Neutron therapy for malignant tumours of the salivary glands. A report of the Edinburgh experience

The efficacy of neutron radiation therapy in treating salivary gland malignancies

OBJECTIVES

Radiation therapy is commonly used to treat head and neck malignancies. While there is abundant research regarding photon radiation therapy, literature on neutron radiotherapy (NRT) and oral complications is limited. This study aims to determine: (1) the 6-year and 10-year locoregional control and survival rates, (2) factors associated with locoregional control and survival and (3) the frequency of oral complications in patients undergoing NRT for salivary gland malignancies.

MATERIALS AND METHODS

This is a retrospective cohort study. The sample was composed of patients with salivary gland malignancies treated with NRT between 1997 and 2010. Data were extracted from patient charts, telephone surveys, and social security records. Multivariate competing risk and Cox regression models were used to assess predictors of locoregional control and survival.

RESULTS

The sample was composed of 545 subjects with a mean age of 54.2 years (±16). The predominant tumor and location were adenoid cystic carcinoma (47%) and the parotid (56%). Multivariate analysis indicated that positive surgical margins, biopsied/inoperable malignancies, neck involvement, and lymphovascular invasion were prognostic risk factors associated with decreased survival. The 6- and 10-year locoregional control rates were 84% and 79%. The 6- and 10-year survival rates were 72% and 62%. Osteoradionecrosis developed in 3.4% of subjects.

CONCLUSIONS

The 6- and 10-year locoregional control and survival rates compare favorably to rates reported for conventional photon radiation. Osteoradionecrosis rates were comparable to that of photon radiation treatment (2-7%). Given the potential benefits of NRT, healthcare professionals should be educated regarding its indications and oral complications.

Neutron exposures in human cells: bystander effect and relative biological effectiveness

Bystander effects have been observed repeatedly in mammalian cells following photon and alpha particle irradiation. However, few studies have been performed to investigate bystander effects arising from neutron irradiation. Here we asked whether neutrons also induce a bystander effect in two normal human lymphoblastoid cell lines. These cells were exposed to fast neutrons produced by targeting a near-monoenergetic 50.5 MeV proton beam at a Be target (17 MeV average neutron energy), and irradiated-cell conditioned media (ICCM) was transferred to unirradiated cells. The cytokinesis-block micronucleus assay was used to quantify genetic damage in radiation-naïve cells exposed to ICCM from cultures that received 0 (control), 0.5, 1, 1.5, 2, 3 or 4 Gy neutrons. Cells grown in ICCM from irradiated cells showed no significant increase in the frequencies of micronuclei or nucleoplasmic bridges compared to cells grown in ICCM from sham irradiated cells for either cell line. However, the neutron beam has a photon dose-contamination of 5%, which may modulate a neutron-induced bystander effect. To determine whether these low doses of contaminating photons can induce a bystander effect, cells were irradiated with cobalt-60 at doses equivalent to the percent contamination for each neutron dose. No significant increase in the frequencies of micronuclei or bridges was observed at these doses of photons for either cell line when cultured in ICCM. As expected, high doses of photons induced a clear bystander effect in both cell lines for micronuclei and bridges (p<0.0001). These data indicate that neutrons do not induce a bystander effect in these cells. Finally, neutrons had a relative biological effectiveness of 2.0 ± 0.13 for micronuclei and 5.8 ± 2.9 for bridges compared to cobalt-60. These results may be relevant to radiation therapy with fast neutrons and for regulatory agencies setting standards for neutron radiation protection and safety.

