Does pelvic lymph nodes irradiation using intensity modulated radiation therapy increase rectal and bladder toxicities in patients with prostate carcinoma?

PURPOSE: this study compared the radiation-related rectal (R) and bladder (B) toxicities in prostate carcinoma patients receiving additional pelvic lymph nodes (PLN) irradiation with those receiving prostate (P) and seminal vesicle (SV) irradiation only. METHODS: thirty-three patients treated with intensity modulated radiation therapy (IMRT) were included. RT doses ranged between 60- 66.6 Gy to SV, 74-77.7 Gy to P and 50.4- 60 Gy to PLN. Max acute R toxicity was graded by a physician according to the RTOG side effect criteria during the period from the initiation of therapy until the end of the third month. Max late R and B toxicities were graded 3 months after the completion of RT by a physician using the RTOG GI and urogenital toxicity score and by patients using EORTC QLQ - PR25 self questionnaire separately. The effects of R and B doses and additional PLN irradiation on acute and late R and B toxicities and compatibility of patient- and physician-graded toxicity scores were investigated. RTOG GI and urogenital toxicity scores and EORTC QLQ - PR25 self questionnaire results were correlated. RESULTS: significant factors for acute R toxicity were: max R; R volume receiving ≥ 68 Gy; and PLN irradiation. PLN irradiation was marginally significant for late R toxicity; the mean B dose was a significant factor for late B toxicity. CONCLUSION: the results of this study suggest that although PLN irradiation increased acute R toxicity, it has no effect on late R and B toxicity. Patient- and physician-evaluated late R and B toxicity scores were concordant.

Effects of immobilization beds on the dose in the entrance and exit dose region for Co-60, 4, 6 and 15 MV photons.

PURPOSE: The aim of this study was to determine the effects of Styrofoam beds used for immobilization on build-up and exit dose regions for high energy photon beams. MATERIALS AND METHODS: Build-up dose and exit dose measurements in central axis of Co-60 and 4, 6 and 15 MV photons at various field sizes and source to phantom distances were made in a water equivalent solid phantom with 2, 5 and 10 cm thick uniform Styrofoam beds at the surface. A Markus type plane-parallel ion chamber with fixed separation between collecting electrodes was used to measure the percent depth doses. RESULTS: The surface dose increased almost linearly with field size for Co-60, 4, 6 and 15 MV X-ray beams. The effect of immobilization (Styrofoam beds) on the surface dose increased with the thickness and this effect was lower with higher energies. When a 2 cm thick Styrofoam bed was used for immobilization, the surface dose in a 10x10 cm field was higher (43.9, 36.8, 28.8 and 14.9% for Co-60, 4, 6 and 15 MV, respectively). CONCLUSION: As the Styrofoam bed was thicker, the maximum dose point moved closer to the surface of the phantom for all energies. The exit surface dose was also enhanced with the presence of Styrofoam beds and similar to the effects on the surface dose. This enhancement was the maximum 5% for high energy photon beams and 6% for Co-60 beam. The introduction of Styrofoam beds in the radiation beam for the immobilization of the patient increases surface and exit doses to a considerable extent.

Determination of output factors for the Leksell gamma knife using ion chamber, thermoluminescence detectors and films.

PURPOSE: In stereotactic radiosurgery by the Leksell gamma knife, small fields of 4-18 mm in diameter are used. The difficulties associated with the dosimetry of small radiosurgical beams are well known. The output factors for small field sizes show a strong field size dependence, with rapidly decreasing output factors as the diameter of the field decreases. The main purpose of this study was to determine output factors of 18, 14, 8 and 4 mm collimators for Leksell gamma knife and to compare them with the values given by the manufacturer. MATERIALS AND METHODS: The relative output factors of the 18, 14 8 and 4 mm collimators for model B Leksell gamma knife were measured. The output factor measurements were prformed using a PTW 0.125 cc ion chamber, G200 thermoluminescence detectors (TLDs), KodakXV and Kodak ERD2 films. RESULTS: For 14 mm collimator, output measurements used with an ion chamber, TLD, Kodak XV film and Kodak ERD2 film were in agreement with the manufacturer's estimates within 1%. For 8 and 4 mm collimators, the best agreement with values given by the manufacturer were obtained by Kodak EDR2 films (2% and 5%, respectively). CONCLUSION: The measured output factors are in good agreement with the values recommended by the manufacturer for 18, 14 and 8 mm collimators. No good agreement was found for 4 mm collimator.

