Utility of a skin marker-less setup procedure using surface-guided imaging: a comparison with the traditional laser-based setup in extremity irradiation.

This study aimed to assess the feasibility of a skin marker-less patient setup using a surface-guided radiotherapy (SGRT) system for extremity radiotherapy. Twenty-five patients who underwent radiotherapy to the extremities were included in this retrospective study. The first group consisted of 10 patients and underwent a traditional setup procedure using skin marks and lasers. The second group comprised 15 patients and had a skin marker-less setup procedure that used an SGRT system only. To compare the two setup procedures for setup accuracy, the mean 3D vector shift magnitude was 0.9 mm for the traditional setup procedure and 0.5 mm for the skin marker-less setup procedure (p < 0.01). In addition, SGRT systems have been suggested to improve the accuracy and reproducibility of patient setups and consistently reduce interfractional setup errors. These results indicate that a skin marker-less patient setup procedure using an SGRT system is useful for extremity irradiation.

Effect of ICRU report 90 recommendations on Monte Carlo calculated kQ for ionization chambers listed in the Addendum to AAPM's TG-51 protocol.

PURPOSE: The ICRU has published new recommendations for ionizing radiation dosimetry. In this work, the effect of recommendations on the water-to-air and graphite-to-air restricted mass electronic stopping power ratios (sw, air and sg, air ) and the individual perturbation correction factors Pi was calculated. The effect on the beam quality conversion factors kQ for reference dosimetry of high-energy photon beams was estimated for all ionization chambers listed in the Addendum to AAPM's TG-51 protocol. METHODS: The sw, air , sg, air , individual Pi, and kQ were calculated using EGSnrc Monte Carlo code system and key data of both ICRU report 37 and ICRU report 90. First, the Pi and kQ were calculated using precise models of eight ionization chambers: NE2571 (Nuclear Enterprise), 30013, 31010, 31021 (PTW), Exradin A12, A12S, A1SL (Standard imaging), and FC-65P (IBA). In this simulation, the radiation sources were one 60 Co beam and ten photon beams with nominal energy between 4 MV and 25 MV. Then, the change in kQ for ionization chambers listed in the Addendum to AAPM's TG-51 protocol was calculated by changing the specification of the simple-model of ionization chamber. The simple-models were made with only cylindrical component modules. In this simulation, the radiation sources of 60 Co beam and 24 MV photon beam were used. RESULTS: The significant changes (p < 0.05) were observed for sw, air , sg, air , the wall correction factor Pwall , and the waterproofing sleeve correction factor Psleeve . The decrease in sw, air varied from -0.57% for a 60 Co beam to -0.36% for the highest beam quality. The decrease in sg, air varied from -0.72% to -1.12% in the same range. The changes in Pwall and Psleeve were up to 0.41% and 0.14% and those maximum changes were observed for the 60 Co beam. All changes in the central electrode correction factor Pcel , the stem correction factor Pstem , and the replacement correction factor Prepl were from -0.02% to 0.12%. Those changes were statistically insignificant (p = 0.07 or more) and were independent of photon energy. The change in kQ was mainly characterized by the change in sw, air , Pwall , and Psleeve . The relationship between the change in kQ and the beam quality index was linear approximately. The changes in kQ of the simple-models were agreed with those of the precise-models within 0.08%. CONCLUSION: The effects of ICRU-90 recommendations on kQ for the ionization chambers listed in the Addendum to AAPM's TG-51 protocol were from -0.15% to 0.30%. To remove the known systematic effect on the clinical reference dosimetry, the kQ based on ICRU-37 should be updated to the kQ based on ICRU-90.

Current status of intensity-modulated radiation therapy (IMRT).

External-beam radiation therapy has been one of the treatment options for prostate cancer. The dose response has been observed for a dose range of 64.8-81 Gy. The problem of external-beam RT for prostate cancer is that as the dose increases, adverse effects also increase. Three-dimensional conformal radiation therapy (3D-CRT) has enabled us to treat patients with up to 72-76 Gy to the prostate, with a relatively acceptable risk of late rectal bleeding. Recently, intensity-modulated radiation therapy (IMRT) has been shown to deliver a higher dose to the target with acceptable low rates of rectal and bladder complications. The most important things to keep in mind when using an IMRT technique are that there is a significant trade-off between coverage of the target, avoidance of adjacent critical structures, and the inhomogeneity of the dose within the target. Lastly, even with IMRT, it should be kept in mind that a "perfect" plan that creates completely homogeneous coverage of the target volume and zero or small dose to the adjacent organs at risk is not always obtained. Participating in many treatment planning sessions and arranging the beams and beam weights create the best approach to the best IMRT plan.

[Dosimetric verification in intensity modulated radiation therapy].

As part of dosimetric verification for IMRT intensity modulated radiation therapy, we examined the selection of a dosimeter in accordance with the purpose of physical measurement and the process of data analysis. Because of the high dose conformation in the target volume and minimum dose in the organs at risk (OAR) in IMRT, dosimetric verification is essential. Because the performance of dosimetric verification in a patient is not allowed, a physical phantom and dosimeter must be used. Dose verification using a physical phantom, from which the beam data optimized for a patient slated for IMRT are transferred, may cause latent error as a result of change in the depth of each beam toward an isocenter. This effect may change the dose distribution and prescription dose. The basic methods of dosimetric verification with physical measurement are point dosimetry, when the reference dose is given at a point by planning software, and volumetric dosimetry, when planning software gives the dose as a volumetric configuration. While the most accurate dosimetry is done using a calibrated ionization chamber, IMRT requires volumetric dosimetry using some kind of portal film or a polymer gel dosimeter, because of the need for dosimetric verification for an irregular dose distribution in IMRT. The importance of indirect dosimetry using these methods is to provide calibration as a dosimeter, absolute dose, and preservation of calibration. In our study, the verification of dose distribution for IMRT using portal film and a RANDO phantom could be performed with an error of less than 2% in all cases. The measurement error for the central dose using a JARP-type ionization chamber and MixDP was less than 3% in all cases except for the case with the maximum error. At the moment, IMRT requires a great deal of effort in the processes of planning, dosimetric verification, and isocenter checking in every fraction to maintain high accuracy. Although the need for a large amount of effort in the service of maintaining accuracy may be reasonable, it could be enough to inhibit the spread of IMRT. It is hoped that an easy method of dosimetric verification that still maintains a high level of accuracy will develop as a result of this great effort.