- Email: [email protected]
Field-In-Field Technique With Intrafractionally Modulated Junction Shifts for Craniospinal Irradiation
Int. J. Radiation Oncology Biol. Phys., Vol. 69, No. 4, pp. 1193–1198, 2007 Copyright Ó 2007 Elsevier Inc. Printed in the USA. All rights reserved 0360-3016/07/$–see front matter
doi:10.1016/j.ijrobp.2007.04.062
CLINICAL INVESTIGATION
Central Nervous System
FIELD-IN-FIELD TECHNIQUE WITH INTRAFRACTIONALLY MODULATED JUNCTION SHIFTS FOR CRANIOSPINAL IRRADIATION SUE S. YOM, M.D., PH.D.,* ERIK K. FRIJA, C.M.D.,* ANITA MAHAJAN, M.D.,* ERIC CHANG, M.D.,* KELLI KLEIN, C.M.D.,* ALMON SHIU, PH.D.,y JARED OHRT, M.S.,y AND SHIAO WOO, M.D.* * Division of Radiation Oncology and y Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX Purpose: To plan craniospinal irradiation with ‘‘field-in-field’’ (FIF) homogenization in combination with daily, intrafractional modulation of the field junctions, to minimize the possibility of spinal cord overdose. Methods and Materials: Lateral cranial fields and posterior spinal fields were planned using a forward-planned, step-and-shoot FIF technique. Field junctions were automatically modulated and custom-weighted for maximal homogeneity within each treatment fraction. Dose–volume histogram analyses and film dosimetry were used to assess results. Results: Plan inhomogeneity improved with FIF. Planning with daily modulated junction shifts provided consistent dose delivery during each fraction of treatment across the junctions. Modulation minimized the impact of a 5-mm setup error at the junction. Film dosimetry confirmed that no point in the junction exceeded the anticipated dose. Conclusions: Field-in-field planning and modulated junction shifts improve the homogeneity and consistency of daily dose delivery, simplify treatment, and reduce the impact of setup errors. Ó 2007 Elsevier Inc. Craniospinal irradiation planning, Junction shift, Field-in-field technique.
INTRODUCTION
METHODS AND MATERIALS
Photon-based techniques for craniospinal irradiation (CSI) may result in dose inhomogeneity within the treatment volume and usually require a weekly manual shift of the field junctions to minimize the possibility of spinal cord overdose. We have begun planning CSI using a multisegmented, intensity-modulated ‘‘field-in-field’’ (FIF) and automated ‘‘junction-shift’’ techniques. To deploy FIF, multiple lower-weighted reduction fields are created on the basis of the primary field. The reduction fields contain blocked segments strategically placed to reduce the highest isodose areas and to force greater homogeneity and conformity to the target volume (1). We combine FIF with a practice of automatically modulated junctions that eliminates the need for weekly junction shifts. During each fraction of treatment, the field edges are shifted in successive 1-cm increments, using customized weighting at each modulated step to obtain greater homogeneity within the volume. Although this planning process is initially more intensive, daily patient setup is simplified and more consistent, using only a single setup point in the cranium.
