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Deformable gel dosimetry I application to externalbeam radiotherapy and brachytherapyTo cite this article U J Yeo et al 2013 J Phys Conf Ser 444 012032

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Deformable gel dosimetry I application to external beam radiotherapy and brachytherapy

UJ Yeo1 ML Taylor123 JR Supple1 RL Smith13 T Kron12 and RD Franich1 1School of Applied Sciences and Health Innovations Research Institute RMIT University Melbourne VIC Australia 2Physical Sciences Peter MacCallum Cancer Centre Melbourne VIC Australia 3William Buckland Radiotherapy Centre The Alfred Hospital Melbourne VIC Australia E-mail rickfranichrmiteduau Abstract Inter- and intra-fractional variation in anatomic structures is a significant challenge in contemporary radiotherapy (RT) In this study we describe the implementation of a novel deformable gel dosimetry system (dubbed lsquoDEFGELrsquo) for application to external beam RT and brachytherapy experimental measurements Complex redistributed dose distributions due to applied deformations were readily observed and the discrepancies relative to a control case with an absence of deformation could be quantified This work has obvious extensions to validation of deformable image registration algorithms deformable dose calculation algorithms and quality assurance of motion compensation strategies in RT

1 Introduction Temporal anatomic changes due to respiratory and other motion are a critical issue in contemporary radiotherapy (RT) The fact that many structures deform as a result of motion adds a further layer of complexity to the problem both inter- and intra-fraction Dose accumulation is a non-trivial practice in this context Polymer gel dosimetry exhibits great utility in the verification of 3D spatial dose distributions of highly conformal treatment plans [1-4] We have previously established a novel tissue-equivalent 3D deformable gel dosimetric phantom DEFGEL [5] for 4D deformable dosimetry In this paper we demonstrate the application of DEFGEL for experimental measurement of complex and redistributed dose in external beam radiotherapy (EBRT) and high dose rate (HDR) brachytherapy

2 Materials and Methods The DEFGEL dosimeterphantom is comprised of a polymer gel in a latex membrane moulded into a cylindrical geometry with 46 mm diameter [5] A bilateral compression of 8 mm from each side (46 mm to 30 mm) was applied to generate a symmetric deformation of the DEFGEL using an acrylic compressor DEFGEL phantoms were irradiated with photons (6 MV) from a Varian 21EX linear accelerator for EBRT and with an Ir192 HDR brachytherapy source For the EBRT delivery a small field stereotactic plan of three dynamic arcs was adapted from a patient plan and 9 Gy was delivered to isocentre ndash half of the clinical prescription dose Samples were irradiated in a water bath to remove dosimetric effects of surface curvature For the HDR brachytherapy irradiation a simple linear interval treatment plan was created using the Oncentra brachytherapy TPS to the CT images of DEFGEL with a

7th International Conference on 3D Radiation Dosimetry (IC3DDose) IOP PublishingJournal of Physics Conference Series 444 (2013) 012032 doi1010881742-65964441012032

Content from this work may be used under the terms of the Creative Commons Attribution 30 licence Any further distributionof this work must maintain attribution to the author(s) and the title of the work journal citation and DOI

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standard catheter inserted Five equally-weighted source dwell positions were planned with a 10 mm step size In both treatment plan delivery schemes doses were delivered to the DEFGEL in two different scenarios (i) without deformation (ii) with deformation (see figure 1(a) and 1(b)) Doses were read out using a cone-beam optical CT scanner (VistaTM Optical Scanner by Modus Medical Devices Inc) [6-11] The measured dose distributions delivered in the deformed state were then compared to those delivered in the undeformed state to quantify the dosimetric difference between the two scenarios

3 Results and Discussion Figure 1(c) depicts a comparison between the treatment delivered with and without deformation for EBRT with the stereotactic field adapted from a patient plan Figure 2 shows a comparison of the HDR brachytherapy treatment delivered with five dwells with and without deformation The impact of deformation on dose distributions is readily seen in the isodose contours and line profiles shown from the two aforementioned scenarios for both radiation delivery techniques In both figures (figure 1 and figure 2) the deformation consisting of compression and release in the y-direction can be seen to elongate the field in that axis coupled with a contraction of the distribution in the orthogonal axes

