Low dose lung radiation therapy for pneumonia: an examination of historical dose distributions.

The novel coronavirus, SARS-CoV-2, that causes the COVID-19 disease currently has healthcare systems around the world dealing with unprecedented numbers of critically ill patients. One of the primary concerns associated with this illness is acute respiratory distress syndrome (ARDS) and the pneumonia that accompanies it. Historical literature dating back to the 1940s and earlier contains many reports of successful treatment of pneumonias with ionizing radiation. Although these were not randomized controlled trials, they do suggest a potential avenue for further investigation. Technical details in these reports however were limited. In this work we review the literature and identify details including nominal kilovoltage ranges, filtration, and focus-skin distances (FSDs). Using a freely available and benchmarked code, we generated spectra and used these as sources for Monte Carlo simulations using the EGSnrc software package. The approximate sources were projected through a radiologically anthropomorphic phantom to provide detailed dose distributions within a targeted lung volume (approximate right middle lobe). After accounting for the reported exposure levels, mean lung doses fell in a relatively narrow range: 30-80 cGy. Variation in patient dimensions and other details are expected to result in an uncertainty on the order of ± 20%. This result is consistent with the dose range expected to induce anti-inflammatory effects.

What Conditions Make Proton Beam Therapy Financially Viable in Western Canada?

Background Proton beam therapy (PBT) is available in many western and Asian countries, but there is no clinical, gantry-based PBT facility in Canada. Methods A cost analysis was conducted from the Alberta Ministry of Health perspective with a 15-year horizon. Estimated costs were: PBT unit, facility development as part of an ongoing capital project, electricity, maintenance contract, and staffing. Revenues were: savings from stopping USA referrals, avoiding the costs of standard radiation therapy (RT) for Albertans receiving PBT instead, and cost-recovery charges for out-of-province patients. Results The Ministry of Health funded 15 Albertans for PBT in the USA in the 2014/15 fiscal year (mean CAD$ 237,348/patient). A single-vault, compact PBT unit operating 10 hours/day could treat 250 patients annually. A 100 Albertans, with accepted indications, such as the curative-intent treatment of chordomas, ocular melanomas, and selected pediatric cancers, would likely benefit annually from PBT's improved conformality and/or reduced integral dose compared to RT. The estimated capital cost was $40 million for a single beamline built within an ongoing capital project. Operating costs were $4.8 million/year at capacity. With 50% capacity reserved for non-Albertans at a cost recovery of $45,000/patient, a Western Canadian PBT facility would achieve net positive cash flow by year eight of clinical operations, assuming Alberta-to-USA referrals reach 21 patients/year by 2024 and increase at 3%/year thereafter. Sensitivity analysis indicates the lifetime net savings is robust to the assumptions made. Conclusion This business case, based on Canadian costing data and estimates, demonstrates the potential for a financially viable PBT facility in Western Canada.

Late Toxicity and Outcomes in High-risk Prostate Cancer Patients Treated With Hypofractionated IMRT and Long-term Androgen Suppression Treatment.

OBJECTIVE: To assess late toxicity and outcomes in high-risk prostate cancer patients treated with hypofractionated radiation treatment with androgen suppression therapy. METHODS: Sixty high-risk prostate cancer patients were enrolled. IMRT prescription was 68 Gy/25 fractions (2.7 Gy/fraction) to the prostate and proximal seminal vesicles (SV). The pelvic lymph nodes (PLN) and distal SV concurrently received 45 Gy/25 fractions (1.8 Gy/fraction). The patients were treated with helical TomoTherapy-based IMRT and underwent daily megavoltage CT image-guided verification before each treatment. RTOG Toxicity scores were recorded for a 5-year period. RESULTS: Sixty patients completed RT with median follow-up of 63 months (range, 7 to 80 mo).At 5 years follow-up timepoint: Grade (G)2 and G3 late genitourinary toxicity was experienced in 7 (17.0%) and 1 (2.44%), respectively; gastrointestinal G2 as highest toxicity recorded in only 1 (2.44%) patient. There was no G3 gastrointestinal toxicity recorded at this timepoint.With 63-month median follow-up (mean of 65.41±1.72 mo), the 5-year overall survival was 86.67%; 5 years freedom from biochemical failure was 91.67% and freedom from clinical failure was 96.67%. CONCLUSIONS: Dose escalation and hypofractionated radiation treatment with IMRT treating the prostate and proximal SV concurrently with the pelvic lymph nodes and distal SV and long-term androgen suppression therapy is well tolerated with respect to acute and late toxicity with 5-year actuarial overall survival 86.67%, freedom from biochemical failure 91.38%, and freedom from clinical failure 96.67%. Longer follow-up will provide more information on 10-year survival outcomes.

