Brent C. Parker

Does treatment of the pelvic nodes with IMRT increase late rectal toxicity over conformal prostate-only radiotherapy to 76 Gy?

Purpose:To compare late rectal toxicity rates after three-dimensional conformal radiotherapy to the prostate alone (P-3D-CRT) and whole-pelvis intensity-modulated radiotherapy along with a prostate boost (WP-IMRT/PB) to the same nominal total dose to the prostate.Patients and Methods:68 patients treated with conformal radiotherapy to the prostate only to 76 Gy at the National Institute for Cancer Research, Genoa, Italy, represented the first group (P-3D-CRT). The second group consisted of 45 patients treated at the University of Texas Medical Branch (UTMB), Galveston, TX, USA, with IMRT covering the pelvic nodes and seminal vesicles to 54 Gy at 1.8 Gy per fraction and the prostate to 60 Gy in the same 30 fractions. A separate phase boosted the prostate to 76 Gy (WP-IMRT/PB). Major aspects of planning were remarkably similar at both institutions leaving the inclusion or not of pelvic nodes as the main treatment-related difference between the two groups. Late rectal toxicity was prospectively scored according to the RTOG scale. All patients have a 12-month minimum follow-up, and mean follow-up, similar in both groups, is 25.9 months (SD [standard deviation]: 8.4 months).Results:At 2 years, the estimated cumulative incidence of grade 2 late rectal toxicity is 6% ± 4% for WP-IMRT/PB and 21.2% ± 6% for P-3D-CRT (p = 0.06). The difference became significant (HR [hazard ratio] = 0.1, 95% CI [confidence interval]: 0.0–0.6; p = 0.01) at multivariate analysis. None of the patients developed grade 3+ toxicity.Conclusion:Despite the larger treated volume, WP-IMRT/PB allows more rectal sparing than P-3D-CRT.Ziel:Vergleich der rektalen Spättoxizität nach alleiniger dreidimensionaler konformaler Strahlentherapie der Prostata (P-3D-CRT) und nach intensitätsmodulierter Radiotherapie des gesamten Beckens mit Prostataradiochirurgie (WP-IMRT/PB) bei gleicher Gesamtdosis.Patienten und Methodik:Die erste Gruppe bestand aus 68 Patienten, die eine alleinige konformale Strahlentherapie der Prostata bis 76 Gy am National Institute for Cancer Research in Genua, Italien, erhielten (P-3D-CRT). Die zweite Gruppe umfasste 45 Patienten, welche am University of Texas Medical Branch (UTMB), Galveston, TX, USA, mit IMRT der Beckenlymphknoten und der Samenbläschen bis 54 Gy zu 1,8 Gy pro Fraktion und der Prostata bis 60 Gy, ebenfalls in 30 Fraktionen, behandelt wurden. Die Radiochirurgie der Prostata erfolgte separat bis 76 Gy (WP-IMRT/PB). Die Hauptaspekte bei der Planung waren an beiden Einrichtungen bemerkenswert ähnlich, so dass lediglich die Frage des Einschlusses der Beckenlymphknoten als Hauptunterschied bei der Behandlung der beiden Gruppen übrig blieb. Die rektale Spättoxizität wurde anhand der RTOG-Skala bewertet. Alle Patienten erhalten eine mindestens 12-monatige Nachsorge; die durchschnittliche Nachsorgedauer beträgt bei beiden Gruppen 25,9 Monate (SD [Standardabweichung]: 8,4 Monate).Ergebnisse:Nach 2 Jahren liegt die geschätzte kumulative Inzidenz der rektalen Spättoxizität Grad 2 bei 6% ± 4% für WP-IMRT/PB und 21,2% ± 6% für P-3D-CRT (p = 0,06). Der Unterschied wurde bei der Multivarianzanalyse signifikant (HR [Hazard-Ratio] = 0,1, 95%-CI [Konfidenzintervall]: 0,0–0,6; p = 0,01). Kein Patient entwickelte eine rektale Spättoxizität Grad 3+.Schlussfolgerung:Trotz des größeren Behandlungsumfangs ermöglicht die WP-IMRT/PB eine schonendere Behandlung des Rektalbereichs als die P-3D-CRT.

