Thermoluminescence characteristics of Nd-doped SiO2 optical fibers irradiated with the 60Co gamma rays

Thermoluminescence (TL) properties (radiation sensitivity, dose response, signal fading) of Nd-doped SiO₂ optical fibers irradiated with 1.25 MeV photons to 1–50 Gy were studied. The peak of the glow curve is around 190 °C regardless of the dose. The dose response is linear up to 50 Gy. The radiation sensitivity is 219 nC mg⁻¹ Gy⁻¹. The fiber can be a potential candidate for photon radiotherapy dosimetry due to its high radiation sensitivity, linear dose response in a wide range, slow fading, and high spatial resolution due to the small size of the fiber.     

Urethral dosimetry and toxicity with high-dose-rate interstitial brachytherapy for vaginal cancer

PurposeThe tolerance and complication rates of the urethra are unknown for the interstitial high-dose-rate brachytherapy (HDR-BT) for vaginal cancer.Methods and MaterialsPatients with vaginal cancer near/involving the urethra who were treated with HDR-BT between 2008 and 2011 were included. Patients received mean external beam dose of 48.0 Gy followed by mean HDR-BT dose of 4.5 Gy/fraction for five fractions. With CT-based planning, the urethra was contoured from the bladder neck to the meatus. Doses were converted to the biologically equivalent dose in 2 Gy/fraction (EQD₂).ResultsA total of 16 patients were included, and the EQD₂ D₉₀ was 74.9 Gy. The urethral volume was 1.31 cm³, and the EQD₂ to 0.1 and 1 cm³ were 76.2 and 48.9 Gy, respectively. Two of the 6 patients with urethral involvement developed urethral necrosis. The D₉₀ for these 2 patients was 76.8 Gy, and the urethral doses to 0.1 and 1 cm³ were 95.1 and 45.8, respectively. Those who developed severe urethral toxicity had a trend to urethral EQD₂ (95.1 Gy vs. 73.4 Gy, p = 0.1) and significantly higher dose per fraction of HDR-BT to 0.1 cm³ of the urethra (5.7 Gy vs. 3.7 Gy, p = 0.02) when compared with those who did not develop severe urethral toxicity.ConclusionsThis study is among the first to assess urethral dosimetry for patients treated with HDR-BT for vaginal cancer. Patients who received five fractions of higher than 5 Gy/fraction to 0.1 cm³ of urethra (estimated EQD₂ of 85 Gy) are at increased risk of severe urethral toxicity.     

Concrete enclosure for shielding a neutron source

In the aim to design a shielding for a 0.185 TBq ²³⁹PuBe isotopic neutron source several Monte Carlo calculations were carried out using MCNP5 code. First, a point-like source was modeled in vacuum and the neutron spectrum and ambient dose equivalent were calculated at several distances ranging from 5 cm up to 150 cm, these calculations were repeated modeling a real source, including air, and a 1×1×1 m³ enclosure with 5, 15, 20, 25, 30, 50 and 80 cm-thick Portland type concrete walls. At all the points located inside the enclosure neutron spectra from 10⁻⁸ up to 0.5 MeV were the same regardless the distance from the source showing the room-return effect in the enclosure, for energies larger than 0.5 MeV neutron spectra are diminished as the distance increases. Outside the enclosure it was noticed that neutron spectra becomes “softer” as the concrete thickness increases due to reduction of mean neutron energy. With the ambient dose values the attenuation curve in terms of concrete thickness was calculated.     

Interstitial preoperative high-dose-rate brachytherapy for early stage cervical cancer: Dose–volume histogram parameters,pathologic response and early clinical outcome

