ICRU 50 & ICRU 62 Paweł Kukołowicz Holycross Cancer Centre Summer School of Radiotherapy Kielce, Poland 2003
ICRU 50Prescribing, Recording, and Reporting Photon Beam Therapy1993 When delivering a radiotherapy tretament, parameters such as volume and dose have to be specified for different purposes: prescription, recording, and reporting. It is important that clear, well defined and unambigous concepts and parameters are used for reporting purposes to ensure a common language between different centers.
Volumes • Gross Tumor Volume The GTV is the gross palpable or visible/demonstrable extent and location of the malignant growth.
Volumes • Clinical Target Volume The CTV is a tissue volume that contains a GTV and/or subclinical microscopic malignant disease, which has to be eliminated. This volume has to be treated adequately in order to achive the aim of the therapy: cure or palliation.
Volumes • Planning Target Volume The PTV is a geometrical concept, and it is defined to selcet appropriate beam sizes and beam arrangements, taking into consideration the net effect of all the possible geometrical varaitions and inaccuracies in order to ensure that the prescribed dose is actually absorbed in the CTV.
Volumes • Treated Volume The TV is the volume enclosed by an isodose surface, selected and specified by the radiation oncologist as being appropriate to achive the purpose of treatment (e.g., tumor eradication, palliation).
Volumes • Irradiated Volume The IrV is that tissue volume which receives a dose that is considered significant in relation to normal tissue tolerance.
Volumes • Organs at Risk The OR are normal tissues whose radiation sensitivity may significantly influence treatment planning and/or prescribed dose.
Volumes • The GTV & CTV • the concept is clear however it is not easyto draw/delineate the GTV and CTV
PTV • ... taking into consideration the net effect of all the possible geometrical variations and inaccuracies in order to ensure thatthe prescribed dose is actually absorbed in the CTV.
Internal margin (IM) A margin that must be added to the CTV to compensate for expected physiologic movements and the variations in size, shape and position of the CTV during therapy in relation to the Internal Reference Point and its corresponding Coordinate System.
Internal Margin The motion occurs when the CTV position changes on a day-to-day level and is mainly associated with organs that are part of or adjacent to the digestive or breath system. Changes in the patient’s condition, such as weight gain/loss, can also affect the relative position of the CTV.
Internal Margin K.M.Langen, D.T.L. Johnes Organ motion and its management. International Journal of Radiation Oncology Biology, Physics Vo. 50, No.1, pp. 265-278, 2001
Internal Margin – ginecological tumorsinterfraction • Mobility of cervical and endometrial tumors in response to bladder and rectum filling levels • Median movements of corpus uteri of 7 mm in the cranial direction and 4 mm in the posterior direction • Cervix did not move significantly in the anterior/posterior direction, nor did the cervix or corpus uteri move significantly laterally
Internal Margin –prostateinterfraction • A lot of data can be found in the literature Netherlands Cancer Instite prostate data Random errors Systematic errors
Internal marginBladder and rectum interfraction • A lot of data, examples • AP rectal diameter from 3 to 46 mm • Weekly average movement of urinary catheter balloon of about 5 mm • An average decrease of in rectal diameter of 15 mm between an initial CT and a second CT obtained after 40 Gy
Internal margin - intrafraction • Liver • Under normal breathing conditions, the mean liver excursion was 11 mm •Diaphragm • Under normal breathing the diaphragm moved about 17 mm •Kidney • Under normal breathing the diaphragm moved about 19 mm •Lung tumors • For 6 tumors located in the hilum region an average lateral movement about 9 mm • For 3 of 4 tumors in the lower lobe the AP and lateral movement between 4 and 22 mm
Set-up Margin (SM) The uncertainties depends on different factors: • variations in patient positioning • mechanical uncertainties of the equipment • dosimetric uncertainties (light-radiation field agreement) • transfer set-up errors • human related uncertainties
Set-up Margin (SM) The margin that must be added to account specifically for uncertainties (inacuracies and lack of reproducibility) in patient positioning and aligment of the therapeutic beams during treatment planning and through all treatment sessions.
Comparison of portal and reference images Reference image Y Anatomical structure X Dy Dx Portal image Displacement vector
Systematic and random errors • Systematic errors – treatment preparation errors (influence all fractions) • Random errors – treatment execution errors (influence only the single fraction)
Systematic and random errors SE = SD(mi) RE = Mean(Sdi)
Set-up margin • Set-up on the CT scanner • Set-up on the simulator • Set-up on the therapeutic maschine
Set-up margin C.W.Hurkmans, P. Remeijer, J.V.Lebesque, B.J.Mijnheer Set-up verification using portal imaging; review of currant clinical practice. Radiotherapy and Oncology,58 (2000) 105-120.
PTV margin recipe van Herk M., Rasch C., Lebesque JV, The probability of correct target dosage: dose-population histograms for deriving tretment margins in radiotherapy. International Journal of Radiation Oncology Biology Physics, 2000;47:1121-1135.
Methods of margins applying • Marcel van Herk • Express the required CTV dose for a specified fraction of patients. E.g. 90% of patients must get a minimal CTV dose of 95% or more • Add margin so that 90% of the systematic errors are covered • Add margin for penumbra and random errors so that CTV + geometrical margins lies within the 95% isodose
PTV margin recipeisotropic model • To cover the CTV for 90% of the patients with the 95%: PTVmargin = 2,5 * Σ + 1,64 *(σ2 +Ψ2)½ -1,64*Ψ Σ – systematic error σ – random error Ψ – half of penumbra
PTV margin recipeisotropic model J.C. Stroom, B.J.M. Heijmen Geometrical uncertainties, radiotherapy planning margins, and the ICRU-62 report. Radiotherapy and Oncologt 64 (2002) 75-83 PTVmargin = 2,5 * Σ + 0,7 *σ Σ = (Σx2+ Σy2+ Σz2) ½ σ = (σx2+ σy2+ σz2) ½
Practice Anisotropic margins with arbitratry chosen values, e.g. rx = 0,5 cm ry = 0,8 cm rz = 1,0 cm
Conclusions • Accurate delineation of the GTV is the most important, • At least to think according to ICRU 50 and 62 ideas, • Minimize set-up error, • To know set-up error, • All the time improve the skill in drawing targets.
Conclusions • Due to the new ideas of biologically based radiotherapy the new recommendations will be needed in the nearest few years