A waiver of informed consent was obtained from our institutional review board for this planning study. Computed tomography scans were obtained for 4 adults and 1 adolescent patient. All patients were prone and immobilized in a head holder and customized thermoplastic mask; the spine was immobilized with a radiotranslucent urethane cushion filled with polystyrene beads and molded to the individual anatomy by vacuum suction. Positioning marks were placed for straightening, but one setup point was designated in the cranium. A source-surface distance setup of 110 cm was used. The Pinnacle3D Radiation Therapy Planning System v7.6c (ADAC Laboratories, Milpitas, CA) was used for planning. Two lateral cranial fields and multiple abutting posterior spinal fields were designed using 6-MV photons. Brain, brainstem, and optic structures were contoured. The thecal sac was contoured from the foramen magnum to the inferior termination, visualized on a magnetic resonance imaging study (2). Adding and removing reduction fields enabled dosimetric comparison with or without FIF implementation. In addition, custom-weighted segmental modulation was created to feather the field edges at each junction during each fraction. The craniospinal match was placed in the low neck, and using multileaf collimator leaf adjustments the junctioned field edges were shifted by successive 1-cm increments during each treatment session. For
Reprint requests to: Shiao Woo, M.D., Division of Radiation Oncology, Box 97, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030. Tel: (713) 563-2324; Fax: (713) 563-1521; E-mail: [email protected]
Presented in part at the 88th Annual Meeting of the American Radium Society, May 6–10, 2006, Maui, HI. Conflict of interest: none. Received March 3, 2007, Accepted for publication April 16, 2007. 1193
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Volume 69, Number 4, 2007
Table 1. Dose to thecal sac predicted with and without FIF and modulated junctions Volume of thecal sac at $100%, $110% or $120% of prescribed dose (%) Without FIF With FIF With FIF and modulated junctions Prescribed dose No. of and fractions reduction fields $100% $110% $120% $100% $110% $120% $100% $110% $120% 180 cGy 17 (3060 cGy) Adult 180 cGy 20 (3600 cGy) Adult 167 cGy 18 (3006 cGy) Adolescent 180 cGy 11 (1980 cGy) Adult 180 cGy 17 (3060 cGy) Mean 2941.2 Adult
10
99
71
31
97
24
0
98
29
0
9
99
67
22
97
1
0
99
3
0
10
99
75
36
96
30
0
98
25
0
7
98
39
6
98
12
0
99
9
0
10
96
46
8
98
8
0
99
4
0
98.2
59.6
15
0
98.6
14
0
9.2
20.8
97.2
Abbreviation: FIF = field-in-field.
3 anticipated weeks of treatment, three approximately equally weighted control points were used, with two successive 1-cm shifts. Additional control points were used as necessary to homogenize the dose distribution across the junction. Collimation was set in the axial plane, and leaf-pair junctions were set behind the jaw to avoid interleaf transmission. Thecal sac volumes were contoured with 1-cm margins around the superior and inferior borders of the modulated segments; these were used in dose–volume histogram analyses to assess predicted coverage. Phantom-based film dosimetry was used to assess the actual dose delivered at the modulated junctions in the coronal and axial planes.
RESULTS Field-in-field technique improved dose conformality and reduced inhomogeneity For the FIF analysis, we studied 5 patients. Between 7 and 10 reduction fields were used (Table 1). Field-in-field was primarily used to improve conformality of dose to the thecal sac, but plans were also evaluated on a single-fraction basis to judge the variation in dose delivered to the junctions each day. Without FIF or modulated junctions, the thecal sac volume receiving $110% of the prescribed dose ranged from 39% to 75% (mean, 59.6%), and the volume receiving $120% ranged from 6% to 36% (mean, 20.6%). Field-infield planning techniques reduced these volumes to a range of 1% to 30% (mean, 15%) and 0 (Table 1). Practical implementation of intrafractionally modulated junction shifts Treatment was shortened and simplified because only one consistent cranial setup point was used throughout the entire radiation course, making the delivery process less prone to manual errors in setup of the junctions. Phantom-based film dosimetry confirmed the safety of modulated treatment delivery, with no point in the junction region in the lower spine reaching >80% of the prescription dose measured in the coronal plane or >99% measured in the axial plane. Actual dose delivery correlated well to predicted values (Fig. 1).