Clinical evaluation of normalized metal artifact reduction in kVCT using MVCT prior images (MVCT-NMAR) for radiation therapy treatment planning.

PURPOSE: To evaluate the metal artifacts in diagnostic kilovoltage computed tomography (kVCT) images of patients that are corrected by use of a normalized metal artifact reduction (NMAR) method with megavoltage CT (MVCT) prior images: MVCT-NMAR. METHODS AND MATERIALS: MVCT-NMAR was applied to images from 5 patients: 3 with dual hip prostheses, 1 with a single hip prosthesis, and 1 with dental fillings. The corrected images were evaluated for visualization of tissue structures and their interfaces and for radiation therapy dose calculations. They were compared against the corresponding images corrected by the commercial orthopedic metal artifact reduction algorithm in a Phillips CT scanner. RESULTS: The use of MVCT images for correcting kVCT images in the MVCT-NMAR technique greatly reduces metal artifacts, avoids secondary artifacts, and makes patient images more useful for correct dose calculation in radiation therapy. These improvements are significant, provided the MVCT and kVCT images are correctly registered. The remaining and the secondary artifacts (soft tissue blurring, eroded bones, false bones or air pockets, CT number cupping within the metal) present in orthopedic metal artifact reduction corrected images are removed in the MVCT-NMAR corrected images. A large dose reduction was possible outside the planning target volume (eg, 59.2 Gy to 52.5 Gy in pubic bone) when these MVCT-NMAR corrected images were used in TomoTherapy treatment plans without directional blocks for a prostate cancer patient. CONCLUSIONS: The use of MVCT-NMAR corrected images in radiation therapy treatment planning could improve the treatment plan quality for patients with metallic implants.

First demonstration of intrafractional tumor-tracked irradiation using 2D phantom MR images on a prototype linac-MR.

PURPOSE: To demonstrate intrafractional MR tumor tracking using a prototype linac-MR by delivering radiation to a moving target undergoing simulated tumor motions. METHODS: A prototype linac-MR at the Cross Cancer Institute was used for intrafractional MR imaging and simultaneous beam delivery. A Varian 52-leaf MK-II multileaf collimator (MLC) was used for beam collimation. The authors used an inhouse built MR compatible motion phantom to simulate tumor motions during tracking with two different motion patterns (sine and modified cosine). Gafchromic film was inserted in the phantom to measure radiation exposure, and this film measurement was converted to dose (cGy) for further analysis. The authors demonstrated intrafractional tracking in various scenarios: [Scenario 0 (S0)] no phantom motion + no beam margin, (S1) no phantom motion + maximum beam margin, (S2) phantom motion + no beam margin, (S3) S2 + MLC tracking, and (S4) S3 + motion prediction. S0 emulates a perfect tumor tracking scenario, and its result was used as a "gold-standard" to evaluate tracking accuracy from other scenarios. The authors compared (1) time difference in phantom and MLC motion curves in S3 and S4, and (2) dose profiles (50% beam width, 80%-20% penumbra width) from scenarios S1-S4 to S0. RESULTS: In S4, no observable time difference exists between the phantom and MLC motion curves, indicating that MLC tracks phantom motion accurately. Comparing S4 to S0, 50% beam width reveals minimal differences of < 0.5 mm, while the increase in 80%-20% penumbra width is limited to 0.4 and 1.7 mm in the sine and modified cosine patterns, respectively. CONCLUSIONS: The authors report the first demonstration of intrafractional tumor tracking using 2D MR images. During 2 min of tracking, the authors delivered highly conformal dose to a moving target that simulates tumor motions. Compared to static target irradiation, the 50% beam width remains essentially the same (within 0.5 mm), with an increase in 80%-20% penumbra width of less than 1.7 mm in moving target irradiation. These results illustrate potential dosimetric advantages of intrafractional MR tumor tracking in treating mobile tumors as shown for the phantom case.

