Pei Fong Wong

Neurocognitive effects of therapeutic irradiation for base of skull tumors.

PURPOSE To determine whether radiation therapy delivered to the paranasal sinuses causes any long-term impairment in neurocognitive function as a result of incidental brain irradiation. METHODS AND MATERIALS Nineteen patients who received paranasal sinus irradiation at least 20 months and up to 20 years before assessment were given a battery of neuropsychologic tests of cognitive function. Radiation was delivered by a three-field (one anteroposterior and two lateral) technique. The median radiation dose was 60 Gy (range 50-68 Gy) in fractions of 1.8 to 2 Gy. The volume of irradiated brain was calculated from planning computed tomography slices or simulation films. The results of the neuropsychologic tests were compared to normative control values. RESULTS Memory impairment was found in 80% of the patients, and one-third manifested difficulty with visual-motor speed, frontal lobe executive functions, and fine motor coordination. Two of the patients had frank brain necrosis with resultant dementia and blindness, and three had evidence of brain atrophy. Three of the fourteen patients without documented cerebral atrophy or necrosis were disabled from their normal activities. Three patients also developed pituitary dysfunction. Neurocognitive symptoms were related to the total dose of radiation delivered but not to the volume of brain irradiated, side of radiation boost, or chemotherapy treatment. The pattern of test findings was consistent with radiation injury to subcortical white matter. CONCLUSIONS Radiation therapy for paranasal sinus cancer may cause delayed neurocognitive side effects. Currently, however, the development of severe adverse effects appears to be decreasing because of improvements in the techniques used to deliver radiation. Lowering the total dose and improving dose distributions should further decrease the incidence of delayed brain injury due to radiation.

Results of radiotherapy for T2N0 glottic carcinoma: Does the "2" stand for twice-daily treatment?

PURPOSE Radiotherapy (RT) is often the therapy of choice for patients with Stage T2 glottic carcinoma. This retrospective study updated the results of RT for patients treated at our center. The primary focus of this study was whether a policy of using hyperfractionated RT for these patients resulted in a therapeutic gain. METHODS AND MATERIALS A search of the database of patients treated in the Department of Radiation Oncology at The University of Texas M. D. Anderson Cancer Center was performed to identify patients with Stage T2 glottic carcinoma treated with RT alone between 1970 and 1998. A total of 230 patients formed the study cohort. RESULTS The median follow-up for all patients was 82 months. Of the 230 patients, 180 were treated with parallel-opposed fields, and the median field size was 30 cm(2). Eighty-one patients (36%) were treated with twice-daily fractionation to 74-80 Gy. Eighty-nine patients (38%) were treated with 32-75 Gy at 2-Gy per fraction once daily, and 57 patients (25%) were treated with 2.06-2.26 Gy, once daily, to 66-70 Gy. The 2- and 5-year actuarial local control rate was 75% and 72%, respectively. After salvage therapy, the ultimate 5-year local control and disease-specific survival rate was 91% and 92%, respectively. The presence of subglottic extension and treatment with a daily dose of < or =2 Gy were associated with poorer local control (p <0.01) on both univariate and multivariate analyses. The 5-year local control rate for patients treated with twice-daily and once-daily RT was 79% and 67%, respectively (p = 0.06). CONCLUSION The 5-year local control rates with hyperfractionated RT for Stage T2 glottic carcinoma approach 80%. Patients treated with twice-daily fractionation to a median dose of 77 Gy had an improvement in local control compared with patients treated with 70 Gy in 35 fractions. The Radiation Therapy Oncology Group is testing these two fractionation schedules in a randomized study. High control rates were also seen in selected patients treated with hypofractionated schedules, leaving the question of the optimal schedule for patients with Stage T2 disease unanswered.

Adaptive radiotherapy for head and neck cancer - Dosimetric results from a prospective clinical trial