Dosimetric effects of modulated junctions on daily homogeneity and setup error In comparing a setup with weekly manual junction shifts with a modulated junction-shift plan, the modulated treatments provided improved dose homogeneity across the junctions on a daily basis because of the constant feathering of the junctions during each fraction and the ability to provide customized modulation using additional control points. With the addition of modulated junctions to the FIF technique, the percentage volume of thecal sac at $110% or $120% of prescribed dose was comparable or slightly better (Table 1). In the modulated technique, setup variation at the junctions was minimized because each junction was self-feathering within each fraction. A 5-mm setup error in the gap on skin was modeled as it might occur at the junction of two fields in the lower spine. This model was based on a single fraction reproduced as a systemic error that was repeated through the entire radiation therapy course. The modulated plan reduced the effect of the error (Fig. 2), and in the upper spine a similar finding was observed (Fig. 3). DISCUSSION Craniospinal irradiation is important in the treatment of central nervous system malignancies, and inadequate coverage of the target volume can compromise ultimate outcomes (3–5). In this type of treatment, the cranial fields typically consist of lateral photon beams, and the spine is treated with posterior photon fields. The depth of the spine is age dependent (7) and determines the length of the gap on the skin that is necessary to avoid overlap of the fields at the depth of the spinal cord. Accuracy of the skin gap is critical: a 5-mm error can result in 10% underdosage of the junction (8). Nonetheless, even with the capability to plan an exact three-dimensional match of abutting beams using CT-based simulation, the junction is usually deliberately underdosed to avoid potential overdosage of the cord, the most serious potential risk of this treatment. In addition, if the curve of
Modulated craniospinal irradiation d S. S. YOM et al.
Fig. 1. Film dosimetry (a) and comparison of predicted and actual dose delivery (b) on coronal film dosimetry; film dosimetry (c) and comparison of predicted and actual dose delivery (d) on axial film dosimetry.
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Volume 69, Number 4, 2007
Fig. 2. A systematic 5-mm setup error in the gap on skin was modeled at the junction of two fields in the lower spine. (a) A greater overdose to the spinal cord results with the standard plan as opposed to the modulated plan; isodose distribution is worse in a (b) traditional (solid) compared with a (c) modulated plan (dashed).
the spinal column is pronounced, the thecal sac lies at different depths along its length, resulting in large inhomogeneities through the target volume. Therefore, to ensure that the field junctions do not result in overdosage but to ensure adequate dose delivery, a commonly used technique is to shift the field junctions by 1-cm or more every 3 to 5 fractions (9). This technique is manually implemented at the machine and introduces the additional possibility of a systematic error (10). For centers with multileaf collimation capability, the FIF technique improves dose conformity and reduces hot spots,
particularly in the spinal axis. Pediatric patients do not usually require the addition of many reduction fields because of the relatively uniform depth of the spinal column, but in adults several fields may be required; these may be weighted as much as 10–12% per field in the lower spine. As a forwardplanned, step-and-shoot process, the use of FIF does not add substantially to the time and effort required for planning and treatment delivery. We have also implemented daily intrafractional modulation of the field junctions, eliminating the need for weekly
Modulated craniospinal irradiation d S. S. YOM et al.
1197
Fig. 3. A systematic 5-mm setup error in the gap on skin was modeled at the junction of two fields at the cranium–cervical spine. (a) A greater overdose to the spinal cord results with the standard plan as opposed to the modulated plan; isodose distribution is worse in a (b) traditional (solid) compared with a (c) modulated plan (dashed).
manual junction shifts and relying instead on a single setup point within the cranial field. The predicted composite dose across the modulated junctions for the entire treatment course is similar compared with a standard FIF plan using traditionally shifted junctions. However, when considered
on the basis of what is delivered each day, daily modulation of the junctions reduces inhomogeneity as considered from one fraction to the next. Film dosimetry confirmed that the actual dose delivery compares favorably to that predicted.
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I. J. Radiation Oncology d Biology d Physics
The most likely source of error in the delivery of craniospinal irradiation results not from a failure in planning but from inaccuracies in patient positioning. The modulated technique shortens and simplifies treatment because one consistent, cranially located setup point is used. All fields are delivered according to their relationship to the initial setup point and cranial field. Modeling of a deliberately introduced error showed that the modulated plan could minimize the effect of a 5-mm setup error due to
Volume 69, Number 4, 2007
field overlap at either the craniospinal or spinal–spinal junction because of the self-feathering of the junctions during each fraction. Field-in-field and modulated junction techniques can be adapted to a variety of clinical situations for irregularly shaped regions prone to inhomogeneity or treatment volumes spanning a range of depths in tissue. They particularly offer a means of addressing the technical and practical challenges of craniospinal irradiation.