Figure 1 Irradiation schemes in two different scenarios (a) Scenario 1 ndash irradiated and readout in undeformed state and (b) Scenario 2 ndash irradiated deformed and read out in undeformed state Photographs of measured dose distributions (1 times 2 cm2 field) are also shown for each scenario Dose distributions of three orthogonal planes for the stereotactic field irradiation are shown in (c) The top row illustrates the three orthogonal planes in DEFGEL The second third and fourth rows represent dose distributions of Scenario 1 and Scenario 2 and the difference thereof respectively The left middle and right columns correspond to the coronal saggital and transverse planes respectively All doses are in Gy and the grid spacing is 5 mm

In figure 1(c) maximum doses were 917 Gy and 903 Gy for scenarios 1 and 2 respectively Substantial dosimetric discrepancies up to approximately 3 Gy or ~30 of the maximum dose delivered are evident in all three planes

For the Ir192 exposure in figure 2 it is plain from the results that there is a dosimetric difference between the planned and measured dose distributions when the dosimeter was in the deformed state during irradiation (Scenario 2) Similar to the external beam case this figure shows elongation of the dose distribution in the direction of compression and relaxation coupled with a contraction of the distribution in the orthogonal axis This discrepancy increases with extent of deformation note that

(b) Scenario 2 Irradiated deformed and read out undeformed

(c) The stereotactic field irradiation

(a) Scenario 1 Undeformed Irradiated and read out

7th International Conference on 3D Radiation Dosimetry (IC3DDose) IOP PublishingJournal of Physics Conference Series 444 (2013) 012032 doi1010881742-65964441012032

2

each dwell position experienced different extents of deformation due to their varying positions relative to the centre of mass in the DEFGEL as shown in figure 2(d) Consequently the apparent dwell positions in the measured distributions appear different when comparing the deformed and undeformed dosimetry data The planned length from the top to bottom dwell position was 400 mm (five dwells with a 10 mm step size) but the measured length between these maxima in the case of Scenario 2 was found to be 331mm (ie a 173 reduction)

Figure 2 HDR brachytherapy irradiation of DEFGEL 5 dwells of equal weighting and 10 mm spacing on a single catheter (a) Scenario 1 and (b) Scenario 2 Planned dose distributions in coronal and transverse planes are presented in left and middle columns respectively The right column shows dose maps in planes indicated by the red dashed arrows (29 mm distance from the catheter) in the transverse plane (middle column) The dashed lines in the dose maps correspond to line profiles in the horizontal and vertical directions of the coronal planes shown in (c) and (d) These figures show an elongated dose distribution in the direction of compression and relaxation coupled with a contraction of the distribution in the orthogonal axis The scale in the measured plane is in ∆OD

For both treatment techniques EBRT and HDR brachytherapy the potential clinical implications of these results represent a decrease in dose to the planning target volume or increased dose to an organ at risk (or both) The use of DEFGEL for studying the effects of deformation on absorbed dose distributions is valid for comparable mass and density conserving deformations Obvious anatomic examples would include prostate breast liver etc The relevant anatomical deformations would be those related to organ geometric changes induced by filling and emptying of the bladder rectum stomach etc as well as respiratory and cardiac motion during irradiation

4 Conclusions This methodology describes the use of a tissue-equivalent 3D dose-integrating deformable phantom that yields dosimetric information for both external beam and HDR brachytherapy It is demonstrated that the system is potentially capable of reproducibly emulating the physical deformation of an organ and therefore can be used to evaluate absorbed doses to deformable targets and to validate deformation algorithms

Transverse (Planned)

Coronal (Planned)

Coronal (Measured)

(b) Scenario 2

Horizontal amp vertical profiles (Measured)

(d) Vertical Line profiles

(c) Horizontal Line profiles (a) Scenario 1

7th International Conference on 3D Radiation Dosimetry (IC3DDose) IOP PublishingJournal of Physics Conference Series 444 (2013) 012032 doi1010881742-65964441012032

3

5 Acknowledgements This work is supported by an RMIT University Research amp Innovation Emerging Researcher Industry Award (Dr R Franich Dr Taylor) Mr Smith is supported by Cancer Australia Grant 616614 funded by the Radiation Oncology Section Australian Government Department of Health and Ageing

