatomy-based definition of the target volumes was performed for all patients. A compartment-related definition of the clinical target volume (CTV) was

Results

Figure 1 illustrates the typical dose distributions in a transverse plane through the center of the paranasal sinuses obtained with conventional RT, three-dimensional conformal RT (3D-CRT), IMRT, and proton-based treatment planning. 1 compares the PTV dose statistics for the conventional three-field photon, 3D-CRT photon, IMRT, and proton-based treatment plans. The mean and maximal doses and inhomogeneities within the PTV are also given in Table 1.

The volume of the 95% isodose ranged from

Discussion

In the treatment of paranasal sinus cancer, the prognosis is strictly related to local control of the primary disease (5). Salvage treatment after local recurrence is rarely successful. Different modes of RT have been described in the literature. The application of conventional RT may either cause significant morbidity in the eye and optic nerve or may underdose a significant part of the posterior ethmoidal and maxillary sinus because of blocking in the lateral fields 4, 7. In this context,

Conclusion

All analyzed treatment modalities (i.e., conventional, conformal, and IMRT photons and proton-based planning techniques) achieved similar optimal dose homogeneity in the target volume. Compared with conventional treatment planning modalities, 3D-CRT and IMRT techniques enabled similar dose reductions to nontarget tissues. Dose conformity and normal tissue exposure to radiation were lowest when using proton-based RT. DVHs favored in every case the use of protons because of an inferior

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    ☆

    Supported by the Med AUSTRON project and the Government of Lower Austria, City Wiener Neustadt, and Federal Ministry for Education, Science and Culture.

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