Brachytherapy for radiotherapy-resistant head and neck cancer: A review of a single center experience.

OBJECTIVES/HYPOTHESIS: Despite advances in radiotherapy and chemotherapy treatments for head and neck cancers, the local failure rate is high. In most radiotherapy-resistant cases, surgery is performed; however, some cases are considered unresectable. No standard treatment for these situations has been established. In this study, we review our experience with brachytherapy (BT), which has a different biological mechanism than standard radiotherapy. METHODS: All patients received prior radiation to the recurrence area. Median high-dose radiation BT dose was 50 Gy, administered in 5 to 10 Gy fractions twice daily for 5 days. High-dose radiation was given via four to 10 catheters inserted under local anesthesia (3 patients) or general anesthesia with preventive tracheostomy (10 patients). RESULTS: Thirteen patients received BT from 2010 to 2014. Male:female ratio was 1.6:1, and median age was 66 years (range 23-89). Of those 13 patients, 10 patients were diagnosed with squamous cell carcinoma (SCC) of the oral cavity, two patients with SCC of the nasal mucosa, and one patient with eccrine duct carcinoma. Prior radiation dose ranged from 60 to 70 Gy. Local control was achieved in 11 of 13 patients; only 15.3% (2 of 13) had in-field recurrence. Five patients developed local out-of-field recurrence, and two developed distant metastases. Five patients are alive with no evidence of disease. No major toxicities were encountered. Two patients had severe mucositis and recovered within several weeks. CONCLUSION: Brachytherapy for radiotherapy-resistant head and neck cancers is feasible with minor adverse events, which enables good local control. However, many advanced head and neck cancers develop regional or distant metastases; therefore, additional treatment should be suggested. LEVEL OF EVIDENCE: 4. Laryngoscope, 126:2246-2251, 2016.

Robotic radiosurgery system patient-specific QA for extracranial treatments using the planar ion chamber array and the cylindrical diode array.

Robotic radiosurgery system has been increasingly employed for extracranial treatments. This work is aimed to study the feasibility of a cylindrical diode array and a planar ion chamber array for patient-specific QA with this robotic radiosurgery system and compare their performance. Fiducial markers were implanted in both systems to enable image-based setup. An in-house program was developed to postprocess the movie file of the measurements and apply the beam-by-beam angular corrections for both systems. The impact of noncoplanar delivery was then assessed by evaluating the angles created by the incident beams with respect to the two detector arrangements and cross-comparing the planned dose distribution to the measured ones with/without the angular corrections. The sensitivity of detecting the translational (1-3 mm) and the rotational (1°-3°) delivery errors were also evaluated for both systems. Six extracranial patient plans (PTV 7-137 cm³) were measured with these two systems and compared with the calculated doses. The plan dose distributions were calculated with ray-tracing and the Monte Carlo (MC) method, respectively. With 0.8 by 0.8 mm² diodes, the output factors measured with the cylindrical diode array agree better with the commissioning data. The maximum angular correction for a given beam is 8.2% for the planar ion chamber array and 2.4% for the cylindrical diode array. The two systems demonstrate a comparable sensitivity of detecting the translational targeting errors, while the cylindrical diode array is more sensitive to the rotational targeting error. The MC method is necessary for dose calculations in the cylindrical diode array phantom because the ray-tracing algorithm fails to handle the high-Z diodes and the acrylic phantom. For all the patient plans, the cylindrical diode array/ planar ion chamber array demonstrate 100% / > 92% (3%/3 mm) and > 96% / ~ 80% (2%/2 mm) passing rates. The feasibility of using both systems for robotic radiosurgery system patient-specific QA has been demonstrated. For gamma evaluation, 2%/2 mm criteria for cylindrical diode array and 3%/3 mm criteria for planar ion chamber array are suggested. The customized angular correction is necessary as proven by the improved passing rate, especially with the planar ion chamber array system.

Planning target volume-to-skin proximity for head-and-neck intensity modulated radiation therapy treatment planning.

