dosimetric comparison of skin surface dose in patients undergoing proton and photon radiation...

1
Conclusions: The preliminary results confirm that the RT algorithm significantly overestimates the dosages delivered confirming previous an- alyses. Finally, subdividing the data into different size regimes increased the correlation for the smaller size PTVs indicating the MC algorithm improvement verses the RT algorithm is dependent upon the size of the PTV. Author Disclosure: A. Pennington: None. R. Selvaraj: None. T. Lev- entouri: None. 3786 Coverage of Posterior Supraclavicular Fossa With Postmastectomy Proton Therapy for Breast Cancer: A Dosimetric Comparison Study and Implications for Target Definition J.J. Cuaron, 1 E. Hug, 2 B.H. Chon, 2 H.K. Tsai, 2 M. Pankuch, 3 S.N. Powell, 1 and O. Cahlon 2 ; 1 Memorial Sloan-Kettering Cancer Center, New York, NY, 2 Procure Proton Therapy Center, Somerset, NJ, 3 ProCure Chicago, Chicago, IL Purpose/Objective(s): The posterior aspect of the supraclavicular fossa (SCF) is a known site of nodal metastases and failure in patients with locally advanced breast cancer, yet it is not included in the RTOG breast nodal atlas. With conventional techniques, this area often receives a large incidental dose even if not purposefully included in the target volume. However, the dose delivered to this area when treating with RTOG con- touring atlas-specified proton therapy and other highly conformal external beam radiation modalities is not well described. The purpose of this study is to dosimetrically compare coverage of the posterior supraclavicular fossa between three-dimensional conformal radiation therapy (3DCRT), helical TomoTherapy (HT), volumetric modulated arc therapy (VMAT), and proton therapy (PT). Materials/Methods: 10 left sided stage III breast cancer patients status post mastectomy were selected for the study. Target volumes were defined as the chest wall, axillary levels I-III, supraclavicular lymph nodes, and internal mammary lymph nodes according to the RTOG atlas. Volumes excluded the posterior aspect of the SCF (defined as posterior to the posterolateral aspect of the sternocleidomastoid muscle, analogous to Level V as defined in the RTOG head and neck contouring atlas), which was contoured as a separate structure. Each patient was planned for 3DCRT, HT, VMAT, and PT to a prescribed dose of 50.4 Gy or 50.4 Gy(RBE) with a goal D95 of 90-95%. Mean dosimetric parameters of posterior SCF coverage were calculated through DVH analysis, and modalities were compared using ANOVA and paired t-tests. Results: The mean dose to the posterior aspect of the SCF was 26.7 Gy(RBE) with PT and 49 Gy, 40.2 Gy and 41.7 Gy with 3DCRT, HT and VMAT, respectively (p <0.01). The minimum point dose was 0.1 Gy(RBE) for PT, 40.6 Gy for 3DCRT, 16.1 Gy for HT, and 19.4 Gy for VMAT (p <0.001). Max dose for PT (52.5 Gy(RBE))was not significantly different than 3DCRT (54.1 Gy, p Z 0.061), but was lower compared to HT (54.6 Gy, p Z 0.001) and VMAT (55.3 Gy, P<0.001). The D95 was 1.0 Gy(RBE) for PT vs. 43.9 Gy for 3DCRT, 22.2 Gy for HT, and 24.5 Gy for VMAT (P<0.001). The V40 with PT was significantly lower compared to 3DCRT (44.4% vs. 99.8%, P <0.001) but did not vary significantly compared to HT (55.8%, P Z 0.335) or VMAT (60.7%, p Z 0.11). Conclusions: By most dosimetric parameters, proton therapy plans delivered significantly lower incidental doses to the posterior SCF compared to 3DCRT, HTor VMAT. The findings of this study point to a potential deficit in the RTOG breast nodal atlas that in its current version of target definition will result in under dosage of the posterior aspect of the SCF by modern conformal techniques, including proton therapy. Given the risk of nodal metastases and failure in this area, our study points towards to paramount importance of oncologically correct target definition to avoid marginal treatment failures. Author Disclosure: J.J. Cuaron: None. E. Hug: None. B.H. Chon: None. H.K. Tsai: None. M. Pankuch: None. S.N. Powell: None. O. Cahlon: None. 3787 Dosimetric Comparison of Skin Surface Dose in Patients Undergoing Proton and Photon Radiation