Le traitement par neutrons : hadronthérapie partie II : bases physiques et expérience clinique

Neutrons have radiobiological characteristics, which differ from those of conventional radiotherapy beams (photons) and which offer a theoretical advantage over photons to fight radioresistance by the differential relative biological effect of them between normal and tumour tissues. Neutron therapy beneficed of great interest between 1975 and 1985. Many of phase III trials were conducted and indications have been definitively deducted of them. After briefly describing the properties of neutron beams, this review discusses the indication of neutron therapy on the basis of the clinical results. Salivary, prostate tumours and sarcomas are the main indications of neutron therapy. In concern to the prostate cancers, other alternative treatments reduce the neutron therapy field. For sarcomas, the lack of randomised trials limits the impact of the interest of neutrons. For other tumours, the ratio benefice/risk of neutron therapy is inferior to these obtained with photons and they could not be considered like classical indications.

[Use of fast neutrons in the treatment of tumors of the salivary glands: rationale, review of the literature and experience in Orleans]

If low LET radiation therapy (photons, electrons), following radical microscopically and complete surgery can improve results in term of local control from 34 to 74% for salivary gland tumors, local control is more difficult to achieve in advanced tumors and only palliative treatment is usually attempted. In this survey, all the patient series treated worldwide were reviewed. They show an overall control rate of 31% with photon vs 64% with neutron therapy. A prospective randomised trial sponsored by the RTOG and the MRC published in 1988 and reviewed in 1993 showed an overall locoregional complete tumor clearance of 67% for neutrons and 17% for photons (P < 0.005), with 68% and 25% survival at two years for neutrons and photons respectively. This study was closed for ethical reasons. In Orleans, since 1987, 59 patients have been treated. At five years the persistent local control probability was 69.5%, the five-year crude survival probability 66% and the five-year tumor free survival probability was 64.5%. This review provides evidence that surgical treatment for salivary gland tumors should be limited to patients presenting a high likelihood of negative surgical margin and a small risk of facial nerve damage. Others patients should receive neutron radiation therapy alone as definitive treatment.

Neutron therapy in malignant salivary gland tumors: results at European centers

Malignant salivary gland tumors are relatively rare and account for only 3%-4% of all head and neck cancers. Especially in adenoid cystic carcinoma, the incidence of local recurrence and distant metastases is influenced by the perineural spread of tumor. In advanced salivary gland tumors, surgery alone has a high incidence of local failure. The results of conventional radiotherapy are suboptimal in inoperable or not completely resected salivary gland tumors and in recurrent disease. The pooled data of some international series for low linear energy transfer radiation show a local control of only 28%. Especially in advanced salivary gland tumors, neutron therapy can improve local control. In Europe at least 570 patients with salivary gland tumors have been treated with neutrons alone or with combined modalities. The clinical data of different centers in Europe and the United States result in a similar local control rate of 67% in gross disease. An analysis of different European series shows on average a complication rate of 10.6% for severe radiation-related morbidity. Modern neutron machines and the use of three-dimensional treatment planning systems are now available in a few institutions and may further reduce side effects.

[Results of the treatment with fast neutrons (d.T 13 MeV) in recurrent rectal carcinoma]

PURPOSE

In spite of improved surgical techniques and the use of multiple modality treatment schemes the local recurrence rate of colorectal carcinomas could not be successfully reduced up to now. Besides surgical treatment of local recurrences in some cases radiation therapy may be indicated.

PATIENTS AND METHOD

In the Department of Radiotherapy of the University of Münster 37 patients with recurrent rectal carcinoma were treated between the end of 1985 and September 1992 either with fast neutrons alone or with a combined photon-neutron therapy. Eighteen patients received radiotherapy with fast neutrons (14 MeV d,T) alone; the tumor dose was between 10 and 15 Gy neutrons. Nineteen patients were irradiated with a mixed-beam schedule consisting of 30 to 45 Gy photons (X 10 MV) and neutron doses ranging from 5 to 10 Gy.

RESULTS

In 30 patients a good or complete pain relief could be observed immediately after the last irradiation. Sixteen out of 37 patients had local tumor regrowth during the follow-up period. The median survival for all 37 patients was 15.9 months. The probability for survival was 86% after 6 months and 61% after 12 months (Kaplan-Meier). The side effects were slight to moderate (EORTC/RTOG I-II).