PurposeTo analyze dose–volume histogram parameters and pathologic response after preoperative high-dose-rate brachytherapy (HDRB) for high-risk early stage cervical cancers (ESCCs).Methods and MaterialsFrom June 2007 to December 2011, 32 patients with a histologically proven invasive cervical cancer with high risk of local recurrence (size >2 cm, adenocarcinoma type, perineural and/or lymphovascular invasion) underwent a preoperative HDRB, which delivered a total dose of 39 Gy in nine fractions over 5 days. All the patients underwent hysterectomy after HDRB.ResultsWith a median clinical target volume of 50 cc (minimum–maximum, 42–74), the median V₁₀₀ was 49 cc (minimum–maximum, 42–50). Median D₉₀ was 45 Gy (equivalent dose at 2 Gy per fraction, 56 Gy_αβ10). Median D_2cc was 34 Gy, 31 Gy, 28 Gy, and 38 Gy_αβ3 for bladder, rectum, sigmoid, and vagina, respectively. Twenty-eight patients (88.5%) achieved a complete histologic response after surgery, whereas for the 4 remaining patients, residual tumor cells (3 patients) and gross residual disease (1 patient) were observed in the pathologic specimen. With a median followup of 24 months (minimum–maximum, 5–48), no local recurrence was observed; 1 patient died of intercurrent cause. Early toxicity occurred within the 30 days after HDRB (Common Terminology Criteria for Adverse Events v3.0) was G1 diarrhea for 15 patients (47%) and G1 urinary frequency or urgency for 13 patients (40.6%). No G2–G3 toxicities were noticed.ConclusionsPreoperative HDRB for high-risk ESCCs represents a well-tolerated procedure, which leads to a high rate of postoperative pathologic response. Dose–volume histogram parameters were at least equivalent to those obtained with a low-dose-rate procedure. Long-term results will help to analyze the place of preoperative brachytherapy in the management of high-risk ESCCs.     

High-dose-rate afterloading intraluminal brachytherapy for advanced inoperable rectal carcinoma

PurposeHigh-dose-rate (HDR) intraluminal brachytherapy for advanced or inoperable tumors of the rectum has been used both palliatively and to dose escalate after chemoradiation for curative treatment.MethodsBetween 1993 and 2007, 79 patients were treated with HDR afterloading brachytherapy for rectal cancer; 70 patients had adenocarcinoma of the rectum; and 9 patients had squamous cell carcinoma of the anal canal. Fifty-two patients had localized disease but were unfit for major surgery and received radiotherapy with radical intent. Twenty-seven patients with advanced or metastatic disease received palliative treatment. The median age was 82 years (range, 33–97). Radical treatment comprised either chemoradiation followed by intraluminal brachytherapy delivering 12 Gy at 1 cm in two fractions or radical monotherapy delivering up to 36 Gy at 1 cm in six fractions two to three times weekly. Palliative HDR brachytherapy schedules were predominantly 10 Gy at 1 cm single dose.ResultsObjective local tumor response was seen in 41 of 48 assessable patients (85%); of whom, 28 patients (58%) had a complete response and 13 (27%) had a partial response. The most common symptom was rectal bleeding, which was controlled with a complete response rate of 63%. The median duration of the symptom response was 3 months (range, 1–73), and the median survival of the palliative patients was 6 months (range, 1 week–37 months). The median survival for patients treated with radical intent was 18.5 months (range, 2–119). Six patients reported late toxicity with three cases of rectal ulcer, two strictures, and one fistula.ConclusionsIntraluminal HDR brachytherapy is effective as local treatment in both the radical and palliative setting, with high tumor and symptom response rates, and acceptable late toxicity.     

Dosimetry for 131Cs and 125I seeds in solid water phantom using radiochromic EBT film

PurposeTo measure the 2D dose distributions with submillimeter resolution for ¹³¹Cs (model CS-1 Rev2) and ¹²⁵I (model 6711) seeds in a Solid Water phantom using radiochromic EBT film for radial distances from 0.06 cm to 5 cm. To determine the TG-43 dosimetry parameters in water by applying Solid Water to liquid water correction factors generated from Monte Carlo simulations.MethodsEach film piece was positioned horizontally above and in close contact with a ¹³¹Cs or ¹²⁵I seed oriented horizontally in a machined groove at the center of a Solid Water phantom, one film at a time. A total of 74 and 50 films were exposed to the ¹³¹Cs and ¹²⁵I seeds, respectively. Different film sizes were utilized to gather data in different distance ranges. The exposure time varied according to the seed air-kerma strength and film size in order to deliver doses in the range covered by the film calibration curve. Small films were exposed for shorter times to assess the near field, while larger films were exposed for longer times in order to assess the far field. For calibration, films were exposed to either 40 kV (M40) or 50 kV (M50) x-rays in air at 100.0 cm SSD with doses ranging from 0.2 Gy to 40 Gy. All experimental, calibration and background films were scanned at a 0.02 cm pixel resolution using a CCD camera-based microdensitometer with a green light source. Data acquisition and scanner uniformity correction were achieved with Microd3 software. Data analysis was performed using ImageJ, FV, IDL and Excel software packages. 2D dose distributions were based on the calibration curve established for 50 kV x-rays. The Solid Water to liquid water medium correction was calculated using the MCNP5 Monte Carlo code. Subsequently, the TG-43 dosimetry parameters in liquid water medium were determined.ResultsValues for the dose-rate constants using EBT film were 1.069±0.036 and 0.923±0.031 cGy U⁻¹ h⁻¹ for ¹³¹Cs and ¹²⁵I seed, respectively. The corresponding values determined using the Monte Carlo method were 1.053±0.014 and 0.924±0.016 cGy U⁻¹ h⁻¹ for ¹³¹Cs and ¹²⁵I seed, respectively. The radial dose functions obtained with EBT film measurements and Monte Carlo simulations were plotted for radial distances up to 5 cm, and agreed within the uncertainty of the two methods. The 2D anisotropy functions obtained with both methods also agreed within their uncertainties.ConclusionEBT film dosimetry in a Solid Water phantom is a viable method for measuring ¹³¹Cs (model CS-1 Rev2) and ¹²⁵I (model 6711) brachytherapy seed dose distributions with submillimeter resolution. With the Solid Water to liquid water correction factors generated from Monte Carlo simulations, the measured TG-43 dosimetry parameters in liquid water for these two seed models were found to be in good agreement with those in the literature.     

