Secondary radiation damage as the main cause for unexpected volume effects: a histopathologic study of the parotid gland

Radiation-induced Xerostomia is Related to Stem Cell Dose-dependent Reduction of Saliva Production

PURPOSE

Previous studies have shown that the mean dose to the parotid gland stem cell rich regions (Dmean,SCR) is the strongest dosimetric predictor for the risk of patient-reported daytime xerostomia. This study aimed to test whether the relationship between patient-reported xerostomia and Dmean,SCR is explained by a dose-dependent reduction of saliva production.

METHODS AND MATERIALS

In 570 patients with head and neck cancer treated with definitive radiation therapy (RT), flow from the parotid (FLOWPAR) and submandibular/sublingual (FLOWSMSL) glands, and patient-reported daytime (XERDAY) and nighttime (XERNIGHT) xerostomia were prospectively measured before, at 6 months, and 12 months after RT. Using linear mixed effect models, the relationship of the mean dose to the parotid glands (Dmean,par), Dmean,SCR, non-SCR parotid gland tissue (Dmean,non-SCR), submandibular glands (Dmean,sub), and oral cavity (Dmean,oral) with salivary flow and xerostomia was analyzed while correcting for known confounders.

RESULTS

Dmean,SCR proved to be responsible for the effect of Dmean,par on FLOWPAR (P ≤ .03), while Dmean,non-SCR did not affect FLOWPAR (P ≥ .11). To illustrate, increasing Dmean,SCR by 10 Gy at a fixed Dmean,non-SCR reduced FLOWPAR by 0.02 mL/min (25%) after RT. However, if the opposite happened, no change in FLOWPAR was observed (0.00 mL/min [4%]). As expected, Dmean,sub was significantly associated with FLOWSMSL (P < .001). For example, increasing Dmean,sub by 10 Gy reduced FLOWSMSL by 0.07 mL/min (26%) after RT. Xerostomia scores were also affected by dose to the salivary glands. Dmean,SCR and Dmean,oral were associated with higher XERDAY scores (P ≤ .05), while Dmean,sub increased XERNIGHT scores (P = .01). For example, an increase of 10 Gy in Dmean,SCR raised XERDAY scores by 2.13 points (5%) after RT, while an additional 10 Gy in Dmean,subs increased XERNIGHT scores by 2.20 points (6%) after RT. Salivary flow was not only associated with radiation dose, but also with xerostomia scores in line with the salivary glands' functions; ie, FLOWPAR only influenced XERDAY (P < .001, 10.92 points lower XERDAY per 1 mL/min saliva), while FLOWSMSL affected XERDAY and XERNIGHT (P ≤ .004, 6.69 and 5.74 points lower XERDAY and XERNIGHT, respectively, per 1 mL/min saliva). Therefore, the observed relationships between dose and xerostomia were corrected for salivary flow. As hypothesized, Dmean,SCR only increased XERDAY scores via reducing FLOWPAR, whereas the effects of Dmean,oral on XERDAY and Dmean,sub on XERNIGHT were independent of salivary flow.

CONCLUSIONS

Higher SCR region dose reduced parotid gland saliva production, subsequently resulting in higher daytime xerostomia scores. Consequently, this study supports the clinical implementation of stem cell sparing RT to preserve salivary flow with the aim of reducing the risk of xerostomia.

Metabolomics analysis of pathways underlying radiation-induced salivary gland dysfunction stages

Salivary gland hypofunction is an adverse side effect associated with radiotherapy for head and neck cancer patients. This study delineated metabolic changes at acute, intermediate, and chronic radiation damage response stages in mouse salivary glands following a single 5 Gy dose. Ultra-high performance liquid chromatography-mass spectrometry was performed on parotid salivary gland tissue collected at 3, 14, and 30 days following radiation (IR). Pathway enrichment analysis, network analysis based on metabolite structural similarity, and network analysis based on metabolite abundance correlations were used to incorporate both metabolite levels and structural annotation. The greatest number of enriched pathways are observed at 3 days and the lowest at 30 days following radiation. Amino acid metabolism pathways, glutathione metabolism, and central carbon metabolism in cancer are enriched at all radiation time points across different analytical methods. This study suggests that glutathione and central carbon metabolism in cancer may be important pathways in the unresolved effect of radiation treatment.

Prediction of Radiation-Induced Parotid Gland-Related Xerostomia in Patients With Head and Neck Cancer: Regeneration-Weighted Dose

PURPOSE

Despite improvements to treatment, patients with head and neck cancer (HNC) still experience radiation-induced xerostomia due to salivary gland damage. The stem cells of the parotid gland (PG), concentrated in the gland's main ducts (stem cell rich [SCR] region), play a critical role in the PG's response to radiation. Treatment optimization requires a dose metric that properly accounts for the relative contributions of dose to this SCR region and the PG's remainder (non-SCR region) to the risk of xerostomia in normal tissue complication probability (NTCP) models for xerostomia.

MATERIALS AND METHODS

Treatment and toxicity data of 1013 prospectively followed patients with HNC treated with definitive radiation therapy (RT) were used. The regeneration-weighted dose, enabling accounting for the hypothesized different effects of dose to the SCR and non-SCR region on the risk of xerostomia, was defined as Dreg PG = Dmean SCR region + r × Dmean non-SCR region, where Dreg is the regeneration-weighted dose, Dmean is the mean dose, and r is the weighting factor. Considering the different volumes of these regions, r > 3.6 in Dreg PG demonstrates an enhanced effect of the SCR region. The most predictive value of r was estimated in 102 patients of a previously published trial testing stem cell sparing RT. For each endpoint, Dreg PG, dose to other organs, and clinical factors were used to develop NTCP models using multivariable logistic regression analysis in 663 patients. The models were validated in 350 patients.

RESULTS

Dose to the contralateral PG was associated with daytime, eating-related, and physician-rated grade ≥2 xerostomia. Consequently, r was estimated and found to be smaller than 3.6 for most PG function-related endpoints. Therefore, the contribution of Dmean SCR region to the risk of xerostomia was larger than predicted by Dmean PG. Other frequently selected predictors were pretreatment xerostomia and Dmean oral cavity. The validation showed good discrimination and calibration.

CONCLUSIONS

Tools for clinical implementation of stem cell sparing RT were developed: regeneration-weighted dose to the parotid gland that accounted for regional differences in radiosensitivity within the gland and NTCP models that included this new dose metric and other prognostic factors.

Possible radioprotection of submandibular glands in gamma-irradiated rats using kaempferol: a histopathological and immunohistochemical study

BACKGROUND AND PURPOSE

Salivary gland damage remains a problem despite advances in radiotherapy schedules for head and neck cancer. Kaempferol, a natural flavonoid, found in several fruits and vegetables, is a good antioxidant. This study was designed to evaluate the possible protective effects of kaempferol on submandibular glands (SMGs) of rats exposed to fractionated gamma irradiation.

MATERIALS AND METHODS

Twenty-four male adult Wistar albino rats were included in this study and assigned to three groups (n = 8). Rats in group K received kaempferol orally in five doses at a dose of 10 mg/kg/2 days for 10 days. Meanwhile, rats in group R were subjected to fractionated whole-body gamma irradiation at a dose of 2 Gy/5 days/week for 2 weeks (20 Gy), and the KR group received kaempferol as group K and then was subjected to a fractionated whole-body gamma irradiation as group R. SMG samples were collected on days 1 and 7 after the last radiation session; and processed for histopathological and immunohistochemical investigations.

