Hypothyroidism following Radiotherapy for Head and Neck Cancer: A Systematic Review of the Literature and Opportunities to Improve the Therapeutic Ratio

(1) Background: Radiotherapy (RT) is a central component for the treatment of many head and neck cancers. In this systematic review of the literature, we aimed to characterize and quantify the published evidence on RT-related hypothyroidism, including estimated incidence, clinical risk factors, and dosimetric parameters that may be used to guide clinical decision making. Furthermore, we aimed to identify potential areas of improvement in the prevention and clinical management of RT-induced hypothyroidism, including the role of modern advanced therapeutic techniques. (2) Methods: We conducted a systemic review of the literature in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. PubMed and Google Scholar were searched to identify original research articles describing the incidence, mechanism, dosimetry, treatment, or prevention of radiation-related hypothyroidism for adults receiving RT for the treatment of head and neck cancers. The snowball method was used to identify additional articles. For identified articles, we tabulated several datapoints, including publication date, patient sample size, estimated hypothyroidism incidence, cancer site/type, follow-up period, radiation modality and technique, use of multimodality therapy, method of thyroid function evaluation, and proposed dosimetric predictors of hypothyroidism. (3) Results: One hundred and eleven articles met inclusion criteria, reflecting a range of head and neck cancer subtypes. There was a large variation in the estimated incidence of RT-related hypothyroidism, with a median estimate of 36% (range 3% to 79%). Reported incidence increased in later publication dates, which was likely related to improved screening and longer follow up. There were a wide variety of predictive metrics used to identify patients at high risk of hypothyroidism, the most common of which were volumetric and mean dosimetrics related to the thyroid gland (Vxx%, Dmean). More recently, there has been increasing evidence to suggest that the thyroid gland volume itself and the volume of the thyroid gland spared from high-dose radiation (VSxx) may better predict thyroid function after RT. There were no identified studies investigating the role of advanced radiotherapeutic techniques such as MRI-guided RT or particle therapy to decrease RT-related hypothyroidism. Conclusions: Hypothyroidism is a common toxicity resulting from therapeutic radiation for head and neck cancer with recent estimates suggesting 40-50% of patients may experience hypothyroidism after treatment. Dosimetric predictive models are increasingly able to accurately identify patients at risk of hypothyroidism, especially those utilizing thyroid VS metrics. Further investigation regarding the potential for advanced radiotherapeutic therapies to decrease RT-induced thyroid dysfunction is needed.

Proton Accelerated Partial Breast Irradiation: Clinical Outcomes at a Planned Interim Analysis of a Prospective Phase 2 Trial

PURPOSE

To perform a planned interim analysis of acute (within 12 months) and late (after 12 months) toxicities and cosmetic outcomes after proton accelerated partial breast irradiation (APBI).

METHODS AND MATERIALS

A total of 100 patients with pTis or pT1-2 N0 (≤3cm) breast cancer status after segmental mastectomy were enrolled in a single-arm phase 2 study from 2010 to 2019. The clinically determined postlumpectomy target volume, including tumor bed surgical clips and operative-cavity soft-tissue changes seen on imaging plus a radial clinical expansion, was irradiated with passively scattered proton APBI (34 Gy in 10 fractions delivered twice daily with a minimum 6-hour interfraction interval). Patients were evaluated at protocol-specific time intervals for recurrence, physician reports of cosmetic outcomes and toxicities, and patient reports of cosmetic outcomes and satisfaction with the treatment or experience.

RESULTS

Median follow-up was 24 months (interquartile range [IQR], 12-43 months). Local control and overall survival were 100% at 12 and 24 months. There were no acute or late toxicities of grade 3 or higher; no patients experienced fat necrosis, fibrosis, infection, or breast shrinkage. Excellent or good cosmesis at 12 months was reported by 91% of patients and 94% of physicians; at the most recent follow-up, these were 94% and 87%, respectively. The most commonly reported late cosmetic effect was telangiectasis (17%). The total patient satisfaction rate for treatment and results at 12 and 24 months was 96% and 100%, respectively. Patients' mean time away from work was 5 days (IQR, 2-5 days), and the median out-of-pocket cost was $700 (IQR, $100-$1600). The mean left-sided heart dose was 2 cGy (range, 0.2-75 cGy), and the mean ipsilateral lung dose was 19 cGy (range, 0.2-164 cGy).

CONCLUSIONS

Proton APBI is a maturing treatment option with high local control, favorable intermediate-term cosmesis, high treatment satisfaction, low treatment burden, and exceptional heart and lung sparing.

A Dosimetric Comparison of Oral Cavity Sparing in the Unilateral Treatment of Early Stage Tonsil Cancer: IMRT, IMPT, and Tongue-Deviating Oral Stents

Introduction

Tongue-deviating oral stents (TDOS) are commonly used during unilateral neck radiation therapy to reduce unnecessary dose to nontarget oral structures. Their benefit in the setting of highly conformal treatment techniques, however, is not defined. The goal of this study was to investigate the potential benefit of TDOS use on dosimetric parameters in unilateral intensity modulated radiation therapy (IMRT) and intensity modulated proton therapy (IMPT).