CONCLUSIONS

This therapy showed good results concerning a fast and effective pain relief. Additionally the results seem to show a good effect concerning local control and overall survival in this negatively selected patients.

Neutron radiotherapy for adenoid cystic carcinoma of minor salivary glands

PURPOSE

To examine the efficacy of fast neutron radiotherapy for the treatment of patients with locally advanced, adenoid cystic carcinoma of minor salivary glands and to identify prognostic variables associated with local control, overall survival, and cause specific survival.

METHODS AND MATERIALS

Eighty-four patients having adenoid cystic carcinoma of minor salivary glands were treated with fast neutron radiotherapy during the years 1985-1994. All patients had either unresectable disease or gross disease remaining after attempted surgical extirpation. Seventeen patients had previously received conventional radiotherapy and their subsequent treatment fields and doses for neutron radiotherapy were modified for critical sites (brainstem, spinal cord, brain). Although the median doses (tumor maximum and tumor minimum) only varied by < or = 10%, treatment portals were substantially smaller in these patients because of normal tissue complication considerations. Twelve patients (13%) had distant metastases at the time of treatment and were only treated palliatively with smaller treatment portals and lower median tumor doses (< or = 80% of the doses delivered to curatively treated patients). Seventy-two patients were treated with curative intent, with nine of these having recurrent tumors after prior full-dose radiotherapy. The median duration of follow-up at the time of analysis was 31.5 months (range 3-115). Sites of disease and number of patients treated per disease site were as follows: paranasal sinus-31; oral cavity-20; oropharynx-12; nasopharynx-11; trachea-6; and other sites in the head and neck-4.

RESULTS

The 5-year actuarial local-regional tumor control rate for all patients treated with curative intent was 47%. Patients without involvement of the cavernous sinus, base of skull, or nasopharynx (51 patients) had a 5-year actuarial local-regional control rate of 59%, whereas local-regional control was significantly lower (15%) for patients with tumors involving these sites (p < 0.005). In the latter cases, normal tissue injury considerations precluded delivery of the full dose to the entire tumor. Patients with no history of prior radiotherapy (63 patients) had an actuarial local control rate of 57% at 5 years compared to 18% for those (9 patients) who had been previously irradiated with conventional photons (p = 0.018). Eliminating the dose-limiting factors of prior radiation therapy and/or high risk sites of involvement, the 5-year actuarial local-regional control rate for these 46 patients was 63%, with an actuarial cause specific survival rate of 79%. Lymph node status was a predictor of distant metastasis: 57% of node positive patients developed distant metastases by 5 years compared to 15% of patients with negative nodes (p < 0.0005), and patients who had nodal involvement developed distant metastases sooner than node negative patients (p < 0.0001). The 5-year actuarial overall survival and cause specific survival for the 72 patients treated with curative intent were 59% and 64%, respectively.

CONCLUSIONS

Fast neutron radiotherapy offers high local-regional control and survival rates for patients with locally advanced, unresectable adenoid cystic carcinomas of minor salivary glands. It should be considered as initial primary treatment for these patients, as well as for other patients in whom surgical extirpation would cause considerable morbidity.

European results in neutron therapy of malignant salivary gland tumors

In Europe to date, 501 patients with salivary gland tumors have been treated with neutrons alone or with combined modalities. The most common histological types are adenoid cystic carcinomas, mucoepidermoid carcinomas and malignant mixed tumors. The results of conventional radiotherapy are suboptimal in inoperable or incompletely resected salivary gland tumors and in recurrent disease. The pooled data of some international series for low linear energy transfer radiation show a local control of 28%. Especially in advanced tumors neutron therapy can improve local control and should be the treatment of choice. The clinical data from different therapy centers in Europe show local control of 67% in gross disease.