Distribution of spatial photoneutrons inside a 70 kg water phantom via neutron activation analysis

This study evaluated spatial Φ_th inside a 70 kg water phantom using the NAA method. Fifty indium foils were placed inside the water phantom and exposed under 15 MV LINAC for 2.5 min to yield the 10 Gy X-ray dose. The Φ_th value at the isocenter of the water was 1.03×10⁶ n cm^?2/Gy-X, and the maximum quantity of Φ_th appeared at the water surface along the z-axis, 3.99×10⁶ n cm^?2/Gy-X. The thermal neutron dose at isocenter of the water phantom occupied approximately 0.151% of the whole photo and neutron dose.     

Hypofractionated accelerated computed tomography–guided interstitial high-dose-rate brachytherapy for liver malignancies

PurposeTo report our results of computed tomography (CT)–guided interstitial high-dose-rate (HDR) brachytherapy (BRT) in the local treatment of inoperable primary and secondary liver malignancies.Methods and MaterialsBetween 2000 and 2009, 31 patients underwent a total of 42 BRT procedures for 36 hepatic lesions exceeding 4 cm and located adjacent to the liver hilum and bile duct bifurcation. The median tumor volume was 99 cm³ (range, 46–1348 cm³). The median age was 64 years (range, 27–85 years). The HDR-BRT delivered a median total physical dose of 13.0 Gy (range, 7.0–32.0 Gy) in twice daily fractions of median 7.0 Gy (range, 4.0–10.0 Gy) in 14 patients and in once daily fractions of median 8.0 Gy (range, 7.0–14.0 Gy) in 17 patients.ResultsThe median followup was 13.3 months with an overall survival rate of 66% at 1 year. The local control rate for patients with metastatic lesions was 79%, 59%, and 59%, and for the subgroup with primary hepatic tumors 88%, 50%, and 50% at 1, 2, and 3 years, respectively. Severe side effects occurred in 4.7% of BRT procedures with no treatment-related deaths.ConclusionsOur results confirm CT–guided interstitial HDR-BRT to be a safe procedure for the local treatment of inoperable liver malignancies unsuitable for thermal ablation.     

Evaluating proton stereotactic body radiotherapy to reduce chest wall dose in the treatment of lung cancer

Stereotactic body radiotherapy (SBRT) can produce excellent local control of several types of solid tumor; however, toxicity to nearby critical structures is a concern. We found previously that in SBRT for lung cancer, the chest wall (CW) volume receiving 20, 30, or 40 Gy (V₂₀, V₃₀, or V₄₀) was linked with the development of neuropathy. Here we sought to determine whether the dosimetric advantages of protons could produce lower CW doses than traditional photon-based SBRT. We searched an institutional database to identify patients treated with photon SBRT for lung cancer with tumors within < 2.5 cm of the CW. We found 260 cases; of these, chronic grade ≥ 2 CW pain was identified in 23 patients. We then selected 10 representative patients from this group and generated proton SBRT treatment plans, using the identical dose of 50 Gy in 4 fractions, and assessed potential differences in CW dose between the 2 plans. The proton SBRT plans reduced the CW doses at all dose levels measured. The median CW V₂₀ was 364.0 cm³ and 160.0 cm³ (p < 0.0001), V₃₀ was 144.6 cm³ vs 77.0 cm³ (p = 0.0012), V₃₅ was 93.9 cm³ vs 57.9 cm³ (p = 0.005), V₄₀ was 66.5 cm³ vs 45.4 cm³ (p = 0.0112), and mean lung dose was 5.9 Gy vs 3.8 Gy (p = 0.0001) for photons and protons, respectively. Coverage of the planning target volume (PTV) was comparable between the 2 sets of plans (96.4% for photons and 97% for protons). From a dosimetric standpoint, proton SBRT can achieve the same coverage of the PTV while significantly reducing the dose to the CW and lung relative to photon SBRT and therefore may be beneficial for the treatment of lesions closer to critical structures.     