RESULTS

The SMGs of group R showed focal atrophy and degeneration. Acini showed vacuolization and had pyknotic hyperchromatic nuclei. Striated ducts degenerated, shrunken, and were surrounded by empty spaces. The percentage of areas covered by cyclooxygenase-2 (COX-2) significantly increased, whereas the percentage of areas covered by proliferating cell nuclear antigen (PCNA) significantly decreased compared with those in group K. Cotreatment with kaempferol (group KR) partially preserved normal gland architecture where acinar vacuolation and degeneration were almost absent; however, some ducts degenerated. A significant decrease in the percentage of areas covered by COX-2 and a significant increase in the percentage of areas covered by PCNA were observed compared with those in group R.

CONCLUSIONS

Kaempferol has a possible radioprotective effect on the SMGs of rats exposed to fractionated gamma irradiation.

Longitudinal Multiparametric MRI Assessment of Irradiated Salivary Gland in a Rat Model: Correlated With Histological Findings

BACKGROUND

Several magnetic resonance imaging (MRI) sequences have been applied to assess injured glands but without histological validation.

PURPOSE

To evaluate longitudinal changes in multiparametric MRI (mp-MRI) of irradiated salivary glands in a rat model and investigate correlations between mp-MRI and histological findings.

STUDY TYPE

Prospective.

ANIMAL MODEL

Submandibular glands of 36 rats were radiated using a single dose of 15 Gy X-ray (irradiation [IR] group), and 6 other rats were enrolled into sham-IR group. mp-MRI were scanned 1 day after sham-IR (n = 6), or 1, 2, 4, 8, 12, 24 weeks after IR (n = 36, 6 per subgroup).

FIELD STRENGTH/SEQUENCE

A 3.0-T/Diffusion-weighted imaging (DWI), readout-segmented echo-planar imaging (EPI) sequence; intravoxel incoherent motion DWI, single-shot EPI sequence; T1 mapping, dual-flip-angle gradient-echo sequence with volumetric interpolated breath-hold examination; T2 mapping, turbo spin-echo sequence.

ASSESSMENT

Parameters including apparent diffusion coefficient (ADC), pure diffusion coefficient (D), pseudo-diffusion coefficient (D^* ), perfusion fraction (f), T1 and T2 value were obtained. Histological examinations, including hematoxylin and eosin staining (for acinar cell fraction [AC%] detection), Masson's trichrome staining (for degree of fibrosis [F%] determination) and CD34-immunohistochemical staining (for microvessel density [MVD] calculation), were performed at corresponding time points.

STATISTICAL TESTS

One-way analysis of variance was used to compare the mp-MRI and histological parameters among different groups. Spearman correlation analysis was applied to determine the correlation between mp-MRI and histological parameters. Two-sided P ≤ 0.05 was considered statistically significant.

RESULTS

Changes of mp-MRI parameters (ADC, D, D^* , f, T1, T2) and histological results (AC%, F%, MVD) among the seven groups were all significant. ADC, D, and T2 values negatively correlated with AC% (ADC, r = -0.728; D, r = -0.773; T2, r = -0.600), f positively correlated with MVD (r = 0.496), and T1 values positively correlated with F% (r = 0.714). DATA CONCLUSION: mp-MRI might be able to noninvasively and quantitatively evaluate the dynamic pathological changes within the irradiated salivary glands.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 2.

Regional Responses in Radiation-Induced Normal Tissue Damage

Normal tissue side effects remain a major concern in radiotherapy. The improved precision of radiation dose delivery of recent technological developments in radiotherapy has the potential to reduce the radiation dose to organ regions that contribute the most to the development of side effects. This review discusses the contribution of regional variation in radiation responses in several organs. In the brain, various regions were found to contribute to radiation-induced neurocognitive dysfunction. In the parotid gland, the region containing the major ducts was found to be critical in hyposalivation. The heart and lung were each found to exhibit regional responses while also mutually affecting each other's response to radiation. Sub-structures critical for the development of side effects were identified in the pancreas and bladder. The presence of these regional responses is based on a non-uniform distribution of target cells or sub-structures critical for organ function. These characteristics are common to most organs in the body and we therefore hypothesize that regional responses in radiation-induced normal tissue damage may be a shared occurrence. Further investigations will offer new opportunities to reduce normal tissue side effects of radiotherapy using modern and high-precision technologies.

Short-term and long-term unstimulated saliva flow following unilateral vs bilateral radiotherapy for oropharyngeal carcinoma

BACKGROUND

We aimed to compare unstimulated saliva flow using 3-minute modified Schirmer test (MST) following bilateral vs unilateral radiotherapy (RT) in oropharyngeal carcinoma (OPC).

METHODS

We reviewed OPC patients treated with definitive intensity-modulated radiation therapy (IMRT) between 2011 and 2017. MST was measured at baseline, 1-/6-/12-/24-month post-RT. MST values were compared between bilateral-RT vs unilateral-RT groups. Multivariable logistic regression analysis (MVA) identified predictors of hyposalivation (MST < 25 mm).

RESULTS

Total 498 bilateral-RT and 36 unilateral-RT patients were eligible. The MST values at 1-/6-/12-/24-month post-RT were all significantly reduced from baseline for the entire cohort. Baseline unilateral-RT and bilateral-RT MST values (in mm) were similar (P = .2), but much higher for unilateral-RT 1-month (mean: 19.1 vs 13.0, P = .03), 6-month (20.5 vs 9.3, P < .001), 12-month (20.1 vs 11.9, P < .01), and 24-month post-RT (22.2 vs 13.9, P = .04). MVA confirmed that unilateral RT reduced the likelihood of hyposalivation vs bilateral RT (OR 2.36, P = .006).

CONCLUSION

Unilateral RT reduces unstimulated salivary flow in OPC patients.

Salivary Gland Hypofunction and Xerostomia in Head and Neck Radiation Patients

BACKGROUND

The most manifest long-term consequences of radiation therapy in the head and neck cancer patient are salivary gland hypofunction and a sensation of oral dryness (xerostomia).

METHODS

This critical review addresses the consequences of radiation injury to salivary gland tissue, the clinical management of salivary gland hypofunction and xerostomia, and current and potential strategies to prevent or reduce radiation injury to salivary gland tissue or restore the function of radiation-injured salivary gland tissue.

RESULTS

Salivary gland hypofunction and xerostomia have severe implications for oral functioning, maintenance of oral and general health, and quality of life. Significant progress has been made to spare salivary gland function chiefly due to advances in radiation techniques. Other strategies have also been developed, e.g., radioprotectors, identification and preservation/expansion of salivary stem cells by stimulation with cholinergic muscarinic agonists, and application of new lubricating or stimulatory agents, surgical transfer of submandibular glands, and acupuncture.

CONCLUSION

Many advances to manage salivary gland hypofunction and xerostomia induced by radiation therapy still only offer partial protection since they are often of short duration, lack the protective effects of saliva, or potentially have significant adverse effects. Intensity-modulated radiation therapy (IMRT), and its next step, proton therapy, have the greatest potential as a management strategy for permanently preserving salivary gland function in head and neck cancer patients.Presently, gene transfer to supplement fluid formation and stem cell transfer to increase the regenerative potential in radiation-damaged salivary glands are promising approaches for regaining function and/or regeneration of radiation-damaged salivary gland tissue.