Methods

A total of 16 patients with T1-2 tonsil cancer treated at a single institution were selected, of which 8 were simulated/treated with a TDOS and 8 without a TDOS. All received definitive unilateral IMRT to a dose of 66 Gy in 30 fx. IMPT plans were generated for each patient for study purposes and optimized according to standard institutional practice.

Results

For IMRT plans, the presence of a TDOS (vs without) was associated with a significantly lower oral mucosa mean dose (31.4 vs 35.3 Gy; P = .020) and V30 (42.7% vs 57.1%; P = .025). For IMPT plans, the presence of TDOS (vs without) was not associated with any improvement in oral mucosa mean dose (18.3 vs 19.9 Gy; P = .274) or V30 (25.0% vs 26.2%; P = .655). IMPT plans without TDOS compared with IMRT plans with TDOS demonstrated reduced oral mucosa mean dose (P < .001) and V30 (P < .001).

Conclusion

The use of a TDOS for the unilateral treatment of well-lateralized tonsil cancers was associated with oral mucosa sparing for IMRT, but not for IMPT. Moreover, mucosa sparing was improved for IMPT plans without a TDOS compared to IMRT plans with a TDOS.

Evaluation of the high definition field of view option of a large-bore computed tomography scanner for radiation therapy simulation

Background and purpose

Computed tomography (CT) scanning is the basis for radiation treatment planning, but the 50-cm standard scanning field of view (sFOV) may be too small for imaging larger patients. We evaluated the 65-cm high-definition (HD) FOV of a large-bore CT scanner for CT number accuracy, geometric distortion, image quality degradation, and dosimetric accuracy of photon treatment plans.

Materials and methods

CT number accuracy was tested by placing two 16-cm acrylic phantoms on either side of a 40-cm phantom to simulate a large patient extending beyond the 50-cm-diameter standard scanning FOV. Dosimetric accuracy was tested using anthropomorphic pelvis and thorax phantoms, with additional acrylic body parts on either side of the phantoms. Two volumetric modulated arc therapy beams (a 15-MV and a 6-MV) were used to cover the planning target volumes. Two-dimensional dose distributions were evaluated with GAFChromic film and point dose accuracy was checked with multiple thermoluminescent dosimeter (TLD) capsules placed in the phantoms. Image quality was tested by placing an American College of Radiology accreditation phantom inside the 40-cm phantom.

Results

The HD FOV showed substantial changes in CT numbers, with differences of 314 HU–725 HU at different density levels. The volume of the body parts extending into the HD FOV was distorted. However, TLD-reported doses for all PTVs agreed within ±3%. Dose agreement in organs at risk were within the passing criteria, and the gamma index pass rate was >97%. Image quality was degraded.

Conclusions

The HD FOV option is adequate for RT simulation and met accreditation standards, although care should be taken during contouring because of reduced image quality.

Evaluation of the accuracy of deformable image registration on MRI with a physical phantom

Background and purpose

Magnetic resonance imaging (MRI) has gained popularity in radiation therapy simulation because it provides superior soft tissue contrast, which facilitates more accurate target delineation compared with computed tomography (CT) and does not expose the patient to ionizing radiation. However, image registration errors in commercial software have not been widely reported. Here we evaluated the accuracy of deformable image registration (DIR) by using a physical phantom for MRI.

Methods and materials

We used the “Wuphantom” for end‐to‐end testing of DIR accuracy for MRI. This acrylic phantom is filled with water and includes several fillable inserts to simulate various tissue shapes and properties. Deformations and changes in anatomic locations are simulated by changing the rotations of the phantom and inserts. We used Varian Velocity DIR software (v4.0) and CT (head and neck protocol) and MR (T1‐ and T2‐weighted head protocol) images to test DIR accuracy between image modalities (MRI vs CT) and within the same image modality (MRI vs MRI) in 11 rotation deformation scenarios. Large inserts filled with Mobil DTE oil were used to simulate fatty tissue, and small inserts filled with agarose gel were used to simulate tissues slightly denser than water (e.g., prostate). Contours of all inserts were generated before DIR to provide a baseline for contour size and shape. DIR was done with the MR Correctable Deformable DIR method, and all deformed contours were compared with the original contours. The Dice similarity coefficient (DSC) and mean distance to agreement (MDA) were used to quantitatively validate DIR accuracy. We also used large and small regions of interest (ROIs) during between‐modality DIR tests to simulate validation of DIR accuracy for organs at risk (OARs) and propagation of individual clinical target volume (CTV) contours.

