1/6. The potential for sparing of parotids and escalation of biologically effective dose with intensity-modulated radiation treatments of head and neck cancers: a treatment design study.PURPOSE: Conventional radiotherapy for cancers of the head and neck (HN) can yield acceptable locoregional tumor control rates, but toxicity of many normal tissues limits our ability to escalate dose. xerostomia represents one of the most common complications. The purpose of this study is to investigate the potential of intensity-modulated radiotherapy (IMRT) to achieve adequate sparing of parotids and to escalate nominal and/or biologically-effective dose to achieve higher tumor control without exceeding normal tissue tolerances. methods AND MATERIALS: An IMRT optimization system, developed at our institution for research and clinical purposes, and coupled to a commercial radiation treatment planning system, has been applied to a number of cases of HN carcinomas. IMRT plans were designed using dose- and dose-volume-based criteria for 4 and 6 MV coplanar but non-collinear beams ranging in number from 5 to 15 placed at equi-angular steps. Detailed analysis of one of the cases is presented, while the results of the other cases are summarized. For the first case, the IMRT plans are compared with the standard 3D conformal radiation treatment (3DCRT) plan actually used to treat the patient, and with each other. The aim of the 3DCRT plan for this particular case was to deliver 73 Gy to the tumor volume in 5 fractions of 2 Gy and 28 fractions of 2.25 Gy/fx; and 46 Gy to the nodes in 2 Gy/fx while maintaining critical normal tissues to below specified tolerances. The IMRT plans were designed to be delivered as a "simultaneous integrated boost" (SIB) using the "sweeping window" technique with a dynamic MLC. The simultaneous integrated boost strategy was chosen, partly for reasons of efficiency in planning and delivery of IMRT treatments, and partly with the assumption that dose distributions in such treatments are more conformal and spare normal tissues to a greater extent than those with sequential boost strategy. Biologically equivalent dose normalized to 2 Gy/fx, termed here as normalized total dose (NTD), for this strategy was calculated using published head and neck fractionation data. RESULTS: IMRT plans were more conformal than the 3DCRT plans. For equivalent coverage of the tumor and the nodes, and for the dose to the spinal cord and the brainstem maintained within tolerance limits, the dose to parotids was greatly reduced. For the detailed example presented, it was shown that the tumor and the nodes in the 3DCRT plan receive NTDs of 78 and 46 Gy, respectively. For the IMRT plan, a nominal dose of 70 Gy could be delivered to the tumor in 28 fractions of 2.5 Gy each, simultaneously with 50.4 Gy to nodes with 1.8 Gy/fx. The two are biologically equivalent to 82 and 46 Gy, respectively, if delivered in 2 Gy/fx. Similar computations were carried out for other cases as well. The quality of IMRT plans was found to improve with increasing number of beams, up to 9 beams. Dose-volume-based criteria led to a modest improvement in IMRT plans and required less trial and error. CONCLUSION: IMRT has the potential to significantly improve radiotherapy of HN cancers by reducing normal tissue dose and simultaneously allowing escalation of dose. SIB strategy is not only more efficient and yields better dose distributions, but may also be biologically more effective. Dose-volume-based criteria is better than purely dose-based criteria. The quality of plans improves with number of beams, reaching a saturation level for a certain number of beams, which for the plans studied was found to be 9.- - - - - - - - - - ranking = 1keywords = intensity-modulated (Clic here for more details about this article) |
2/6. Potential of tomotherapy for total scalp treatment.PURPOSE: Total scalp radiotherapy is required in a variety of clinical situations. We compared conventional lateral photon-electron (LPE) technique with tomotherapy (intensity-modulated radiotherapy [IMRT]). methods AND MATERIALS: A patient with Merkel cell carcinoma was treated at our institution using conventional treatment techniques. Treatment plans were conducted using conventional three-dimensional treatment planning and IMRT. The clinical target volume included the entire scalp tissue volumes to the surface of underlying cranial bone, as well as superficial and deep neck nodes in the bilateral neck. To provide a consistent comparison between the IMRT and three-dimensional conventional treatment plans, the dose distributions were normalized such that 90% of the target volumes received the prescription dose. RESULTS: Examination of our results revealed an acceptable dose-volume histogram and adequate coverage of the clinical target volume using the conventional LPE technique. The IMRT plan provided a more homogeneous dose to the target volume; however, critical structure doses were uniformly higher than for the conventional treatment plan. CONCLUSIONS: The IMRT plan resulted in a substantial dose to the lens, brain, and orbit, making it clinically unacceptable compared with the LPE technique. overall, the LPE technique was superior.- - - - - - - - - - ranking = 0.2keywords = intensity-modulated (Clic here for more details about this article) |
