The influence of pre-radiation salivary flow rates and radiation dose on parotid salivary gland dysfunction in patients receiving radiotherapy for head and neck cancers

The effect of parotid gland-sparing intensity-modulated radiotherapy on salivary composition, flow rate and xerostomia measures

OBJECTIVES

To describe parotid gland (PG) saliva organic and inorganic composition and flow rate changes, after curative intensity-modulated radiotherapy (IMRT) for head and neck cancer (HNC), and analyse the relationship between PG saliva analytes and xerostomia measures.

METHODS AND MATERIALS

Twenty-six patients recruited to five prospective phase 2 or 3 trials which assessed toxicity and efficacy of IMRT by HNC subsite, provided longitudinal PG saliva. Salivary flow rate, and subjective and objective xerostomia measures were prospectively collected and saliva tested for inorganic and organic analytes. Statistical comparisons of longitudinal analyte changes and analysis for a relationship between dichotomized xerostomia score and saliva analytes were performed.

RESULTS

One hundred and forty-two PG saliva samples from 26 patients were analysed. At 3-6 months after IMRT, stimulated and unstimulated saliva showed significantly decreased flow rate, total protein (TP) secretion rate, phosphate concentration and increased lactoferrin (LF) concentration. Stimulated saliva alone had elevated LF secretion rate and beta-2-microglobulin (B₂ M) concentration with decreased calcium (Ca²⁺ ) and magnesium (Mg²⁺ ) concentrations and Ca²⁺ secretion rate. At >12 months, under stimulated and unstimulated conditions, increased LF concentration and decreased Mg²⁺ and phosphate concentration persisted and, in stimulated saliva, there was decreased potassium (K⁺ ) and Mg²⁺ concentration. Unstimulated TP secretion rate was lower in the presence of high-grade xerostomia. Otherwise, no relationship between xerostomia grade and PG salivary flow rate, TP and Ca²⁺ secretion rate was found.

CONCLUSION

Fewer significant differences in PG saliva analytes >12 months after IMRT indicate good functional recovery. Residual xerostomia after IMRT will only be further reduced by addressing the sparing of subsites of the PG or other salivary gland tissues, in addition to the PG.

Recovery of Salivary Function: Contralateral Parotid-sparing Intensity-modulated Radiotherapy versus Bilateral Superficial Lobe Parotid-sparing Intensity-modulated Radiotherapy

AIMS

To establish whether there is a difference in recovery of salivary function with bilateral superficial lobe parotid-sparing intensity-modulated radiotherapy (BSLPS-IMRT) versus contralateral parotid-sparing IMRT (CLPS-IMRT) in patients with locally advanced head and neck squamous cell cancers.

MATERIALS AND METHODS

A dosimetric analysis was carried out on data from two studies in which patients received BSLPS-IMRT (PARSPORT II) or CLPS-IMRT (PARSPORT). Acute (National Cancer Institute, Common Terminology Criteria for adverse events - NCI CTCAEv3.0) and late (Late Effects of Normal Tissue- subjective, objective, management analytical - LENTSOMA and Radiation Therapy Oncology Group) xerostomia scores were dichotomised: recovery (grade 0-1) versus no recovery (≥grade 2). Incidence of recovery of salivary function was compared between the two techniques and dose-response relationships were determined by fitting dose-response curves to the data using non-linear logistic regression analysis.