High-resolution gel dosimetry using flat-panel detector cone-beam computed tomography: Preliminary study

This study compares the dose response of irradiated polymer gel with acrylic and styrofoam housing while applying multi-detector CT (MDCT) and cone-beam CT (CBCT). The dose response for MDCT and CBCT, while using an acrylic phantom is 1.34 and 0.67 ΔHU Gy^?1, respectively, and becomes 1.54 and 0.84 ΔHU Gy^?1 while using styrofoam, suggesting styrofoam is the better housing material. While the dose response of MDCT is better than that of CBCT, CBCT is yet a promising 3D dosimetry technique, given its potentially better spatial resolution and sensitive dose interpretation capability.     

Evaluating adjacent organ radiation doses from postoperative intracavitary vaginal vault brachytherapy for endometrial cancer

PurposeTo document doses received by critical organs during adjuvant high-dose-rate (HDR) vaginal vault brachytherapy.Methods and MaterialsPatients treated with HDR vaginal vault radiation between January 1, 2009, and January 31, 2012, who had a CT simulation with the treatment cylinder in situ were included. The CT scans were retrospectively reviewed and the rectum, sigmoid, small bowel, and bladder were contoured. Standardized plans treating the upper 4 cm of the vaginal vault were used to deliver a total of 21 Gy (Gy) at 0.5 cm from the apex of the vaginal vault in three fractions.ResultsThere were 41 patients. Median age was 62 years. The median vaginal cylinder diameter was 3 cm. The mean 2cc dose to the rectum, sigmoid, small bowel, and bladder were 5.7, 4.7, 4.0, and 5.6 Gy, respectively. Bladder volume ranged from 67–797 cc. Assuming minimal interfraction organ variation, the equivalent dose in 2 Gy/fraction was extrapolated from data and may be near or beyond organ tolerance for rectum, sigmoid, and small bowel in some cases. Spearman correlation found that increased bladder volume was not associated with adjacent organs at risk dose but may be associated with a trend (p = 0.06) toward increased bladder dose (R = 0.30).ConclusionsThis study describes the dose received by adjacent critical structures during vaginal vault HDR brachytherapy. This is important information for documentation in the rare setting of treatment-related toxicity or recurrence. Bladder volume was not associated with dose to adjacent organs.     

Dosimetric comparison of multichannel with one single-channel vaginal cylinder for vaginal cancer treatments with high-dose-rate brachytherapy

PurposeTo compare the three-dimensional (3D) image (CT/MR)-based planning with a multichannel vaginal cylinder (MVC) to a single-channel vaginal cylinder (SVC) for the treatment of vaginal cancer.Methods and MaterialsA total of 20 consecutive patients were treated with 3D CT/MR image-based high-dose-rate (HDR) brachytherapy using an MVC. All patients received external beam radiation therapy before HDR brachytherapy. A brachytherapy dose of 20–25 Gy of more than five fractions was delivered to clinical target volume (CTV). Retrospectively, treatment plans for all patients were generated using the central channel only to mimic an SVC applicator. The SVC plans were optimized to match CTV coverage with MVC plans. Dose homogeneity index as well as bladder, rectum, sigmoid, and urethral doses were compared.ResultsThe mean D₉₀ for CTV was 74.2 Gy (range: 48.8–84.1 Gy). The mean (±standard deviation) of dose homogeneity index for MVC vs. SVC was 0.49 (±0.19) and 0.52 (±0.23), respectively (p = 0.09). Mean bladder 0.1, 1, and 2 cc doses for MVC vs. SVC were 69 vs. 71.2 Gy (p = 0.35), 61.4 vs. 63.8 Gy (p = 0.1), and 59.5 vs. 60.9 Gy (p = 0.31), respectively. Similarly, mean rectum 0.1, 1, and 2 cc doses for MVC vs. SVC were 67.2 vs. 75.4 Gy (p = 0.005), 60.0 vs. 65.6 Gy (p = 0.008), and 57.3 vs. 62.0 Gy (p = 0.015), respectively, and mean sigmoid doses were 56.3 vs. 60.5 Gy (p = 0.10), 50.9 vs. 53.1 Gy (p = 0.09), and 49.1 vs. 50.7 Gy (p = 0.10), respectively.ConclusionThe 3D CT-/MR-based plan with MVC may provide better dose distribution in the management of certain clinical situations of vaginal cancer requiring intracavitary brachytherapy, especially in minimizing potential late rectal complications.     

