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T. Landberg et al. / Medical Physics in the Baltic States 7 (2009) 43 - 51 fibrotic tissue may prevent, at least temporarily, malignant cell dissemination). (Note that if an adequate dose cannot be given to the whole GTV, the whole aim of therapy shifts from radical to palliative). PRV Fig. 6. Patient with cancer of the left breast after lumpectomy (no GTV present) considered for postoperative radiotherapy to the whole breast (not shown here), and a boost (shown here) to the tumor bed. The relations between the different volumes and margins are shown in one planar section. The internal and external reference points are indicated. Due to respiratory movements, the PTV extends outside the average position of the body contour. Central circle = CTV (Clinical Target Volume), Dark grey = ITV (Internal Target Volume), Light grey(outer circle) = PTV (Planning Target Volume), ←⎯⎯→ = OR (Organ at Risk, in this case the Left Anterior Descending Coronary Artery, shown here as projected onto the section), PRV (Planning Organ at Risk Volume), ————— = Average position of the contour and tissues, - - - - - - - - = Extreme position of the normal tissues, ▲ = Internal Reference Point, ■ = External Reference Point. Central dose As a general principle, the present system of recommendations for reporting doses is based on the 49 selection of a point within the PTV, which is referred to as the ICRU Reference Point. The ICRU Reference Point shall be selected according to the following general criteria: 1) the dose at the point should be clinically relevant and representative of the dose throughout the Planning Target Volume (PTV); 2) the point should be easy to define in a clear and unambiguous way; 3) the point should be selected where the dose can be accurately determined (physical accuracy); 4) the point should be in a region where there is no steep dose gradient. These recommendations will be fulfilled if the ICRU Reference Point is located: - firstly (always) at the center (or in a central part) of the PTV, and - secondly (when possible) on (or near) the central axis of the beam(s). The dose at the ICRU Reference Point is the ICRU Reference Dose, and shall always be reported. The dose variation throughout the CTV. The dose variation in the CTV is the relevant information. It can generally be estimated from the dose variation in the PTV, but is always confined within the dose limits for the PTV. A certain degree of inhomogeneity of the absorbed dose throughout the PTV can never be avoided in radiation therapy (i.e. the dose varies from the maximum dose value (Note the volume restriction for maximum dose) to the minimum dose value). As a basic requirement, the maximum dose and the minimum dose to the PTV shall be reported together with the dose at the ICRU Reference Point. These three dose values then indicate the dose profile to the PTV. Following ICRU Report # 50 (1993), it is recommended to keep the dose variation in the PTV within + 7 % and - 5 % of the prescribed CTV-dose. The three levels of dose evaluation for reporting. The level of completeness and accuracy of reporting therapeutic irradiation depends to a large extent on the situation in the department and on the aim of the treatment. For different clinical and practical considerations, different levels of ambition for dose evaluation can be identified. Three levels have been selected for reasons given below, but it is recognized that intermediate levels could also be identified. In the following paragraphs, only the basic, minimal requirements at the three levels are listed. However, as a general rule, it is recommended to report any additional available information considered to be clinically relevant.
T. Landberg et al. / Medical Physics in the Baltic States 7 (2009) 43 - 51 Fig. 7. Level 1: The requirements should be followed in all centers, for all patients. They constitute the standards below which safe and accurate radiotherapy cannot be performed. At this level, it is assumed that the dose at the ICRU Reference Point can be accurately determined as well as an estimate of the maximum and minimum doses to the PTV, using at least central-axis depth dose tables and standard isodose charts. Level 2: The standards of dose planning at this level allow the exchange of more complete and relevant information between different centers. At this level, it is assumed that the GTV, CTV, OR, PTV, and PRV can be defined using reliable patient data acquisition tools, and/or modern imaging techniques under reliable conditions (e.g., a series of CT and/or MRI sections). It is also assumed that complete dose distributions are available in planes or volumes, with inhomogeneity corrections, when appropriate. There must be a full quality assurance program covering the whole procedure. Level 3: Level 3 includes the development of new techniques for which reporting criteria are not yet established (e.g. BNCT, intensity modulation, etc.). Some procedures which are now at level 3 can become level 2 with the development of techniques, equipment and standards. Fig 8. 50 At any level, the dose at the ICRU Reference Point and the best estimation of the maximum and the minimum dose to the PTV should be reported. Furthermore, any additional relevant information should be given, when available, e.g. Dose-Volume-Histograms (DVHs). The absorbed doses to the Organs at Risk should also be given. Reporting Doses in a Series of Patients. ICRU Reports 29, 50, 62 & 71 dealt with reporting dose in external beam therapy in an individual patient. Different issues are encountered when reporting treatments for a series of patients. Fig. 9. Diagram showing the dose delivered to 125 patients in a non-small cell lung cancer trial. The prescribed dose was 60 Gy ±5% at the ICRU Reference Point. The patients are sorted in descending order of 1.) dose at the ICRU point, and 2.) minimum dose. The dotted lines indicate the permissible dose variation of ±5% from the prescribed dose. As regards dose to the ICRU point, 102 patients fulfilled the criteria; whereas, 23 patients received higher or lower doses to the ICRU Reference Point. (Courtesy of Ann-Margret Engström, RN, Oncological Centre, Lund, Sweden). Graph showing the proportion of a series of patients receiving an absorbed dose within three defined deviations from the prescribed dose in the protocol (same patient material as in Fig. 9.). Upper: dose at ICRU point. Lower: minimum dose to the PTV. (Courtesy of Ann-Margret Engström, RN, Oncological Centre, Lund, Sweden). First, the treatment prescription or protocol should be described in detail, including the volumes, absorbed dose levels, and fractionation. The treatments should be reported following the above recommendations, and the deviations from the prescription should be stated. In particular, the proportion of patients in whom the dose variation is less than ±5%, ±5-10%, and more than ±10% of the prescribed dose at the ICRU
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