RESULTS

Seventy-one patients received BSLPS-IMRT and 35 received CLPS-IMRT. Patients received 65 Gy in 30 fractions to the primary site and involved nodal levels and 54 Gy in 30 fractions to elective nodal levels. There were significant differences in mean doses to contralateral parotid gland (29.4 Gy versus 24.9 Gy, P < 0.005) and superficial lobes (26.8 Gy versus 30.5 Gy, P = 0.02) for BSLPS and CLPS-IMRT, respectively. Lower risk of long-term ≥grade 2 subjective xerostomia (LENTSOMA) was reported with BSLPS-IMRT (odds ratio 0.50; 95% confidence interval 0.29-0.86; P = 0.012). The percentage of patients who reported recovery of parotid saliva flow at 1 year was higher with BSLPS-IMRT compared with CLPS-IMRT techniques (67.1% versus 52.8%), but the difference was not statistically significant (P = 0.12). For the whole parotid gland, the tolerance doses, D50, were 25.6 Gy (95% confidence interval 20.6-30.5), k = 2.7 (0.9-4.5) (CLPS-IMRT) and 28.9 Gy (26.1-31.9), k = 2.4 (1.4-3.4) (BSLPS-IMRT). For the superficial lobe, D50 were similar: BSLPS-IMRT 23.5 Gy (19.3-27.6), k = 1.9 (0.5-3.8); CLPS-IMRT 24.0 Gy (17.7-30.1), k = 2.1 (0.1-4.1).

CONCLUSION

BSLPS-IMRT reduces the risk of developing high-grade subjective xerostomia compared with CLPS-IMRT. The D50 of the superficial lobe may be a more reliable predictor of recovery of parotid function than the whole gland mean dose.

Simultaneous integrated boost-intensity-modulated radiotherapy in head and neck cancer

OBJECTIVES/HYPOTHESIS

To review toxicity and outcomes in patients with head and neck cancer treated with simultaneous integrated boost-intensity-modulated radiotherapy (SIB-IMRT).

STUDY DESIGN

Review of experience with the SIB-IMRT technique.

METHODS

Fifty patients were treated with the SIB-IMRT technique. Two possible schedules of radiation therapy (RT) were used: SIB 70 (70/60/54 in 33 fractions) and SIB 66 (66/60/54 in 33 fractions). Forty-one patients also received chemotherapy.

RESULTS

All but two patients completed treatment as prescribed. No G4 acute toxicity has been reported in our series. We did not observe any G3 to G4 chronic toxicity, apart from one case of cutaneous necrosis. After a median follow-up of 23.3 months (range, 1-60 months), 41 patients (82%) were alive and negative for disease, and one patient (2%) was alive with distant metastases. Eight patients (16%) died, seven because of progressive disease and one for other causes.

CONCLUSIONS

SIB-IMRT is a highly effective and safe technique of RT in the treatment of head and neck cancer.

Dose-response analysis of parotid gland function: what is the best measure of xerostomia?

PURPOSE

To describe the dose-response relationships for the different measures of salivary gland recovery following radical radiotherapy for locally advanced head and neck squamous cell cancers (LA-HNSCC).

METHODS AND MATERIALS

Dosimetric analysis of data from the PARSPORT trial, a Phase III study of conventional RT (RT) and intensity modulated radiotherapy (IMRT) for LA-HNSCC was undertaken to determine the relationship between parotid gland mean dose and toxicity endpoints: high-grade subjective and objective xerostomia and xerostomia-related quality of life scores. LKB-NTCP parameters (TD50, m and n) were generated and tolerance doses (D50) reported using non-linear logistic regression analysis.

RESULTS

Data were available on 63 patients from the PARSPORT trial. Parotid saliva flow rate provided the strongest association between mean dose and recovery, D50=23.4 Gy (20.6-26.2) and k=3.2 (1.9-4.5), R(2)=0.85. Corresponding LKB parameters were TD50=26.3 Gy (95% CI: 24.0-30.1), m=0.25 (0.18-1.0 and n=1). LENTSOMA subjective xerostomia also demonstrated a strong association D50=33.3 Gy (26.7-39.8), k=2.8 (91.4-4.4), R(2)=0.77).

CONCLUSION

We recommend using the LENT SOMA subjective xerostomia score to predict recovery of salivation due to its strong association with dosimetry and ease of recording.

The effect of concomitant chemotherapy on parotid gland function following head and neck IMRT

PURPOSE

To determine whether concomitant chemotherapy increases the incidence of high grade xerostomia following parotid-sparing intensity-modulated radiotherapy (IMRT) in patients with locally advanced head and neck squamous cell cancer.