Acute toxicity of whole-pelvis IMRT in 87 patients with localized prostate cancer

Purpose. To assess the acute toxicity profile of whole pelvis IMRT (WP-IMRT) for localized prostate cancer. Materials. Eighty seven patients treated with definitive WP-IMRT at UTMB from May 2002 to November 2006 were retrospectively reviewed. Treatment consisted of two sequential phases, WP-IMRT to 54 Gy at 1.8 Gy per fraction to the pelvic nodes and seminal vesicles and 60 Gy at 2 Gy to the prostate, and a separate external beam boost, 3DCRT or IMRT, to bring the dose to the prostate to 76 Gy. Acute toxicity was prospectively scored weekly during treatment and at 3 month follow-up according to CTC v2.0 for 10 genitourinary (GU) and gastrointestinal (GI) domains. The proportion of patients experiencing a given level of peak acute toxicity at a given point is reported. Results. Treatment was feasible with delivered doses to PTVs not significantly lower than planned ones and with only two patients experiencing treatment gaps longer than 5 days. About 2/3 and 1/10 of the patients experienced peak grade 2 and grade 3 reactions at least once during RT, respectively. Frequency/urgency (Grade 2+: 37.9%) and diarrhea (36.7%) were the most prevalent symptoms followed by proctitis (21.8%) and dysuria (16.1%). GI reactions were generally shorter lasting compared to GU ones which accumulated progressively during treatment. At 3 months, almost half of the patients were asymptomatic and most of observed reactions (89.2%) were mild, with GI ones more likely to be fully resolved (92.5%) than GU ones (68.7%, χ2, p=0.001). Conclusion. Our approach is dosimetrically and clinically feasible with intense, but transient, acute toxicity.

Comparison of action levels for patient‐specific quality assurance of intensity modulated radiation therapy and volumetric modulated arc therapy treatments

PURPOSE To perform a comprehensive and systematic comparison of fixed-beam IMRT and volumetric modulated arc therapy (VMAT) patient-specific QA measurements for a common set of geometries using typical measurement methods. METHODS Fixed-beam IMRT and VMAT plans were constructed for structure set geometries provided by AAPM Task Group 119. The plans were repeatedly delivered across multiple measurement sessions, and the resulting dose distributions were measured with (1) radiochromic film and ionization chamber and (2) a commercial two-dimensional diode array. The resulting QA measurements from each delivery technique were then analyzed, compared, and tested for statistically significant differences. RESULTS Although differences were noted between QA results for some plans, neither modality showed consistently better agreement of measured and planned doses: of the 22 comparisons, IMRT showed better QA results in 11 cases, and VMAT showed better QA results in 11 cases. No statistically significant differences (p < 0.05) between IMRT and VMAT QA results were found for point doses measured with an ionization chamber, planar doses measured with radiochromic film, or planar doses measured with a two-dimensional diode array. CONCLUSIONS These results suggest that it is appropriate to apply patient-specific QA action levels derived from fixed-beam IMRT to VMAT.PURPOSE To perform a comprehensive and systematic comparison of fixed-beam IMRT and volumetric modulated arc therapy (VMAT) patient-specific QA measurements for a common set of geometries using typical measurement methods. METHODS Fixed-beam IMRT and VMAT plans were constructed for structure set geometries provided by AAPM Task Group 119. The plans were repeatedly delivered across multiple measurement sessions, and the resulting dose distributions were measured with (1) radiochromic film and ionization chamber and (2) a commercial two-dimensional diode array. The resulting QA measurements from each delivery technique were then analyzed, compared, and tested for statistically significant differences. RESULTS Although differences were noted between QA results for some plans, neither modality showed consistently better agreement of measured and planned doses: of the 22 comparisons, IMRT showed better QA results in 11 cases, and VMAT showed better QA results in 11 cases. No statistically significant differences (p < 0.05) between IMRT and VMAT QA results were found for point doses measured with an ionization chamber, planar doses measured with radiochromic film, or planar doses measured with a two-dimensional diode array. CONCLUSIONS These results suggest that it is appropriate to apply patient-specific QA action levels derived from fixed-beam IMRT to VMAT.

