Shane P. Krafft

Effectiveness of image-guided radiotherapy for laryngeal sparing in head and neck cancer

We would like to compare the effectiveness of image-guided (IGRT) and intensity-modulated (IMRT) radiotherapy to spare the larynx in head and neck cancer patients. A retrospective review of 48 patients undergoing radiation for non-laryngeal and non-hypopharyngeal head and neck cancers. Mean laryngeal and hypopharyngeal dose was compared between 11 patients treated with IMRT and 37 patients treated with IGRT. Mean laryngeal dose was, respectively, 41.2 Gy and 22.8 Gy for the IMRT and IGRT technique (p<0.001). The radiation dose to the middle and inferior pharyngeal muscles was also significantly reduced with the IGRT technique. Mean pharyngeal dose was, respectively, 52 Gy and 26 Gy for the IMRT and IGRT technique (p=0.0001). Laryngeal sparing IGRT technique for head and neck cancer minimizes radiotherapy dose to the larynx and pharynx without sacrificing target coverage, even in the presence of neck lymph nodes.

Feasibility of Tomotherapy to spare the cochlea from excessive radiation in head and neck cancer

We would like to evaluate the effectiveness of Tomotherapy for decreasing radiation dose to the cochlea in head and neck cancer patients. A retrospective review of 72 patients undergoing radiation for head and neck cancer was performed. Cochlea dose was compared between 20 patients treated with conventional intensity modulated radiotherapy (IMRT) and 52 treated with Tomotherapy. A review of literature was performed to assess cochlea dose reported with the IMRT technique for head and neck cancer. Mean total cochlea dose was 36 Gy for IMRT compared to 12.1 Gy for Tomotherapy (p=0.002). Mean right cochlea dose was respectively, 16.6 and 6.2 Gy for IMRT and Tomotherapy (p=0.007), and 19.3 and 5.9 Gy for the left. Cochlea (p=0.002). Mean cochlea dose reported in the literature ranged from 16 to 55 Gy with IMRT for head and neck cancer. Helical Tomotherapy for head and neck cancer may significantly decrease radiation dose to the cochlea without sacrificing target volume coverage.

Feasibility of tomotherapy to reduce normal lung and cardiac toxicity for distal esophageal cancer compared to three-dimensional radiotherapy

PURPOSE To compare the effectiveness of tomotherapy and three-dimensional (3D) conformal radiotherapy to spare normal critical structures (spinal cord, lungs, and ventricles) from excessive radiation in patients with distal esophageal cancers. MATERIALS AND METHODS A retrospective dosimetric study of nine patients who had advanced gastro-esophageal (GE) junction cancer (7) or thoracic esophageal cancer (2) extending into the distal esophagus. Two plans were created for each of the patients. A three-dimensional plan was constructed with either three (anteroposterior, right posterior oblique, and left posterior oblique) or four (right anterior oblique, left anterior oblique, right posterior oblique, and left posterior oblique) fields. The second plan was for tomotherapy. Doses were 45 Gy to the PTV with an integrated boost of 5 Gy for tomotherapy. RESULTS Mean lung dose was respectively 7.4 and 11.8 Gy (p=0.004) for tomotherapy and 3D plans. Corresponding values were 12.4 and 18.3 Gy (p=0.006) for cardiac ventricles. Maximum spinal cord dose was respectively 31.3 and 37.4 Gy (p < 0.007) for tomotherapy and 3D plans. Homogeneity index was two for both groups. CONCLUSIONS Compared to 3D conformal radiotherapy, tomotherapy decreased significantly the amount of normal tissue irradiated and may reduce treatment toxicity for possible dose escalation in future prospective studies.