The Wnt-Driven Mll1 Epigenome Regulates Salivary Gland and Head and Neck Cancer

We identified a regulatory system that acts downstream of Wnt/β-catenin signaling in salivary gland and head and neck carcinomas. We show in a mouse tumor model of K14-Cre-induced Wnt/β-catenin gain-of-function and Bmpr1a loss-of-function mutations that tumor-propagating cells exhibit increased Mll1 activity and genome-wide increased H3K4 tri-methylation at promoters. Null mutations of Mll1 in tumor mice and in xenotransplanted human head and neck tumors resulted in loss of self-renewal of tumor-propagating cells and in block of tumor formation but did not alter normal tissue homeostasis. CRISPR/Cas9 mutagenesis and pharmacological interference of Mll1 at sequences that inhibit essential protein-protein interactions or the SET enzyme active site also blocked the self-renewal of mouse and human tumor-propagating cells. Our work provides strong genetic evidence for a crucial role of Mll1 in solid tumors. Moreover, inhibitors targeting specific Mll1 interactions might offer additional directions for therapies to treat these aggressive tumors.

Limited Regeneration of Adult Salivary Glands after Severe Injury Involves Cellular Plasticity

In the adult salivary glands, the origin of replacement and regenerated acinar cells remains unclear. Although many reports describe the identification of stem cells in adult salivary glands, we have shown that differentiated acinar cells can be maintained and regenerated through self-duplication. Here, we have used genetic mouse models to further investigate acinar cell replacement and regeneration during homeostasis and after injury. Under normal conditions or after duct ligation, replacement of duct and acinar cells occurs through lineage-restricted progenitors. In contrast, after irradiation, in vivo lineage tracing shows that acinar, as well as duct, cells contribute to acinar cell regeneration, revealing that cellular plasticity is involved in salivary gland repair. Our results also indicate that even after radiation damage, several cell populations have regenerative potential for restoring salivary gland function.

Multifactorial Contribution of Notch Signaling in Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) defines a group of solid tumors originating from the mucosa of the upper aerodigestive tract, pharynx, larynx, mouth, and nasal cavity. It has a metastatic evolution and poor prognosis and is the sixth most common cancer in the world, with 600,000 new cases reported every year. HNSCC heterogeneity and complexity is reflected in a multistep progression, involving crosstalk between several molecular pathways. The Notch pathway is associated with major events supporting cancerogenic evolution: cell proliferation, self-renewal, angiogenesis, and preservation of a pro-oncogenic microenvironment. Additionally, Notch is pivotal in tumor development and plays a dual role acting as both oncogene and tumor suppressor. In this review, we summarize the role of the Notch pathway in HNSCC, with a special focus on its compelling role in major events of tumor initiation and growth.

Machine Learning Methods Uncover Radiomorphologic Dose Patterns in Salivary Glands that Predict Xerostomia in Patients with Head and Neck Cancer

Purpose

Patients with head-and-neck cancer (HNC) may experience xerostomia after radiation therapy (RT), which leads to compromised quality of life. The purpose of this study is to explore how the spatial pattern of radiation dose (radiomorphology) in the major salivary glands influences xerostomia in patients with HNC.

Methods and materials

A data-driven approach using spatially explicit dosimetric predictors, voxel dose (ie, actual radiation dose in voxels in parotid glands [PG] and submandibular glands [SMG]) was used to predict whether patients would develop xerostomia 3 months after RT. Using planned radiation dose data and other nondose covariates including baseline xerostomia grade of 427 patients with HNC in our database, the machine learning methods were used to investigate the influence of dose patterns across subvolumes in PG and SMG on xerostomia.

Results

Of the 3 supervised learning methods studied, ridge logistic regression yielded the best predictive performance. Ridge logistic regression was also preferred to evaluate the influence pattern of highly correlated dose on xerostomia, which showed a discriminative pattern of influence of doses in the PG and SMG on xerostomia. Moreover, the superior–anterior portion of the contralateral PG and medial portion of the ipsilateral PG were determined to be the most influential regions regarding dose effect on xerostomia. The area under the receiver operating characteristic curve from a 10-fold cross-validation was 0.70 ± 0.04.

Conclusions

Radiomorphology, combined with machine learning methods, is able to suggest patterns of dose in PG and SMG that are the most influential on xerostomia. The influence pattern identified by this data-driven approach and machine learning methods may help improve RT treatment planning and reduce xerostomia after treatment.

Early evaluation of radiation-induced parotid damage in patients with nasopharyngeal carcinoma by T2 mapping and mDIXON Quant imaging: initial findings

BACKGROUND

Radiation-induced parotid damage is a common complication in patients with nasopharyngeal carcinoma (NPC) treated with radiotherapy to head and neck region, which severely reduce the life quality of those patients. The aim of this study was to early evaluate the changes of irradiated parotid glands with T2 mapping and mDIXON Quant imaging.

METHODS

Forty-one patients with NPC underwent conventional magnetic resonance imaging for nasopharynx and neck, and T2 mapping and mDIXON Quant imaging for bilateral parotid glands within 2 weeks before radiotherapy (pre-RT), 5 weeks after the beginning of radiotherapy (mid-RT), and 4 weeks after radiotherapy (post-RT). Parotid volume, T2 values, fat fraction (FF) values, and mean radiation dose were recorded and analyzed.

RESULTS

From pre-RT to mid-RT, parotid volume decreased (atrophy rate, 27.0 ± 11.5%), while parotid T2 and FF values increased (change rate, 6.0 ± 6.2% for T2 value and 9.1 ± 9.9% for FF value) significantly. From mid-RT to post-RT, parotid T2 value continuously increased (change rate, 4.6 ± 7.7%), but parotid FF value decreased (change rate, - 9.9 ± 18.2%) significantly. Change rate of parotid T2 value significantly correlated with parotid atrophy rate from pre-RT to post-RT (r = 0.313, P = 0.027). Multiple linear regression analysis showed that parotid T2 value (standardized coefficient [SC] = - 0.259, P = 0.001) and FF value (SC = - 0.320, P = 0.014) negatively correlated with parotid volume, while parotid T2 value positively correlated with MR scan time point (SC = 0.476, P = 0.001) significantly. Parotid T2 and FF values showed excellent reproducibility (intraclass correlation coefficient, 0.935-0.992).

CONCLUSIONS

T2 mapping and mDIXON Quant imaging is useful for noninvasive evaluation of radiation-induced parotid damage.

Early evaluation of radiation-induced parotid damage with diffusion kurtosis imaging: a preliminary study

Background Radiation-induced parotid gland damage is a common complication of radiotherapy (RT) in patients with nasopharyngeal carcinoma (NPC), which always causes xerostomia, dysphagia, dental caries, and even sleep disorders. Early evaluation of radiation-induced parotid damage is required to facilitate early interventions. Purpose To early-evaluate radiation-induced parotid damage using diffusion kurtosis imaging (DKI) in patients with NPC undergoing RT. Material and Methods Thirty-two patients with NPC underwent DKI for parotid glands pre-RT (two weeks before RT), mid-RT (five weeks after RT began), and post-RT (four weeks after RT). Parotid volume, apparent diffusion coefficient (ADC), corrected diffusion coefficient (D), excess diffusion kurtosis coefficient (K) values, mean radiation dose, and xerostomia degrees were recorded and analyzed. Results During RT, parotid ADC (change rates = 41.3 ± 25.2% at mid-RT, 70.8 ± 34.3% at post-RT) and D (change rates = 41.9 ± 25.2% at mid-RT, 63.2 ± 30.2% at post-RT) increased, while parotid volume (atrophy rates = 31.5 ± 7.9% at mid-RT, 30.6 ± 10.3% at post-RT) and K (change rates = -17.8 ± 11.0% at mid-RT, -29.8 ± 9.0% at post-RT) decreased significantly (all P < 0.001). At post-RT, the change rate of parotid D values was significantly positively correlated with the mean radiation dose ( r = 0.455, P < 0.001). Parotid ADC, D, and K values showed excellent intra- and inter-observer agreement (intraclass correlation coefficient = 0.946-0.985). Conclusion Radiation-induced parotid damage in patients with NPC undergoing RT could be effectively evaluated by DKI in the early stage.

