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Correlation between bladder volume and bowel radiation dose for rectum cancer patients
Abstracts / Physica Medica 32 (2016) 196–221
The same differences were obtained for the mean calculated dose in both conditions. Conclusion. Despite some discordant results in literature, one found from the present results, that skin sparing effect is better achieved with VMAT technique. Disclosure. The authors have no relevant financial or nonfinancial relationships to disclose. http://dx.doi.org/10.1016/j.ejmp.2016.07.680
PROSTATE SBRT: THE USE OF ERB AND MOSFET IN VIVO DOSIMETRY FEASIBILITY A.G. Dias a,b,*, L.T. Cunha a,b, A. Oliveira c, J.A.M. Santos a,b, J. Lencart a,b a
Medical Physics Department, Portuguese Institute of Oncology, Porto, Portugal b Medical Physics, Radiobiology and Radiation Protection Group, Research Centre, Portuguese Institute of Oncology, Porto, Portugal c Radiotherapy Department, Portuguese Institute of Oncology, Porto, Portugal ⇑ Corresponding author. Introduction. Hypofractionated treatment regimens are indicated for some stages of prostate cancer. In order to provide the reproducibility of the relative position between rectum and prostate and to allow that only a small volume of the rectal wall remains close to the prostate, an endorectal balloon (ERB) may be used. Purpose. This work aims to assess the dose on the rectal wall in the presence of the ERB filled with water or air and evaluate the deviation between the measured and calculated doses using two different algorithms (Eclipse AAA and iPlan PencilBeam) Materials and methods. Two CT scans were obtained for a modified Rando phantom where an ERB (filled with water or air) with three MOSFET detectors was inserted. A simple 4 field in box plan and an IMRT (6MV beam) clinical plan were calculated in both CT sets, using two different algorithms. The treatment plans were delivered to the phantom using a Varian Novalis linac. Four sets of measurements were obtained and the results were compared with the calculated values. Results. The difference between the calculated and measured doses around the ERB is lower when it is filled with water for both algorithms. The maximum relative differences when the ERB is filled with air are 1.8% for Eclipse and 5.5% for iPlan. Conclusion. Both algorithms show a better a performance in the presence of water. Water filled ERB seems to be a suitable option. MOSFET dosimetry in association with ERBs for real-time in vivo during hypofractionated treatment of the prostate is a practical and reliable procedure. Disclosure. The authors have no relevant financial or nonfinancial relationships to disclose. http://dx.doi.org/10.1016/j.ejmp.2016.07.681
CHARACTERIZATION OF THE EXRADIN A26 MICROCHAMBER FOR SMALL FIELD DOSIMETRY M. Pasquino, C. Cutaia, L. Radici, E. Gino, M. Stasi * Medical Physics Department, AO Mauriziano, Torino, Italy Corresponding author.
⇑
Introduction. In modern radiation therapy accurate dosimetry within small photon fields is a challenge. The aim of the study is
201
to investigate the main dosimetric characteristics of a new small field detector. Material and methods. An Exradin A26 microionization chamber was tested. Short term stability, dose linearity, polarity effect, angular dependence and energy dependence were evaluated for field sizes up to 10 10 cm2. Results were compared with those obtained with an Exradin A1SL IC. PDD curves, OAR profiles and OF values were measured for different field sizes. The results were compared with those obtained with an IC and an EDGE diode. Results. A26 IC readings showed a 0.2% and 0.1% relative standard deviation for 3 3 and 10 10 cm2 fields, respectively. Dose response was linear to within 0.5%. The microchamber showed the maximum variation from the reference condition at the lowest dose rate. The polarity effect is within 0.5% for field size greater than 2 2 cm2; for field size less than 2 2 cm2 the effect increases, still remaining within 1%. No energy and angular dependence were observed. A26 IC PDD measurements agreed with those obtained with the EDGE diode. FWHM values show a better agreement with the EDGE diode values than A1SL. The penumbra values were greater than those obtained with the EDGE diode. Of values showed a good agreement with EDGE diode ones. Conclusions. The study confirms A26 IC as a reference detector for PDD and OAR measurements. http://dx.doi.org/10.1016/j.ejmp.2016.07.682
CORRELATION BETWEEN BLADDER VOLUME AND RADIATION DOSE FOR RECTUM CANCER PATIENTS Lina Andersson a,b,*, Claus F. Behrens b, David Sjöström b
BOWEL
a Department of Medical Radiation Physics, Lund University, 221 85 Lund, Sweden b Radiotherapy Research Unit, Department of Oncology, Herlev Hospital, University of Copenhagen, Herlev Ringvej 75, DK-2730 Herlev, Denmark ⇑ Corresponding author.