MATERIALS AND METHODS

The incidence of high grade (≥G2) acute (CTCAEv3.0) and late (LENTSOMA and RTOG) xerostomia was compared between patients treated with either IMRT or concomitant chemo-IMRT (c-IMRT) in 2 prospective studies. Parotid gland mean tolerance doses (D₅₀) were reported using non-linear logistic regression analysis.

RESULTS

Thirty-six patients received IMRT alone and 60 patients received c-IMRT. Patients received 65 Gy in 30 daily fractions to the primary site and involved nodal groups and 54 Gy in 30 fractions to elective nodal groups, mean doses to the parotid glands were comparable. Concomitant cisplatin 100mg/m(2) was administered on days 1 and 29 of IMRT. The incidence of ≥G2 subjective xerostomia was similar in both groups; acute-64.7% (IMRT) versus 60.3% (c-IMRT), p=0.83; late-43% (IMRT) versus 34% (c-IMRT), p=0.51. Recovery of parotid salivary flow at 1 year was higher with IMRT (64% vs 50%), but not statistically significant (p=0.15). D₅₀ for absence of parotid saliva flow at 1 year was 23.2 Gy (95% CI: 17.7-28.7) for IMRT and 21.1 Gy (11.8-30.3) for c-IMRT.

CONCLUSION

Concomitant c-IMRT does not increase the incidence of acute or late xerostomia relative to IMRT alone.

Toxicity and outcome of intensity-modulated radiotherapy versus 3-dimensional conformal radiotherapy for oropharyngeal cancer: a matched-pair analysis

Because of the scarcity of randomized trials comparing toxicity and outcomes of intensity-modulated radiotherapy (IMRT) for oropharyngeal cancer (OPC) with 3D-conformal radiotherapy (3DCRT), we performed a matched-pair analysis from prospectively collected data from the Head and Neck Tumor Registry of our institution. In the absence of phase III trials, we believe this approach provides the highest quality data possible. Ninety-two patients treated with 3DCRT were matched (1:1) to 92 patients treated with IMRT for 9 potential predictive factors for toxicity and outcome: gender, age, T-stage, N-stage, tumor subsite, unilateral neck irradiation, chemotherapy, neck dissection and boost technique. Groups were compared for acute and late toxicity, locoregional control (LRC), disease-free survival (DFS), and overall survival (OS). Oncologic outcomes were estimated using Kaplan-Meier analyses and toxicity was analyzed according to Common Terminology Criteria for Adverse Events v3.0. The overall incidence of grade 3 acute toxicity was significantly reduced by IMRT, compared to 3DCRT (45% vs. 70%, p = 0.001). The need for tube feeding was reduced from 50% to 37% (p = 0.04). The 3-year actuarial incidence of grade ≥2 late toxicity was also significantly reduced by IMRT, compared to 3DCRT (20% vs. 45%, respectively; p ≤ 0.0001). The incidence of grade ≥ 2 late dysphagia and xerostomia for IMRT vs. 3DCRT were 10% vs. 31% for dysphagia, p = 0.004 and 13% vs. 37%, for xerostomia, respectively (p = 0.001). The 3-year Kaplan-Meier estimates of LRC, DFS, and OS for IMRT vs. 3DCRT were 90% vs. 82% (p = 0.1), 82% vs. 76% (p = 0.3), and 72% vs. 64% (p = 0.2), respectively. In conclusion, the presented non-randomized comparative study of well-matched groups demonstrates the superiority of IMRT vs. 3DCRT for OPC by significantly reducing radiation-induced toxicity without jeopardizing outcomes. The improved therapeutic ratio achieved by the use of IMRT would allow dose escalation of radiotherapy to further improve outcomes of patients with OPC.

Parotid-sparing intensity modulated versus conventional radiotherapy in head and neck cancer (PARSPORT): a phase 3 multicentre randomised controlled trial

Background

Xerostomia is the most common late side-effect of radiotherapy to the head and neck. Compared with conventional radiotherapy, intensity-modulated radiotherapy (IMRT) can reduce irradiation of the parotid glands. We assessed the hypothesis that parotid-sparing IMRT reduces the incidence of severe xerostomia.

