Can Volume-Based MRI-Guided Planning for Interstitial Gynecologic Brachytherapy Overcome Clinicopathologic Risk Factors for Fistula Formation?

PURPOSE/OBJECTIVE(S)

Tumor and patient factors requiring an interstitial (IS) approach for gynecologic tract brachytherapy (BT) may be associated with high morbidity despite the conformality maximizing effect of ISBT. We reviewed outcomes from a diverse, high-volume center to evaluate the association of clinical features and planning parameters with toxicity, with the hypothesis that MRI-guided volume-based planning mitigates clinicopathologic risk factors associated with treatment related fistula (TRF) after ISBT.

MATERIALS/METHODS

We retrospectively reviewed patients treated with Syed-based ISBT at a single institution from 2014-2019. Fisher's exact was used for group comparison with p<0.05. Kaplan-Meier method was used to estimate local control (LC), overall survival (OS), and fistula-free survival (FFS). Cox regression was used for univariate (UVA) and multivariate analysis (MVA) to estimate hazard ratios (HR). Collinearity was assessed using variable inflation factor and Pearson's correlation.

RESULTS

A total of 54 patients (median age 58 [IQR 46-67], 54% Caucasian, 39% African American, 15% Hispanic) treated with ISBT (89% MRI-guided) with median follow-up 32 months had initial (89%) or recurrent (11%) disease from cervical (70%), vaginal (15%), urethral (6%), and other cancers. At presentation 5.5% had clinically evident fistula. There was radiographic rectal and bladder involvement in 22.0% and 19.2%, respectively. 89% received concurrent chemotherapy and 98% received EBRT prior to ISBT with a cumulative median high-risk CTV (HRCTV) dose 80.8 Gy (IQR 76.8-84.3), bladder D2cc 84.3 Gy (IQR 75.8-89.0), and rectal D2cc 73.8 Gy (IQR 67.7-80.0 Gy). All 7 patients who developed a TRF (rectovaginal in 6/7 and vesicovaginal in 5/7) were former or current smokers, had primary cervical cancer, and received chemotherapy. Management included surgical intervention in 6 (85.7%). LC, OS, and FFS at 2-years was 89.3% (95% CI 75.9-95.4%), 87.8% (95% CI 66.9-89.8%), and 85.2% (95% CI 69.9-93.1%), respectively. On UVA, current smoking (HR 4.60, 95% CI 1.02-20.74), BT bladder D2cc (HR 1.63, 95% CI 1.07-2.47) and BT rectal Dmax (HR 1.30, 95% CI 1.07-1.58) predicted for increased risk of TRF. Most factors were non-significant including Charlson Comorbidity Index, age, BMI, surgical history, extent of vaginal involvement, race, HRCTV volume and number of needles used. No patients with radiographic bladder or rectal invasion developed TRF. On MVA, only smoking status (HR 14.05, 95% CI 1.48-133.1) remained significant. 0% of never (0/26), 20% of former (3/15) and 31% of current (4/13) smokers developed fistulas from toxicities (p<0.05).

CONCLUSION

In patients with locally advanced cancers of the gynecologic tract treated with MRI-guided volume-based ISBT, smoking was the only factor predictive of TRF formation, occurring primarily in cervical cancer patients. This highlights the importance of smoking cessation during treatment and appropriately counseling patients at high risk for this morbidity.

Clinical Outcomes with Triple Tandem Brachytherapy for Medically Inoperable Endometrial Cancer in a Predominantly Black Patient Population

PURPOSE/OBJECTIVE(S)

Radiation outcomes for Black patients with medically inoperable endometrial cancer (MIEC) is limited, despite this demographic comprising a higher proportion of the MIEC patient population. We report clinical outcomes and toxicities using triple tandem brachytherapy (TTB) with or without external beam radiation therapy (EBRT) for MIEC in predominantly Black patients.

MATERIALS/METHODS

An IRB approved retrospective review was performed of all MIEC patients treated definitively with TTB ± EBRT from 2014-2021 at a single institution. Patients were divided based on stage. Group 1 = FIGO stage 1A/1B and Group 2 = FIGO stage 2-4B. Patients with cervical involvement were treated with TTB + ovoids. The Kaplan-Meier estimates were generated to estimate overall survival (OS) and local failure-free survival (LFFS). Local control (LC) was evaluated clinically. Acute and late toxicities were evaluated. Planning parameters for target volume(s) and OARs (organs at risk) were per ABS guidelines. Statistics reported are median values and ranges.