Introduction. For rectum cancer patients, the bladder volume varies during the course of treatment. This results in a delivered dose distribution different than planned. Purpose. To study the effect of bladder filling on dose distributions of bowel for rectum cancer patients. Materials and methods. Twenty-eight rectal cancer patients treated with preoperative radiotherapy in the period February 2015 to January 2016 were included in the study. Each patient had a planning CT scan and weekly CBCT were acquired the first three, four, five and six weeks for 23, 1, 1 and 3 patients, respectively. Bladder and bowel was delineated on the CBCT images and the delineations were transferred to the CT image. Results. Out of the 28 patients, 6 patients had bladders that were larger on all CBCTs than on the CT. For 13 patients, the bladder on all the CBCTs was smaller than on the CT. For 9 patients, the relationship between the bladder volume on the CT and CBCT images varied. The bladder volumes on the CBCTs ranged from 0.1 to 3.5 times the bladder volume on the corresponding CT, with the majority (81/96) in the range between 0.3 and 2. The change in bladder filling did not result in a violation of the constraint V45Gy < 195 cc for any patient. Conclusion. There is a correlation between bladder volume and bowel radiation dose, however, the dose constraint for the small bowel was not violated for any of the patients in this study. http://dx.doi.org/10.1016/j.ejmp.2016.07.683
The same differences were obtained for the mean calculated dose in both conditions. Conclusion. Despite some discordant results in literature, one found from the present results, that skin sparing effect is better achieved with VMAT technique. Disclosure. The authors have no relevant financial or nonfinancial relationships to disclose. http://dx.doi.org/10.1016/j.ejmp.2016.07.680
PROSTATE SBRT: THE USE OF ERB AND MOSFET IN VIVO DOSIMETRY FEASIBILITY A.G. Dias a,b,*, L.T. Cunha a,b, A. Oliveira c, J.A.M. Santos a,b, J. Lencart a,b a
Medical Physics Department, Portuguese Institute of Oncology, Porto, Portugal b Medical Physics, Radiobiology and Radiation Protection Group, Research Centre, Portuguese Institute of Oncology, Porto, Portugal c Radiotherapy Department, Portuguese Institute of Oncology, Porto, Portugal ⇑ Corresponding author. Introduction. Hypofractionated treatment regimens are indicated for some stages of prostate cancer. In order to provide the reproducibility of the relative position between rectum and prostate and to allow that only a small volume of the rectal wall remains close to the prostate, an endorectal balloon (ERB) may be used. Purpose. This work aims to assess the dose on the rectal wall in the presence of the ERB filled with water or air and evaluate the deviation between the measured and calculated doses using two different algorithms (Eclipse AAA and iPlan PencilBeam) Materials and methods. Two CT scans were obtained for a modified Rando phantom where an ERB (filled with water or air) with three MOSFET detectors was inserted. A simple 4 field in box plan and an IMRT (6MV beam) clinical plan were calculated in both CT sets, using two different algorithms. The treatment plans were delivered to the phantom using a Varian Novalis linac. Four sets of measurements were obtained and the results were compared with the calculated values. Results. The difference between the calculated and measured doses around the ERB is lower when it is filled with water for both algorithms. The maximum relative differences when the ERB is filled with air are 1.8% for Eclipse and 5.5% for iPlan. Conclusion. Both algorithms show a better a performance in the presence of water. Water filled ERB seems to be a suitable option. MOSFET dosimetry in association with ERBs for real-time in vivo during hypofractionated treatment of the prostate is a practical and reliable procedure. Disclosure. The authors have no relevant financial or nonfinancial relationships to disclose. http://dx.doi.org/10.1016/j.ejmp.2016.07.681
CHARACTERIZATION OF THE EXRADIN A26 MICROCHAMBER FOR SMALL FIELD DOSIMETRY M. Pasquino, C. Cutaia, L. Radici, E. Gino, M. Stasi * Medical Physics Department, AO Mauriziano, Torino, Italy Corresponding author.