PURPOSE To conduct a clinical trial evaluating adaptive head and neck radiotherapy (ART). METHODS Patients with locally advanced oropharyngeal cancer were prospectively enrolled. Daily CT-guided setup and deformable image registration permitted mapping of dose to avoidance structures and CTVs. We compared four planning scenarios: (1) original IMRT plan aligned daily to marked isocenter (BB); (2) original plan aligned daily to bone (IGRT); (3) IGRT with one adaptive replan (ART1); and (4) actual treatment received by each study patient (IGRT with one or two adaptive replans, ART2). RESULTS All 22 study patients underwent one replan (ART1); eight patients had two replans (ART2). ART1 reduced mean dose to contralateral parotid by 0.6 Gy or 2.8% (paired t-test; p=0.003) and ipsilateral parotid by 1.3 Gy (3.9%) (p=0.002) over the IGRT alone. ART2 further reduced the mean contralateral parotid dose by 0.8 Gy or 3.8% (p=0.026) and ipsilateral parotid by 4.1 Gy or 9% (p=0.001). ART significantly reduced integral body dose. CONCLUSIONS This pilot trial suggests that head and neck ART dosimetrically outperforms IMRT. IGRT that leverages conventional PTV margins does not improve dosimetry. One properly timed replan delivers the majority of achievable dosimetric improvement. The clinical impact of ART must be confirmed by future trials.

Utilization of custom electron bolus in head and neck radiotherapy

Conventional methods of treating superficial head and neck tumors, such as the wedge pair technique or the use of multiple electron fields of varying energies, can result in excellent tumor control. However, in some cases, these techniques irradiate healthy tissue unnecessarily and/or create hot and cold spots injunction regions, particularly in patients with complex surface contour modification or varying planning target volume (PTV) thickness. The objective of this work is to demonstrate how bolus electron conformal therapy can be used for these patients. Two patients treated using this technique are presented. The first patient was diagnosed with malignant fibrous histiocytoma involving the right ear concha and was treated with 12‐MeV electrons. The second patient was diagnosed with acinic cell carcinoma of the left parotid gland and was treated with 20‐MeV electrons after having undergone a complete parotidectomy. Each patients bolus was designed using bolus design tools implemented in an in‐house treatment‐planning system (TPS). The bolus was fabricated using a computer‐controlled milling machine. As part of the quality assurance process to ensure proper fabrication and placement of the bolus, the patients underwent a second computed tomography (CT) scan with the bolus in place. Using that data, the final dose distribution was computed using the Philips Pinnacle 3 TPS (Philips Medical Systems, Andover, MA). Results showed that the 90% isodose surface conformed well to the PTV and that the dose to critical structures such as cord, brain, and lung was well below tolerance limits. Both patients showed no evidence of disease six months post‐radiotherapy. In conclusion, electron bolus conformal therapy is a viable option for treating head and neck tumors, particularly patients having a variable thickness PTV or surface anatomy with surgical defects. PACS number(s): 87.53.Kn

Water bolus for electron irradiation of the ear canal

PURPOSE To demonstrate that water bolus in the external ear can decrease the dose inhomogeneity caused by auricular surface irregularities when the ear is in an electron-beam field. METHODS AND MATERIALS Three-dimensional (3D) dose distributions with and without water bolus in the external ear were calculated for a representative patient. The electron dose calculations were made using the Hogstrom pencil beam algorithm as implemented in 3D by Starkschall. To demonstrate the use of water bolus in the ear clinically, the case of a patient with squamous carcinoma of the concha who was treated with electrons is presented. RESULTS Water bolus markedly lessens the dose heterogeneity caused by the surface irregularities of the ear and the air in the external auditory canal. In the test case, the maximum dose was reduced by 25% using this technique. CONCLUSION When the ear is in an electron beam field, warm water should be placed in the external auditory canal and concha. This maneuver may reduce the incidence of auricular complications that occur after electron-beam therapy.

Verification techniques and dose distribution for computed tomographic planned supine craniospinal radiation therapy.

A modified 3-field technique was designed with opposed cranial fields and a single spinal field encompassing the entire spinal axis. Two methods of plan verifications were performed before the first treatment. First, a system of orthogonal rulers plus the thermoplastic head holder was used to visualize the light fields at the craniospinal junction. Second, film phantom measurements were taken to visualize the gap between the fields at the level of the spinal cord. Treatment verification entailed use of a posterior-anterior (PA) portal film and placement of radiopaque wire on the inferior border of the cranial field. More rigorous verification required a custom-fabricated orthogonal film holder. The isocenter positions of both fields when they matched were recorded using a record-and-verify system. A single extended distance spinal field collimated at 42 degrees encompassed the entire spinal neuraxis. Data were collected from 40 fractions of craniospinal irradiation (CSI). The systematic error observed for the actual daily treatments was -0.5 mm (underlap), while the stochastic error was represented by a standard deviation of 5.39 mm. Measured data across the gapped craniospinal junction with junction shifts included revealed a dose ranging from 89.3% to 108%. CSI can be performed without direct visualization of the craniospinal junction by using the verification methods described. While the use of rigorous film verification for supine technique may have reduced the systematic error, the inability to visualize the supine craniospinal junction on skin appears to have increased the stochastic error compared to published data on such errors associated with prone craniospinal irradiation.