Phase I study of hypofractionated intensity modulated radiation therapy with concurrent and adjuvant temozolomide in patients with glioblastoma multiforme.

PURPOSE: To determine the safety and efficacy of hypofractionated intensity modulated radiation therapy (Hypo-IMRT) using helical tomotherapy (HT) with concurrent low dose temozolomide (TMZ) followed by adjuvant TMZ in patients with glioblastoma multiforme (GBM). METHODS AND MATERIALS: Adult patients with GBM and KPS > 70 were prospectively enrolled between 2005 and 2007 in this phase I study. The Fibonacci dose escalation protocol was implemented to establish a safe radiation fractionation regimen. The protocol defined radiation therapy (RT) dose level I as 54.4 Gy in 20 fractions over 4 weeks and dose level II as 60 Gy in 22 fractions over 4.5 weeks. Concurrent TMZ followed by adjuvant TMZ was given according to the Stupp regimen. The primary endpoints were feasibility and safety of Hypo-IMRT with concurrent TMZ. Secondary endpoints included progression free survival (PFS), pattern of failure, overall survival (OS) and incidence of pseudoprogression. The latter was defined as clinical or radiological suggestion of tumour progression within three months of radiation completion followed by spontaneous recovery of the patient. RESULTS: A total of 25 patients were prospectively enrolled with a median follow-up of 12.4 months. The median age at diagnosis was 53 years. Based on recursive partitioning analysis (RPA) criteria, 16%, 52% and 32% of the patients were RPA class III, class IV and class V, respectively. All patients completed concurrent RT and TMZ, and 19 patients (76.0%) received adjuvant TMZ. The median OS was 15.67 months (95% CI 11.56 - 20.04) and the median PFS was 6.7 months (95% CI 4.0 - 14.0). The median time between surgery and start of RT was 44 days (range of 28 to 77 days). Delaying radiation therapy by more than 6 weeks after surgery was an independent prognostic factor associated with a worse OS (4.0 vs. 16.1 months, P = 0.027). All recurrences occurred within 2 cm of the original gross tumour volume (GTV). No cases of pseudoprogression were identified in our cohort of patients. Three patients tolerated dose level I with no dose limiting toxicity and hence the remainder of the patients were treated with dose level II according to the dose escalation protocol. Grade 3-4 hematological toxicity was limited to two patients and one patient developed Grade 4 Pneumocystis jiroveci pneumonia. CONCLUSION: Hypo-IMRT using HT given with concurrent TMZ is feasible and safe. The median OS and PFS are comparable to those observed with conventional fractionation. Hypofractionated radiation therapy offers the advantage of a shorter treatment period which is imperative in this group of patients with limited life expectancy.

An artificial neural network (ANN)-based lung-tumor motion predictor for intrafractional MR tumor tracking.

PURPOSE: To address practical issues of implementing artificial neural networks (ANN) for lung-tumor motion prediction in MRI-based intrafractional lung-tumor tracking. METHODS: A feedforward four-layered ANN structure is used to predict future tumor positions. A back-propagation algorithm is used for ANN learning. Adaptive learning is incorporated by continuously updating weights and learning rate during prediction. An ANN training scheme specific for MRI-based tracking is developed. A multiple-ANN structure is developed to reduce tracking failures caused by the lower imaging rates of MRI. We used particle swarm optimization to optimize the ANN structure and initial weights (IW) for each patient and treatment fraction. Prediction accuracy is evaluated using the 1D superior-inferior lung-tumor motions of 29 lung cancer patients for system delays of 120-520 ms, in increments of 80 ms. The result is compared with four different scenarios: (1), (2) ANN structure optimization + with∕without IW optimization, and (3), (4) no ANN structure optimization + with∕without IW optimization, respectively. An additional simulation is performed to assess the value of optimizing the ANN structure for each treatment fraction. RESULTS: For 120-520 ms system delays, mean RMSE values (ranges 0.0-2.8 mm from 29 patients) of 0.5-0.9 mm are observed, respectively. Using patient specific ANN structures, a 30%-60% decrease in mean RMSE values is observed as a result of IW optimization, alone. No significant advantages in prediction performance are observed, however, by optimizing for each fraction. CONCLUSIONS: A new ANN-based lung-tumor motion predictor is developed for MRI-based intrafractional tumor tracking. The prediction accuracy of our predictor is evaluated using a realistic simulated MR imaging rate and system delays. For 120-520 ms system delays, mean RMSE values of 0.5-0.9 mm (ranges 0.0-2.8 mm from 29 patients) are achieved. Further, the advantage of patient specific ANN structure and IW in lung-tumor motion prediction is demonstrated by a 30%-60% decrease in mean RMSE values.