Feasibility of tomotherapy for Graves’ ophthalmopathy

PurposeTo compare the dosimetry of tomotherapy and the conventional half-beam technique (HBT) or non-split beam technique (NSBT) for target coverage and radiation dose to the lacrimal glands and lens.Patients and MethodsA retrospective review of 7 patients with Graves’ ophthalmopathy who had radiotherapy because of disease progression on high steroid dose is reported: 3 patients were treated with tomotherapy and 4 patients with HBT.ResultsCompared to HBT, tomotherapy may provide better target coverage and significant reduction of radiation dose to the lacrimal glands and a higher dose to the lens. The NSBT improved target coverage but resulted in significantly higher doses to the lens and lacrimal glands.ConclusionTomotherapy may provide better coverage of the target volume and may be more effective in reducing severe exophthalmos compared to the conventional radiotherapy technique.ZusammenfassungZielVergleich zwischen Dosimetrie der Tomotherapie und der konventionellen Half-beam-Technik (HBT) oder Non-split-beam-Technik (NSBT) für die Erfassung des Zielvolumens und der Strahlendosis an Tränendrüsen und Linse.Patienten und MethodenEine retrospektive Analyse von 7 Patienten mit Graves’ Ophthalmopathie, die wegen Progression der Erkrankung zur Notwendigkeit hochdosierter Steroidgabe eine Strahlentherapie erhielten. 3 Patienten wurden mit Tomotherapie und 4 Patienten mit HBT behandelt.ErgebnisseIm Vergleich zu HBT konnte die Tomotherapie bessere Erfassung des Zielvolumens und signifikante Reduktion der Strahlendosis an den Tranendrüsen sowie eine höhere Strahlendosis an der Linse erreichen. NSBT verbesserte die Erfassung des Zielvolumens, resultierte aber in signifikant höherer Strahlendosis an Linse und Tränendrüsen.SchlussfolgerungTomotherapie kann – verglichen mit konventioneller Strahlentherapietechnik – zu besserer Erfassung des Zielvolumens und wirksamerer Verminderung des schweren Exophthalmus führen.

Feasibility of tomotherapy for Graves' ophthalmopathy: Dosimetry comparison with conventional radiotherapy.

PurposeTo compare the dosimetry of tomotherapy and the conventional half-beam technique (HBT) or non-split beam technique (NSBT) for target coverage and radiation dose to the lacrimal glands and lens.Patients and MethodsA retrospective review of 7 patients with Graves’ ophthalmopathy who had radiotherapy because of disease progression on high steroid dose is reported: 3 patients were treated with tomotherapy and 4 patients with HBT.ResultsCompared to HBT, tomotherapy may provide better target coverage and significant reduction of radiation dose to the lacrimal glands and a higher dose to the lens. The NSBT improved target coverage but resulted in significantly higher doses to the lens and lacrimal glands.ConclusionTomotherapy may provide better coverage of the target volume and may be more effective in reducing severe exophthalmos compared to the conventional radiotherapy technique.ZusammenfassungZielVergleich zwischen Dosimetrie der Tomotherapie und der konventionellen Half-beam-Technik (HBT) oder Non-split-beam-Technik (NSBT) für die Erfassung des Zielvolumens und der Strahlendosis an Tränendrüsen und Linse.Patienten und MethodenEine retrospektive Analyse von 7 Patienten mit Graves’ Ophthalmopathie, die wegen Progression der Erkrankung zur Notwendigkeit hochdosierter Steroidgabe eine Strahlentherapie erhielten. 3 Patienten wurden mit Tomotherapie und 4 Patienten mit HBT behandelt.ErgebnisseIm Vergleich zu HBT konnte die Tomotherapie bessere Erfassung des Zielvolumens und signifikante Reduktion der Strahlendosis an den Tranendrüsen sowie eine höhere Strahlendosis an der Linse erreichen. NSBT verbesserte die Erfassung des Zielvolumens, resultierte aber in signifikant höherer Strahlendosis an Linse und Tränendrüsen.SchlussfolgerungTomotherapie kann – verglichen mit konventioneller Strahlentherapietechnik – zu besserer Erfassung des Zielvolumens und wirksamerer Verminderung des schweren Exophthalmus führen.

MOSFET sensitivity dependence on integrated dose from high‐energy photon beams

The ability of a commercially available dual bias, dual MOSFET dosimetry system to measure therapeutic doses reproducibly throughout its vendor-defined dose-based lifetime has been evaluated by characterizing its sensitivity variation to integrated/cumulative doses from,high-energy (6 and 15 MV) photon radiotherapy beams. The variation of sensitivity as a function of total integrated dose was studied for three different dose-per-fraction levels; namely, 50, 200, and 1200 cGy/fraction. In standard sensitivity mode (i.e., measurements involving dose-per-fraction levels > or =100 cGy), the response of the MOSFET system to identical irradiations increased with integrated dose for both energies investigated. Dose measurement reproducibility for the low (i.e., 50 cGy) dose fractions was within 2.1% (if the system was calibrated before each in-phantom measurement) and 3.1% [if the system was calibrated prior to first use, with no intermediate calibration(s)]. Similarly, dose measurement reproducibility was between 2.2% and 6.6% for the conventional (i.e., 200 cGy) dose fractions and between 1.8% and 7.9% for escalated (i.e., 1200 cGy) dose fractions. The results of this study suggest that, due to the progressively increasing sensitivity resulting from the dual-MOSFET design, frequent calibrations are required to achieve measurement accuracy of < or =3% (within one standard deviation).