PURPOSE: The goal of this work is to evaluate planning target volume (PTV)-to-skin proximity versus plan quality as well as the effects of calculation voxel size on dose uncertainty in the surface region. METHODS AND MATERIALS: A right-sided clinical target volume with the lateral border 5 mm from the surface was delineated on the computed tomographic data of a head-and-neck phantom. A 5-mm PTV expansion was generated except laterally where distances of 0-5 mm were used. A 7-field intensity modulated radiation therapy plan was generated using the Eclipse treatment planning system. Optimization was performed where 95% of the PTV receives the prescription dose using a voxel size of 2 mm(3). Dose calculations were repeated for voxel sizes of 1, 3, and 5 mm(3). For each plan, 9 point dose values were obtained just inside the phantom surface, corresponding to a 2 cm × 2 cm grid near the central target region. Nine ultrathin thermoluminescent dosimeters were placed on the phantom surface corresponding to the grid. Measured and calculated dose values were compared. Conformality, homogeneity, and target coverage were compared as well. This process was repeated for volumetric modulated arc therapy (VMAT) calculated with a 2-mm(3) voxel size. RESULTS: Surface dose is overestimated by the treatment planning system (TPS) by approximately 21% and 9.5% for 5- and 3-mm(3) voxels, respectively, and is accurately predicted for 2-mm(3) voxels. A voxel size of 1 mm(3) results in underestimation by 11%. Conformality improves with increasing PTV-to-skin distance and a conformality index of unity is obtained for grid sizes between 1 and 3 mm(3) and PTV-to-skin distances of 4-4.5 mm. Hot spot also improves and falls below 110% at 4-mm PTV-to-skin distance. Underdosage worsens as the PTV approaches the skin. All of the above appear to hold for volumetric modulated arc therapy. CONCLUSIONS: For decreasing PTV-to-skin distance with this TPS, isodose conformality decreases, "hot spot" increases, and target coverage degrades. Surface dose is overestimated when voxel sizes greater than 2 mm(3) are chosen, and underestimated for smaller voxels.

Measurement comparison and Monte Carlo analysis for volumetric-modulated arc therapy (VMAT) delivery verification using the ArcCHECK dosimetry system.

The objective of this study is to validate the capabilities of a cylindrical diode array system for volumetric-modulated arc therapy (VMAT) treatment quality assurance (QA). The VMAT plans were generated by the Eclipse treatment planning system (TPS) with the analytical anisotropic algorithm (AAA) for dose calculation. An in-house Monte Carlo (MC) code was utilized as a validation tool for the TPS calculations and the ArcCHECK measurements. The megavoltage computed tomography (MVCT) of the ArcCHECK system was adopted for the geometry reconstruction in the TPS and for MC simulations. A 10 × 10 cm2 open field validation was performed for both the 6 and 10 MV photon beams to validate the absolute dose calibration of the ArcCHECK system and also the TPS dose calculations for this system. The impact of the angular dependency on noncoplanar deliveries was investigated with a series of 10 × 10 cm2 fields delivered with couch rotation 0° to 40°. The sensitivity of detecting the translational (1 to 10 mm) and the rotational (1° to 3°) misalignments was tested with a breast VMAT case. Ten VMAT plans (six prostate, H&N, pelvis, liver, and breast) were investigated to evaluate the agreement of the target dose and the peripheral dose among ArcCHECK measurements, and TPS and MC dose calculations. A customized acrylic plug holding an ion chamber was used to measure the dose at the center of the ArcCHECK phantom. Both the entrance and the exit doses measured by the ArcCHECK system with and without the plug agreed with the MC simulation to 1.0%. The TPS dose calculation with a 2.5 mm grid overestimated the exit dose by up to 7.2% when the plug was removed. The agreement between the MC and TPS calculations for the ArcCHECK without the plug improved significantly when a 1 mm dose calculation grid was used in the TPS. The noncoplanar delivery test demonstrated that the angular dependency has limited impact on the gamma passing rate (< 1.2% drop) for the 2%-3% dose and 2mm-3 mm DTA criteria. A 1° rotational misalignment introduces 11.3% (3%/3mm) to 21.3% (1%/1 mm) and 0.2% (3%/3 mm) to 0.8% (1%/1 mm) Gamma passing rate drop for ArcCHECK system and MatriXX system, respectively. Both systems have comparable sensitivity to the AP misalignments. However, a 2 mm RL misalignment introduces gamma passing rate drop ranging from 0.9% (3%/3 mm) to 4.0% (1%/1 mm) and 5.0% (3%/3 mm) to 12.0% (1%/1 mm) for ArcCHECK and MatriXX measurements, respectively. For VMAT plan QA, the gamma analysis passing rates ranged from 96.1% (H&N case) to 99.9% (prostate case), when using the 3%/3 mm DTA criteria for the peripheral dose validation between the TPS and ArcCHCEK measurements. The peripheral dose validation between the MC simulation and ArcCHECK measurements showed at least 97.9% gamma passing rates. The central dose validation also showed an agreement within 2.2% between TPS/MC calculations and ArcCHECK measurements. The worst discrepancy was found in the H&N case, which is the most complex VMAT case. The ArcCHECK system is suitable for VMAT QA evaluation based on the sensitivity to detecting misalignments, the clinical impact of the angular dependency, and the correlation between the dose agreements in the peripheral region and the central region. This work also demonstrated the importance of carrying out a thorough validation of both the TPS and the dosimetry system prior to utilizing it for QA, and the value of having an independent dose calculation tool, such as the MC method, in clinical practice.