Skin-sparing helical tomotherapy vs 3D-conformal radiotherapy for adjuvant breast radiotherapy: in vivo skin dosimetry study.

PURPOSE: We investigated whether treatment-planning system (TPS)-calculated dose accurately reflects skin dose received for patients receiving adjuvant breast radiotherapy (RT) with standard three-dimensional conformal RT (3D-CRT) or skin-sparing helical tomotherapy (HT). METHODS AND MATERIALS: Fifty patients enrolled in a randomized controlled trial investigating acute skin toxicity from adjuvant breast RT with 3D-CRT compared to skin-sparing HT, where a 5-mm strip of ipsilateral breast skin was spared. Thermoluminescent dosimetry or optically stimulated luminescence measurements were made in multiple locations and were compared to TPS-calculated doses. Skin dosimetric parameters and acute skin toxicity were recorded in these patients. RESULTS: With HT there was a significant correlation between calculated and measured dose in the medial and lateral ipsilateral breast (r = 0.67, P<.001; r = 0.44, P=.03, respectively) and the medial and central contralateral breast (r = 0.73, P<.001; r = 0.88, P<.001, respectively). With 3D-CRT there was a significant correlation in the medial and lateral ipsilateral breast (r = 0.45, P=.03; r = 0.68, P<.001, respectively); the medial and central contralateral breast (r = 0.62, P=.001; r = 0.86, P<.001, respectively); and the mid neck (r = 0.42, P=.04, respectively). On average, HT-calculated dose overestimated the measured dose by 14%; 3D-CRT underestimated the dose by 0.4%. There was a borderline association between highest measured skin dose and moist desquamation (P=.05). Skin-sparing HT had greater skin homogeneity (homogeneity index of 1.39 vs 1.65, respectively; P=.005) than 3D-CRT plans. HT plans had a lower skin(V50) (1.4% vs 5.9%, respectively; P=.001) but higher skin(V40) and skin(V30) (71.7% vs 64.0%, P=.02; and 99.0% vs 93.8%, P=.001, respectively) than 3D-CRT plans. CONCLUSION: The 3D-CRT TPS more accurately reflected skin dose than the HT TPS, which tended to overestimate dose received by 14% in patients receiving adjuvant breast RT.

Evaluation of a lung tumor autocontouring algorithm for intrafractional tumor tracking using low-field MRI: a phantom study.