⇑
Introduction. In modern radiation therapy accurate dosimetry within small photon fields is a challenge. The aim of the study is
201
to investigate the main dosimetric characteristics of a new small field detector. Material and methods. An Exradin A26 microionization chamber was tested. Short term stability, dose linearity, polarity effect, angular dependence and energy dependence were evaluated for field sizes up to 10 10 cm2. Results were compared with those obtained with an Exradin A1SL IC. PDD curves, OAR profiles and OF values were measured for different field sizes. The results were compared with those obtained with an IC and an EDGE diode. Results. A26 IC readings showed a 0.2% and 0.1% relative standard deviation for 3 3 and 10 10 cm2 fields, respectively. Dose response was linear to within 0.5%. The microchamber showed the maximum variation from the reference condition at the lowest dose rate. The polarity effect is within 0.5% for field size greater than 2 2 cm2; for field size less than 2 2 cm2 the effect increases, still remaining within 1%. No energy and angular dependence were observed. A26 IC PDD measurements agreed with those obtained with the EDGE diode. FWHM values show a better agreement with the EDGE diode values than A1SL. The penumbra values were greater than those obtained with the EDGE diode. Of values showed a good agreement with EDGE diode ones. Conclusions. The study confirms A26 IC as a reference detector for PDD and OAR measurements. http://dx.doi.org/10.1016/j.ejmp.2016.07.682
CORRELATION BETWEEN BLADDER VOLUME AND RADIATION DOSE FOR RECTUM CANCER PATIENTS Lina Andersson a,b,*, Claus F. Behrens b, David Sjöström b
BOWEL
a Department of Medical Radiation Physics, Lund University, 221 85 Lund, Sweden b Radiotherapy Research Unit, Department of Oncology, Herlev Hospital, University of Copenhagen, Herlev Ringvej 75, DK-2730 Herlev, Denmark ⇑ Corresponding author.
Introduction. For rectum cancer patients, the bladder volume varies during the course of treatment. This results in a delivered dose distribution different than planned. Purpose. To study the effect of bladder filling on dose distributions of bowel for rectum cancer patients. Materials and methods. Twenty-eight rectal cancer patients treated with preoperative radiotherapy in the period February 2015 to January 2016 were included in the study. Each patient had a planning CT scan and weekly CBCT were acquired the first three, four, five and six weeks for 23, 1, 1 and 3 patients, respectively. Bladder and bowel was delineated on the CBCT images and the delineations were transferred to the CT image. Results. Out of the 28 patients, 6 patients had bladders that were larger on all CBCTs than on the CT. For 13 patients, the bladder on all the CBCTs was smaller than on the CT. For 9 patients, the relationship between the bladder volume on the CT and CBCT images varied. The bladder volumes on the CBCTs ranged from 0.1 to 3.5 times the bladder volume on the corresponding CT, with the majority (81/96) in the range between 0.3 and 2. The change in bladder filling did not result in a violation of the constraint V45Gy < 195 cc for any patient. Conclusion. There is a correlation between bladder volume and bowel radiation dose, however, the dose constraint for the small bowel was not violated for any of the patients in this study. http://dx.doi.org/10.1016/j.ejmp.2016.07.683