RESULTS

Of 30 patients, 93.3% received TTB + EBRT. Mean age at diagnosis was 65.3 years (40.5-88.7 years). 70% of patients were Black. Median prescribed doses were 45 Gy (range: 21-50.4 Gy) for EBRT and 22.25 Gy (range: 16.5-49.1 Gy) for brachytherapy. Median BMI was 48.1 (27.8- 69) and Charlson Comorbidity Index was 4 (1-11). Patient stages were FIGO 1A/B (n = 19), 2 (n = 1), 3 (n = 1), 3b (n = 1), 3C1 (n = 3), 3C2 (n = 2), and 4B (n = 2) due to inguinal lymphadenopathy. 90% had endometrioid histology while 6.7% and 3.3% had clear cell and serous carcinoma, respectively. Median follow up was 32.1 months (1.7-93.6). Median OS for Group 1 was 50.9 months and 43.5 months for Group 2, while 1-/4-year OS was 84.2%/54.4% and 90.9%/17.5% for Group 1 and 2, respectively (p = 0.616). 53.3% of patients died of non-EC causes. The 1-/4-year LFFS was 100%/93.3% for Group 1 and 90%/70.5% for Group 2 (p = 0.113). Four patients (13.3%) developed recurrence (stage 1A/B, 2, 3C1, and 4B), but only 1 died of disease (Stage 2 with clear cell histology). After EBRT but pre-TTB, 50% (n = 15) and 16.6% (n = 5) had acute grade 2 gastrointestinal (GI) and genitourinary (GU) toxicities, respectively. After TTB treatment, 2 more patients developed acute grade 2 GU toxicity. Late toxicities were Grade 2: GU (n = 1) and GI (n = 1) and Grade 4 GI bleed (n = 1) treated with argon plasma coagulation.

CONCLUSION

TTB ± EBRT for MIEC in predominantly Black patients was associated with excellent LFFS and acceptable toxicity rates, especially in early-stage MIEC with endometrioid histology. Furthermore, even in patients at high risk of death from other causes, LC may help preserve quality of life. Additional studies are needed to evaluate and optimize outcomes for Black patients with MIEC.

The dosimetric effects of tissue heterogeneities in intensity-modulated radiation therapy (IMRT) of the head and neck

The dosimetric effects of bone and air heterogeneities in head and neck IMRT treatments were quantified. An anthropomorphic RANDO phantom was CT-scanned with 16 thermoluminescent dosimeter (TLD) chips placed in and around the target volume. A standard IMRT plan generated with CORVUS was used to irradiate the phantom five times. On average, measured dose was 5.1% higher than calculated dose. Measurements were higher by 7.1% near the heterogeneities and by 2.6% in tissue. The dose difference between measurement and calculation was outside the 95% measurement confidence interval for six TLDs. Using CORVUS' heterogeneity correction algorithm, the average difference between measured and calculated doses decreased by 1.8% near the heterogeneities and by 0.7% in tissue. Furthermore, dose differences lying outside the 95% confidence interval were eliminated for five of the six TLDs. TLD doses recalculated by Pinnacle3's convolution/superposition algorithm were consistently higher than CORVUS doses, a trend that matched our measured results. These results indicate that the dosimetric effects of air cavities are larger than those of bone heterogeneities, thereby leading to a higher delivered dose compared to CORVUS calculations. More sophisticated algorithms such as convolution/superposition or Monte Carlo should be used for accurate tailoring of IMRT dose in head and neck tumours.

MRI measurements correctly predict the relative effects of tumor oxygenating agents on hypoxic fraction in rodent BA1112 tumors

PURPOSE

We evaluate whether magnetic resonance imaging (MRI) with blood oxygenation level-dependent (BOLD) contrast correctly predicts the relative effects of tumor-oxygenating agents on hypoxic fraction in BA1112 rhabdomyosarcomas in WAG/Rij rats.

METHODS AND MATERIALS

The response of ten tumors to carbogen (95% O(2)/5% CO(2)), a perfluorocarbon emulsion (PFC), and the combination of PFC + carbogen was studied with high spectral and spatial resolution MR imaging of the water resonance at 4.7 Tesla. Decreases in MR signal linewidth indicate increases in tumor blood oxygen levels.

RESULTS

Average MR signal linewidth was decreased 2.0% by carbogen, 2.5% by PFC + air, and 4.9% by PFC + carbogen. PFC + carbogen caused a larger linewidth decrease than either treatment alone (p < 0.04 by ANOVA). Maps of pixels responding to treatment indicate that combining PFC with carbogen significantly enlarges the area of the tumor in which oxygen levels are increased (p < 0.01 by ANOVA).