PURPOSE: The first aim of this study is to investigate the feasibility of online autocontouring of tumor in low field MR images (0.2 and 0.5 T) by means of a phantom and simulation study for tumor-tracking in linac-MR systems. The second aim of this study is to develop an MR compatible, lung tumor motion phantom. METHODS: An autocontouring algorithm was developed to determine both the position and shape of a lung tumor from each intra fractional MR image. To initiate the algorithm, an expert user contours the tumor and its maximum anticipated range of motion (herein termed the Background) using pretreatment scan data. During treatment, the algorithm processes each intrafractional MR image and automatically contours the tumor. To evaluate this algorithm, the authors built a phantom that replicates the low field contrast parameters (proton density, T(1), T(2)) of lung tumors and healthy lung parenchyma. This phantom allows simulation of MR images with the expected lung tumor CNR at 0.2 and 0.5 T by using a single 3 T scanner. Dynamic bSSFP images (approximately 4 images per second) are acquired while the phantom undergoes a series of preprogrammed motions based on patient lung tumor motion data. These images are autocontoured off-line using our algorithm. The fidelity of autocontouring is assessed by comparing autocontoured tumor shape and its centroid position to the actual tumor shape and its position. RESULTS: The algorithm successfully contoured the shape of a moving tumor model from dynamic MR images acquired every 275 ms. Dice's coefficients of > 0.96 and > 0.93 are achieved in 0.5 and 0.2 T equivalent images, respectively. Also, the algorithm tracked tumor position during dynamic studies, with root mean squared error (RMSE) values of < 0.55 and < 0.92 mm for 0.5 and 0.2 T equivalent images, respectively. Autocontouring speed is approximately 5 ms for each image. CONCLUSIONS: Dice's coefficients of > 0.96 and > 0.93 are achieved between autocontoured and real tumor shapes, and the position of a tumor can be tracked with RMSE values of < 0.55 and < 0.92 mm in 0.5 and 0.2 T equivalent images, respectively. These results demonstrate the feasibility of lung tumor autocontouring in low field MR images, and, by extension, intrafractional lung tumor tracking with our laboratory's linac-MR system.

Acute toxicity in high-risk prostate cancer patients treated with androgen suppression and hypofractionated intensity-modulated radiotherapy.

PURPOSE: To report acute toxicity resulting from radiotherapy (RT) dose escalation and hypofractionation using intensity-modulated RT (IMRT) treatment combined with androgen suppression in high-risk prostate cancer patients. METHODS AND MATERIALS: Sixty patients with a histological diagnosis of high-risk prostatic adenocarcinoma (having either a clinical Stage of > or =T3a or an initial prostate-specific antigen [PSA] level of > or =20 ng/ml or a Gleason score of 8 to 10 or a combination of a PSA concentration of >15 ng/ml and a Gleason score of 7) were enrolled. RT prescription was 68 Gy in 25 fractions (2.72 Gy/fraction) over 5 weeks to the prostate and proximal seminal vesicles. The pelvic lymph nodes and distal seminal vesicles concurrently received 45 Gy in 25 fractions. The patients were treated with helical TomoTherapy-based IMRT and underwent daily megavoltage CT image-guided verification prior to each treatment. Acute toxicity scores were recorded weekly during RT and at 3 months post-RT, using Radiation Therapy Oncology Group acute toxicity scales. RESULTS: All patients completed RT and follow up for 3 months. The maximum acute toxicity scores were as follows: 21 (35%) patients had Grade 2 gastrointestinal (GI) toxicity; 4 (6.67%) patients had Grade 3 genitourinary (GU) toxicity; and 30 (33.33%) patients had Grade 2 GU toxicity. These toxicity scores were reduced after RT; there were only 8 (13.6%) patients with Grade 1 GI toxicity, 11 (18.97%) with Grade 1 GU toxicity, and 5 (8.62%) with Grade 2 GU toxicity at 3 months follow up. Only the V60 to the rectum correlated with the GI toxicity. CONCLUSION: Dose escalation using a hypofractionated schedule to the prostate with concurrent pelvic lymph node RT and long-term androgen suppression therapy is well tolerated acutely. Longer follow up for outcome and late toxicity is required.

Assessment of extended-field radiotherapy for stage IIIC endometrial cancer using three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, and helical tomotherapy.

PURPOSE: To perform a dosimetric comparison of three-dimensional conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), and helical tomotherapy (HT) plans for pelvic and para-aortic RT in postoperative endometrial cancer patients; and to evaluate the integral dose (ID) received by critical structures within the radiation fields. METHODS AND MATERIALS: We selected 10 patients with Stage IIIC endometrial cancer. For each patient, three plans were created with 3D-CRT, IMRT, and HT. The IMRT and HT plans were both optimized to keep the mean dose to the planning target volume (PTV) the same as that with 3D-CRT. The dosimetry and ID for the critical structures were compared. A paired two-tailed Student t test was used for data analysis. RESULTS: Compared with the 3D-CRT plans, the IMRT plans resulted in lower IDs in the organs at risk (OARs), ranging from -3.49% to -17.59%. The HT plans showed a similar result except that the ID for the bowel increased 0.27%. The IMRT and HT plans both increased the IDs to normal tissue (see Table 1 and text for definition), pelvic bone, and spine (range, 3.31-19.7%). The IMRT and HT dosimetry showed superior PTV coverage and better OAR sparing than the 3D-CRT dosimetry. Compared directly with IMRT, HT showed similar PTV coverage, lower Ids, and a decreased dose to most OARs. CONCLUSION: Intensity-modulated RT and HT appear to achieve excellent PTV coverage and better sparing of OARs, but at the expense of increased IDs to normal tissue and skeleton. HT allows for additional improvement in dosimetry and sparing of most OARs.