Apparent diffusion coefficient histogram analysis can evaluate radiation-induced parotid damage and predict late xerostomia degree in nasopharyngeal carcinoma

We investigated apparent diffusion coefficient (ADC) histogram analysis to evaluate radiation-induced parotid damage and predict xerostomia degrees in nasopharyngeal carcinoma (NPC) patients receiving radiotherapy. The imaging of bilateral parotid glands in NPC patients was conducted 2 weeks before radiotherapy (time point 1), one month after radiotherapy (time point 2), and four months after radiotherapy (time point 3). From time point 1 to 2, parotid volume, skewness, and kurtosis decreased (P < 0.001, = 0.001, and < 0.001, respectively), but all other ADC histogram parameters increased (all P < 0.001, except P = 0.006 for standard deviation [SD]). From time point 2 to 3, parotid volume continued to decrease (P = 0.022), and SD, 75th and 90th percentiles continued to increase (P = 0.024, 0.010, and 0.006, respectively). Early change rates of parotid ADCmean, ADCmin, kurtosis, and 25th, 50th, 75th, 90th percentiles (from time point 1 to 2) correlated with late parotid atrophy rate (from time point 1 to 3) (all P < 0.05). Multiple linear regression analysis revealed correlations among parotid volume, time point, and ADC histogram parameters. Early mean change rates for bilateral parotid SD and ADCmax could predict late xerostomia degrees at seven months after radiotherapy (three months after time point 3) with AUC of 0.781 and 0.818 (P = 0.014, 0.005, respectively). ADC histogram parameters were reproducible (intraclass correlation coefficient, 0.830 - 0.999). ADC histogram analysis could be used to evaluate radiation-induced parotid damage noninvasively, and predict late xerostomia degrees of NPC patients treated with radiotherapy.

Radiation therapy and serum salivary amylase in head and neck cancer

Radiation therapy (RT) is a valid treatment option for head and neck cancer (HNC). The risk of RT-induced toxicities is significant, especially due to extended treatment fields. The raise in amylase activity is strictly dependent on the volume of salivary glands included in the irradiated target volume and it is firmly related to the dose. The aim of this review is to report the effects on salivary amylase activity after radiation exposure of salivary glands, in patients with HNC.

Acute Radiation-Induced Changes in Sprague-Dawley Rat Submandibular Glands: A Histomorphometric Analysis

Background

Radiation-induced xerostomia is a distressing clinical condition that starts appearing from the initial stages of radiotherapy in head and neck cancer patients. Though submandibular glands contribute to maximum of the "resting salivary" secretions, most of the acute xerostomia experiments so far reported have been on animal parotid glands. Therefore, we assessed and quantified the histologic changes in submandibular glands of Sprague-Dawley (SD) rats using histomorphometry, 24 hours after radiation.

Methods

Three SD rats were given single-dose radiation of 15 Gray from a gamma cobalt-60 irradiator. Same number of non-radiated animals was the controls. Animals were sacrificed at 24 hours followed by histopathology and histomorphometry of submandibular glands, where the mean values were analyzed by Student's t-test.

Results

Irradiated submandibular glands showed highly significant reduction in acinar area (53%: 77.16±5.05% to 36.55±4.90%) and acinar size (87%: 3,447.53 ± 461.03 mm² to 428.25 ± 75.22 mm²) with concomitant increase in inter-acinar space (3.46 ± 0.67 mm to 10.08 ± 0.60 mm). Acini nuclei displayed anisonucleosis, poikilonucleosis and pyknosis. "Serous acini" had marked morphologic changes, with fluid accumulation between cells, generalized cytoplasmic vacuolation and vascular congestion, while "mucous acini" largely retained cell architecture. Similarly, ductal cells and nuclei also did not show apparent differences. This demonstrated radiosensitivity variations among different submandibular gland cell types.

Conclusion

Evaluation of acute submandibular acinar cell dysfunctions has helped in quantifying the histologic elements, which mainly contribute to the resting salivary secretions. Findings would aid in future research of radioprotector drugs, salivary glandular regeneration modalities and in devising prudent radiotherapy protocols to address radiation-induced xerostomia.

Sparing the region of the salivary gland containing stem cells preserves saliva production after radiotherapy for head and neck cancer

Each year, 500,000 patients are treated with radiotherapy for head and neck cancer, resulting in relatively high survival rates. However, in 40% of patients, quality of life is severely compromised because of radiation-induced impairment of salivary gland function and consequent xerostomia (dry mouth). New radiation treatment technologies enable sparing of parts of the salivary glands. We have determined the parts of the major salivary gland, the parotid gland, that need to be spared to ensure that the gland continues to produce saliva after irradiation treatment. In mice, rats, and humans, we showed that stem and progenitor cells reside in the region of the parotid gland containing the major ducts. We demonstrated in rats that inclusion of the ducts in the radiation field led to loss of regenerative capacity, resulting in long-term gland dysfunction with reduced saliva production. Then we showed in a cohort of patients with head and neck cancer that the radiation dose to the region of the salivary gland containing the stem/progenitor cells predicted the function of the salivary glands one year after radiotherapy. Finally, we showed that this region of the salivary gland could be spared during radiotherapy, thus reducing the risk of post-radiotherapy xerostomia.

A Nomogram to predict parotid gland overdose in head and neck IMRT

Purposes

To generate a nomogram to predict parotid gland (PG) overdose and to quantify the dosimetric benefit of weekly replanning based on its findings, in the context of intensity-modulated radiotherapy (IMRT) for locally-advanced head and neck carcinoma (LAHNC).

Material and methods

Twenty LAHNC patients treated with radical IMRT underwent weekly computed tomography (CT) scans during IMRT. The cumulated PG dose was estimated by elastic registration. Early predictors of PG overdose (cumulated minus planned doses) were identified, enabling a nomogram to be generated from a linear regression model. Its performance was evaluated using a leave-one-out method. The benefit of weekly replanning was then estimated for the nomogram-identified PG overdose patients.

Results

Clinical target volume 70 (CTV70) and the mean PG dose calculated from the planning and first weekly CTs were early predictors of PG overdose, enabling a nomogram to be generated. A mean PG overdose of 2.5Gy was calculated for 16 patients, 14 identified by the nomogram. All patients with PG overdoses >1.5Gy were identified. Compared to the cumulated delivered dose, weekly replanning of these 14 targeted patients enabled a 3.3Gy decrease in the mean PG dose.

Conclusion

Based on the planning and first week CTs, our nomogram allowed the identification of all patients with PG overdoses >2.5Gy to be identified, who then benefitted from a final 4Gy decrease in mean PG overdose by means of weekly replanning.