Dosimetric predictors of diarrhea during radiotherapy for prostate cancer

Purpose:To investigate dosimetric predictors of diarrhea during radiotherapy (RT) for prostate cancer.Patients and Methods:All patients who underwent external-beam radiotherapy as part of treatment for localized prostate cancer at the University of Texas Medical Branch, Galveston, TX, USA, from May 2002 to November 2006 were extracted from the own database. From the cumulative dose-volume histogram (DVH), the absolute volumes (V-value) of intestinal cavity (IC) receiving 15, 30, and 45 Gy were extracted for each patient. Acute gastrointestinal toxicity was prospectively scored at each weekly treatment visit according to CTC (Common Toxicity Criteria) v2.0. The endpoint was the development of peak grade ≥ 2 diarrhea during RT. Various patient, tumor, and treatment characteristics were evaluated using logistic regression.Results:149 patients were included in the analysis, 112 (75.2%) treated with whole-pelvis intensity-modulated radiotherapy (WP-IMRT) and 37 (24.8%) with prostate-only RT, including or not including, the seminal vesicles (PORT ± SV). 45 patients (30.2%) developed peak grade ≥ 2 diarrhea during treatment. At univariate analysis, IC-V15 and IC-V30, but not IC-V45, were correlated to the endpoint; at multivariate analysis, only IC-V15 (p = 0.047) along with peak acute proctitis (p = 0.041) was independently correlated with the endpoint.Conclusion:These data provide a novel and prostate treatment-specific “upper limit” DVH for IC.Ziel:Untersuchung der dosimetrischen Prädiktoren einer Diarrhö bei der Strahlentherapie (RT) von Prostatakarzinomen.Patienten und Methodik:Alle Patienten, die sich von Mai 2002 bis November 2006 am UTMB (University of Texas Medical Branch), Galveston, TX, USA, im Rahmen der Behandlung lokalisierter Prostatakarzinome einer externen Strahlentherapie unterzogen, wurden aus der eigenen Datenbank extrahiert. Aus dem kumulativen Dosis-Volumen-Histogramm (DVH) wurden für jeden Patienten die absoluten Volumina (V-Wert) der Eingeweidehöhle (IC [„intestinal cavity“]), die 15, 30 und 45 Gy erhalten hatten, extrahiert. Die akute gastrointestinale Toxizität wurde prospektiv bei jeder wöchentlichen Therapiesitzung gemäß den CTC (Common Toxicity Criteria) v2.0 erfasst. Endpunkt war die Entwicklung einer Diarrhö Grad ≥ 2 während der RT. Verschiedene Patienten-, Tumor- und Behandlungscharakteristika wurden mit Hilfe der logistischen Regression bewertet.Ergebnisse:149 Patienten wurden in die Analyse eingeschlossen, wovon 112 (75,2%) eine intensitätsmodulierte Bestrahlung des gesamten Beckens (B-IMRT) und 37 (24,8%) eine alleinige Prostata-RT unter Ein- oder Ausschluss der Samenbläschen (PORT ± SV) erhielten. 45 Patienten (30,2%) entwickelten während der Behandlung eine Diarrhö Grad ≥ 2. Bei der univariaten Analyse korrelierten IC-V15 und IC-V30, nicht dagegen IC-V45 mit dem Endpunkt; bei der multivariaten Analyse fand sich nur für IC-V15 (p = 0,047) mit hochgradiger akuter Proktitis (p = 0,041) eine unabhängige Korrelation mit dem Endpunkt.Schlussfolgerung:Diese Daten stellen ein neues und für die Behandlung der Prostata spezifisches „Obergrenzen“-DVH für IC zur Verfügung.

PTV margin determination in conformal SRT of intracranial lesions

The planning target volume (PTV) includes the clinical target volume (CTV) to be irradiated and a margin to account for uncertainties in the treatment process. Uncertainties in miniature multileaf collimator (mMLC) leaf positioning, CT scanner spatial localization, CT‐MRI image fusion spatial localization, and Gill‐Thomas‐Cosman (GTC) relocatable head frame repositioning were quantified for the purpose of determining a minimum PTV margin that still delivers a satisfactory CTV dose. The measured uncertainties were then incorporated into a simple Monte Carlo calculation for evaluation of various margin and fraction combinations. Satisfactory CTV dosimetric criteria were selected to be a minimum CTV dose of 95% of the PTV dose and at least 95% of the CTV receiving 100% of the PTV dose. The measured uncertainties were assumed to be Gaussian distributions. Systematic errors were added linearly and random errors were added in quadrature assuming no correlation to arrive at the total combined error. The Monte Carlo simulation written for this work examined the distribution of cumulative dose volume histograms for a large patient population using various margin and fraction combinations to determine the smallest margin required to meet the established criteria. The program examined 5 and 30 fraction treatments, since those are the only fractionation schemes currently used at our institution. The fractionation schemes were evaluated using no margin, a margin of just the systematic component of the total uncertainty, and a margin of the systematic component plus one standard deviation of the total uncertainty. It was concluded that (i) a margin of the systematic error plus one standard deviation of the total uncertainty is the smallest PTV margin necessary to achieve the established CTV dose criteria, and (ii) it is necessary to determine the uncertainties introduced by the specific equipment and procedures used at each institution since the uncertainties may vary among locations. PACS number(s): 87.53.Kn, 87.53.Ly