6 References [1] Baldock C et al 2010 Phys Med Biol 55 R1-63 [2] Lopatiuk-Tirpak O et al 2008 Med Phys 35 3847-59 [3] De Deene Y et al 2002 Phys Med Biol 47 2459-70 [4] Hurley C et al 2006 Nucl Instrum Methods Phys Res A 565 801-11 [5] Yeo U J et al 2012 Med Phys 39 2203-13 [6] Islam K et al 2003 Med Phys 30 2159 [7] Bosi S et al 2007 Phys Med Biol 52 2893-903 [8] Bosi S G et al 2009 Phys Med Biol 54 275-83 [9] Bosi S G et al 2009 Appl Opt 48 2427-34 [10] Olding T et al 2010 Phys Med Biol 55 2819-40 [11] Olding T and Schreiner L J 2011 Phys Med Biol 56 1259-79

7th International Conference on 3D Radiation Dosimetry (IC3DDose) IOP PublishingJournal of Physics Conference Series 444 (2013) 012032 doi1010881742-65964441012032

4

standard catheter inserted Five equally-weighted source dwell positions were planned with a 10 mm step size In both treatment plan delivery schemes doses were delivered to the DEFGEL in two different scenarios (i) without deformation (ii) with deformation (see figure 1(a) and 1(b)) Doses were read out using a cone-beam optical CT scanner (VistaTM Optical Scanner by Modus Medical Devices Inc) [6-11] The measured dose distributions delivered in the deformed state were then compared to those delivered in the undeformed state to quantify the dosimetric difference between the two scenarios

3 Results and Discussion Figure 1(c) depicts a comparison between the treatment delivered with and without deformation for EBRT with the stereotactic field adapted from a patient plan Figure 2 shows a comparison of the HDR brachytherapy treatment delivered with five dwells with and without deformation The impact of deformation on dose distributions is readily seen in the isodose contours and line profiles shown from the two aforementioned scenarios for both radiation delivery techniques In both figures (figure 1 and figure 2) the deformation consisting of compression and release in the y-direction can be seen to elongate the field in that axis coupled with a contraction of the distribution in the orthogonal axes

Figure 1 Irradiation schemes in two different scenarios (a) Scenario 1 ndash irradiated and readout in undeformed state and (b) Scenario 2 ndash irradiated deformed and read out in undeformed state Photographs of measured dose distributions (1 times 2 cm2 field) are also shown for each scenario Dose distributions of three orthogonal planes for the stereotactic field irradiation are shown in (c) The top row illustrates the three orthogonal planes in DEFGEL The second third and fourth rows represent dose distributions of Scenario 1 and Scenario 2 and the difference thereof respectively The left middle and right columns correspond to the coronal saggital and transverse planes respectively All doses are in Gy and the grid spacing is 5 mm

In figure 1(c) maximum doses were 917 Gy and 903 Gy for scenarios 1 and 2 respectively Substantial dosimetric discrepancies up to approximately 3 Gy or ~30 of the maximum dose delivered are evident in all three planes

For the Ir192 exposure in figure 2 it is plain from the results that there is a dosimetric difference between the planned and measured dose distributions when the dosimeter was in the deformed state during irradiation (Scenario 2) Similar to the external beam case this figure shows elongation of the dose distribution in the direction of compression and relaxation coupled with a contraction of the distribution in the orthogonal axis This discrepancy increases with extent of deformation note that

(b) Scenario 2 Irradiated deformed and read out undeformed

(c) The stereotactic field irradiation

(a) Scenario 1 Undeformed Irradiated and read out

7th International Conference on 3D Radiation Dosimetry (IC3DDose) IOP PublishingJournal of Physics Conference Series 444 (2013) 012032 doi1010881742-65964441012032

2

each dwell position experienced different extents of deformation due to their varying positions relative to the centre of mass in the DEFGEL as shown in figure 2(d) Consequently the apparent dwell positions in the measured distributions appear different when comparing the deformed and undeformed dosimetry data The planned length from the top to bottom dwell position was 400 mm (five dwells with a 10 mm step size) but the measured length between these maxima in the case of Scenario 2 was found to be 331mm (ie a 173 reduction)