Clinical trials of neutron radiotherapy in the United States

The development of clinical neutron facilities in the 1980s, capable of delivering high energy neutrons spurred full scale phase III testing of neutron beam radiotherapy in a number of tumors including salivary gland, head and neck, prostate, and non small-cell lung cancer. The Radiation Therapy Oncology Group (RTOG) and the Medical Research Council (MRC) jointly sponsored a randomized trial for the treatment of advanced stage salivary gland tumors comparing neutron to conventional photon and/or electron radiotherapy. Although no improvement in survival was seen, the study demonstrated a striking and statistically significant difference in the local-regional control of unresectable salivary gland tumors (56 vs 17%), favoring neutron beam irradiation. Subsequent clinical trials of neutron beam irradiation were initiated by the Neutron Therapy Collaborative Working Group (NTCWG) sponsored by the National Cancer Institute (NCI). A phase III trial comparing neutron to photon radiotherapy for inoperable regional non-small cell lung cancer showed no overall improvement in survival. However, a statistically significant improvement in survival was observed in the subset of patients with squamous cell histology. The NTCWG trial comparing fast-neutron therapy versus conventional photon irradiation in the treatment of advanced squamous cell carcinomas of the head and neck showed a statistically significant improvement in initial complete response (70 vs 52%) favoring neutrons. However, subsequent failures erased any difference in ultimate local-regional control rates and survival curves were essentially the same in both arms. The randomized study of the NTCWG for locally advanced prostate cancer demonstrated a significant decrease in local-regional failure (11 vs 32%) at 5 years, favoring the neutron arm. Furthermore, biochemical measures of disease control also favored the neutron arm with prostate specific antigen (PSA) levels elevated in 17% of the neutron-treated patients compared to 45% of the photon-treated patients at 5 years. At the 5-year analysis, no significant difference in survival was observed between the two arms; however, longer follow-up is necessary to assess the ultimate impact of improved local-regional control on survival. An analysis of complications in this series revealed the importance of beam shaping and treatment planning capabilities in maintaining long-term sequelae following neutron irradiation at an acceptably low level.

Hyperthermia and radiation therapy for inoperable or recurrent parotid carcinoma. A phase I/II study

BACKGROUND

The treatment of advanced, inoperable, or recurrent parotid tumors represents a clinical challenge. The results obtained with conventional radiotherapy are disappointing. To improve the early response and local control of parotid tumors, local microwave hyperthermia was used in combination with ionizing radiation in a biinstitutional Phase I/II study.

METHODS

From 1984 to 1991, 13 patients (20 lesions) with advanced (10 lesions) or recurrent (10 lesions) parotid tumors (15 primaries and the remaining 5 nodal metastases), were treated with 300-915 MHz of external hyperthermia after external irradiation. Heat was applied twice weekly at a minimum desired temperature of 42.0 degrees C for 30 minutes at steady state. Ionizing radiation was delivered using photon, electron, or mixed electron-photon beams; the prescribed total dose was 70 Gy and 30 Gy for untreated and previously treated lesions, respectively; the median computed total dose was 66 Gy for previously untreated patients (range, 56-70 Gy) and 30 Gy for previously irradiated patients (range, 28-32 Gy).

RESULTS

Acute side effects were limited. Major acute toxicities included three patients (15%) with superficial necrosis, two of three who healed spontaneously in 4 and 6 months. Clinical response evaluated during the third month after the completion of therapy found that 16/20 patients (80%) had a complete response (CR), and 4 (20%) had a partial response. Four out of 16 patients who had CRs (20%) had a local recurrence, resulting in an actuarial local control at 5 years of 62.3 +/- 13.2%.

CONCLUSIONS

The combined treatment of local microwave hyperthermia and ionizing radiation proved to be feasible and moderately toxic for patients with advanced, inoperable, or recurrent parotid tumors. Even if clinical result evaluation was not the study endpoint, early response, and 5-year local control rates were encouraging.