4D patient dose reconstruction using online measured EPID cine images for lung SBRT treatment validation.

PURPOSE: This study aims to develop an EPID-guided 4D patient dose reconstruction framework and to investigate its feasibility for lung SBRT treatment validation. METHODS: Both the beam apertures and tumor movements were detected based on the continuously acquired EPID images during the treatment. Instead of directly using the transit photon fluence measured by the EPID, this method reconstructed the entrance fluence with the measured beam apertures and the delivered MUs. The entrance fluence distributions were sorted into their corresponding phases based on the detected tumor motion pattern and then accumulated for each phase. Together with the in-room 4DCT taken before every treatment to consider the interfractional-motion, the entrance fluence was then used for the patient dose calculation. Deformable registration was performed to sum up the phase doses for final treatment assessment. The feasibility of using the transit EPID images for entrance fluence reconstruction was evaluated against EPID in-air measurements. The accuracy of 3D- and 4D-dose reconstruction was validated by experiments with a motor-driven cylindrical diode array for six clinical-SBRT plans. RESULTS: The average difference between the measured and reconstructed fluence maps was within 0.16%. The reconstructed 3D-dose showed a less than 1.4% difference for the CAX-dose and at least a 98.3% gamma-passing-rate (2%∕2 mm) for the peripheral dose. Distorted dose distributions were observed in the measurement with the moving phantom. The comparison between the measured and the reconstructed 4D-dose without considering temporal information failed the gamma-evaluation for most cases. In contrast, when temporal information was considered, the dose distortion phenomena were successfully represented in the reconstructed dose (97.6%-99.7% gamma-passing rate). CONCLUSIONS: The proposed method considered uncertainties of the beam delivery system, the interfractional- and intrafractional-motion, and the interplay effect. The experimental validation demonstrates that this method is practical and accurate for online or offline SBRT patient dose verification.

Investigation of pulsed low dose rate radiotherapy using dynamic arc delivery techniques.

There has been no consensus standard of care to treat recurrent cancer patients who have previously been irradiated. Pulsed low dose rate (PLDR) external beam radiotherapy has the potential to reduce normal tissue toxicities while still providing significant tumor control for recurrent cancers. This work investigates the dosimetry feasibility of PLDR treatment using dynamic arc delivery techniques. Five treatment sites were investigated in this study including breast, pancreas, prostate, head and neck, and lung. Dynamic arc plans were generated using the Varian Eclipse system and the RapidArc delivery technique with 6 and 10 MV photon beams. Each RapidArc plan consisted of two full arcs and the plan was delivered five times to achieve a daily dose of 200 cGy. The dosimetry requirement was to deliver approximately 20 cGy/arc with a 3 min interval to achieve an effective dose rate of 6.7 cGy min⁻¹. Monte Carlo simulations were performed to calculate the actual dose delivered to the planning target volume (PTV) per arc taking into account beam attenuation/scattering and intensity modulation. The maximum, minimum and mean doses to the PTV were analyzed together with the dose volume histograms and isodose distributions. The dose delivery for the five plans was validated using solid water phantoms inserted with an ionization chamber and film, and a cylindrical detector array. Two intensity-modulated arcs were used to efficiently deliver the PLDR plans that provided conformal dose distributions for treating complex recurrent cancers. For the five treatment sites, the mean PTV dose ranged from 18.9 to 22.6 cGy/arc. For breast, the minimum and maximum PTV dose was 8.3 and 35.2 cGy/arc, respectively. The PTV dose varied between 12.9 and 27.5 cGy/arc for pancreas, 12.6 and 28.3 cGy/arc for prostate, 12.1 and 30.4 cGy/arc for H&N, and 16.2 and 27.6 cGy/arc for lung. Advanced radiation therapy can provide superior target coverage and normal tissue sparing for PLDR reirradiation of recurrent cancers, which can be delivered using dynamic arc delivery techniques with ten full arcs and an effective dose rate of 6.7 ± 4.0 cGy min⁻¹.