REFERENCES 1. de la Torre N, Figueroa CT, Martinez K, et al. A comparative study of surface dose and dose distribution for intact breast following irradiation with field-in-field technique vs. the use of conventional wedges. Med Dosim 2004;29: 109–114. 2. Scharf CB, Paulino AC, Goldberg KN. Determination of the inferior border of the thecal sac using magnetic resonance imaging: Implications on radiation therapy treatment planning. Int J Radiat Oncol Biol Phys 1998;41:621– 624. 3. Carrie C, Hoffstetter S, Gomez F, et al. Impact of targeting deviations on outcome in medulloblastoma: Study of the French Society of Pediatric Oncology (SFOP). Int J Radiat Oncol Biol Phys 1999;45:435–439. 4. Grabenbauer GG, Beck JD, Erhardt J, et al. Postoperative radiotherapy of medulloblastoma. Impact of radiation quality on treatment outcome. Am J Clin Oncol 1996;19: 73–77.
5. Halperin EC. Impact of radiation technique upon the outcome of treatment for medulloblastoma. Int J Radiat Oncol Biol Phys 1996;36:233–239. 6. Bernier V. Technical aspects in cerebrospinal irradiation. Pediatr Blood Cancer 2004;42:447–451. 7. Van Dyk J, Jenkin RD, Leung PM, Cunningham JR. Medulloblastoma: Treatment technique and radiation dosimetry. Int J Radiat Oncol Biol Phys 1977;2:993–1005. 8. Tatcher M, Glicksman AS. Field matching considerations in craniospinal irradiation. Int J Radiat Oncol Biol Phys 1989;17:865–869. 9. Urie M, FitzGerald TJ, Followill D, et al. Current calibration, treatment, and treatment planning techniques among institutions participating in the Children’s Oncology Group. Int J Radiat Oncol Biol Phys 2003;55:245–260. 10. Holupka EJ, Humm JL, Tarbell NJ, et al. Effect of set-up error on the dose across the junction of matching cranial-spinal fields in the treatment of medulloblastoma. Int J Radiat Oncol Biol Phys 1993;27:345–352.
doi:10.1016/j.ijrobp.2007.04.062
CLINICAL INVESTIGATION
Central Nervous System
FIELD-IN-FIELD TECHNIQUE WITH INTRAFRACTIONALLY MODULATED JUNCTION SHIFTS FOR CRANIOSPINAL IRRADIATION SUE S. YOM, M.D., PH.D.,* ERIK K. FRIJA, C.M.D.,* ANITA MAHAJAN, M.D.,* ERIC CHANG, M.D.,* KELLI KLEIN, C.M.D.,* ALMON SHIU, PH.D.,y JARED OHRT, M.S.,y AND SHIAO WOO, M.D.* * Division of Radiation Oncology and y Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX Purpose: To plan craniospinal irradiation with ‘‘field-in-field’’ (FIF) homogenization in combination with daily, intrafractional modulation of the field junctions, to minimize the possibility of spinal cord overdose. Methods and Materials: Lateral cranial fields and posterior spinal fields were planned using a forward-planned, step-and-shoot FIF technique. Field junctions were automatically modulated and custom-weighted for maximal homogeneity within each treatment fraction. Dose–volume histogram analyses and film dosimetry were used to assess results. Results: Plan inhomogeneity improved with FIF. Planning with daily modulated junction shifts provided consistent dose delivery during each fraction of treatment across the junctions. Modulation minimized the impact of a 5-mm setup error at the junction. Film dosimetry confirmed that no point in the junction exceeded the anticipated dose. Conclusions: Field-in-field planning and modulated junction shifts improve the homogeneity and consistency of daily dose delivery, simplify treatment, and reduce the impact of setup errors. Ó 2007 Elsevier Inc. Craniospinal irradiation planning, Junction shift, Field-in-field technique.