Methods

We undertook a randomised controlled trial between Jan 21, 2003, and Dec 7, 2007, that compared conventional radiotherapy (control) with parotid-sparing IMRT. We randomly assigned patients with histologically confirmed pharyngeal squamous-cell carcinoma (T1–4, N0–3, M0) at six UK radiotherapy centres between the two radiotherapy techniques (1:1 ratio). A dose of 60 or 65 Gy was prescribed in 30 daily fractions given Monday to Friday. Treatment was not masked. Randomisation was by computer-generated permuted blocks and was stratified by centre and tumour site. Our primary endpoint was the proportion of patients with grade 2 or worse xerostomia at 12 months, as assessed by the Late Effects of Normal Tissue (LENT SOMA) scale. Analyses were done on an intention-to-treat basis, with all patients who had assessments included. Long-term follow-up of patients is ongoing. This study is registered with the International Standard Randomised Controlled Trial register, number ISRCTN48243537.

Findings

47 patients were assigned to each treatment arm. Median follow-up was 44·0 months (IQR 30·0–59·7). Six patients from each group died before 12 months and seven patients from the conventional radiotherapy and two from the IMRT group were not assessed at 12 months. At 12 months xerostomia side-effects were reported in 73 of 82 alive patients; grade 2 or worse xerostomia at 12 months was significantly lower in the IMRT group than in the conventional radiotherapy group (25 [74%; 95% CI 56–87] of 34 patients given conventional radiotherapy vs 15 [38%; 23–55] of 39 given IMRT, p=0·0027). The only recorded acute adverse event of grade 2 or worse that differed significantly between the treatment groups was fatigue, which was more prevalent in the IMRT group (18 [41%; 99% CI 23–61] of 44 patients given conventional radiotherapy vs 35 [74%; 55–89] of 47 given IMRT, p=0·0015). At 24 months, grade 2 or worse xerostomia was significantly less common with IMRT than with conventional radiotherapy (20 [83%; 95% CI 63–95] of 24 patients given conventional radiotherapy vs nine [29%; 14–48] of 31 given IMRT; p<0·0001). At 12 and 24 months, significant benefits were seen in recovery of saliva secretion with IMRT compared with conventional radiotherapy, as were clinically significant improvements in dry-mouth-specific and global quality of life scores. At 24 months, no significant differences were seen between randomised groups in non-xerostomia late toxicities, locoregional control, or overall survival.

Interpretation

Sparing the parotid glands with IMRT significantly reduces the incidence of xerostomia and leads to recovery of saliva secretion and improvements in associated quality of life, and thus strongly supports a role for IMRT in squamous-cell carcinoma of the head and neck.

Funding

Cancer Research UK (CRUK/03/005).

A systematic review of salivary gland hypofunction and xerostomia induced by cancer therapies: prevalence, severity and impact on quality of life

PURPOSE

This systematic review aimed to assess the literature for prevalence, severity, and impact on quality of life of salivary gland hypofunction and xerostomia induced by cancer therapies.

METHODS

The electronic databases of MEDLINE/PubMed and EMBASE were searched for articles published in English since the 1989 NIH Development Consensus Conference on the Oral Complications of Cancer Therapies until 2008 inclusive. Two independent reviewers extracted information regarding study design, study population, interventions, outcome measures, results and conclusions for each article.

RESULTS

The inclusion criteria were met by 184 articles covering salivary gland hypofunction and xerostomia induced by conventional, 3D conformal radiotherapy or intensity-modulated radiotherapy in head and neck cancer patients, cancer chemotherapy, total body irradiation/hematopoietic stem cell transplantation, radioactive iodine treatment, and immunotherapy.

CONCLUSIONS

Salivary gland hypofunction and xerostomia are induced by radiotherapy in the head and neck region depending on the cumulative radiation dose to the gland tissue. Treatment focus should be on optimized/new approaches to further reduce the dose to the parotids, and particularly submandibular and minor salivary glands, as these glands are major contributors to moistening of oral tissues. Other cancer treatments also induce salivary gland hypofunction, although to a lesser severity, and in the case of chemotherapy and immunotherapy, the adverse effect is temporary. Fields of sparse literature included pediatric cancer populations, cancer chemotherapy, radioactive iodine treatment, total body irradiation/hematopoietic stem cell transplantation, and immunotherapy.