Evaluation of a commercial flatbed document scanner and radiographic film scanner for radiochromic EBT film dosimetry

The purpose of this study was to quantify the performance and assess the utility of two different types of scanners for radiochromic EBT film dosimetry: a commercial flatbed document scanner and a widely used radiographic film scanner. We evaluated the Epson Perfection V700 Photo flatbed scanner and the Vidar VXR Dosimetry Pro Advantage scanner as measurement devices for radiochromic EBT film. Measurements were made of scan orientation effects, response uniformity, and scanner noise. Scanners were tested using films irradiated with eight separate 3×3 cm2 fields to doses ranging from 0.115–5.119 Gy. ImageJ and RIT software was used for analyzing the Epson and Vidar scans, respectively. For repeated scans of a single film, the measurements in each dose region were reproducible to within ±0.3% standard deviation (SD) with both scanners. Film‐to‐film variations for corresponding doses were measured to be within ±0.4% SD for both Epson scanner and Vidar scanners. Overall, the Epson scanner showed a 10% smaller range of pixel value compared to the Vidar scanner. Scanner noise was small: ±0.3% SD for the Epson and ±0.2% for the Vidar. Overall measurement uniformity for blank film in both systems was better than ±0.2%, provided that the leading and trailing 2 cm film edges were neglected in the Vidar system. In this region artifacts are attributed to the film rollers. Neither system demonstrated a clear measurement advantage. The Epson scanner is a relatively inexpensive method for analyzing radiochromic film, but there is a lack of commercially available software. For a clinic already using a Vidar scanner, applying it to radiochromic film is attractive because commercial software is available. However, care must be taken to avoid using the leading and trailing film edges. PACS number: 87.55.Qr

A phase I/II study of altered fractionated imrt alone for intermediate t-stage oropharyngeal carcinoma

Background and Purpose:To prospectively assess the feasibility and efficacy of an accelerated and hyperfractionated intensity- modulated radiation therapy (IMRT) schedule for intermediate T-stage oropharyngeal cancer.Patients and Methods:Patients with T3 or unfavorable T2 oropharyngeal squamous cell carcinoma were eligible; a three-dose level simultaneous integrated boost IMRT strategy was used, delivering 78, 69, and 60 Gy to gross disease, high-risk and low-risk target areas, respectively, in 60 twice daily fractions over 6 weeks. No sequential/concomitant systemic treatment or up-front radical surgery was allowed. Median follow-up is 41.7 months (range: 3.5–80.8 months).Results:25 patients were treated from 11/2002 to 11/2005. 92% of the individual fractions were delivered as scheduled. Grade 3 mucosal and skin toxicity was 100% and 72%, respectively, none of which persisted beyond 12 weeks; a percutaneous endoscopic gastrostomy tube was temporarily placed in 60% of patients. The estimated locoregional progression-free, distant metastases-free, and overall survival rates at 3 years were 86.3% ± 7.4%, 76.4% ± 9.6%, and 70.0% ± 9.6%, respectively. At the same time interval, the actuarial prevalence of grade 3+ CTCAE v3.0 toxicity was 26.1%.Conclusion:While the routine clinical use of this exploratory schedule is discouraged, it may represent the basis for future developments.ZusammenfassungHintergrund und Ziel:Untersuchung der Durchführbarkeit und Wirksamkeit einer akzelerierten und hyperfraktionierten intensitätsmodulierten Strahlentherapie (IMRT) bei Oropharynxkarzinom im T-Zwischenstadium im Rahmen einer prospektiven Studie.Patienten und Methodik:Für die Studienteilnahme eigneten sich Patienten mit T3- oder ungünstigem T2-Plattenepithelkarzinom der Oropharynxregion; es wurde eine IMRT-Strategie mit simultanem integrierten Boost und drei Bestrahlungsdosen von 78, 69 und 60 Gy auf stark betroffene Krankheitsbereiche und Zielbereiche mit hohem und niedrigem Risiko in 60 Fraktionen zweimal täglich über 6 Wochen eingesetzt. Eine folgende/gleichzeitige systemische Behandlung oder vorausgehende Radikaloperation war nicht erlaubt. Die mittlere Nachbeobachtungszeit betrug 41,7 Monate (Bereich: 3,5–80,8 Monate).Ergebnisse:25 Patienten wurden von 11/2002 bis 11/2005 behandelt. 92% der einzelnen Fraktionen wurden wie geplant verabreicht. Die Schleimhaut- bzw. Hauttoxizität des Grads 3 betrug 100% bzw. 72%. Bei 60% der Patienten musste vorübergehend eine perkutane endoskopische Gastrostomiesonde gelegt werden. Die geschätzte lokoregionale progressionsfreie Überlebensrate, die fernmetastasenfreie Überlebensrate und die Gesamtüberlebensrate nach 3 Jahren betrugen 86,3% ± 7,4%, 76,4% ± 9,6% bzw. 70,0% ± 9,6%. Im gleichen Zeitintervall lag die aktuarische Prävalenz der Toxizität des Grads 3+ nach CTCAE v3.0 bei 26,1%.Schlussfolgerung:Der routinemäßige klinische Einsatz dieses experimentellen Bestrahlungsplans wird nicht empfohlen, er kann aber als Basis für zukünftige Entwicklungen dienen.