INTRODUCTION
METHODS AND MATERIALS
Photon-based techniques for craniospinal irradiation (CSI) may result in dose inhomogeneity within the treatment volume and usually require a weekly manual shift of the field junctions to minimize the possibility of spinal cord overdose. We have begun planning CSI using a multisegmented, intensity-modulated ‘‘field-in-field’’ (FIF) and automated ‘‘junction-shift’’ techniques. To deploy FIF, multiple lower-weighted reduction fields are created on the basis of the primary field. The reduction fields contain blocked segments strategically placed to reduce the highest isodose areas and to force greater homogeneity and conformity to the target volume (1). We combine FIF with a practice of automatically modulated junctions that eliminates the need for weekly junction shifts. During each fraction of treatment, the field edges are shifted in successive 1-cm increments, using customized weighting at each modulated step to obtain greater homogeneity within the volume. Although this planning process is initially more intensive, daily patient setup is simplified and more consistent, using only a single setup point in the cranium.
A waiver of informed consent was obtained from our institutional review board for this planning study. Computed tomography scans were obtained for 4 adults and 1 adolescent patient. All patients were prone and immobilized in a head holder and customized thermoplastic mask; the spine was immobilized with a radiotranslucent urethane cushion filled with polystyrene beads and molded to the individual anatomy by vacuum suction. Positioning marks were placed for straightening, but one setup point was designated in the cranium. A source-surface distance setup of 110 cm was used. The Pinnacle3D Radiation Therapy Planning System v7.6c (ADAC Laboratories, Milpitas, CA) was used for planning. Two lateral cranial fields and multiple abutting posterior spinal fields were designed using 6-MV photons. Brain, brainstem, and optic structures were contoured. The thecal sac was contoured from the foramen magnum to the inferior termination, visualized on a magnetic resonance imaging study (2). Adding and removing reduction fields enabled dosimetric comparison with or without FIF implementation. In addition, custom-weighted segmental modulation was created to feather the field edges at each junction during each fraction. The craniospinal match was placed in the low neck, and using multileaf collimator leaf adjustments the junctioned field edges were shifted by successive 1-cm increments during each treatment session. For
Reprint requests to: Shiao Woo, M.D., Division of Radiation Oncology, Box 97, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030. Tel: (713) 563-2324; Fax: (713) 563-1521; E-mail: [email protected]
Presented in part at the 88th Annual Meeting of the American Radium Society, May 6–10, 2006, Maui, HI. Conflict of interest: none. Received March 3, 2007, Accepted for publication April 16, 2007. 1193
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I. J. Radiation Oncology d Biology d Physics
Volume 69, Number 4, 2007
Table 1. Dose to thecal sac predicted with and without FIF and modulated junctions Volume of thecal sac at $100%, $110% or $120% of prescribed dose (%) Without FIF With FIF With FIF and modulated junctions Prescribed dose No. of and fractions reduction fields $100% $110% $120% $100% $110% $120% $100% $110% $120% 180 cGy 17 (3060 cGy) Adult 180 cGy 20 (3600 cGy) Adult 167 cGy 18 (3006 cGy) Adolescent 180 cGy 11 (1980 cGy) Adult 180 cGy 17 (3060 cGy) Mean 2941.2 Adult
10
99
71
31
97
24
0
98
29
0
9
99
67
22
97
1
0
99
3
0
10
99
75
36
96
30
0
98
25
0
7
98
39
6
98
12
0
99
9
0
10
96
46
8
98
8
0
99
4
0
98.2
59.6
15
0
98.6
14
0
9.2
20.8
97.2
Abbreviation: FIF = field-in-field.
3 anticipated weeks of treatment, three approximately equally weighted control points were used, with two successive 1-cm shifts. Additional control points were used as necessary to homogenize the dose distribution across the junction. Collimation was set in the axial plane, and leaf-pair junctions were set behind the jaw to avoid interleaf transmission. Thecal sac volumes were contoured with 1-cm margins around the superior and inferior borders of the modulated segments; these were used in dose–volume histogram analyses to assess predicted coverage. Phantom-based film dosimetry was used to assess the actual dose delivered at the modulated junctions in the coronal and axial planes.