Radiotherapy for parotid cancer

BACKGROUND

Parotid malignancies represent a heterogeneous group of tumors primarily managed by surgical extirpation. Moderately high recurrence rates are seen after surgery alone, and postoperative radiotherapy has been used for patients with higher risks for local failure.

METHODS

To assess the role of radiotherapy in the management of patients with malignant tumors of the parotid gland, the records of 68 patients receiving megavoltage therapy at our institution from 1966 to 1989 were reviewed. Patients were placed into three groups for analyses. Group I was composed of 41 patients receiving radiotherapy following total gross removal of parotid cancer by surgical procedures, varying from excisional biopsy through total parotidectomy. Radiation dose for this group ranged from 4,995 to 6,500 cGy. Group II was composed of 10 patients treated with radiotherapy after incisional biopsy or excision with positive margins. These patients received radiation doses of 4,000-9,470 cGy. Group III was composed of 17 patients receiving radiotherapy for a postsurgical local recurrence. Their radiation dose ranged from 4,300 to 8,400 cGy.

RESULTS

Two of the 41 patients from group I developed a local recurrence. Two of these patients also developed distant metastases, one concurrent. Two of 10 group II patients failed locally, whereas three developed distant metastases. Only nine of the 17 patients in group III were controlled locally, and four patients developed distant dissemination.

CONCLUSION

Total gross excision of parotid cancer, sparing facial nerve if possible and followed by regional radiotherapy, provides excellent rates of local control and survival with modest toxicity. Patients presenting postoperatively with gross residual tumor or recurrence after surgery should be considered for trials of more aggressive treatment with combined chemotherapy or altered fractionation schemes of irradiation.

Ultrastructural changes in the cochlea of the guinea pig after fast neutron irradiation

Guinea pigs were irradiated with fast neutrons. After a single dose of 2, 6, 10, or 15 Gy was applied, scanning and transmission electron microscopy of the temporal bone was performed to assess the effect of fast neutron irradiation on the cochlea. Outer hair cell damage appeared with neutron irradiation of more than 10 Gy, and inner hair cell damage with neutron irradiation of more than 15 Gy. Outer hair cells were more severely damaged than inner hair cells. No statistically significant differences were found in damage of basal, middle, and apical turns. The second and third rows of outer hair cells were more severely damaged than the first row of outer hair cells. The most significant findings in transmission electron microscopy were clumping of chromatin and extension of the heterochromatin in the nuclei of hair cells. The cytoplasmic changes were sequestration of cytoplasm, various changes of mitochondria, formation of vacuoles, and irregularly arranged stereocilia. The morphologic change in stria vascularis was intercellular and perivascular fluid accumulation. It appeared to be a reversible process.

Present results of neutron therapy. The German experience

Results of fast neutron therapy are reviewed with special reference to the main indications for this type of treatment and the experience of five German centers. Neutron therapy seems beneficial compared to conventional radiotherapy in advanced salivary gland tumors, inoperable or unresectable soft tissue sarcomas, some bone tumors, prostate cancer stage C and some rare low-grade tumors. About 3,000 patients with malignancies have been treated with neutrons at the German centers Berlin/Rossendorf, Essen, Hamburg, Heidelberg and Münster. Treatment results and treatment-related morbidity depend on the treatment techniques and the physical selectivity of the neutron machines. A critical appraisal suggests that fast neutrons are of advantage in about 5% of all radiotherapy patients.

Fast neutron radiotherapy. The University of Washington experience

An overview of the University of Washington neutron radiotherapy facility is presented. The utility of the multi-leaf, programmable, variable collimator is emphasized. Due to success in the treatment of salivary gland tumors, such patients comprise an ever increasing portion of the patients being treated. A cooperative randomized clinical trial for the treatment of salivary gland tumors was undertaken comparing fast neutrons against photon/electron radiation. At ten years, there was a statistically significant improvement in local/regional control for the neutron group (56% vs 25%, p = 0.009), but there was no improvement in survival (15% vs 25%, p = n.s.). Distant metastases were the primary reason for the failure of improved local/regional control to impact survival in the neutron group. The University of Washington experience is summarized with special emphasis on the treatment of adenoid cystic carcinomas. Excellent local/regional control can be achieved with neutrons even for large tumors arising in the paranasal sinuses. We conclude that the potential morbidity of a surgical debulking procedure is not warranted in most clinical situations.