Results

No significant differences in DIR accuracy were found for T1:T1 and T2:T2 comparisons (P > 0.05). DIR was less accurate for between‐modality comparisons than for same‐modality comparisons, and was less accurate for T1 vs CT than for T2 vs CT (P < 0.001). For between‐modality comparisons, use of a small ROI improved DIR accuracy for both T1 and T2 images.

Conclusion

The simple design of the Wuphantom allows seamless testing of DIR; here we validated the accuracy of MRI DIR in end‐to‐end testing. T2 images had superior DIR accuracy compared with T1 images. Use of small ROIs improves DIR accuracy for target contour propagation.

Quantifying the accuracy of deformable image registration for cone-beam computed tomography with a physical phantom

PURPOSE

Kilo-voltage cone-beam computed tomography (CBCT) is widely used for patient alignment, contour propagation, and adaptive treatment planning in radiation therapy. In this study, we evaluated the accuracy of deformable image registration (DIR) for CBCT under various imaging protocols with different noise and patient dose levels.

METHODS

A physical phantom previously developed to facilitate end-to-end testing of the DIR accuracy was used with Varian Velocity v4.0 software to evaluate the performance of image registration from CT to CT, CBCT to CT, and CBCT to CBCT. The phantom is acrylic and includes several inserts that simulate different tissue shapes and properties. Deformations and anatomic changes were simulated by changing the rotations of both the phantom and the inserts. CT images (from a head and neck protocol) and CBCT images (from pelvis, head and "Image Gently" protocols) were obtained with different image noise and dose levels. Large inserts were filled with Mobil DTE oil to simulate soft tissue, and small inserts were filled with bone materials. All inserts were contoured before the DIR process to provide a ground truth contour size and shape for comparison. After the DIR process, all deformed contours were compared with the originals using Dice similarity coefficient (DSC) and mean distance to agreement (MDA). Both large and small volume of interests (VOIs) for DIR volume selection were tested by simulating a DIR process that included whole patient image volume and clinical target volumes (CTV) only (for CTVs propagation).

RESULTS

For cross-modality DIR registration (CT to CBCT), the DSC were >0.8 and the MDA were <3 mm for CBCT pelvis, and CBCT head protocols. For CBCT to CBCT and CT to CT, the DIR accuracy was improved relative to the cross-modality tests. For smaller VOIs, the DSC were >0.8 and MDA <2 mm for all modalities.

CONCLUSIONS

The accuracy of DIR depends on the quality of the CBCT image at different dose and noise levels.

A maternal warm-reactive autoantibody presenting as a positive direct antiglobulin test in a neonate

Autoimmune hemolytic anemia in pregnancy is a rare cause of hemolytic disease of the newborn. This report describes a neonate with a mild hemolytic process and a positive direct antiglobulin test (DAT) presenting as the first manifestations of a maternal warm-reactive autoantibody. A full-term male neonate, blood group O, had a strongly positive DAT and laboratory evidence suggestive of a mild hemolytic process. The neonate's mother was also group O and had a negative antibody screen. Umbilical cord blood testing revealed a panreactive eluate though the antibody was not detected in cord serum. The neonate's mother was also found to have a positive DAT. A panagglutinin was identified in an eluate of her red cells, although the autoantibody could not be detected in her serum by a variety of sensitive techniques. There was no clinical or laboratory evidence of maternal hemolysis.

Mechanisms involved in the cardiovascular-renal actions of nitric oxide inhibition

The roles of the sympathetic nervous system, angiotensin II, and arginine vasopressin in the cardiovascular-renal responses to nitric oxide synthesis inhibition were examined in eight conscious dogs equipped with arterial and venous catheters and a nonoccluding bladder catheter. Nitric oxide inhibition was achieved by intravenous infusion of NG-nitro-L-arginine methyl ester (L-NAME) at 37.1 nmol/kg per minute for 140 minutes in the control group. The same dogs, after a 1-week recovery, were pretreated for 2 days with either prazosin for alpha 1 blockade, prazosin plus propranolol for alpha 1 plus beta blockade, L-158,809 for angiotensin receptor blockade, or d(CH2)Tyr(Me)arginine vasopressin for vasopressin-V1 blockade, and the L-NAME infusion was repeated. After 140 minutes of L-NAME infusion into the control group, mean arterial pressure and renal vascular resistance had increased 16% and 71%, and renal blood flow, glomerular filtration rate, urine flow, and urinary sodium excretion had decreased 33%, 16%, 61%, and 64%, respectively. The decrement in renal blood flow and glomerular filtration during L-NAME administration was unaffected by any of the neurohumoral blockers. During V1 blockade L-NAME resulted in only a 3% increase in arterial pressure, attenuation of the renal vascular resistance response, and almost total elimination of the decrease in urine flow. During angiotensin blockade the L-NAME-induced increase in arterial pressure was markedly attenuated, and the decrease in urinary sodium excretion was attenuated in the alpha 1 plus beta blockade group.(ABSTRACT TRUNCATED AT 250 WORDS)