The effect of titanium stabilization rods on spinal cord radiation dose

The purpose of this study was to investigate the dosimetric effect of a titanium-rod spinal stabilization system on surrounding tissue, especially the spinal cord. Ion chamber dosimetry was performed for 6- and 18-MV photon beams in a water phantom containing a titanium-rod spinal stabilization system. Isodose curves were obtained in the phantom with and without rods. To assess the ability of a treatment planning system to reproduce the effects of the stabilization system on the radiation dose delivered to surrounding tissue, dose distributions were calculated after appropriate modifications were made in the computed tomography number-to-density conversion table to account for the increased density of the titanium rods. The resultant heterogeneity-corrected plans were compared with uncorrected plans. At a 7-cm depth in the water phantom, corresponding to the depth of the spinal cord, the beam was attenuated by 4% under the rods alone and by 13% rods under the rods with screws for the 6-MV photon beam as compared with curves generated in the absence of rods. The beam was attenuated by 3% and 11%, respectively, for the 18-MV beam. Using anteroposterior (18-MV) and posteroanterior (6-MV) photon beams, with and without heterogeneity correction for the rods, the corrected isodose plan showed an approximately 2% beam attenuation 4 cm anterior to the rods as compared with the uncorrected plan. No significant difference in the spinal cord dose was observed between the 2 plans, however. The titanium-rod spinal stabilization system tested in this study caused a decrease in the dose delivered distal to the rods but did not significantly affect the dose delivered to the spinal cord.

SU‐FF‐T‐94: Clinical Evaluation of Direct Machine Parameter Optimization Algorithm for Head and Neck IMRT Treatment

Purpose: Because many critical structures are in close proximity to target volumes, cancers of the head and neck (H&N) are often suited for treatment with IMRT. However, the time required to generate and deliver a clinically acceptable IMRT plan can be significantly longer than a conventional plan. This study evaluated a new inverse planning algorithm, DMPO (direct machine parameter optimization), with attention to parameter settings, plan quality and treatment efficiency for H&N cancers. Method and Materials: The Pinnacle treatment planning system version 7.4 was used. The DMPO allows users to limit the number of total MLC segments (N) for treatment. After a user-defined number of iterations (n) for pencil beam optimization, the DMPO generates MLC segments for each field for dose calculations using a convolution algorithm. Both the MLC leaf positions and the weight of each segment are then optimized until cost tolerance or iteration number is reached. Treatment plans generated using DMPO were compared with H&N cases that were previously treated using an older version (6.2). The plan quality was compared using cost functions and DVHs of target volumes and critical structures. The total monitor units and MLC segments for treatment were compared for different combinations of n and N. Results: The DMPO provided plans of DVHs similar to clinical cases with significantly less planning time. More importantly, the total MU and MLC segments for treatment delivery were reduced by 40% to 50%. Cost functions changed only slightly on n and N and total MU increased as n increased, but was independent of N. Our preliminary data indicated a combination of n=10–15 with 10 segments per field appeared to be optimal for most H&N cases. Conclusion: The DMPO algorithm generated more efficient plans while providing equal or better quality than the previous plans for IMRT treatment.

Improved setup and positioning accuracy using a three-point customized cushion/mask/bite-block immobilization system for stereotactic reirradiation of head and neck cancer

