Intensity-modulated radiotherapy of nasopharyngeal carcinoma: a comparative treatment planning study of photons and protons

<p>Abstract</p> <p>Background</p> <p>The aim of this treatment planning study was to investigate the potential advantages of intensity-modulated (IM) proton therapy (IMPT) compared with IM photon therapy (IMRT) in nasopharyngeal carcinoma (NPC).</p> <p>Methods</p> <p>Eight NPC patients were chosen. The dose prescriptions in cobalt Gray equivalent (Gy_E) for gross tumor volumes of the primary tumor (GTV-T), planning target volumes of GTV-T and metastatic (PTV-TN) and elective (PTV-N) lymph node stations were 72.6 Gy_E, 66 Gy_E, and 52.8 Gy_E, respectively. For each patient, nine coplanar fields IMRT with step-and-shoot technique and 3D spot-scanned three coplanar fields IMPT plans were prepared. Both modalities were planned in 33 fractions to be delivered with a simultaneous integrated boost technique. All plans were prepared and optimized by using the research version of the inverse treatment planning system KonRad (DKFZ, Heidelberg).</p> <p>Results</p> <p>Both treatment techniques were equal in terms of averaged mean dose to target volumes. IMPT plans significantly improved the tumor coverage and conformation (<it>P </it>< 0.05) and they reduced the averaged mean dose to several organs at risk (OARs) by a factor of 2–3. The low-to-medium dose volumes (0.33–13.2 Gy_E) were more than doubled by IMRT plans.</p> <p>Conclusion</p> <p>In radiotherapy of NPC patients, three-field IMPT has greater potential than nine-field IMRT with respect to tumor coverage and reduction of the integral dose to OARs and non-specific normal tissues. The practicality of IMPT in NPC deserves further exploration when this technique becomes available on wider clinical scale.</p

Nasopharyngeal carcinoma: past, present and future directions

Nasopharyngeal carcinoma (NPC) is a rare disease in Sweden. The purpose of this thesis was to investigate the clinicopathological manifestations of the disease and its treatment outcomes in a cohort of Swedish NPC patients to identify key features for future improvements in patient care. From 1991 to 2002, 50 NPC patients were treated with radical three-dimensional conformal radiotherapy (3DCRT) +/- intracavitary brachytherapy (IBT) +/- chemotherapy at Jubileumskliniken, Sahlgrenska University Hospital. Retrospective analysis of the data showed 5-year local, regional, and distant relapse-free survival rates of 70%, 92%, and 77% for 49 nondisseminated patients. Patients with locoregionally advanced disease fared worse with respect to local and distant tumor control rates. Furthermore, the long-term side effects of irradiation were adverse and frequent in the whole cohort of patients. A comparative treatment planning study between intensity-modulated radiotherapy (IMRT) and 3DCRT + IBT was performed for eight NPC patients. The prescription physical dose for planning target volume of the primary tumor was 72.6 Gy in IMRT and 72 Gy in the combined plans. The comparison of the plans using quantitative parameters revealed that IMRT plans provided more conformal plans with possibility of dose escalation in primary tumor and simultaneous sparing of several normal structures. These were translated into improved tumor control probability of the primary tumor and reduction of normal tissue complication probability for several organs. However IMRT plans resulted in significant increase of the mean volumes of low to intermediate isodoses (0.66 Gy to 19.8 Gy) by 30% to 44%. A comparative treatment planning study between IMRT and intensity-modulated proton therapy (IMPT) with equivalent dose prescriptions for primary tumour (72.6 GyE) in the same cohort of patients showed that conformity of treatment plans and tumor coverage especially for locally advanced tumors were improved further by IMPT plans. Moreover, the integral dose (mean dose) was significantly reduced by a factor of 2 to 3 in several organs. The mean volume of low to intermediate isodoses (0.66 Gy to 19.8 Gy) were 2 to 2.7-fold larger in IMRT plans than in IMPT plans. Expression of EBV-encoded LMP1, Ki-67, cyclin-B1, and EGFR were analyzed by immunohistochemical assays for 44 (45 for LMP1) NPC patients. LMP1 was expressed in 33% of the patients and its presence was significantly correlated with advanced nodal and tumour stage. Statistically, expression of Ki-67 and cyclin-B1 showed no significant clinical relevance. Strong EGFR staining intensity was significantly correlated with worse 5-year local and locoregional tumor control probabilities as well as poorer disease-free and overall survival rates

Assessment of volume segmentation in radiotherapy of adolescents : a treatment planning study by the Swedish Workgroup for Paediatric Radiotherapy.

Background and purpose. The variability in target delineation for similar cases between centres treating paediatric and adolescent patients, and the apparent differences in interpretation of radiotherapy guidelines in the treatment protocols encouraged us to perform a dummy-run study as a part of our quality assurance work. The aim was to identify and quantify differences in the segmentation of target volumes and organs at risk (OARs) and to analyse the treatment plans and dose distributions. Materials and methods. Four patient cases were selected: Wilm's tumour, Hodgkin's disease, rhabdomyosarcoma of the prostate and chordoma of the skull base. The five participating centres received the same patient-related material. They introduced the cases in their treatment planning system, delineated target volumes and OARs and created treatment plans. Dose-volume histograms were retrieved for relevant structures and volumes and dose metrics were derived and compared, e.g. target volumes and their concordance, dose homogeneity index (HI), treated and irradiated volumes, remaining volume at risk and relevant Vx and Dx values. Results. We found significant differences in target segmentation in the majority of the cases. The planning target volumes (PTVs) varied two- to four-fold and conformity indices were in the range of 0.3-0.6. This resulted in large variations in dose distributions to OARs as well as in treated and irradiated volumes even though the treatment plans showed good conformity to the PTVs. Potential reasons for the differences in target delineation were analysed. Conclusion. Considerations of the growing child and difficulties in interpretation of the radiotherapy information in the treatment protocols were identified as reasons for the variation. As a result, clarified translated detailed radiotherapy guidelines for paediatric/adolescent patients have been recognised as a way to reduce this variation

Comparison of dose distributions between IMPT (right) and IMRT (left) plans in T4N1M0 NPC in axial (above) and sagittal (below) views

Dotted lines denote 95% of the prescribed dose to GTV-T.<p><b>Copyright information:</b></p><p>Taken from "Intensity-modulated radiotherapy of nasopharyngeal carcinoma: a comparative treatment planning study of photons and protons"</p><p>http://www.ro-journal.com/content/3/1/4</p><p>Radiation Oncology (London, England) 2008;3():4-4.</p><p>Published online 24 Jan 2008</p><p>PMCID:PMC2265732.</p><p></p