Individualized radiotherapy by combining high-end irradiation and magnetic resonance imaging

Image-guided radiotherapy (IGRT) has been integrated into daily clinical routine and can today be considered the standard especially with high-dose radiotherapy. Currently imaging is based on MV- or kV-CT, which has clear limitations especially in soft-tissue contrast. Thus, combination of magnetic resonance (MR) imaging and high-end radiotherapy opens a new horizon. The intricate technical properties of MR imagers pose a challenge to technology when combined with radiation technology. Several solutions that are almost ready for routine clinical application have been developed. The clinical questions include dose-escalation strategies, monitoring of changes during treatment as well as imaging without additional radiation exposure during treatment.

A split-parotid delineation approach for dose optimization in volumetric modulated arc therapy for nasopharyngeal carcinoma patients with parapharyngeal space invasion and level IIa cervical lymph node involvements

OBJECTIVE

This study evaluated the potential benefit of a split-parotid delineation approach on the parotid gland in the treatment planning of patients with nasopharyngeal carcinoma (NPC).

METHODS

50 patients with NPC with parapharyngeal space (PPS) and/or level IIa cervical node involvements were divided into three groups: PPS only, level IIa cervical node only and both. Two volumetric-modulated arc therapy plans were computed. The first plan (control) was generated based on the routine treatment-planning protocol, while the second plan (test) was computed with the split-parotid delineation approach, in which a line through the anterolateral margin of the retromandibular vein was created that divided the parotid gland into anterolateral and posteromedial subsegments. For the test plan, the anterolateral subsegment was prescribed, with a dose constraint of 25 Gy in the plan optimization. Dosimetric data of the parotid gland, target volumes and selected organs at risk (OARs) were compared between the control and test plans.

RESULTS

The mean dose to the anterolateral subsegment of the parotid gland in all three groups was kept below 25 Gy. The test plan demonstrated significantly lower mean parotid dose than the control plan in the entire gland and the anterolateral subsegment in all three groups. The difference was the greatest in Group 3.

CONCLUSION

The split-parotid delineation approach significantly lowered the mean dose to the anterolateral subsegment and overall gland without greatly compromising the doses to target volumes and other OARs. The effect was more obvious for both PPS and level IIa cervical node involvements than for either of them alone.

ADVANCES IN KNOWLEDGE

It is the first article based on the assumption that parotid gland stem cells are situated at the anterolateral segment of the gland, and applied the split-parotid delineation approach to the parotid gland in the treatment planning of patients with NPC with PPS and level IIa cervical node involvements, so that the function of the post-radiotherapy parotid gland might be better preserved.

Emerging Treatment Paradigms in Radiation Oncology

Rapid advancements in radiotherapy and molecularly targeted therapies have resulted in the development of potential paradigm-shifting use of radiotherapy in the treatment of cancer. In this review, we discuss some of the most promising therapeutic approaches in the field of radiation oncology. These strategies include the use of highly targeted stereotactic radiotherapy and particle therapy as well as combining radiotherapy with agents that modulate the DNA damage response, augment the immune response, or protect normal tissues.

Impact of head and neck cancer adaptive radiotherapy to spare the parotid glands and decrease the risk of xerostomia

BACKGROUND

Large anatomical variations occur during the course of intensity-modulated radiation therapy (IMRT) for locally advanced head and neck cancer (LAHNC). The risks are therefore a parotid glands (PG) overdose and a xerostomia increase. The purposes of the study were to estimate: - the PG overdose and the xerostomia risk increase during a "standard" IMRT (IMRTstd); - the benefits of an adaptive IMRT (ART) with weekly replanning to spare the PGs and limit the risk of xerostomia.

MATERIAL AND METHODS

Fifteen patients received radical IMRT (70 Gy) for LAHNC. Weekly CTs were used to estimate the dose distributions delivered during the treatment, corresponding either to the initial planning (IMRTstd) or to weekly replanning (ART). PGs dose were recalculated at the fraction, from the weekly CTs. PG cumulated doses were then estimated using deformable image registration. The following PG doses were compared: pre-treatment planned dose, per-treatment IMRTstd and ART. The corresponding estimated risks of xerostomia were also compared. Correlations between anatomical markers and dose differences were searched.

RESULTS

Compared to the initial planning, a PG overdose was observed during IMRTstd for 59% of the PGs, with an average increase of 3.7 Gy (10.0 Gy maximum) for the mean dose, and of 8.2% (23.9% maximum) for the risk of xerostomia. Compared to the initial planning, weekly replanning reduced the PG mean dose for all the patients (p<0.05). In the overirradiated PG group, weekly replanning reduced the mean dose by 5.1 Gy (12.2 Gy maximum) and the absolute risk of xerostomia by 11% (p<0.01) (30% maximum). The PG overdose and the dosimetric benefit of replanning increased with the tumor shrinkage and the neck thickness reduction (p<0.001).

CONCLUSION

During the course of LAHNC IMRT, around 60% of the PGs are overdosed of 4 Gy. Weekly replanning decreased the PG mean dose by 5 Gy, and therefore by 11% the xerostomia risk.

Treatment improvement and better patient care: which is the most important one in oral cavity cancer?

Due to substantial improvement in diagnosis and treatment of oral cavity cancer, a better understanding of the patient care needs to be revised. We reviewed literature related to OCC and discussed current general management approaches and related long-term radiation toxicities to emphasize the multidisciplinary team involvement. New technical modalities and patient quality of life parameters should be an integral and paramount state in the clinical evaluation to significantly contribute to reduce secondary side effects.

Diagnostic accuracy of ultrasonic histogram features to evaluate radiation toxicity of the parotid glands: a clinical study of xerostomia following head-and-neck cancer radiotherapy

RATIONALE AND OBJECTIVES

To investigate the diagnostic accuracy of ultrasound histogram features in the quantitative assessment of radiation-induced parotid gland injury and to identify potential imaging biomarkers for radiation-induced xerostomia (dry mouth)-the most common and debilitating side effect after head-and-neck radiotherapy (RT).

MATERIALS AND METHODS

Thirty-four patients, who have developed xerostomia after RT for head-and-neck cancer, were enrolled. Radiation-induced xerostomia was defined by the Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer morbidity scale. Ultrasound scans were performed on each patient's parotids bilaterally. The 34 patients were stratified into the acute-toxicity groups (16 patients, ≤ 3 months after treatment) and the late-toxicity group (18 patients, > 3 months after treatment). A separate control group of 13 healthy volunteers underwent similar ultrasound scans of their parotid glands. Six sonographic features were derived from the echo-intensity histograms to assess acute and late toxicity of the parotid glands. The quantitative assessments were compared to a radiologist's clinical evaluations. The diagnostic accuracy of these ultrasonic histogram features was evaluated with the receiver operating characteristic (ROC) curve.

RESULTS

With an area under the ROC curve greater than 0.90, several histogram features demonstrated excellent diagnostic accuracy for evaluation of acute and late toxicity of parotid glands. Significant differences (P < .05) in all six sonographic features were demonstrated between the control, acute-toxicity, and late-toxicity groups. However, subjective radiologic evaluation cannot distinguish between acute and late toxicity of parotid glands.

CONCLUSIONS

We demonstrated that ultrasound histogram features could be used to measure acute and late toxicity of the parotid glands after head-and-neck cancer RT, which may be developed into a low-cost imaging method for xerostomia monitoring and assessment.

Ultrasonic Nakagami-parameter characterization of parotid-gland injury following head-and-neck radiotherapy: a feasibility study of late toxicity

PURPOSE

The study aims to investigate whether Nakagami parameters--estimated from the statistical distribution of the backscattered ultrasound radio-frequency (RF) signals--could provide a means for quantitative characterization of parotid-gland injury resulting from head-and-neck radiotherapy.