Therapy for Breast Cancer J.J. Cuaron, 1 C. Cheng, 2 H. Joseph, 3 S. McNeeley, 3 E.B. Hug, 4 B.H. Chon, 5 H.K. Tsai, 2 S.N. Powell, 1 and O. Cahlon 2 ; 1 Memorial Sloan- Kettering Cancer Center, New York, NY, 2 Procure Proton Therapy Center, Somerset, NJ, 3 Princeton Radiation Oncology, Princeton, NJ, 4 Procure Proton Therapy Center, Somerset, NJ, 5 Procure Proton Therapy Center, Somerset, NJ Purpose/Objective(s): We compared the doses to the surface of the skin between proton therapy, photon therapy and photon therapy with bolus for patients undergoing treatment for breast cancer. Materials/Methods: There were 14 patients undergoing post-operative external beam radiation therapy for breast cancer selected for this study, including 4 post-mastectomy patients that were treated with photons with bolus over the chest wall, 4 post-lumpectomy patients treated with photons without bolus (2 in the prone position and 2 in the supine position), and 6 patients treated with protons (4 in the post mastectomy setting and 2 to the intact breast after lumpectomy). Prior to delivery of one fraction, 3 - 5 thermoluminescent dosimeters (TLDs) or optically stimulated lumines- cence (OSLs) were placed at various locations over the chest wall or intact breast (including superior, inferior, medial, lateral and apical aspects and within the supraclavicular nodal field for post mastectomy patients treated with photons). Photon therapy was typically delivered with 6 MV opposed tangents with daily 0.5 cm bolus. Two patients also received part of the dose with 23MV photons and 1.0 cm bolus every other day. Proton therapy fractions were generally delivered with uniform scanning beams using 4 anterior directed fields per day with a feathered match line. After treatment delivery, TLDs and OSLs were processed and absolute doses were collected. Percent doses were calculated as the percentage of the pre- scription dose. The mean dose percentages for each treatment approach were compared using ANOVA and paired t-tests. Results: The mean surface dose to the skin with prone non bolus photons, supine non bolus photons, protons and photons with bolus was 72.2%, 70.9%, 98.1% and 108.4% respectively (p<0.001). For post-mastectomy patients treated to the chest wall, both protons and photons with bolus showed no significant skin sparing (98.1% and 108.4%, respectively). Within the supraclavicular field outside of the bolus, however, there was significant sparing with photons (35%) but not with protons. For patients with an intact breast, protons delivered significantly higher surfaces doses (98.1%) than both supine (70.9%, p <0.001) and prone (72.2%, p<0.001) non-bolus photons. Conclusions: For patients with an intact breast, there was significant skin sparing observed with photons compared to protons. No significant dif- ferences were seen in the post mastectomy setting, except in the photon non-bolus photon supraclavicular field, where significant skin sparing was observed compared to proton therapy. Long-term clinical follow up will be needed to determine if the differences in skin doses have a significant impact on cosmetic outcomes. In the meantime, patients receiving proton therapy should be counseled regarding the higher skin dose to the intact breast and supraclavicular region. Author Disclosure: J.J. Cuaron: None. C. Cheng: None. H. Joseph: None. S. McNeeley: None. E.B. Hug: None. B.H. Chon: None. H.K. Tsai: None. S.N. Powell: None. O. Cahlon: None. 3788 Development of a Novel Compact Particle Therapy Facility With Laser Driven Ion Beams via Gantry Systems Based on Pulsed Magnets U. Masood, 1 M. Baumann, 1 M. Bussmann, 2 T. Cowan, 2 W. Enghardt, 1 T. Herrmannsdoerfer, 2 K. Hofmann, 3 M. Kaluza, 4 L. Karsch, 1 F. Kroll, 2 U. Schramm, 2 M. Schuerer, 1 J. Wilkens, 3 and J. Pawelke 1 ; 1 OncoRay- National Centre for Radiation Research in Oncology, Technical University Dresden, Medical Faculty, Dresden, Germany, 2 Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany, 3 TechnischeUniversita¨t Mu¨nchen Klinikum Rechts der IsarKlinik und Poliklinik fu¨r International Journal of Radiation Oncology Biology Physics S914