Neutron versus photon irradiation for unresectable salivary gland tumors: final report of an RTOG-MRC randomized clinical trial. Radiation Therapy Oncology Group. Medical Research Council

PURPOSE

To compare the efficacy of fast neutron radiotherapy versus conventional photon and/or electron radiotherapy for unresectable, malignant salivary gland tumors a randomized clinical trial comparing was sponsored by the Radiation Therapy Oncology Group in the United States and the Medical Research Council in Great Britain.

METHODS AND MATERIALS

Eligibility criteria included either inoperable primary or recurrent major or minor salivary gland tumors. Patients were stratified by surgical status (primary vs. recurrent), tumor size (less than or greater than 5 cm), and histology (squamous or malignant mixed versus other). After a total of 32 patients were entered onto this study, it appeared that the group receiving fast neutron radiotherapy had a significantly improved local/regional control rate and also a borderline improvement in survival and the study was stopped earlier than planned for ethical reasons. Twenty-five patients were study-eligible and analyzable.

RESULTS

Ten-year follow-up data for this study is presented. On an actuarial basis, there continues to be a statistically-significant p = 0.009) but there is no improvement in overall survival (15% vs. 25%, p = n.s.). Patterns of failure are analyzed and it is shown that distant metastases account for the majority of failures on the neutron arm and local/regional failures account for the majority of failures on the photon arm. Long-term, treatment-related morbidity is analyzed and while the incidence of morbidity graded "severe" was greater on the neutron arm, there was no significant difference in "life-threatening" complications. This work is placed in the context of other series of malignant salivary gland tumors treated with definitive radiotherapy.

CONCLUSIONS

Fast neutron radiotherapy appears to be the treatment-of-choice for patients with inoperable primary of recurrent malignant salivary gland tumors.

The role of fast neutron radiation therapy in the management of advanced salivary gland malignant neoplasms

Fifty-three patients with locally advanced salivary gland malignant neoplasm were treated with fast neutron radiation therapy. All patients received treatment for gross inoperable, residual unresectable, or recurrent disease--clinical situations in which results using photon irradiation were suboptimal. With a median follow-up of 42 months and a minimum follow-up of 1 year, locoregional tumor control in the treatment field was achieved in 92% (48 of 52) of patients. An additional eight patients had regional failures outside the treatment field, resulting in an overall locoregional tumor control rate of 77% (40 of 52). The 5-year actuarial locoregional control rates were 65% overall and 75% in patients with node-positive disease. 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. The P values associated with these differences were 0.12 and 0.01, respectively. There were no instances of radiation-induced facial nerve damage. This study suggests that neutron irradiation alone should be the therapy of choice in the treatment of advanced-stage 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 warranted by an improvement in loco-regional control over that achievable with neutron therapy alone.

Diagnosis and pitfalls in the treatment of parotid tumors

Any swelling near the ear is best considered a parotid neoplasm until proved otherwise. The diagnosis is primarily based on the clinical examination. Imaging studies are best reserved for patients who present with palate or tonsil swellings, which must be distinguished from parapharyngeal or minor salivary gland tumors. Almost all benign, and most malignant parotid tumors can be resected with preservation of the facial nerve. Aspiration biopsy can add useful information, but is not essential for treatment planning as the extent of the surgical procedure is primarily determined by the extent of the tumor. Survival rates in patients with malignant tumors are most significantly influenced by tumor stage. Results seem to have improved in recent years, possibly because we are treating a larger proportion with favorable lesions. Another factor may relate to the enhancement of locoregional control now achieved with postoperative radiotherapy, particularly in patients with Stage III or IV tumors.