Skin-sparing radiation using intensity-modulated radiotherapy after conservative surgery in early-stage breast cancer: a planning study.

PURPOSE: To evaluate the feasibility of skin-sparing by configuring it as an organ-at-risk (OAR) while delivering whole-breast intensity-modulated radiotherapy (IMRT) in early breast cancer. METHODS AND MATERIALS: Archival computed tomography scan images of 14 left-sided early-breast tumor patients who had undergone lumpectomy were selected for this study. Skin was contoured as a 4- to 5-mm strip extending from the patient outline to anterior margin of the breast planning target volume (PTV). Two IMRT plans were generated by the helical tomotherapy approach to deliver 50 Gy in 25 fractions to the breast alone: one with skin dose constraints (skin-sparing plan) and the other without (non-skin-sparing plan). Comparison of the plans was done using a two-sided paired Student t test. RESULTS: The mean skin dose and volume of skin receiving 50 Gy were significantly less with the skin-sparing plan compared with non-skin-sparing plan (42.3 Gy vs. 47.7 Gy and 12.2% vs. 57.8% respectively; p < 0.001). The reduction in skin dose was confirmed by TLD measurements in anthropomorphic phantom using the same plans. Dose-volume analyses for other OARs were similar in both plans. CONCLUSIONS: By configuring the skin as an OAR, it is possible to achieve skin dose reduction while delivering whole-breast IMRT without compromising dose profiles to PTV and OARs.

Sparing the parotid glands and surgically transferred submandibular gland with helical tomotherapy in post-operative radiation of head and neck cancer: a planning study.

BACKGROUND AND PURPOSE: To evaluate the feasibility of sparing the parotid glands and surgically transferred submandibular gland (SMG) by intensity modulated radiotherapy (IMRT) in post-operative cases of head and neck cancer (HNC). MATERIALS AND METHODS: Ten patients (larynx-2, base of tongue-4, tonsil-3, and unknown primary-1; pathologic stages III-IV) who underwent SMG transfers on the side of N0 neck along with definitive surgery were selected for this study. IMRT planning was done retrospectively using helical tomotherapy approach. Planning objective was to deliver 60 Gy to PTV1 and 54 Gy to PTV2 while maintaining the mean dose to the total parotid volume (TPV) and SMG less than 26 Gy. RESULTS: The mean dose (+/-SD) to the TPV and SMG were 25+/-0.6 Gy and 23+/-1.9 Gy, respectively. The D(95) for PTV1 and PTV2 were 59.9+/-0.1 Gy and 54.9+/-0.3 Gy, respectively, satisfying our planning goal for PTV coverage. The D(99) for PTV1 and PTV2 were 58.2+/-0.7 Gy and 49.5+/-2.2 Gy, respectively, showing that sparing the salivary glands did not result in underdosing of the PTVs. CONCLUSIONS: By combining the gland transfer and IMRT, the mean dose to TPV and transferred SMG could be reduced to less than 26 Gy in post-operative patients of HNC.

Quantifying appropriate PTV setup margins: analysis of patient setup fidelity and intrafraction motion using post-treatment megavoltage computed tomography scans.