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Page 1: Dosimetric Comparison of Skin Surface Dose in Patients Undergoing Proton and Photon Radiation Therapy for Breast Cancer

International Journal of Radiation Oncology � Biology � PhysicsS914

Conclusions: The preliminary results confirm that the RT algorithm

significantly overestimates the dosages delivered confirming previous an-

alyses. Finally, subdividing the data into different size regimes increased

the correlation for the smaller size PTVs indicating the MC algorithm

improvement verses the RT algorithm is dependent upon the size of the

PTV.

Author Disclosure: A. Pennington: None. R. Selvaraj: None. T. Lev-

entouri: None.

3786Coverage of Posterior Supraclavicular Fossa With PostmastectomyProton Therapy for Breast Cancer: A Dosimetric Comparison Studyand Implications for Target DefinitionJ.J. Cuaron,1 E. Hug,2 B.H. Chon,2 H.K. Tsai,2 M. Pankuch,3 S.N. Powell,1

and O. Cahlon2; 1Memorial Sloan-Kettering Cancer Center, New York, NY,2Procure Proton Therapy Center, Somerset, NJ, 3ProCure Chicago,

Chicago, IL

Purpose/Objective(s): The posterior aspect of the supraclavicular fossa

(SCF) is a known site of nodal metastases and failure in patients with

locally advanced breast cancer, yet it is not included in the RTOG breast

nodal atlas. With conventional techniques, this area often receives a large

incidental dose even if not purposefully included in the target volume.

However, the dose delivered to this area when treating with RTOG con-

touring atlas-specified proton therapy and other highly conformal external

beam radiation modalities is not well described. The purpose of this study

is to dosimetrically compare coverage of the posterior supraclavicular

fossa between three-dimensional conformal radiation therapy (3DCRT),

helical TomoTherapy (HT), volumetric modulated arc therapy (VMAT),

and proton therapy (PT).

Materials/Methods: 10 left sided stage III breast cancer patients status

post mastectomy were selected for the study. Target volumes were

defined as the chest wall, axillary levels I-III, supraclavicular lymph

nodes, and internal mammary lymph nodes according to the RTOG

atlas. Volumes excluded the posterior aspect of the SCF (defined as

posterior to the posterolateral aspect of the sternocleidomastoid

muscle, analogous to Level V as defined in the RTOG head and neck

contouring atlas), which was contoured as a separate structure. Each

patient was planned for 3DCRT, HT, VMAT, and PT to a prescribed

dose of 50.4 Gy or 50.4 Gy(RBE) with a goal D95 of 90-95%. Mean

dosimetric parameters of posterior SCF coverage were calculated

through DVH analysis, and modalities were compared using ANOVA

and paired t-tests.

Results: The mean dose to the posterior aspect of the SCF was 26.7

Gy(RBE) with PT and 49 Gy, 40.2 Gy and 41.7 Gy with 3DCRT, HT

and VMAT, respectively (p <0.01). The minimum point dose was 0.1

Gy(RBE) for PT, 40.6 Gy for 3DCRT, 16.1 Gy for HT, and 19.4 Gy

for VMAT (p <0.001). Max dose for PT (52.5 Gy(RBE))was not

significantly different than 3DCRT (54.1 Gy, p Z 0.061), but was

lower compared to HT (54.6 Gy, p Z 0.001) and VMAT (55.3 Gy,

P<0.001). The D95 was 1.0 Gy(RBE) for PT vs. 43.9 Gy for 3DCRT,

22.2 Gy for HT, and 24.5 Gy for VMAT (P<0.001). The V40 with PT

was significantly lower compared to 3DCRT (44.4% vs. 99.8%, P

<0.001) but did not vary significantly compared to HT (55.8%, P Z0.335) or VMAT (60.7%, p Z 0.11).

Conclusions: By most dosimetric parameters, proton therapy plans

delivered significantly lower incidental doses to the posterior SCF

compared to 3DCRT, HT or VMAT. The findings of this study point to a

potential deficit in the RTOG breast nodal atlas that in its current version of

target definition will result in under dosage of the posterior aspect of the

SCF by modern conformal techniques, including proton therapy. Given the

risk of nodal metastases and failure in this area, our study points towards to

paramount importance of oncologically correct target definition to avoid

marginal treatment failures.

Author Disclosure: J.J. Cuaron: None. E. Hug: None. B.H. Chon: None.

H.K. Tsai: None. M. Pankuch: None. S.N. Powell: None. O. Cahlon:

None.