Verification of Calculated Skin Doses in Postmastectomy Helical Tomotherapy

PURPOSE To verify the accuracy of calculated skin doses in helical tomotherapy for postmastectomy radiation therapy (PMRT). METHODS AND MATERIALS In vivo thermoluminescent dosimeters (TLDs) were used to measure the skin dose at multiple points in each of 14 patients throughout the course of treatment on a TomoTherapy Hi·Art II system, for a total of 420 TLD measurements. Five patients were evaluated near the location of the mastectomy scar, whereas 9 patients were evaluated throughout the treatment volume. The measured dose at each location was compared with calculations from the treatment planning system. RESULTS The mean difference and standard error of the mean difference between measurement and calculation for the scar measurements was -1.8% ± 0.2% (standard deviation [SD], 4.3%; range, -11.1% to 10.6%). The mean difference and standard error of the mean difference between measurement and calculation for measurements throughout the treatment volume was -3.0% ± 0.4% (SD, 4.7%; range, -18.4% to 12.6%). The mean difference and standard error of the mean difference between measurement and calculation for all measurements was -2.1% ± 0.2% (standard deviation, 4.5%: range, -18.4% to 12.6%). The mean difference between measured and calculated TLD doses was statistically significant at two standard deviations of the mean, but was not clinically significant (i.e., was <5%). However, 23% of the measured TLD doses differed from the calculated TLD doses by more than 5%. CONCLUSIONS The mean of the measured TLD doses agreed with TomoTherapy calculated TLD doses within our clinical criterion of 5%.

AAPM Medical Physics Practice Guideline 2.a: Commissioning and quality assurance of X-ray-based image-guided radiotherapy systems.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8,000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized.The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8,000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized.

Target localization accuracy in a respiratory phantom using BrainLab ExacTrac and 4DCT imaging

This study evaluated the accuracy of measuring the motion of an internal target using four‐dimensional computed tomography (4DCT) scanning and the BrainLAB ExacTrac X‐ray imaging system. Displacements of a metal coil implanted in a commercial respiratory phantom were measured in each system and compared to the known motion. A commercial respiratory motion phantom containing a metal coil as a surrogate target was used. Phantom longitudinal motions were sinusoidal with a 4.0 second period and amplitudes ranging from 5–25 mm. We acquired 4DCT and ExacTrac images of the coil at specified respiratory phases and recorded the coordinates of the coil ends. Coil displacement relative to the 0% phase (full‐inhale) position were computed for the ExacTrac and 4DCT imaging systems. Coil displacements were compared to known displacements based on the phantoms sinusoidal motion. Coil length distortion due to 4DCT phase binning was compared to the known physical length of the coil (31 mm). The maximum localization error for both coil endpoints for all motion settings was 3.5 mm for the 4DCT and 0.8 mm for the ExacTrac gating system. Coil length errors measured on the 4DCT were less than 0.8 mm at end inhale/exhale phases, but up to 8.3 mm at mid‐inhalation phases at the largest motion amplitude (25 mm). Due to the fast image acquisition time (100 ms), no coil distortion was observable in the ExacTrac system. 4DCT showed problems imaging the coil during mid‐respiratory phases of higher velocity (phases 20%–30% and 70%–80%) due to distortion caused by residual motion within the 4DCT phase bin. The ExacTrac imaging system was able to accurately localize the coil in the respiratory phantom over all phases of respiration. For our clinic, where end‐respiration phases from 4DCT may be used for treatment planning calculations, the ExacTrac system is used to measure internal target motion. With the ExacTrac system, planning target size and motion uncertainties are minimized, potentially reducing internal target volume margins in gated radiotherapy. PACS number: 87.56.‐v