Performance characteristics of a gated fiber-optic-coupled dosimeter in high-energy pulsed photon radiation dosimetry

Fiber-optic-coupled dosimeters (FOCDs) are a new class of in vivo dosimetry systems that are finding increased clinical applications. Utility of FOCDs has been limited in dosimetric applications due Cerenkov-ray signal contamination. The current study reports on the characterization of a novel FOCD, with a gated detection system for the discrimination and effective elimination of the direct contribution of Cerenkov radiation, for use in the radiotherapeutic realm. System reproducibility, linearity and output dependence on dose rate, energy, field size, and temperature response were characterized for 6, 10, and 15MV photon energies. The system exhibited a linear response to absorbed dose ranging from 1 to 2400cGy and showed little dependence to dose rate variations. Overall system reproducibility was 0.52% with no field-geometry and temperature dependence.

Feasibility of image-guided radiotherapy based on helical tomotherapy to reduce contralateral parotid dose in head and neck cancer

BackgroundTo evaluate the feasibility of image-guided radiotherapy based on helical Tomotherapy to spare the contralateral parotid gland in head and neck cancer patients with unilateral or no neck node metastases.MethodsA retrospective review of 52 patients undergoing radiotherapy for head and neck cancers with image guidance based on daily megavoltage CT imaging with helical tomotherapy was performed.ResultsMean contralateral parotid dose and the volume of the contralateral parotid receiving 40 Gy or more were compared between radiotherapy plans with significant constraint (SC) of less than 20 Gy on parotid dose (23 patients) and the conventional constraint (CC) of 26 Gy (29 patients). All patients had PTV coverage of at least 95% to the contralateral elective neck nodes. Mean contralateral parotid dose was, respectively, 14.1 Gy and 24.7 Gy for the SC and CC plans (p < 0.0001). The volume of contralateral parotid receiving 40 Gy or more was respectively 5.3% and 18.2% (p < 0.0001)ConclusionTomotherapy for head and neck cancer minimized radiotherapy dose to the contralateral parotid gland in patients undergoing elective node irradiation without sacrificing target coverage.

Confidence limit variation for a single IMRT system following the TG119 protocol.

PURPOSE To evaluate the robustness of TG119-based quality assurance metrics for an IMRT system. METHODS Four planners constructed treatment plans for the five IMRT test cases described in TG119. All plans were delivered to a 30 cm x 30 cm x 15 cm solid water phantom in one treatment session in order to minimize session-dependent variation from phantom setup, film quality, machine performance, etc. Composite measurements utilized film and an ionization chamber. Per-field measurements were collected using a diode array device at an effective depth of 5 cm. All data collected were analyzed using the TG119 specifications to determine the confidence limit values for each planner separately and then compared. RESULTS The mean variance of ion chamber measurements for each planner was within 1.7% of the planned dose. The resulting confidence limits were 3.13%, 1.98%, 3.65%, and 4.39%. Confidence limit values determined by composite film analysis were 8.06%, 13.4%, 9.30%, and 16.5%. Confidence limits from per-field measurements were 1.55%, 0.00%, 0.00%, and 2.89%. CONCLUSIONS For a single IMRT system, the accuracy assessment provided by TG119-based quality assurance metrics showed significant variations in the confidence limits between planners across all composite and per-field evaluations. This observed variation is likely due to the different levels of modulation between each planners set of plans. Performing the TG119 evaluation using plans produced by a single planner may not provide an adequate estimation of IMRT system accuracy.

Feasibility of Tomotherapy-Based Image-Guided Radiotherapy to Reduce Aspiration Risk in Patients with Non-Laryngeal and Non-Pharyngeal Head and Neck Cancer

Purpose The study aims to assess the feasibility of Tomotherapy-based image-guided radiotherapy (IGRT) to reduce the aspiration risk in patients with non-laryngeal and non-hypopharyngeal cancer. A retrospective review of 48 patients undergoing radiation for non-laryngeal and non-hypopharyngeal head and neck cancers was conducted. All patients had a modified barium swallow (MBS) prior to treatment, which was repeated one month following radiotherapy. Mean middle and inferior pharyngeal dose was recorded and correlated with the MBS results to determine aspiration risk. Results Mean pharyngeal dose was 23.2 Gy for the whole group. Two patients (4.2%) developed trace aspiration following radiotherapy which resolved with swallowing therapy. At a median follow-up of 19 months (1–48 months), all patients were able to resume normal oral feeding without aspiration. Conclusion and Clinical Relevance IGRT may reduce the aspiration risk by decreasing the mean pharyngeal dose in the presence of large cervical lymph nodes. Further prospective studies with IGRT should be performed in patients with non-laryngeal and non-hypopharyngeal head and neck cancers to verify this hypothesis.