RESULTS Field-in-field technique improved dose conformality and reduced inhomogeneity For the FIF analysis, we studied 5 patients. Between 7 and 10 reduction fields were used (Table 1). Field-in-field was primarily used to improve conformality of dose to the thecal sac, but plans were also evaluated on a single-fraction basis to judge the variation in dose delivered to the junctions each day. Without FIF or modulated junctions, the thecal sac volume receiving $110% of the prescribed dose ranged from 39% to 75% (mean, 59.6%), and the volume receiving $120% ranged from 6% to 36% (mean, 20.6%). Field-infield planning techniques reduced these volumes to a range of 1% to 30% (mean, 15%) and 0 (Table 1). Practical implementation of intrafractionally modulated junction shifts Treatment was shortened and simplified because only one consistent cranial setup point was used throughout the entire radiation course, making the delivery process less prone to manual errors in setup of the junctions. Phantom-based film dosimetry confirmed the safety of modulated treatment delivery, with no point in the junction region in the lower spine reaching >80% of the prescription dose measured in the coronal plane or >99% measured in the axial plane. Actual dose delivery correlated well to predicted values (Fig. 1).
Dosimetric effects of modulated junctions on daily homogeneity and setup error In comparing a setup with weekly manual junction shifts with a modulated junction-shift plan, the modulated treatments provided improved dose homogeneity across the junctions on a daily basis because of the constant feathering of the junctions during each fraction and the ability to provide customized modulation using additional control points. With the addition of modulated junctions to the FIF technique, the percentage volume of thecal sac at $110% or $120% of prescribed dose was comparable or slightly better (Table 1). In the modulated technique, setup variation at the junctions was minimized because each junction was self-feathering within each fraction. A 5-mm setup error in the gap on skin was modeled as it might occur at the junction of two fields in the lower spine. This model was based on a single fraction reproduced as a systemic error that was repeated through the entire radiation therapy course. The modulated plan reduced the effect of the error (Fig. 2), and in the upper spine a similar finding was observed (Fig. 3). DISCUSSION Craniospinal irradiation is important in the treatment of central nervous system malignancies, and inadequate coverage of the target volume can compromise ultimate outcomes (3–5). In this type of treatment, the cranial fields typically consist of lateral photon beams, and the spine is treated with posterior photon fields. The depth of the spine is age dependent (7) and determines the length of the gap on the skin that is necessary to avoid overlap of the fields at the depth of the spinal cord. Accuracy of the skin gap is critical: a 5-mm error can result in 10% underdosage of the junction (8). Nonetheless, even with the capability to plan an exact three-dimensional match of abutting beams using CT-based simulation, the junction is usually deliberately underdosed to avoid potential overdosage of the cord, the most serious potential risk of this treatment. In addition, if the curve of
Modulated craniospinal irradiation d S. S. YOM et al.
Fig. 1. Film dosimetry (a) and comparison of predicted and actual dose delivery (b) on coronal film dosimetry; film dosimetry (c) and comparison of predicted and actual dose delivery (d) on axial film dosimetry.
1195
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I. J. Radiation Oncology d Biology d Physics
Volume 69, Number 4, 2007
Fig. 2. A systematic 5-mm setup error in the gap on skin was modeled at the junction of two fields in the lower spine. (a) A greater overdose to the spinal cord results with the standard plan as opposed to the modulated plan; isodose distribution is worse in a (b) traditional (solid) compared with a (c) modulated plan (dashed).
the spinal column is pronounced, the thecal sac lies at different depths along its length, resulting in large inhomogeneities through the target volume. Therefore, to ensure that the field junctions do not result in overdosage but to ensure adequate dose delivery, a commonly used technique is to shift the field junctions by 1-cm or more every 3 to 5 fractions (9). This technique is manually implemented at the machine and introduces the additional possibility of a systematic error (10). For centers with multileaf collimation capability, the FIF technique improves dose conformity and reduces hot spots,
particularly in the spinal axis. Pediatric patients do not usually require the addition of many reduction fields because of the relatively uniform depth of the spinal column, but in adults several fields may be required; these may be weighted as much as 10–12% per field in the lower spine. As a forwardplanned, step-and-shoot process, the use of FIF does not add substantially to the time and effort required for planning and treatment delivery. We have also implemented daily intrafractional modulation of the field junctions, eliminating the need for weekly
Modulated craniospinal irradiation d S. S. YOM et al.