Pre-trial quality assurance processes for an intensity-modulated radiation therapy (IMRT) trial: PARSPORT, a UK multicentre Phase III trial comparing conventional radiotherapy and parotid-sparing IMRT for locally advanced head and neck cancer

The purpose of this study was to compare conventional radiotherapy with parotid gland-sparing intensity-modulated radiation therapy (IMRT) using the PARSPORT trial. The validity of such a trial depends on the radiotherapy planning and delivery meeting a defined standard across all centres. At the outset, many of the centres had little or no experience of delivering IMRT; therefore, quality assurance processes were devised to ensure consistency and standardisation of all processes for comparison within the trial. The pre-trial quality assurance (QA) programme and results are described. Each centre undertook exercises in target volume definition and treatment planning, completed a resource questionnaire and produced a process document. Additionally, the QA team visited each participating centre. Each exercise had to be accepted before patients could be recruited into the trial. 10 centres successfully completed the quality assurance exercises. A range of treatment planning systems, linear accelerators and delivery methods were used for the planning exercises, and all the plans created reached the standard required for participation in this multicentre trial. All 10 participating centres achieved implementation of a comprehensive and robust IMRT programme for treatment of head and neck cancer.

Target volume definition for head and neck intensity modulated radiotherapy: pre-clinical evaluation of PARSPORT trial guidelines

AIMS

There is considerable controversy surrounding target volume definition for parotid-sparing intensity modulated radiotherapy (IMRT) for head and neck cancer. The aim of this study was to evaluate the dosimetric and radiobiological predictors of outcome anticipated by application of the detailed target volume definition guidelines agreed for the UK multicentre randomised controlled trial of parotid-sparing IMRT (PARSPORT).

MATERIALS AND METHODS

Five patients eligible for the study were delineated using the trial guidelines. Following the protocol, plans were produced to treat these volumes with three-dimensional radiotherapy (control arm) and IMRT aimed to spare dose to the contralateral parotid gland (experimental arm). Dosimetric comparisons were made between plans, and normal tissue complication probability (NTCP) modelling for salivary glands was carried out.

RESULTS

Doses delivered to the planning target volumes (PTV) were similar with each technique, although IMRT produced more homogeneous irradiation of the PTV. Mean doses to the contralateral parotid gland were 22.4+/-1.7 Gy with the IMRT plans vs 60.0+/-7.2 Gy with three-dimensional radiotherapy, P=0.0003. Calculated contralateral parotid gland NTCP values for grade 2 xerostomia were 20-22% for IMRT and 98-100% for three-dimensional radiotherapy (P<0.0001).

CONCLUSION

Pre-clinical evaluation of the PARSPORT trial target volume definition guidelines provides theoretical support for a significant reduction in xerostomia rates. These data await confirmation from the clinical trial results.

The impact of dose on parotid salivary recovery in head and neck cancer patients treated with radiation therapy

PURPOSE

A common side effect experienced by head and neck cancer patients after radiation therapy (RT) is impairment of the parotid glands' ability to produce saliva. Our purpose is to investigate the relationship between radiation dose and saliva changes in the 2 years after treatment.

METHODS AND MATERIALS

The study population includes 142 patients treated with conformal or intensity-modulated radiotherapy. Saliva flow rates from 266 parotid glands are measured before and 1, 3, 6, 12, 18, and 24 months after treatment. Measurements are collected separately from each gland under both stimulated and unstimulated conditions. Bayesian nonlinear hierarchical models were developed and fit to the data.

