The Dilemma of Target Delineation with PET/CT in Radiotherapy Planning for Malignant Tumors

Currently there are many unanswered questions concerning contouring a target with PET/CT in radiotherapy planning. Who should contour the PET volume-the radiation oncologist or the nuclear medicine physician？ Which factors will contribute to the dual-observer variability between them？ What should be taken as the optimal SUV threshold to demarcate a malignant tumor from the normal tissue？ When the PET volume does not coincide with the local area CT findings, which portion should be contoured as the target？ If a reginal lymph node,draining area or a remote region is shown to be PET positive but CT negative, or PET negative but CT positive, how is the target identified and selected？ Further studies concerning the relationship between PET/CT and the cancerous tissue are needed. The long-term clinical results showing an increased therapeutic ratio will finally verify the applicability of guidelines to contour the target with PET/CT in radiotherapy planning.

Complex Target Volume Delineation and Treatment Planning in Radiotherapy for Malignant Pleural Mesothelioma (MPM)

Introduction: Radiotherapy alone or combined with surgery and/or chemotherapy is being investigated in the treatment of malignant pleural mesothelioma (MPM). This study aimed to simulate a Volumetric Modulated Arc Therapy (VMAT) treatment of a patient with MPM. Materials and Methods: CT images from a patient with intact lungs were imported via DICOM into the Pinnacle3 treatment planning (TP) system (TPS) and used as a model for MPM to delineate organs at risk (OAR) and both clinical and planning target volumes (CTV and PTV) with a margin of 5 mm. Elekta Synergy with 6 MV photons and 80 leafs MLCi2 was employed. VMAT plans were generated using two coplanar arcs with gantry rotation angles of 178° - 182°, the collimator angles of each arc were set to 90°, Octavius® 4D 729 was employed for quality assurance while the calculated and measured doses were compared using VeriSoft. Results: A TP was achieved. The Gamma volume analysis with criteria of 3 mm distance to agreement and 3% dose difference yielded the gamma passing rate = 99.9%. The reference isodose was 42.75 Gy with the coverage constraints for the PTV D95 and V95 = 95.0% of 45 Gy. The remaining dosimetric parameters met the recommendations from the clinically acceptable guidelines for the radiotherapy of MPM. Conclusion: Using well-defined TV and VMAT, a consistent TP compared to similar ones from publications was achieved. We obtained a high agreement between the 3D dose reconstructed and the dose calculated.

Neoadjuvent androgen deprivation for seminal vesicle reduction:The optimal portion of seminal vesicle included in the high-dose CTV in localized prostate cancer radiotherapy

Objective:To clarify the length and volume reduction of seminal vesicles(SVs)after neo-adjuvant hormonal therapy(NHT),in order to help contour the optimal SV included into high-dose clinical target volume(CTV)for radiotherapy in intermediate-and high-risk patients.Methods:MR images both before and after NHT(5.3±2.2 months)were collected from thirty-one patients with cT2-4N0M0 prostate cancer.SV volume was measured in axial T1WI,while SV length was obtained in a reconstructed oblique coronary plane through its long axial from a 3D sequence.Results:SVs showed evident reduction both in length and volume(length:median 12.1%,range 4.0%–28.0%;volume:median 39.9%,range 9.4%–66.2%).For SVs with and without MR detected involvement,length shortening were(16.7±4.8)%and(11.1±4.4)%(P<0.001);for involved SVs and lesions,volume reduction were(41.0±16.0)%and(66.3±14.4)%,respectively(P<0.001),both indicating a more sensitive response to NHT of the involved portion than normal SV.Conclusions:Both volume and length of the SV will be reduced after receiving NHT.Besides,the invaded segments shrink more than normal SV tissue,indicating that SV portion included within the CTV can be reduced.