1197
Fig. 3. A systematic 5-mm setup error in the gap on skin was modeled at the junction of two fields at the cranium–cervical spine. (a) A greater overdose to the spinal cord results with the standard plan as opposed to the modulated plan; isodose distribution is worse in a (b) traditional (solid) compared with a (c) modulated plan (dashed).
manual junction shifts and relying instead on a single setup point within the cranial field. The predicted composite dose across the modulated junctions for the entire treatment course is similar compared with a standard FIF plan using traditionally shifted junctions. However, when considered
on the basis of what is delivered each day, daily modulation of the junctions reduces inhomogeneity as considered from one fraction to the next. Film dosimetry confirmed that the actual dose delivery compares favorably to that predicted.
1198
I. J. Radiation Oncology d Biology d Physics
The most likely source of error in the delivery of craniospinal irradiation results not from a failure in planning but from inaccuracies in patient positioning. The modulated technique shortens and simplifies treatment because one consistent, cranially located setup point is used. All fields are delivered according to their relationship to the initial setup point and cranial field. Modeling of a deliberately introduced error showed that the modulated plan could minimize the effect of a 5-mm setup error due to
Volume 69, Number 4, 2007
field overlap at either the craniospinal or spinal–spinal junction because of the self-feathering of the junctions during each fraction. Field-in-field and modulated junction techniques can be adapted to a variety of clinical situations for irregularly shaped regions prone to inhomogeneity or treatment volumes spanning a range of depths in tissue. They particularly offer a means of addressing the technical and practical challenges of craniospinal irradiation.
REFERENCES 1. de la Torre N, Figueroa CT, Martinez K, et al. A comparative study of surface dose and dose distribution for intact breast following irradiation with field-in-field technique vs. the use of conventional wedges. Med Dosim 2004;29: 109–114. 2. Scharf CB, Paulino AC, Goldberg KN. Determination of the inferior border of the thecal sac using magnetic resonance imaging: Implications on radiation therapy treatment planning. Int J Radiat Oncol Biol Phys 1998;41:621– 624. 3. Carrie C, Hoffstetter S, Gomez F, et al. Impact of targeting deviations on outcome in medulloblastoma: Study of the French Society of Pediatric Oncology (SFOP). Int J Radiat Oncol Biol Phys 1999;45:435–439. 4. Grabenbauer GG, Beck JD, Erhardt J, et al. Postoperative radiotherapy of medulloblastoma. Impact of radiation quality on treatment outcome. Am J Clin Oncol 1996;19: 73–77.
5. Halperin EC. Impact of radiation technique upon the outcome of treatment for medulloblastoma. Int J Radiat Oncol Biol Phys 1996;36:233–239. 6. Bernier V. Technical aspects in cerebrospinal irradiation. Pediatr Blood Cancer 2004;42:447–451. 7. Van Dyk J, Jenkin RD, Leung PM, Cunningham JR. Medulloblastoma: Treatment technique and radiation dosimetry. Int J Radiat Oncol Biol Phys 1977;2:993–1005. 8. Tatcher M, Glicksman AS. Field matching considerations in craniospinal irradiation. Int J Radiat Oncol Biol Phys 1989;17:865–869. 9. Urie M, FitzGerald TJ, Followill D, et al. Current calibration, treatment, and treatment planning techniques among institutions participating in the Children’s Oncology Group. Int J Radiat Oncol Biol Phys 2003;55:245–260. 10. Holupka EJ, Humm JL, Tarbell NJ, et al. Effect of set-up error on the dose across the junction of matching cranial-spinal fields in the treatment of medulloblastoma. Int J Radiat Oncol Biol Phys 1993;27:345–352.