RESULTS

Parotids receiving higher radiation produce less saliva. The largest reduction is at 1-3 months after RT followed by gradual recovery. When mean doses are lower (e.g., <25 Gy), the model-predicted average stimulated saliva recovers to pretreatment levels at 12 months and exceeds it at 18 and 24 months. For higher doses (e.g., >30 Gy), the stimulated saliva does not return to original levels after 2 years. Without stimulation, at 24 months, the predicted saliva is 86% of pretreatment levels for 25 Gy and <31% for >40 Gy. We do not find evidence to support that the overproduction of stimulated saliva at 18 and 24 months after low dose in 1 parotid gland is the result of low saliva production from the other parotid gland.

CONCLUSIONS

Saliva production is affected significantly by radiation, but with doses <25-30 Gy, recovery is substantial and returns to pretreatment levels 2 years after RT.

Recent Advances in Radiation Therapy for Head and Neck Cancer

The treatment of locally advanced or recurrent head and neck cancers has improved from single modality interventions of surgery and radiation therapy alone to include combined modality therapy with surgery, chemotherapy and radiation. Combined therapy has led to improved local control and disease-free survival. New developments in radiation oncology such as altered fractionation, three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, stereotactic radiosurgery, fractionated stereotactic radiotherapy, charged-particle radiotherapy, neutron-beam radiotherapy, and brachytherapy have helped to improve this outlook even further. These recent advances allow for a higher dose to be delivered to the tumor while minimizing the dose delivered to the surrounding normal tissue. This article provides an update of the new developments in radiotherapy in the management of head and neck cancers.

Structural and functional characteristics of irradiation damage to parotid glands in the miniature pig

PURPOSE

To evaluate the effects of a solitary megadose protocol of ionizing radiation (IR) on the structure and function of the miniature pig (minipig) parotid gland.

METHODS AND MATERIALS

Fourteen minipigs were subjected to either 15 or 20 Gy to one parotid gland with a linear accelerator, whereas another four minipigs served as non-IR controls. Salivary flow rates and salivary chemistries were measured pre-IR and 4 and 16 weeks post-IR. A quantitative assessment of gland weight and acinar area and detailed serum chemistry and hematologic analyses were also performed.

RESULTS

Parotid flow rates decreased by approximately 50% either with 20 Gy at 4 weeks, or 15 Gy at 16 weeks post-IR. In the 20 Gy group, salivary flow rates were reduced by approximately 80% at 16 weeks post-IR. A significant decrease in salivary calcium and amylase and an increase of salivary potassium levels were found in both IR groups. There were also transient alterations in serum chemistry and hematology parameters post-IR. Parotid gland weights were significantly decreased (-50%) in the 15 and 20 Gy groups at 4 and 16 weeks post-IR. Additionally, the acinar cell area in glands of both IR groups was significantly reduced from that in control glands at both the 4 and 16 weeks time points.

CONCLUSION

Structural changes in salivary gland parenchyma occurred relatively early after IR, whereas the alterations in salivary output were relatively delayed. Further, reductions in salivary flow were not proportional to acinar cell area loss. Together, these findings suggest that nonparenchymal IR damage likely contributes to IR-induced salivary hypofunction.

Clinical use of intensity-modulated radiotherapy: part I

Intensity-modulated radiotherapy (IMRT) is a novel conformal radiotherapy technique which is gaining increasing clinical use worldwide. This article aims to summarize the published data pertaining to clinical indications of this therapy for head and neck, central nervous system, and lung tumours. The main indications in head and neck cancer are parotid gland sparing and dose escalation to tumours close to organs at risk. For central nervous system tumours, IMRT has been used to reduce normal tissue radiation by more conformal dose distributions. To date, the majority of reports concern patients treated in the context of clinical trials, and for most tumour types longer term follow up of treated patients will be required to confirm the clinical benefits of IMRT.

The influence of clinical factors on human stimulated parotid flow rate in cancer and other patients

Reduced salivary secretion can produce a wide variety of complaints, having a negative impact on the daily life of a patient. Multiple causes of salivary hypofunction are described, however, there are no consistent data about the influence of clinical parameters on parotid gland function. We studied a group of patients with head and neck malignancies before treatment with radiotherapy. We used Lashley cups to collect stimulated parotid saliva simultaneously from both parotid glands. Sizes of the parotid gland, gender, age, tobacco and alcohol consumption, and tumour characteristics were related to the function of the parotid gland. A considerable variability in parotid output was found with a range of 0.03-1.66 ml/min (mean 0.34 ml/min). None of the variables were correlated with parotid flow. These results are important, especially when evaluating effects of radiation on parotid gland function.