A comparison of HDR near source dosimetry using a treatment planning system,Monte Carlo simulation,and radiochromic film

This study aimed to investigate the high-dose rate Iridium-192 brachytherapy, including near source dosimetry, of a catheter-based applicator from 0.5 mm to 1 cm along the transverse axis. Radiochromic film and Monte Carlo (MC) simulation were used to generate absolute dose for the catheter-based applicator. Results from radiochromic film and MC simulation were compared directly to the treatment planning system (TPS) based on the American Association of Physicists in Medicine Updated Task Group 43 (TG-43U1) dose calculation formalism. The difference between dose measured using radiochromic film along the transverse plane at 0.5 mm from the surface and the predicted dose by the TPS was 24%±13%. The dose difference between the MC simulation along the transverse plane at 0.5 mm from the surface and the predicted dose by the TPS was 22.1%±3%. For distances from 1.5 mm to 1 cm from the surface, radiochromic film and MC simulation agreed with TPS within an uncertainty of 3%. The TPS under-predicts the dose at the surface of the applicator, i.e., 0.5 mm from the catheter surface, as compared to the measured and MC simulation predicted dose. MC simulation results demonstrated that 15% of this error is due to neglecting the beta particles and discrete electrons emanating from the sources and not considered by the TPS, and 7% of the difference was due to the photon alone, potentially due to the differences in MC dose modeling, photon spectrum, scoring techniques, and effect of the presence of the catheter and the air gap. Beyond 1 mm from the surface, the TPS dose algorithm agrees with the experimental and MC data within 3%.     

EBT GAFCHROMICTM film dosimetry in compensator-based intensity modulated radiation therapy

The electron benefit transfer (EBT) GAFCHROMIC films possess a number of features making them appropriate for high-quality dosimetry in intensity-modulated radiation therapy (IMRT). Compensators to deliver IMRT are known to change the beam-energy spectrum as well as to produce scattered photons and to contaminate electrons; therefore, the accuracy and validity of EBT-film dosimetry in compensator-based IMRT should be investigated. Percentage-depth doses and lateral-beam profiles were measured using EBT films in perpendicular orientation with respect to 6 and 18 MV photon beam energies for: (1) different thicknesses of cerrobend slab (open, 1.0, 2.0, 4.0, and 6.0 cm), field sizes (5×5, 10×10, and 20×20 cm²), and measurement depths (D_max, 5.0 and 10.0 cm); and (2) step-wedged compensator in a solid phantom. To verify results, same measurements were implemented using a 0.125 cm³ ionization chamber in a water phantom and also in Monte Carlo simulations using the Monte Carlo N-particle radiation transport computer code. The mean energy of photons was increased due to beam hardening in comparison with open fields at both 6 and 18 MV energies. For a 20×20 cm² field size of a 6 MV photon beam and a 6.0 cm thick block, the surface dose decreased by about 12% and percentage-depth doses increased up to 3% at 30.0 cm depth, due to the beam-hardening effect induced by the block. In contrast, at 18 MV, the surface dose increased by about 8% and depth dose reduced by 3% at 30.0 cm depth. The penumbral widths (80% to 20%) increase with block thickness, field size, and beam energy. The EBT film results were in good agreement with the ionization chamber dose profiles and Monte Carlo N-particle radiation transport computer code simulation behind the step-wedged compensator. Also, there was a good agreement between the EBT-film and the treatment-planning results on the anthropomorphic phantom. The EBT films can be accurately used as a 2D dosimeter for dose verification and quality assurance of compensator-based C-IMRT.