Figure 2 HDR brachytherapy irradiation of DEFGEL 5 dwells of equal weighting and 10 mm spacing on a single catheter (a) Scenario 1 and (b) Scenario 2 Planned dose distributions in coronal and transverse planes are presented in left and middle columns respectively The right column shows dose maps in planes indicated by the red dashed arrows (29 mm distance from the catheter) in the transverse plane (middle column) The dashed lines in the dose maps correspond to line profiles in the horizontal and vertical directions of the coronal planes shown in (c) and (d) These figures show an elongated dose distribution in the direction of compression and relaxation coupled with a contraction of the distribution in the orthogonal axis The scale in the measured plane is in ∆OD

For both treatment techniques EBRT and HDR brachytherapy the potential clinical implications of these results represent a decrease in dose to the planning target volume or increased dose to an organ at risk (or both) The use of DEFGEL for studying the effects of deformation on absorbed dose distributions is valid for comparable mass and density conserving deformations Obvious anatomic examples would include prostate breast liver etc The relevant anatomical deformations would be those related to organ geometric changes induced by filling and emptying of the bladder rectum stomach etc as well as respiratory and cardiac motion during irradiation

4 Conclusions This methodology describes the use of a tissue-equivalent 3D dose-integrating deformable phantom that yields dosimetric information for both external beam and HDR brachytherapy It is demonstrated that the system is potentially capable of reproducibly emulating the physical deformation of an organ and therefore can be used to evaluate absorbed doses to deformable targets and to validate deformation algorithms

Transverse (Planned)

Coronal (Planned)

Coronal (Measured)

(b) Scenario 2

Horizontal amp vertical profiles (Measured)

(d) Vertical Line profiles

(c) Horizontal Line profiles (a) Scenario 1

7th International Conference on 3D Radiation Dosimetry (IC3DDose) IOP PublishingJournal of Physics Conference Series 444 (2013) 012032 doi1010881742-65964441012032

3

5 Acknowledgements This work is supported by an RMIT University Research amp Innovation Emerging Researcher Industry Award (Dr R Franich Dr Taylor) Mr Smith is supported by Cancer Australia Grant 616614 funded by the Radiation Oncology Section Australian Government Department of Health and Ageing

6 References [1] Baldock C et al 2010 Phys Med Biol 55 R1-63 [2] Lopatiuk-Tirpak O et al 2008 Med Phys 35 3847-59 [3] De Deene Y et al 2002 Phys Med Biol 47 2459-70 [4] Hurley C et al 2006 Nucl Instrum Methods Phys Res A 565 801-11 [5] Yeo U J et al 2012 Med Phys 39 2203-13 [6] Islam K et al 2003 Med Phys 30 2159 [7] Bosi S et al 2007 Phys Med Biol 52 2893-903 [8] Bosi S G et al 2009 Phys Med Biol 54 275-83 [9] Bosi S G et al 2009 Appl Opt 48 2427-34 [10] Olding T et al 2010 Phys Med Biol 55 2819-40 [11] Olding T and Schreiner L J 2011 Phys Med Biol 56 1259-79

7th International Conference on 3D Radiation Dosimetry (IC3DDose) IOP PublishingJournal of Physics Conference Series 444 (2013) 012032 doi1010881742-65964441012032

4

each dwell position experienced different extents of deformation due to their varying positions relative to the centre of mass in the DEFGEL as shown in figure 2(d) Consequently the apparent dwell positions in the measured distributions appear different when comparing the deformed and undeformed dosimetry data The planned length from the top to bottom dwell position was 400 mm (five dwells with a 10 mm step size) but the measured length between these maxima in the case of Scenario 2 was found to be 331mm (ie a 173 reduction)

Figure 2 HDR brachytherapy irradiation of DEFGEL 5 dwells of equal weighting and 10 mm spacing on a single catheter (a) Scenario 1 and (b) Scenario 2 Planned dose distributions in coronal and transverse planes are presented in left and middle columns respectively The right column shows dose maps in planes indicated by the red dashed arrows (29 mm distance from the catheter) in the transverse plane (middle column) The dashed lines in the dose maps correspond to line profiles in the horizontal and vertical directions of the coronal planes shown in (c) and (d) These figures show an elongated dose distribution in the direction of compression and relaxation coupled with a contraction of the distribution in the orthogonal axis The scale in the measured plane is in ∆OD