3/6. Electron conformal radiotherapy using bolus and intensity modulation.PURPOSE: Conformal electron beam therapy can be delivered using shaped bolus, which varies the penetration of the electrons across the incident beam so that the 90% isodose surface conforms to the distal surface of the planning target volume (PTV). Previous use of this modality has shown that the irregular proximal surface of the bolus causes the dose heterogeneity in the PTV to increase from 10%, the typical dose spread of a flat-water surface to approximately 20%. The present work evaluates the ability to restore dose homogeneity by varying the incident electron intensity. methods AND MATERIALS: Three patients, one each with chest wall, thorax, and head-and-neck cancer, were planned using electron conformal therapy with bolus, with and without intensity modulation. Resulting dose distributions and dose-volume histograms were compared with non-intensity-modulated bolus plans. RESULTS: In all cases, the DeltaD(90%-10%) for the PTV was reduced; for example, for the head-and-neck case, the DeltaD(90%-10%) for the PTV was reduced from 14.9% to 9.2%. This reduction in dose spread is a direct result of intensity modulation. CONCLUSIONS: The results showed that intensity-modulated electron beams could significantly improve the dose homogeneity in the PTV for patients treated with electron conformal therapy using shaped bolus.- - - - - - - - - - ranking = 0.4keywords = intensity-modulated (Clic here for more details about this article) |
4/6. A case of cervical metastases from temporal bone carcinoid.BACKGROUND: Carcinoids are neuroendocrine tumors that typically occur in the gastrointestinal tract and lung and less frequently in the head and neck region. Whereas the metastatic potential of laryngeal carcinoid is well documented, only one case of metastasis of temporal bone carcinoid to the cervical lymph nodes has been reported. We present the case of a 55-year-old woman with cervical metastases almost 3 years after a primary diagnosis of temporal bone carcinoid. methods: The patient had undergone a subtotal petrosectomy for a temporal bone carcinoid and, 29 months later, revision surgery for a local recurrence. Four months later, multiple laterocervical swelling appeared, and the patient underwent modified radical neck dissection. RESULTS: Histologic examination after the neck dissection was suggestive of lymph node metastases from a carcinoid tumor. Immunohistochemical analysis of the lymph node metastases showed neoplastic cells positive for keratin, vimentin, chromogranin, and neuron-specific enolase and negative for thyroglobulin, calcitonin, S-100, and parathyroid hormone. The patient was treated with intensity-modulated radiation therapy and neck irradiation. CONCLUSIONS: We believe that temporal bone carcinoids have metastatic potential not predictable by histologic features. Surgical excision is the treatment of choice for patients with temporal bone carcinoids, with the approach and technique determined by the extent of the mass. Moreover, before planning surgery and during follow-up, neck node status must be carefully detected.- - - - - - - - - - ranking = 0.2keywords = intensity-modulated (Clic here for more details about this article) |
5/6. Treatment of extensive scalp lesions with segmental intensity-modulated photon therapy.PURPOSE: To compare static electron therapy, electron arc therapy, and photon intensity-modulated radiation therapy (IMRT) for treatment of extensive scalp lesions and to examine the dosimetric accuracy of the techniques. methods AND MATERIALS: A retrospective treatment-planning study was performed to evaluate the relative merits of static electron fields, arcing electron fields, and five-field photon IMRT. Thermoluminescent dosimeters (TLD) were used to verify the accuracy of the techniques. The required thickness of bolus was investigated, and an anthropomorphic phantom was also used to examine the effects of air gaps between the wax bolus used for the IMRT technique and the patient's scalp. RESULTS: Neither static nor arcing electron techniques were able to provide a reliable coverage of the planning target volume (PTV), owing to obliquity of the fields in relation to the scalp. The IMRT technique considerably improved PTV dose uniformity, though it irradiated a larger volume of brain. Either 0.5 cm or 1.0 cm of wax bolus was found to be suitable. air gaps of up to 1 cm between the bolus and the patient's scalp were correctly handled by the treatment-planning system and had negligible influence on the dose to the scalp. CONCLUSIONS: Photon IMRT provides a feasible alternative to electron techniques for treatment of large scalp lesions, resulting in improved homogeneity of dose to the PTV but with a moderate increase in dose to the brain.- - - - - - - - - - ranking = 1keywords = intensity-modulated (Clic here for more details about this article) |
6/6. Pitfalls in normalization for intensity-modulated radiation therapy planning.Three-dimensional (3D) treatment planning often involves complex combinations of beam energies, treatment fields, and beam modifying devices. Even when a plan is devised that meets many treatment-planning objectives, limitations in the planner's ability to further adjust beam characteristics may require the radiation dose prescription to be normalized to an isodose level that best covers the target volume. While these normalizations help meet the volume coverage goals, they also result in adjustment of the dose delivered to the normal tissues and must be carefully evaluated. Intensity-modulated radiation therapy (IMRT) treatment planning allows combinations of complex dose patterns, in order to achieve the desired treatment planning goals. These dose patterns are created by defining a set of treatment planning objectives and then allowing the treatment planning computer to create intensity patterns, through the use of moving multileaf collimation that will meet the requested goals. Often, when an IMRT treatment plan is created that meets many of the treatment planning goals but falls short of volume coverage requirements, the planner is tempted to apply normalization principles similar to those utilized with 3D treatment planning. Again, these normalizations help meet the volume coverage goals, but unlike 3D planning situations, may result in avoidable delivery of additional doses to the normal tissues. The focus of this study is to evaluate the effect of application of normalization for IMRT planning using multiple patient situations. Recommendations would favor re-optimization over normalization in most planning situations.- - - - - - - - - - ranking = 0.8keywords = intensity-modulated (Clic here for more details about this article) |