Do collimator angle setup errors cause dose inhomogeneity at the junction zone during craniospinal irradiation? A phantom study.

PURPOSE: Craniospinal irradiation (CSI) has some geometric uncertainties, especially at the junction zone. In this study we tried to evaluate how possible random setup errors of the collimator angle may contribute to these uncertainties. MATERIALS AND METHODS: Cranial and spinal fields were drawn on RW3 solid water phantom in accordance with the divergence matching technique (DMT). Field dimensions were 18x18 cm and 6x30 cm, respectively. We placed light-insulated Kodak X-Omat V films at the junction zone, then we irradiated the films with different collimator angles with both Co-60 and 4 MV conditions, and determined how the junction zone was affected from random setup errors in DMT. RESULTS: 10.6 degrees collimator angle was proper for 30 cm upper spinal field. For Co-60 machine the dose homogeneity of this angle was +4.5%. For the angles of 8, 9, 11 and 12 degrees the homogeneities were -13%, - 11%, +5% and +10 %, respectively. For 4 MV photon the dose homogeneity of the 10.6 degrees collimator angle was +3%. For the angles of 8, 9, 11 and 12 degrees the homogeneities were -17%, -14%, +6 % and +13%, respectively. CONCLUSION: As the CSI has some geometric uncertainties, serious dose inhomogeneities may occur at the junction zone. The collimator angle is of great importance and any random setup errors may not be tolerated.

Determination of dose distributions and dose rates in the gamma knife.

PURPOSE: To measure the dose parameters of the Leksell gamma knife unit and compare them with the treatment planning data. MATERIALS AND METHODS: The dose distributions taken from treatment planning computer were confirmed with film dosimetry using a spherical uniform density polystyrene phantom. The dose rate measurements were made by using a 0.125 cc ion chamber and the spherical phantom for 4, 8, 14 and 18 mm helmets. The dose rate measurements were compared with the estimates given by the manufacturer. RESULTS: The dose distributions obtained by film dosimetry were in agreement with those taken from the treatment planning computer only for the 70% and 50% isodose line. The results of dose rate measurement showed that the 0.125 cc ion chamber was suitable only for 18 and 14 mm helmets. Conversely, it was not suitable for 8 and 4 mm helmets. CONCLUSION: This study showed that both computergenerated treatment plans and film densitometry estimates provided similar dose distributions without special beam blocking.

Effect of field placement errors on dose at junction between divergence matching and half-beam block techniques in craniospinal irradiation.

PURPOSE: In craniospinal irradiation, both overlapping and gapping between the cranial and upper spinal field may occur due to patient's daily position (setup). This can cause dose inhomogeneities at the craniospinal junction. In this study we tried to find out possible dose changes at the craniospinal junction due to setup mistakes. MATERIALS AND METHODS: Both divergence matching technique (DMT) and half-beam block technique (HBBT) were used. At first step, a gap between cranial and spinal field borders was used, and at the second step overlapping between the fields for both techniques was applied. We irradiated films located in water equivalents solid phantoms with Co60 teletherapy machine. RESULTS: Dose homogeneity was 4% when no gap was used. When 2, 5, 8 and 10 mm gap were used, overlap occurred. Dose inhomogeneities were 6%, 17%, 27%,34% and 16%, 24%, 29%, 43%, respectively for DMT. Dose inhomogeneity was 5% with no gap used. With gaps of 2, 5, 8, and 10 mm, overlap occurred. Dose inhomogeneities were 8%, 12%, 36%, 51% and 17%, 29%, 35%, and 47%, respectively for HBBT. CONCLUSION: With no gap or with 2mm gap between the fields the dose homogeneity is in acceptable dose variation limits (10%) for both techniques (DMT and HBBT). Beyond this distance the setup mistakes are not tolerable.