PURPOSE: To present a technique that can be implemented in-house to evaluate the efficacy of immobilization and image-guided setup of patients with different treatment sites on helical tomotherapy. This technique uses an analysis of alignment shifts between kilovoltage computed tomography and post-treatment megavoltage computed tomography images. The determination of the shifts calculated by the helical tomotherapy software for a given site can then be used to define appropriate planning target volume internal margins. METHODS AND MATERIALS: Twelve patients underwent post-treatment megavoltage computed tomography scans on a helical tomotherapy machine to assess patient setup fidelity and net intrafraction motion. Shifts were studied for the prostate, head and neck, and glioblastoma multiforme. Analysis of these data was performed using automatic and manual registration of the kilovoltage computed tomography and post-megavoltage computed tomography images. RESULTS: The shifts were largest for the prostate, followed by the head and neck, with glioblastoma multiforme having the smallest shifts in general. It appears that it might be more appropriate to use asymmetric planning target volume margins. Each margin value reported is equal to two standard deviations of the average shift in the given direction. CONCLUSION: This method could be applied using individual patient post-image scanning and combined with adaptive planning to reduce or increase the margins as appropriate.

Experimental validation of the Eclipse AAA algorithm.

The present study evaluates the performance of a newly released photon-beam dose calculation algorithm that is incorporated into an established treatment planning system (TPS). We compared the analytical anisotropic algorithm (AAA) factory-commissioned with "golden beam data" for Varian linear accelerators with measurements performed at two institutions using 6-MV and 15-MV beams. The TG-53 evaluation regions and criteria were used to evaluate profiles measured in a water phantom for a wide variety of clinically relevant beam geometries. The total scatter factor (TSF) for each of these geometries was also measured and compared against the results from the AAA. At one institute, TLD measurements were performed at several points in the neck and thoracic regions of a Rando phantom; at the other institution, ion chamber measurements were performed in a CIRS inhomogeneous phantom. The phantoms were both imaged using computed tomography (CT), and the dose was calculated using the AAA at corresponding detector locations. Evaluation of measured relative dose profiles revealed that 97%, 99%, 97%, and 100% of points at one institute and 96%, 88%, 89%, and 100% of points at the other institution passed TG-53 evaluation criteria in the outer beam, penumbra, inner beam, and buildup regions respectively. Poorer results in the inner beam regions at one institute are attributed to the mismatch of the measured profiles at shallow depths with the "golden beam data." For validation of monitor unit (MU) calculations, the mean difference between measured and calculated TSFs was less than 0.5%; test cases involving physical wedges had, in general, differences of more than 1%. The mean difference between point measurements performed in inhomogeneous phantoms and Eclipse was 2.1% (5.3% maximum) and all differences were within TG-53 guidelines of 7%. By intent, the methods and evaluation techniques were similar to those in a previous investigation involving another convolution-superposition photon-beam dose calculation algorithm in another TPS, so that the current work permitted an independent comparison between the two algorithms for which results have been provided.

Comparing step-and-shoot IMRT with dynamic helical tomotherapy IMRT plans for head-and-neck cancer.

PURPOSE: The goal of this planning study was to compare step-and-shoot intensity-modulated radiotherapy (IMRT) plans with helical dynamic IMRT plans for oropharynx patients on the basis of dose distribution. METHODS AND MATERIALS: Five patients with oropharynx cancer had been previously treated by step-and-shoot IMRT at the University Medical Centre Utrecht, The Netherlands, applying five fields and approximately 60-90 segments. Inverse planning was carried out using Plato, version 2.6.2. For each patient, an inverse IMRT plan was also made using Tomotherapy Hi-Art System, version 2.0, and using the same targets and optimization goals. Statistical analysis was performed by a paired t test. RESULTS: All tomotherapy plans compared favorably with the step-and-shoot plans regarding sparing of the organs at risk and keeping an equivalent target dose homogeneity. Tomotherapy plans in particular realized sharper dose gradients compared with the step-and-shoot plans. The mean dose to all parotid glands (n = 10) decreased on average 6.5 Gy (range, -4 to 14; p = 0.002). The theoretical reduction in normal tissue complication probabilities in favor of the tomotherapy plans depended on the parotid normal tissue complication probability model used (range, -3% to 32%). CONCLUSION: Helical tomotherapy IMRT plans realized sharper dose gradients compared with the clinically applied step-and shoot plans. They are expected to be able to reduce the parotid normal tissue complication probability further, keeping a similar target dose homogeneity.