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Titolo:
PORTAL IMAGING PROTOCOL FOR RADICAL DOSE-ESCALATED RADIOTHERAPY TREATMENT OF PROSTATE-CANCER
Autore:
MUBATA CD; BIDMEAD AM; ELLINGHAM LM; THOMPSON V; DEARNALEY DP;
Indirizzi:
ROYAL MARSDEN NHS TRUST,JOINT DEPT PHYS,FULHAM RD LONDON SW3 6JJ ENGLAND INST CANC RES LONDON SW3 6JJ ENGLAND ROYAL MARSDEN NHS TRUST,DEPT RADIOTHERAPY LONDON SW3 6JJ ENGLAND
Titolo Testata:
International journal of radiation oncology, biology, physics
fascicolo: 1, volume: 40, anno: 1998,
pagine: 221 - 231
SICI:
0360-3016(1998)40:1<221:PIPFRD>2.0.ZU;2-U
Fonte:
ISI
Lingua:
ENG
Soggetto:
CONFORMAL RADIATION-THERAPY; PATIENT SETUP; ORGAN MOTION; IMAGES; CARCINOMA; UNCERTAINTIES; VERIFICATION; REGISTRATION; IRRADIATION; INSPECTION;
Keywords:
PORTAL IMAGES; TREATMENT SETUP ERRORS; DOSE ESCALATION; TREATMENT PLANNING;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Science Citation Index Expanded
Citazioni:
34
Recensione:
Indirizzi per estratti:
Citazione:
C.D. Mubata et al., "PORTAL IMAGING PROTOCOL FOR RADICAL DOSE-ESCALATED RADIOTHERAPY TREATMENT OF PROSTATE-CANCER", International journal of radiation oncology, biology, physics, 40(1), 1998, pp. 221-231

Abstract

Purpose: The use of escalated radiation doses to improve local control in conformal radiotherapy of prostatic cancer is becoming the focus of many centers. There are, however, increased side effects associatedwith increased radiotherapy doses that are believed to be dependent on the volume of normal tissue irradiated. For this reason, accurate patient positioning, CT planning with 3D reconstruction of volumes of interest, clear definition of treatment margins and verification of treatment fields are necessary components of the quality control for theseprocedures. In this study electronic portal images are used to (a) evaluate the magnitude and effect of the setup errors encountered in patient positioning techniques, and (b) verify the multileaf collimator (MLC) held patterns for each of the treatment fields. Methods and Materials: The Phase I volume, with a planning target volume (PTV) composedof the gross tumour volume (GTV) plus a 1.5 cm margin is treated conformally with a three-field plan (usually an anterior field and tao lateral or oblique fields). A Phase II, with no margin around the GTV, istreated using two lateral and four oblique fields. Portal images are acquired and compared to digitally reconstructed radiographs (DRR) and/or simulator films during Phase I to assess the systematic (CT planning or simulator to treatment error) and the daily random errors. The match results from these images are used to correct for the systematic errors, if necessary, and to monitor the time trends and effectivenessof patient immobilization systems used during the Phase I treatment course. For the Phase II, portal images of an anterior and lateral field (larger than the treatment fields) matched to DRRs (or simulator images) are used to verify the isocenter position 1 week before start of Phase II. The Portal images are acquired for all the treatment fields on the first day to verify the MLC field patterns and archived for records. The final distribution of the setup errors was used to calculatemodified dose-volume histograms (DVHs). This procedure was carried out on 36 prostate cancer patients, 12 with vacuum-molded (VacFix) bags for immobilization and 24 with no immobilization. Results: The systematic errors can be visualized and corrected for before the doses are increased above the conventional levels. The requirement for correction of these errors (e.g., 2.5 mm AP shift) was demonstrated, using DVHs, in the observed 10% increase in rectal volume receiving at least 60 Gy. The random (daily) errors observed showed the need for patient fixation devices when treating with reduced margins. The percentage of fields with displacements of less than or equal to 5.0 mm increased from 82 to 96% with the use of VacFix bags. The rotation of the pelvis is also minimized when the bags are used, with over 95% of the fields with rotations of less than or equal to 2.0 degrees compared to 85% without. Currently, a combination of VacFix and thermoplastic casts is being investigated. Conclusion: The systematic errors can easily be identified and corrected for in the early stages of the Phase I treatment course. The time trends observed during the course of Phase I in conjunction with the isocenter verification at the start of Phase II give good prediction of the accuracy of the setup during Phase II, where visibility of identifiable structures is reduced in the small fields. The acquisition and inspection of the portal images for the small Phase II fields has been found to be an effective way of keeping a record of the MLC field patterns used. Incorporation of the distribution of the setup errors into the planning system also gives a clearer picture of how the prescribed dose was delivered. This information can be useful in dose-escalation studies in determining the relationship between the local control or morbidity rates and prescribed dose. (C) 1998 Elsevier Science Inc.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 15/07/20 alle ore 04:35:54