The purpose of this study was to investigate the setup and positioning uncertainty of a custom cushion/mask/bite-block (CMB) immobilization system and determine PTV margin for image-guided head and neck stereotactic ablative radiotherapy (HN-SABR). We analyzed 105 treatment sessions among 21 patients treated with HN-SABR for recurrent head and neck cancers using a custom CMB immobilization system. Initial patient setup was performed using the ExacTrac infrared (IR) tracking system and initial setup errors were based on comparison of ExacTrac IR tracking system to corrected online ExacTrac X-rays images registered to treatment plans. Residual setup errors were determined using repeat verification X-ray. The online ExacTrac corrections were compared to cone-beam CT (CBCT) before treatment to assess agreement. Intrafractional positioning errors were determined using prebeam X-rays. The systematic and random errors were analyzed. The initial translational setup errors were -0.8±1.3 mm, -0.8±1.6 mm, and 0.3±1.9 mm in AP, CC, and LR directions, respectively, with a three-dimensional (3D) vector of 2.7±1.4 mm. The initial rotational errors were up to 2.4° if 6D couch is not available. CBCT agreed with ExacTrac X-ray images to within 2 mm and 2.5°. The intrafractional uncertainties were 0.1±0.6 mm, 0.1±0.6 mm, and 0.2±0.5 mm in AP, CC, and LR directions, respectively, and 0.0∘±0.5°, 0.0∘±0.6°, and -0.1∘±0.4∘ in yaw, roll, and pitch direction, respectively. The translational vector was 0.9±0.6 mm. The calculated PTV margins mPTV(90,95) were within 1.6 mm when using image guidance for online setup correction. The use of image guidance for online setup correction, in combination with our customized CMB device, highly restricted target motion during treatments and provided robust immobilization to ensure minimum dose of 95% to target volume with 2.0 mm PTV margin for HN-SABR. PACS number(s): 87.55.ne.The purpose of this study was to investigate the setup and positioning uncertainty of a custom cushion/mask/bite‐block (CMB) immobilization system and determine PTV margin for image‐guided head and neck stereotactic ablative radiotherapy (HN‐SABR). We analyzed 105 treatment sessions among 21 patients treated with HN‐SABR for recurrent head and neck cancers using a custom CMB immobilization system. Initial patient setup was performed using the ExacTrac infrared (IR) tracking system and initial setup errors were based on comparison of ExacTrac IR tracking system to corrected online ExacTrac X‐rays images registered to treatment plans. Residual setup errors were determined using repeat verification X‐ray. The online ExacTrac corrections were compared to cone‐beam CT (CBCT) before treatment to assess agreement. Intrafractional positioning errors were determined using prebeam X‐rays. The systematic and random errors were analyzed. The initial translational setup errors were −0.8±1.3 mm, −0.8±1.6 mm, and 0.3±1.9 mm in AP, CC, and LR directions, respectively, with a three‐dimensional (3D) vector of 2.7±1.4 mm. The initial rotational errors were up to 2.4° if 6D couch is not available. CBCT agreed with ExacTrac X‐ray images to within 2 mm and 2.5°. The intrafractional uncertainties were 0.1±0.6 mm, 0.1±0.6 mm, and 0.2±0.5 mm in AP, CC, and LR directions, respectively, and 0.0∘±0.5°, 0.0∘±0.6°, and −0.1∘±0.4∘ in yaw, roll, and pitch direction, respectively. The translational vector was 0.9±0.6 mm. The calculated PTV margins mPTV(90,95) were within 1.6 mm when using image guidance for online setup correction. The use of image guidance for online setup correction, in combination with our customized CMB device, highly restricted target motion during treatments and provided robust immobilization to ensure minimum dose of 95% to target volume with 2.0 mm PTV margin for HN‐SABR. PACS number(s): 87.55.ne

SU‐E‐T‐389: Effect of Interfractional Shoulder Motion On Low Neck Nodal Targets for Patients Treated Using Volume Modulated Arc Therapy (VMAT)

PURPOSE To quantify the dosimetric impact of interfractional shoulder motion on targets in the low neck for head and neck patients treated with volume modulated arc therapy (VMAT). METHODS Three patients with head and neck cancer were selected. All three required treatment to nodal regions in the low neck in addition to the primary tumor. The patients were immobilized during simulation and treatment with a custom thermoplastic mask covering the head and shoulders. One VMAT plan was created for each patient utilizing two full 360° arcs. A second plan was created consisting of two superior VMAT arcs matched to an inferior static AP supraclavicular field. A CT-on-rails alignment verification was performed weekly during each patients treatment course. The weekly CT images were registered to the simulation CT and the target contours were deformed and applied to the weekly CT. The two VMAT plans were copied to the weekly CT datasets and recalculated to obtain the dose to the low neck contours. RESULTS The average observed shoulder position shift in any single dimension relative to simulation was 2.5 mm. The maximum shoulder shift observed in a single dimension was 25.7 mm. Low neck target mean doses, normalized to simulation and averaged across all weekly recalculations were 0.996, 0.991, and 1.033 (Full VMAT plan) and 0.986, 0.995, and 0.990 (Half-Beam VMAT plan) for the three patients, respectively. The maximum observed deviation in target mean dose for any individual weekly recalculation was 6.5%, occurring with the Full VMAT plan for Patient 3. CONCLUSION Interfractional variation in dose to low neck nodal regions was quantified for three head and neck patients treated with VMAT. Mean dose was 3.3% higher than planned for one patient using a Full VMAT plan. A Half-Beam technique is likely a safer choice when treating the supraclavicular region with VMAT.