3787Dosimetric Comparison of Skin Surface Dose in PatientsUndergoing Proton and Photon Radiation Therapy for Breast CancerJ.J. Cuaron,1 C. Cheng,2 H. Joseph,3 S. McNeeley,3 E.B. Hug,4

B.H. Chon,5 H.K. Tsai,2 S.N. Powell,1 and O. Cahlon2; 1Memorial Sloan-

Kettering Cancer Center, New York, NY, 2Procure Proton Therapy Center,

Somerset, NJ, 3Princeton Radiation Oncology, Princeton, NJ, 4Procure

Proton Therapy Center, Somerset, NJ, 5Procure Proton Therapy Center,

Somerset, NJ

Purpose/Objective(s): We compared the doses to the surface of the skin

between proton therapy, photon therapy and photon therapy with bolus for

patients undergoing treatment for breast cancer.

Materials/Methods: There were 14 patients undergoing post-operative

external beam radiation therapy for breast cancer selected for this study,

including 4 post-mastectomy patients that were treated with photons with

bolus over the chest wall, 4 post-lumpectomy patients treated with photons

without bolus (2 in the prone position and 2 in the supine position), and 6

patients treated with protons (4 in the post mastectomy setting and 2 to the

intact breast after lumpectomy). Prior to delivery of one fraction, 3 - 5

thermoluminescent dosimeters (TLDs) or optically stimulated lumines-

cence (OSLs) were placed at various locations over the chest wall or intact

breast (including superior, inferior, medial, lateral and apical aspects and

within the supraclavicular nodal field for post mastectomy patients treated

with photons). Photon therapy was typically delivered with 6 MVopposed

tangents with daily 0.5 cm bolus. Two patients also received part of the

dose with 23MV photons and 1.0 cm bolus every other day. Proton therapy

fractions were generally delivered with uniform scanning beams using 4

anterior directed fields per day with a feathered match line. After treatment

delivery, TLDs and OSLs were processed and absolute doses were

collected. Percent doses were calculated as the percentage of the pre-

scription dose. The mean dose percentages for each treatment approach

were compared using ANOVA and paired t-tests.

Results: The mean surface dose to the skin with prone non bolus photons,

supine non bolus photons, protons and photons with bolus was 72.2%,

70.9%, 98.1% and 108.4% respectively (p<0.001). For post-mastectomy

patients treated to the chest wall, both protons and photons with bolus

showed no significant skin sparing (98.1% and 108.4%, respectively).

Within the supraclavicular field outside of the bolus, however, there was

significant sparing with photons (35%) but not with protons. For patients

with an intact breast, protons delivered significantly higher surfaces doses

(98.1%) than both supine (70.9%, p <0.001) and prone (72.2%, p<0.001)

non-bolus photons.

Conclusions: For patients with an intact breast, there was significant skin

sparing observed with photons compared to protons. No significant dif-

ferences were seen in the post mastectomy setting, except in the photon

non-bolus photon supraclavicular field, where significant skin sparing was

observed compared to proton therapy. Long-term clinical follow up will be

needed to determine if the differences in skin doses have a significant

impact on cosmetic outcomes. In the meantime, patients receiving proton

therapy should be counseled regarding the higher skin dose to the intact

breast and supraclavicular region.

Author Disclosure: J.J. Cuaron: None. C. Cheng: None. H. Joseph:

None. S. McNeeley: None. E.B. Hug: None. B.H. Chon: None. H.K.

Tsai: None. S.N. Powell: None. O. Cahlon: None.

3788Development of a Novel Compact Particle Therapy Facility WithLaser Driven Ion Beams via Gantry Systems Based on PulsedMagnetsU. Masood,1 M. Baumann,1 M. Bussmann,2 T. Cowan,2 W. Enghardt,1

T. Herrmannsdoerfer,2 K. Hofmann,3 M. Kaluza,4 L. Karsch,1 F. Kroll,2

U. Schramm,2 M. Schuerer,1 J. Wilkens,3 and J. Pawelke1; 1OncoRay-

National Centre for Radiation Research in Oncology, Technical University

Dresden, Medical Faculty, Dresden, Germany, 2Helmholtz-Zentrum

Dresden-Rossendorf, Dresden, Germany, 3Technische Universitat

Munchen Klinikum Rechts der IsarKlinik und Poliklinik fur