METHODS

A preliminary clinical study was conducted with 12 postradiotherapy patients and 12 healthy volunteers. Each participant underwent one ultrasound study in which ultrasound scans were performed in the longitudinal, i.e., vertical orientation on the bilateral parotids. For the 12 patients, the mean radiation dose to the parotid glands was 37.7 ± 9.5 Gy, and the mean follow-up time was 16.3 ± 4.8 months. All enrolled patients experienced grade 1 or 2 late salivary-gland toxicity (RTOG/EORTC morbidity scale). The normal parotid glands served as the control group. The Nakagami-scaling and Nakagami-shape parameters were computed from the RF data to quantify radiation-induced parotid-gland changes.

RESULTS

Significant differences in Nakagami parameters were observed between the normal and postradiotherapy parotid glands. Compared with the control group, the Nakagami-scaling parameter of the postradiotherapy group decreased by 25.8% (p < 0.001), and the Nakagami-shape parameter decreased by 31.3% (p < 0.001). The area under the receiver operating characteristic curve was 0.85 for the Nakagami-scaling parameter and was 0.95 for the Nakagami-shape parameter, which further demonstrated the diagnostic efficiency of the Nakagami parameters.

CONCLUSIONS

Nakagami parameters could be used to quantitatively measure parotid-gland injury following head-and-neck radiotherapy. Moreover, the clinical feasibility was demonstrated and this study provides meaningful preliminary data for future clinical investigation.

Adult stem cells and tissue engineering strategies for salivary gland regeneration: a review

Saliva is an important compound produced by the salivary glands and performs numerous functions. Hyposalivation (dry mouth syndrome) is a deleterious condition often resulting from radiotherapy for patients with head and neck cancer, Sjogren's Syndrome, or as a side effect of certain medications. Hyposalivation negatively affects speaking, mastication, and swallowing in afflicted patients, greatly reducing their quality of life. Current treatments for this pathology include modifying lifestyle, synthetic saliva supplementation, and the utilization of salivary gland stimulants and sialagogues. However, many of these treatments do not address the underlying issues and others are pervaded by numerous side effects. In order to address the shortcomings related to current treatment modalities, many groups have diverted their attention to utilizing tissue engineering and regenerative medicine approaches. Tissue engineering is defined as the application of life sciences and materials engineering toward the development of tissue substitutes that are capable of mimicking the structure and function of their natural analogues within the body. The general underlying strategy behind the development of tissue engineered organ substitutes is the utilization of a combination of cells, biomaterials, and biochemical cues intended to recreate the natural organ environment. The purpose of this review is to highlight current bioengineering approaches for salivary gland tissue engineering and the adult stem cell sources used for this purpose. Additionally, future considerations in regard to salivary gland tissue engineering strategies are discussed.

Biological considerations when comparing proton therapy with photon therapy

Owing to the limited availability of data on the outcome of proton therapy, treatments are generally optimized based on broadly available data on photon-based treatments. However, the microscopic pattern of energy deposition of protons differs from that of photons, leading to a different biological effect. Consequently, proton therapy needs a correction factor (relative biological effectiveness) to relate proton doses to photon doses, and currently, a generic value is used. Moreover, the macroscopic distribution of dose in proton therapy differs compared with photon treatments. Although this may offer new opportunities to reduce dose to normal tissues, it raises the question whether data obtained from photon-based treatments offer sufficient information on dose-volume effects to optimally use unique features of protons. In addition, there are potential differences in late effects due to low doses of secondary radiation outside the volume irradiated by the primary beam. This article discusses the controversies associated with these 3 issues when comparing proton and photon therapy.

A pragmatic contouring guideline for salivary gland structures in head and neck radiation oncology: the MOIST target

OBJECTIVES

One of the main normal tissue toxicities in head and neck radiation oncology is xerostomia. In several studies, reduced radiation dose to the salivary glands has been shown to diminish the effects of gland dysfunction. However, no clear guidelines exist to define the anatomic location of the involved glands on cross-sectional imaging in a pragmatic manner. This study presents an anatomic, computed tomography (CT)-based definition of the major and minor salivary glands.

METHODS

On the basis of information from normal structure anatomy, the location of major and minor salivary glands was identified and translated into a cross-sectional CT-based description of the salivary glands.

RESULTS

The major salivary glands include the parotids and submandibular glands. The minor salivary glands are presented as a part of a surrogate structure (the Minor Oral Including Sublingual Salivary Tissue target), including the minor glands located in the oral mucosa of the tongue, hard and soft palate, buccal mucosa, and inner surface of the lips.

CONCLUSIONS

Clinical implementation of CT-based delineations of the salivary glands according to the proposed guideline should reduce interobserver variability. This may lead to an improved understanding of the relationship between radiation dose and volume and effects on salivary function.

Ultrasound GLCM texture analysis of radiation-induced parotid-gland injury in head-and-neck cancer radiotherapy: an in vivo study of late toxicity

PURPOSE

Xerostomia (dry mouth), secondary to irradiation of the parotid glands, is one of the most common side effects of head-and-neck cancer radiotherapy. Diagnostic tools able to accurately and efficiently measure parotid gland injury have yet to be introduced into the clinic. This study's purpose is to investigate sonographic textural features as potential imaging signatures for quantitative assessment of parotid-gland injury after head-and-neck radiotherapy.

METHODS

The authors have investigated a series of sonographic features obtained from the gray level co-occurrence matrix (GLCM) - a second order statistical method of texture analysis. These GLCM textural features were selected based on empirical observations that the normal parotid gland exhibits homogeneous echotexture, whereas the postradiotherapy parotid gland often exhibits heterogeneous echotexture. We employed eight sonographic features: (1) angular second moment (ASM), (2) inverse differential moment (IDM), (3) contrast, (4) variance, (5) correlation, (6) entropy, (7) cluster shade, and (8) cluster prominence. Altogether, sonographic properties of the parotid glands were quantified by their degrees of homogeneity (ASM and IDM), heterogeneity (contrast and variance), smoothness (correlation), randomness (entropy), and symmetry (cluster shade and prominence). The sonographic features were tested in a pilot study of 12 postradiotherapy patients and 7 healthy volunteers. The mean follow-up time for the postradiotherapy patients was 17.2 months (range: 12.1-23.9 months) and the mean radiation dose to the parotid glands was 32.3 Gy (range: 11.0-63.4 Gy). Each participant underwent one ultrasound study in which longitudinal (vertical) ultrasound scans were performed on the bilateral parotids - a total of 24 postirradiation and 14 normal parotid glands were examined. The 14 normal parotid glands served as the control group. A radiologist contoured the parotid glands on the B-mode images and the sonographic features were computed from the contoured region-of-interest.

RESULTS

The authors observed significant differences (p < 0.05) in all sonographic features between the normal and postradiotherapy parotid glands. The sonographic findings were consistent with the clinical observations of the ultrasound images: normal parotid glands exhibited homogeneous texture, while the postradiotherapy parotid glands exhibited heterogeneous echotexture (e.g., hyperechoic lines and spots), which likely represents fibrosis.

CONCLUSIONS

The authors have demonstrated the feasibility of ultrasonic texture evaluation of parotid glands; and the sonographic features may serve as imaging signatures to assess radiation-induced parotid injury.