Quantitative dose-volume response analysis of changes in parotid gland function after radiotherapy in the head-and-neck region

PURPOSE

To study the radiation tolerance of the parotid glands as a function of dose and volume irradiated.

METHODS AND MATERIALS

One hundred eight patients treated with primary or postoperative radiotherapy for various malignancies in the head-and-neck region were prospectively evaluated. Stimulated parotid flow rate was measured before radiotherapy and 6 weeks, 6 months, and 1 year after radiotherapy. Parotid gland dose-volume histograms were derived from CT-based treatment planning. The normal tissue complication probability model proposed by Lyman was fit to the data. A complication was defined as stimulated parotid flow rate <25% of the preradiotherapy flow rate.

RESULTS

The mean stimulated preradiotherapy flow rate of 174 parotid glands was 0.34 mL/min. The mean flow rate reduced to 0.12 mL/min 6 weeks postradiotherapy, but recovered to a mean flow rate of 0.20 mL/min at 1 year after radiotherapy. Reduction in postradiotherapy flow rate correlated significantly with mean parotid dose. No threshold dose was found. Increasing the irradiated volume of parotid glands from 0%-40% to 90-100% in patients with a mean parotid dose of 35-45 Gy resulted in a decrease in flow ratio from, respectively, approximately 100% to less than 10% 6 weeks after radiation. The flow ratio of the 90%-100% group partially recovered to 15% at 6 months and to 30% at 1 year after radiotherapy. The normal tissue complication probability model parameter TD(50) (the dose to the whole organ leading to a complication probability of 50%) was found to be 31, 35, and 39 Gy at 6 weeks, 6 months, and 1 year postradiotherapy, respectively. The volume dependency parameter n was around 1, which means that the mean parotid dose correlates best with the observed complications. There was no steep dose-response curve (m = 0.45 at 1 year postradiotherapy).

CONCLUSIONS

This study on dose/volume/parotid gland function relationships revealed a linear correlation between postradiotherapy flow ratio and parotid gland dose and a strong volume dependency. No threshold dose was found. Recovery of parotid gland function was shown at 6 months and 1 year after radiotherapy. In radiation planning, attempts should be made to achieve a mean parotid gland dose at least below 39 Gy (leading to a complication probability of 50%).

Optimisation of radiotherapy for carcinoma of the parotid gland: a comparison of conventional, three-dimensional conformal, and intensity-modulated techniques

BACKGROUND AND PURPOSE

To compare external beam radiotherapy techniques for parotid gland tumours using conventional radiotherapy (RT), three-dimensional conformal radiotherapy (3DCRT), and intensity-modulated radiotherapy (IMRT). To optimise the IMRT techniques, and to produce an IMRT class solution.

MATERIALS AND METHODS

The planning target volume (PTV), contra-lateral parotid gland, oral cavity, brain-stem, brain and cochlea were outlined on CT planning scans of six patients with parotid gland tumours. Optimised conventional RT and 3DCRT plans were created and compared with inverse-planned IMRT dose distributions using dose-volume histograms. The aim was to reduce the radiation dose to organs at risk and improve the PTV dose distribution. A beam-direction optimisation algorithm was used to improve the dose distribution of the IMRT plans, and a class solution for parotid gland IMRT was investigated.

