Dose optimization for the treatment of anaplastic thyroid carcinoma: a comparison of treatment planning techniques.

PURPOSE: To evaluate and compare dose optimization for the treatment of anaplastic thyroid carcinoma using a 3D conformal plan, and two 3D intensity-modulated inverse plans. METHODS AND MATERIALS: After patient immobilization using an alpha cradle and head-mask system, a postoperative CT scan was obtained to delineate the gross tumor volume (GTV), the clinical tumor volume (CTV), and adjacent critical structures. Treatment plans were generated using UM-Plan (University of Michigan), PeacockPlan and Corvus (NOMOS Corporation, Sewickley, PA). Isodoses were displayed in the sagittal, coronal, and multiple axial planes, and dose-volume histograms (DVH) were generated for the GTV, CTV, and critical normal tissues. Treatment times were estimated to compare the practicality of delivering each plan in a busy radiotherapy department. RESULTS: All three treatment planning systems were able to deliver a minimum dose of 60 Gy to the GTV while keeping the maximum spinal cord dose at or below 45 Gy. However, there were differences in the doses delivered to 50% and 5% of the cord, the minimum CTV dose, and the overall treatment time. The PeacockPlan best spared the uninvolved tissues of the posterior neck, and provided the lowest dose to the cord without compromising the CTV. CONCLUSIONS: Inverse treatment planning provides superior dose optimization for the treatment of anaplastic thyroid carcinoma. The radiobiologic impact of intensity modulation for this tumor should be further tested clinically.

Three dimensional comparison of blocked arcs vs. four and six field conformal treatment of the prostate.

PURPOSE: The purpose of this study is to compare five different techniques for treatment the prostate without seminal vesicles. Dose volume histograms and a time survey are the tools that were used for this analysis. METHODS AND MATERIALS: For this study we compared 3D techniques using four and six field conformal treatments, to open and blocked 8 x 8 cm2 120 degrees bilateral arcs. All the plans were normalized to deliver 100% to the central axis, and full 3D calculations were performed. Blocked arcs were created using the 'average beam's eye view' (A-BEV) technique. RESULTS: Analysis of the dose volume histograms revealed: (1) Arcs with blocks result in an improved dose distribution compared to standard arcs and four field 3DCRT techniques, (2) The DVH associated with blocked arcs, using block margins of 1.3 cm, resulted in a somewhat lower dose to the rectum but a 'tighter' margin around the prostate compared to the DVH generated using the six field 3DCRT technique. CONCLUSION: This technique is for treatment of the prostate only, when treatment of the seminal vesicle is not required. The use of blocked arcs significantly improved the dose distribution compared to using standard arcs and 4-field conformal techniques. The DVHs associated with using blocked arcs is comparable to the SFC technique. It is likely to be less expensive, faster to set-up and may allow for safe dose escalation when only the prostate is receiving treatment.

Bilateral arcs using "averaged beam's eye views": a simplified technique for delivering 3-D based conformal radiotherapy.

The purpose of this study is to describe a conformal radiotherapy technique for treating only the prostate with bilateral 120 degrees arcs using "averaged beams-eye-views" (A-BEV). For this study a CT scan from a patient with a large prostate but with a low risk for seminal vesicle involvement was chosen for comparing several different treatment techniques. Dose volume histograms (DVHs) of the prostate, femoral heads, bladder, and rectum were compared for plans using "standard" bilateral 120 degree unblocked arcs (8 x 8 and 9 x 9 cm), similar sized arcs with "generic" (small corner) blocks applied, arcs using hand drawn "semi-conformal" blocks added, and arcs using the A-BEV. The A-BEV was generated by averaging the shapes of fixed lateral and oblique BEVs from a six-field plan. These arc techniques were compared to four-field conformal (4-FC) and six-field conformal (6-FC) techniques. The addition of generic corner blocks to a 9 x 9 field resulted in a more favorable dose distribution than using open unblocked 9 x 9 arcs. The technique employing the A-BEV resulted in an improvement in the DVHs compared to other arc techniques and to 4-FC techniques. The dose volume histograms associated with using this technique approached those associated with using a 6-FC technique. Treating only the prostate with blocked arcs generated using an A-BEV results in an improved dose distribution compared to unblocked arcs and 4-FC techniques. This blocked arc technique also results in a DVH that is comparable to using a more complex 6-FC technique. Blocks that are drawn on manually reduce the dose to the surrounding normal tissues but are associated with a greater risk of underdosing the target volume. This problem is diminished when computer generated conformal blocks are used.