Ultrasound histogram assessment of parotid gland injury following head-and-neck radiotherapy: a feasibility study

Xerostomia (dry mouth), resulting from radiation damage to the parotid glands, is one of the most common and distressing side effects of head-and-neck cancer radiotherapy. A noninvasive, objective imaging method to assess parotid injury is lacking, but much needed in the clinic. Therefore, we investigated echo histograms to quantitatively evaluate the morphologic and microstructural integrity of the parotid glands. Six sonographic features were derived from the echo-intensity histograms to assess the echogenicity, homogeneity and heterogeneity of the parotid gland: (1) peak intensity value (I(peak)), (2) -3-dB intensity width (W(3-dB)), (3) the low (<50% I(peak)) intensity width (W(low)), (4) the high (>50% I(peak)) intensity width (W(high)), (5) the area of low intensity (A(low)) and (6) the area of high intensity (A(high)). In this pilot study, 12 post-radiotherapy patients and seven healthy volunteers were enrolled. Significant differences (p < 0.05) were observed in four sonographic features between 24 irradiated and 14 normal parotid glands. In summary, we developed a family of sonographic features derived from echo histograms and demonstrated the feasibility of quantitative evaluation of radiation-induced parotid-gland injury.

Metabolic imaging biomarkers of postradiotherapy xerostomia

PURPOSE

Xerostomia is a major complication of head and neck radiotherapy (RT). Available xerostomia measures remain flawed. [(18)F]fluorodeoxyglucose-labeled positron emission tomography-computed tomography (FDG-PET-CT) is routinely used for staging and response assessment of head and neck cancer. We investigated quantitative measurement of parotid gland FDG uptake as a potential biomarker for post-RT xerostomia.

METHODS AND MATERIALS

Ninety-eight locally advanced head and neck cancer patients receiving definitive RT underwent baseline and post-RT FDG-PET-CT on a prospective imaging trial. A separate validation cohort of 14 patients underwent identical imaging while prospectively enrolled in a second trial collecting sialometry and patient-reported outcomes. Radiation dose and pre- and post-RT standard uptake values (SUVs) for all voxels contained within parotid gland ROI were deformably registered.

RESULTS

Average whole-gland or voxel-by-voxel models incorporating parotid D(Met) (defined as the pretreatment parotid SUV weighted by dose) accurately predicted posttreatment changes in parotid FDG uptake (e.g., fractional parotid SUV). Fractional loss of parotid FDG uptake closely paralleled early parotid toxicity defined by posttreatment salivary output (p < 0.01) and Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer xerostomia scores (p < 0.01).

CONCLUSIONS

In this pilot series, loss of parotid FDG uptake was strongly associated with acute clinical post-RT parotid toxicity. D(Met) may potentially be used to guide function-sparing treatment planning. Prospective validation of FDG-PET-CT as a convenient, quantifiable imaging biomarker of parotid function is warranted and ongoing.

Biological mechanisms of normal tissue damage: importance for the design of NTCP models

The normal tissue complication probability (NTCP) models that are currently being proposed for estimation of risk of harm following radiotherapy are mainly based on simplified empirical models, consisting of dose distribution parameters, possibly combined with clinical or other treatment-related factors. These are fitted to data from retrospective or prospective clinical studies. Although these models sometimes provide useful guidance for clinical practice, their predictive power on individuals seems to be limited. This paper examines the radiobiological mechanisms underlying the most important complications induced by radiotherapy, with the aim of identifying the essential parameters and functional relationships needed for effective predictive NTCP models. The clinical features of the complications are identified and reduced as much as possible into component parts. In a second step, experimental and clinical data are considered in order to identify the gross anatomical structures involved, and which dose distributions lead to these complications. Finally, the pathogenic pathways and cellular and more specific anatomical parameters that have to be considered in this pathway are determined. This analysis is carried out for some of the most critical organs and sites in radiotherapy, i.e. spinal cord, lung, rectum, oropharynx and heart. Signs and symptoms of severe late normal tissue complications present a very variable picture in the different organs at risk. Only in rare instances is the entire organ the critical target which elicits the particular complication. Moreover, the biological mechanisms that are involved in the pathogenesis differ between the different complications, even in the same organ. Different mechanisms are likely to be related to different shapes of dose effect relationships and different relationships between dose per fraction, dose rate, and overall treatment time and effects. There is good reason to conclude that each type of late complication after radiotherapy depends on its own specific mechanism which is triggered by the radiation exposure of particular structures or sub-volumes of (or related to) the respective organ at risk. Hence each complication will need the development of an NTCP model designed to accommodate this structure.

Salivary gland sparing in the treatment of head and neck cancer

Radiotherapy is an important component of the multimodality treatment of head and neck cancer. Although an effective treatment for many patients, it can have significant long-term sequelae. In particular, xerostomia - or dry mouth - caused by salivary gland injury is a serious problem suffered by most patients and leads to problems with oral comfort, dental health, speech and swallowing. This article explores the mechanisms behind radiation injury to the major salivary glands, as well as different strategies to minimize and alleviate xerostomia. This includes technical approaches to minimize radiation dose to salivary tissue, such as intensity-modulated radiotherapy and surgical transfer of salivary glands, as well as pharmacologic approaches to stimulate or protect the salivary tissue. The scientific literature will be critically examined to see what works and what strategies have been less effective in attempting to minimize xerostomia in head and neck cancer patients.

Changes of parotid and submandibular glands caused by radiotherapy--an ultrasound evaluation

OBJECTIVE

Radiotherapy may alter the normal morphology of salivary glands located in the radiation field. These changes could be evaluated safely by sonography; however, there have been few studies in this regard. This study is aimed at evaluating the sonographic changes of the parotid and submandibular glands in patients undergoing radiotherapy for head and neck malignancies.

METHODS

20 patients (16 males and 4 females) with head and neck malignancies who had been referred for radiotherapy to the Qaem Hospital in Mashhad, Iran, entered the study. Length, height, depth, echotexture, echogenicity and margins of parotid and submandibular glands were evaluated in three stages (I, before radiotherapy; II, 2 weeks after radiotherapy; and III, 6-7 weeks after radiotherapy) using sonography. Peak systolic velocity (PSV), end diastolic velocity (EDV) and resistive index (RI) were also evaluated by Doppler sonography.

RESULTS

Significant differences in length, height and depth (p = 0.000, p = 0.000, and p = 0.39, respectively) and also echotexture, echogenicity and gland margins (p = 0.000) were observed before and after radiotherapy. Doppler sonography results showed no significant differences regarding PSV, EDV and RI between sonographic stages. Echotexture and echogenicity were the only independent parameters that showed significant differences in sonographic stages I and II (p = 0.000). Length in stage I and II (p = 0.000) and echogenicity in stage III (p = 0.038) were the only parameters that showed significant differences between the two glands.

CONCLUSION

Radiotherapy may change the echotexture, echogenicity and margins of the salivary glands from homogenic to heterogenic, hyperechoic to hypoechoic and regular to irregular, respectively, and may reduce their size.

External validation of three dimensional conformal radiotherapy based NTCP models for patient-rated xerostomia and sticky saliva among patients treated with intensity modulated radiotherapy

PURPOSE

The purpose of this study was to investigate the ability of predictive models for patient-rated xerostomia (XER(6M)) and sticky saliva (STIC(6M)) at 6 months after completion of primary (chemo)radiation developed in head and neck cancer patients treated with 3D-conformal radiotherapy (3D-CRT) to predict outcome in patients treated with intensity modulated radiotherapy (IMRT).

