Radiotherapy For Inoperable Tumors

Over the past decade, there has been substantial evidence that fast-neutron radiation therapy provides higher rates of locoregional control of unresectable salivary gland cancer compared to photon or electron radiation therapy27-31 and perhaps should be considered the initial treatment of choice in such cases.32 Buchholz et al.33 reported the outcome of 53 patients with locally advanced salivary gland malignant neoplasms treated with fast neutron radiation therapy. All patients received treatment for gross inoperable, residual unresectable, or recurrent disease. With a median follow-up of 42 months and a minimum follow-up of 1 year, the overall locoregional tumor control rate was 77%. The 5-year actuarial overall locoregional control rate was 65%. Grouping patients according to prior treatment status, actuarial 5-year locoregional control rates were 92% for patients treated definitively (without a prior surgical procedure), 63% for those treated postoperatively for gross residual disease, and 51% for those treated for recurrent disease after a surgical procedure. This study suggested that neutron irradiation alone may be the therapy of choice in the treatment of advanced-stage unresectable salivary gland tumors, and that surgery should be limited to those patients in whom disease-free margins can be obtained. The potential morbidity of a debulking surgical procedure before neutron irradiation is not accompanied by an improvement in locoregional control over that achievable with neutron therapy alone.33 These impressive results are encouraging; however, the use of fastneutron radiotherapy is hampered by its lack of widespread availability. Currently, only few facilities are equipped with the technology and expertise of delivering fast-neutron radiotherapy.

Other investigators described their experience with photon-beam radiotherapy for the treatment of unresectable salivary gland cancer, and reported comparable results to those obtained by fast-neutron therapy. Wang and Goodman34 presented their experience with 24 patients with inoperable and/or unresectable cancer of the parotid (9 patients), or the minor salivary glands (15 patients) treated by photon irradiation. The 5-year actuarial local control of parotid gland lesions after photon irradiation was 100%, and the survival rate was 65%. For the minor salivary gland lesions, the 5-year actuarial local control was 78% and the survival rate with or without disease was 93%. All lesions were irradiated by accelerated hyperfractionated photons (bid) with 1.6 Gy per fraction, intermixed with various boost techniques, including electron beam, intraoral cone, interstitial implant, and/or submental photons for a total of 65 to 70 Gy.

The Radiation Therapy Oncology Group (RTOG) in the United States and the Medical Research Council (MRC) in Great Britain sponsored a study comparing the efficacy of fast neutron radiotherapy versus conventional photon and/or electron radiotherapy for unresectable malignant salivary gland tumors. In 1993, Laramore et al.35 published the final report on this study, demonstrating that at 10-year follow-up, there was a statistically significant improvement in local/regional control for the neutron group (56% vs 25%, P = 0.009), but there was no difference in survival between both arms of the study. Distant metastases accounted for the majority of failures in the neutron arm, and local/regional failures accounted for most failures in the photon arm. Although the incidence of morbidity graded "severe" was greater on the neutron arm, there was no significant difference in life-threatening complications. This well-executed study suggested that fast neutron radiotherapy may be a reasonable treatment option for patients with inoperable primary or recurrent malignant salivary gland tumors. It is hoped that fast-neutron therapy will be more widely available for patients with unresectable salivary gland malignancy.

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