RESULTS

3DCRT plans produced an equivalent PTV irradiation and reduced the dose to the cochlea, oral cavity, brain, and other normal tissues compared with conventional RT. IMRT further reduced the radiation dose to the cochlea and oral cavity compared with 3DCRT. For nine- and seven-field IMRT techniques, there was an increase in low-dose radiation to non-target tissue and the contra-lateral parotid gland. IMRT plans produced using three to five optimised intensity-modulated beam directions maintained the advantages of the more complex IMRT plans, and reduced the contra-lateral parotid gland dose to acceptable levels. Three- and four-field non-coplanar beam arrangements increased the volume of brain irradiated, and increased PTV dose inhomogeneity. A four-field class solution consisting of paired ipsilateral coplanar anterior and posterior oblique beams (15, 45, 145 and 170 degrees from the anterior plane) was developed which maintained the benefits without the complexity of individual patient optimisation.

CONCLUSIONS

For patients with parotid gland tumours, reduction in the radiation dose to critical normal tissues was demonstrated with 3DCRT compared with conventional RT. IMRT produced a further reduction in the dose to the cochlea and oral cavity. With nine and seven fields, the dose to the contra-lateral parotid gland was increased, but this was avoided by optimisation of the beam directions. The benefits of IMRT were maintained with three or four fields when the beam angles were optimised, but were also achieved using a four-field class solution. Clinical trials are required to confirm the clinical benefits of these improved dose distributions.

Preserved salivary output and xerostomia-related quality of life in head and neck cancer patients receiving parotid-sparing radiotherapy

Radiotherapy (RT) for head and neck cancers causes salivary dysfunction and diminished xerostomia-related quality of life. We have demonstrated that three-dimensional treatment planning and conformational dose-delivery techniques can minimize RT doses to contralateral parotid glands while providing therapeutic doses to tumors. This study's purpose was to assess parotid salivary function up to 1 year post-RT in patients receiving bilateral neck parotid-sparing RT, and to determine if parotid preservation would significantly improve xerostomia-related quality of life. Unstimulated (UPFR) and stimulated (SPFR) parotid flow rates were collected from 20 head and neck cancer patients. All subjects completed a 15-item xerostomia-related quality of life scale (XeQoLS) prior to RT, at the completion of RT, 1, 3, 6 and 12 months post-RT. Salivary flow rates from spared and treated glands were significantly decreased at the completion of RT. After RT completion, spared UPFR and SPFR function increased and was not significantly different from baseline values. Output from treated glands remained statistically indistinguishable from zero throughout the post-RT period. Subjects had a significantly worse xerostomia-related quality of life at the completion of RT compared to baseline, and XeQoLS responses improved significantly 1 month post-RT. Responses at 1 year were markedly better than at the completion of RT, but still significantly worse than baseline. These findings suggest that despite parotid-sparing RT, salivary flow rates from treated and spared glands and xerostomia-related quality of life decrease at the completion of RT. However, with the use of parotid-sparing RT, contralateral glands are preserved at 1 year post-RT with a concomitant improvement in xerostomia-related quality of life.

Natural history and prevention of radiation injury

Radiation therapy for cancers of the head and neck can irreversibly damage the salivary glands. Xerostomia (subjective oral dryness) develops within the first week of therapy and is progressive, with devastating effects on the quality of life of the individual. The xerostomia does not correlate with the degree of salivary gland hypofunction. The mechanism of tissue injury in humans is still unclear, but much progress has been made with animal models. This paper reviews the natural history of radiation damage to human salivary glands and highlights the inter-individual variations in the responses to and recovery from therapeutic radiation. The degree of salivary gland damage is correlated to the dose of radiation delivered and the volume of gland included in the field of radiation. The molecular mechanism of acute radiation damage is not fully understood; however, long-term salivary gland dysfunction is associated with both loss of gland weight and loss of acinar cells. Various strategies have been used to prevent or alleviate the problem of salivary gland hypofunction following therapeutic radiation. This paper reviews the progress made to date and the possibilities for future interventions to prevent radiation damage.

Intensity modulated radiation therapy: a clinical review

Intensity modulated radiotherapy represents a significant advance in conformal radiotherapy. In particular, it allows the delivery of dose distributions with concave isodose profiles such that radiosensitive normal tissue close to, or even within a concavity of, a tumour may be spared from radiation injury. This article reviews the clinical application of this technique to date, and discusses the practical issues of treatment planning and delivery from the clinician's perspective.