METHODS AND MATERIALS

Recently, we published the results of a prospective study on predictive models for patient-rated xerostomia and sticky saliva in head and neck cancer patients treated with 3D-CRT (3D-CRT based NTCP models). The 3D-CRT based model for XER(6M) consisted of three factors, including the mean parotid dose, age, and baseline xerostomia (none versus a bit). The 3D-CRT based model for STIC(6M) consisted of the mean submandibular dose, age, the mean sublingual dose, and baseline sticky saliva (none versus a bit). In the current study, a population consisting of 162 patients treated with IMRT was used to test the external validity of these 3D-CRT based models. External validity was described by the explained variation (R(2) Nagelkerke) and the Brier score. The discriminative abilities of the models were calculated using the area under the receiver operating curve (AUC) and calibration (i.e. the agreement between predicted and observed outcome) was assessed with the Hosmer-Lemeshow "goodness-of-fit" test.

RESULTS

Overall model performance of the 3D-CRT based predictive models for XER(6M) and STIC(6M) was significantly worse in terms of the Brier score and R(2) Nagelkerke among patients treated with IMRT. Moreover the AUC for both 3D-CRT based models in the IMRT treated patients were markedly lower. The Hosmer-Lemeshow test showed a significant disagreement for both models between predicted risk and observed outcome.

CONCLUSION

3D-CRT based models for patient-rated xerostomia and sticky saliva among head and neck cancer patients treated with primary radiotherapy or chemoradiation turned out to be less valid for patients treated with IMRT. The main message from these findings is that models developed in a population treated with a specific technique cannot be generalised and extrapolated to a population treated with another technique without external validation.

MRI to quantify early radiation-induced changes in the salivary glands

PURPOSE

We investigated radiation-induced changes in the salivary glands, 6 weeks after RT, using MRI.

MATERIALS AND METHODS

Eighteen oropharyngeal cancer patients were treated with salivary gland sparing IMRT. All patients received a 3T MRI exam before and 6 weeks after the end of RT, including a T(1)-weighted (T(1)w), a T(2)-weighted (T(2)w), and a dynamic contrast-enhanced (DCE) MRI. For both time points separately, the parotid and submandibular glands were delineated on the MR images. Differences in median signal intensity and signal variation within the glands were tested for significance. Correlations were studied between the MR changes and the planned RT dose.

RESULTS

The volume of the glands reduced significantly by 25%. The T(1)w signal decreased by 10% and the T(2)w signal increased by 23%. The k(ep) value decreased, while the v(e) increased. A correlation of the changes in T(2)w signal with the mean dose was found in both glands.

CONCLUSIONS

Overall radiation-induced changes and volume loss were observed in the parotid and submandibular gland using MR. The observed differences indicated an increased water content such as found in oedema. The overall changes could be related to the mean dose, with a slightly greater impact in the high dose area.

Introducing the Jacobian-volume-histogram of deforming organs: application to parotid shrinkage evaluation

The Jacobian of the deformation field of elastic registration between images taken during radiotherapy is a measure of inter-fraction local deformation. The histogram of the Jacobian values (Jac) within an organ was introduced (JVH-Jacobian-volume-histogram) and first applied in quantifying parotid shrinkage. MVCTs of 32 patients previously treated with helical tomotherapy for head-neck cancers were collected. Parotid deformation was evaluated through elastic registration between MVCTs taken at the first and last fractions. Jac was calculated for each voxel of all parotids, and integral JVHs were calculated for each parotid; the correlation between the JVH and the planning dose-volume histogram (DVH) was investigated. On average, 82% (±17%) of the voxels shrinks (Jac < 1) and 14% (±17%) shows a local compression >50% (Jac < 0.5). The best correlation between the DVH and the JVH was found between V10 and V15, and Jac < 0.4-0.6 (p < 0.01). The best constraint predicting a higher number of largely compressing voxels (Jac0.5<7.5%, median value) was V15 ≥ 75% (OR: 7.6, p = 0.002). Jac and the JVH are promising tools for scoring/modelling toxicity and for evaluating organ/contour variations with potential applications in adaptive radiotherapy.

New insights in the vascular supply of the human parotid gland - consequences for parotid gland-sparing irradiation

BACKGROUND

Xerostomia is caused by irradiation for head and neck cancer, depending on the dose to the parotid gland. To investigate which part of the parotid gland has to be spared with radiotherapy, detailed information about the vascular supply of the parotid gland is necessary.

METHODS

Arterial vessels of the head of a human cadaver were colored. A 3-dimensional reconstruction of the parotid gland and the arterial vessels was made and analyzed.

RESULTS

Five arterial vessels were responsible for the vascular supply of the parotid gland: the posterior auricular artery, 2 branches so far unnamed, the superficial temporal artery, and the transverse facial artery. All arteries were branches off the external carotid artery, and supplied different parts of the parotid gland.

CONCLUSIONS

This study describes the detailed vascular supply of the human parotid gland. These results may contribute to improve parotid sparing radiotherapy, thus reducing complications such as xerostomia in the future.

Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC): an introduction to the scientific issues

Advances in dose-volume/outcome (or normal tissue complication probability, NTCP) modeling since the seminal Emami paper from 1991 are reviewed. There has been some progress with an increasing number of studies on large patient samples with three-dimensional dosimetry. Nevertheless, NTCP models are not ideal. Issues related to the grading of side effects, selection of appropriate statistical methods, testing of internal and external model validity, and quantification of predictive power and statistical uncertainty, all limit the usefulness of much of the published literature. Synthesis (meta-analysis) of data from multiple studies is often impossible because of suboptimal primary analysis, insufficient reporting and variations in the models and predictors analyzed. Clinical limitations to the current knowledge base include the need for more data on the effect of patient-related cofactors, interactions between dose distribution and cytotoxic or molecular targeted agents, and the effect of dose fractions and overall treatment time in relation to nonuniform dose distributions. Research priorities for the next 5-10 years are proposed.

Sensitivity of salivary glands to radiation: from animal models to therapies

Radiation therapy for head and neck cancer causes significant secondary side-effects in normal salivary glands, resulting in diminished quality of life for these individuals. Salivary glands are exquisitely sensitive to radiation and display acute and chronic responses to radiotherapy. This review will discuss clinical implications of radiosensitivity in normal salivary glands, compare animal models used to investigate radiation-induced salivary gland damage, address therapeutic advances, and project future directions in the field.

Bath and shower effects in the rat parotid gland explain increased relative risk of parotid gland dysfunction after intensity-modulated radiotherapy

PURPOSE

To assess in a rat model whether adding a subtolerance dose in a region adjacent to a high-dose irradiated subvolume of the parotid gland influences its response (bath-and-shower effect).

METHODS AND MATERIALS

Irradiation of the whole, cranial 50%, and/or the caudal 50% of the parotid glands of Wistar rats was performed using 150-MeV protons. To determine suitable (i.e., subtolerance) dose levels for a bath-dose, both whole parotid glands were irradiated with 5 to 25 Gy. Subsequently groups of Wistar rats received 30 Gy to the caudal 50% (shower) and 0 to 10 Gy to the cranial 50% (bath) of both parotid glands. Stimulated saliva flow rate (function) was measured before and up to 240 days after irradiation.

RESULTS

Irradiation of both glands up to a dose of 10 Gy did not result in late loss of function and is thus regarded subtolerance. Addition of a dose bath of 1 to 10 Gy to a high-dose in the caudal 50% of the glands resulted in enhanced function loss.

CONCLUSION

Similar to the spinal cord, the parotid gland demonstrates a bath and shower effect, which may explain the less-than-expected sparing of function after IMRT.