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