For both treatment techniques EBRT and HDR brachytherapy the potential clinical implications of these results represent a decrease in dose to the planning target volume or increased dose to an organ at risk (or both) The use of DEFGEL for studying the effects of deformation on absorbed dose distributions is valid for comparable mass and density conserving deformations Obvious anatomic examples would include prostate breast liver etc The relevant anatomical deformations would be those related to organ geometric changes induced by filling and emptying of the bladder rectum stomach etc as well as respiratory and cardiac motion during irradiation

4 Conclusions This methodology describes the use of a tissue-equivalent 3D dose-integrating deformable phantom that yields dosimetric information for both external beam and HDR brachytherapy It is demonstrated that the system is potentially capable of reproducibly emulating the physical deformation of an organ and therefore can be used to evaluate absorbed doses to deformable targets and to validate deformation algorithms

Transverse (Planned)

Coronal (Planned)

Coronal (Measured)

(b) Scenario 2

Horizontal amp vertical profiles (Measured)

(d) Vertical Line profiles

(c) Horizontal Line profiles (a) Scenario 1

7th International Conference on 3D Radiation Dosimetry (IC3DDose) IOP PublishingJournal of Physics Conference Series 444 (2013) 012032 doi1010881742-65964441012032

3

5 Acknowledgements This work is supported by an RMIT University Research amp Innovation Emerging Researcher Industry Award (Dr R Franich Dr Taylor) Mr Smith is supported by Cancer Australia Grant 616614 funded by the Radiation Oncology Section Australian Government Department of Health and Ageing

6 References [1] Baldock C et al 2010 Phys Med Biol 55 R1-63 [2] Lopatiuk-Tirpak O et al 2008 Med Phys 35 3847-59 [3] De Deene Y et al 2002 Phys Med Biol 47 2459-70 [4] Hurley C et al 2006 Nucl Instrum Methods Phys Res A 565 801-11 [5] Yeo U J et al 2012 Med Phys 39 2203-13 [6] Islam K et al 2003 Med Phys 30 2159 [7] Bosi S et al 2007 Phys Med Biol 52 2893-903 [8] Bosi S G et al 2009 Phys Med Biol 54 275-83 [9] Bosi S G et al 2009 Appl Opt 48 2427-34 [10] Olding T et al 2010 Phys Med Biol 55 2819-40 [11] Olding T and Schreiner L J 2011 Phys Med Biol 56 1259-79

7th International Conference on 3D Radiation Dosimetry (IC3DDose) IOP PublishingJournal of Physics Conference Series 444 (2013) 012032 doi1010881742-65964441012032

4

5 Acknowledgements This work is supported by an RMIT University Research amp Innovation Emerging Researcher Industry Award (Dr R Franich Dr Taylor) Mr Smith is supported by Cancer Australia Grant 616614 funded by the Radiation Oncology Section Australian Government Department of Health and Ageing

6 References [1] Baldock C et al 2010 Phys Med Biol 55 R1-63 [2] Lopatiuk-Tirpak O et al 2008 Med Phys 35 3847-59 [3] De Deene Y et al 2002 Phys Med Biol 47 2459-70 [4] Hurley C et al 2006 Nucl Instrum Methods Phys Res A 565 801-11 [5] Yeo U J et al 2012 Med Phys 39 2203-13 [6] Islam K et al 2003 Med Phys 30 2159 [7] Bosi S et al 2007 Phys Med Biol 52 2893-903 [8] Bosi S G et al 2009 Phys Med Biol 54 275-83 [9] Bosi S G et al 2009 Appl Opt 48 2427-34 [10] Olding T et al 2010 Phys Med Biol 55 2819-40 [11] Olding T and Schreiner L J 2011 Phys Med Biol 56 1259-79

7th International Conference on 3D Radiation Dosimetry (IC3DDose) IOP PublishingJournal of Physics Conference Series 444 (2013) 012032 doi1010881742-65964441012032

4