CONCLUSION

MRI predicts that PFC + carbogen will increase radiosensitivity more than either treatment alone; this agrees with the known effects of these treatments on hypoxic fraction. Utilizing MRI to choose the treatment that maximizes the size and extent of increases in tumor oxygenation could reduce hypoxic fraction.

Uptake of a superparamagnetic contrast agent imaged by MR with high spectral and spatial resolution

Conventional MRI implicitly treats the proton signal as a single, narrow Lorentzian. However, water signals in vivo are often in homogeneously broadened and have multiple resolvable components. These components represent discrete populations of water molecules within each pixel which are affected differently by physiology and contrast agents. Accurate measurement of each component of the water resonance can improve anatomic and functional MR images and provide insight into the structure and dynamics of subpixelar microenvironments. This report describes high spectral and spatial resolution (HiSS) MR imaging of rodent prostate tumors before and after injection of a superparamagnetic contrast agent. HiSS datasets were used to synthesize images in which intensity is proportional to peak height, peak frequency, and linewidth. These images showed anatomic features which were not clearly delineated in conventional T(2) and gradient echo images. HiSS images obtained after injection of the contrast agent showed T *(2) and T(1) changes which were not seen in conventional images. These changes are associated with microvessel density and permeability. The results suggest HiSS with superparamagnetic contrast agents has the potential to improve characterization of tumors.

Fast spectroscopic imaging of water and fat resonances to improve the quality of MR images

RATIONALE AND OBJECTIVES

The authors evaluated whether fast spectroscopic imaging of water and fat resonances can produce high-quality anatomic magnetic resonance (MR) images of rodent tumors and human breast.

MATERIALS AND METHODS

Fast MR spectroscopic images of eight rats with mammary tumors were acquired by using a 4.7-T MR unit equipped with self-shielded gradient coils. MR spectroscopic images of four human breasts were acquired with a 1.5-T MR unit.

RESULTS

Artifacts due to eddy currents were minimal. Images synthesized from MR spectroscopic data, in which intensity was proportional to water signal peak height, were similar to T2-weighted MR images. Boundaries of rodent mammary tumors are similar but not identical on peak height-weighted and T2-weighted images. MR spectroscopic images of human breast showed improved detail compared to gradient-echo MR images.

CONCLUSION

Preliminary results suggest that incorporation of fast MR spectroscopic imaging methods into many standard clinical MR imaging procedures may substantially improve image quality.

Correlation of magnetic resonance and oxygen microelectrode measurements of carbogen-induced changes in tumor oxygenation

PURPOSE

The aim of this work was to test the hypothesis that decreases in the linewidth of magnetic resonance (MR) water signals in tumors caused by oxygenating treatments are due to increases in capillary and venous oxygen saturation of hemoglobin, which are tightly coupled to increases in extravascular oxygen tension (pO2). To establish this link, changes measured by MR were compared to changes in tissue pO2 measured directly by oxygen microelectrodes during carbogen (95% O2/5% CO2) inhalation.

METHODS AND MATERIALS

Mammary adenocarcinomas (R3230AC) in nine rats were imaged at 4.7 Tesla. T1-weighted (TR = 200 ms, flip angle = 45 degrees) spectroscopic images of the water resonance in a single slice through each tumor were acquired with spectral resolution of 3.9 Hz and bandwidth of +/-1000 Hz. In the same slices in these tumors, microelectrode measurements were made using a non-Clark style oxygen electrode with a 350-micron tip. MR and microelectrode measurements were made during alternating periods of air and carbogen inhalation.

RESULTS

Water resonance linewidth decreased significantly during carbogen-induced hyperoxia. Paired Student's t-test analysis of microelectrode data indicated that pO2 was significantly (p < 0.05) increased as a result of carbogen inhalation. MR and microelectrode data averaged over each tumor demonstrated that decreased MR water signal linewidth is strongly correlated (r = 0.92, p < 0.05) with increased tumor pO2 levels.

CONCLUSION

Although tumor oxygenating agents increase response to radiation in rodent tumors, clinical studies have shown only marginal effects on the radiosensitivity of human tumors. This may be, in part, because the effects of tumor oxygenating treatments are highly heterogeneous both within each tumor and among a population of tumors. The noninvasive, high-resolution MR methods that are validated by the present work could guide the design of new and more effective tumor oxygenating agents and optimize treatments for individual patients.