Further evaluation of radical surgery following radiotherapy for advanced parotid carcinoma

A series of 30 patients who have been treated for advanced carcinoma of the parotid gland using radiotherapy followed by radical surgery is presented. Three patients deteriorated during preoperative radiotherapy and remained unfit for surgery; the remaining 27 underwent radical parotidectomy with block dissection of the neck. Twelve patients received additional radiotherapy after operation. Of those patients undergoing surgery, three have been lost to follow-up, 17 have died and seven remain alive; the period of follow-up ranges from 3 to 133 months. Fourteen patients remained free of recurrent disease at death or when last seen, and six patients developed a local recurrence at a medium period of 10.5 (range 3-36) months after surgery. For all 30 patients, the cumulative proportion surviving for 5 years was 30 per cent.

Conventional megavoltage radiotherapy in the management of malignant epithelial tumours of the parotid gland

This is an evaluation of definitive conventional megavoltage radiotherapy in a consecutive series of 35 patients presenting malignant epithelial tumours of the parotid gland. In this series, the 5-year actuarial locoregional control rate was 41% with a 5-year crude survival rate of 36%. The results are analyzed according to tumour presentation and tumour doses. Six of 15 patients with tumours larger than 6 cm have had a lasting locoregional control. During the same period 43 other patients received radiotherapy as a post-operative modality. Results obtained in this group confirm the previously published data. While recent studies tend to demonstrate the specific efficacy of high LET radiation in the management of locally advanced salivary gland tumours, radical conventional radiotherapy can still be employed with a curative intent when neutron facilities are not available.

Neutron vs photon irradiation of inoperable salivary gland tumors: results of an RTOG-MRC Cooperative Randomized Study

A total of 32 patients with inoperable, recurrent or unresectable malignant salivary gland tumors were entered on a randomized RTOG/MRC study comparing fast neutron radiotherapy with conventional photon radiotherapy. Twenty-five patients were entered from the United States and 7 patients were entered from Scotland. Seventeen patients were randomized to receive neutrons and 15 patients were randomized to receive photons. Sixty-one percent of the neutron-treated patients and 75% of the photon-treated patients presented with inoperable or unresectable tumors, while 39% of the neutron-treated and 25% of the photon-treated patients had recurrent disease. Twenty-five patients were study-eligible and analyzable. The minimum follow-up time is 2 years. The complete tumor clearance rates at the primary site were 85% (11/13) for neutrons and 33% (4/12) for photons following protocol treatment (p = 0.01). The complete tumor clearance rates in the cervical lymph nodes were 86% (6/7) for neutrons and 25% (1/4) for photons. The overall loco/regional complete tumor response rates were 85% and 33% for neutrons and photons respectively. The loco/regional control rates at 2 years for the 2 groups are 67% for neutrons and 17% for photons (p less than 0.005). The 2-year survival rates are 62% and 25% for neutrons and photons respectively (p = 0.10). These findings are consistent with previously published uncontrolled series.

Fast neutron radiotherapy for advanced malignant salivary gland tumors

Thirty-two patients with inoperable, recurrent, or gross residual malignant salivary gland tumors received fast neutron radiotherapy at the University of Washington. Eleven patients were treated with low energy neutrons alone, four received a combined photon-low energy neutron treatment regimen ("mixed beam"), and 17 were treated with high energy neutrons alone. Patients treated for microscopic residual tumor after a surgical resection were excluded from this study. With a minimum follow-up period of one year, (maximum 12 years), the overall locoregional tumor control rate for the entire series was 81%. The 5-year locoregional tumor control rate was 69%. The overall 5-year survival rate was 33% (50% for T3 tumors and 0% for T4 tumors). Compared to results obtained with conventional photon and/or electron treatment for advanced salivary gland tumors, fast neutron radiotherapy appears to offer a significant advantage.