In vivo quality assurance of volumetric modulated arc therapy for ano-rectal cancer with thermoluminescent dosimetry and image-guidance.
OBJECTIVE
To assess in vivo dose distribution using cone-beam computed tomography scans (CBCTs) and thermoluminescent dosimeters (TLDs) in patients with anal or rectal cancer treated with volumetric modulated arc therapy (VMAT).


METHODS
Intracavitary (IC) in vivo dosimetry (IVD) was performed in 11 patients using adapted endorectal probes containing TLDs, with extra measurements at the perianal skin (PS) for anal margin tumors. Measured doses were compared to calculated ones obtained from image fusion of CBCT with CT treatments plans.


RESULTS
A total of 55 IC and 6 PS measurements were analyzed. IC TLD median planned and measured doses were 1.81 Gy (range, 0.25-2.02 Gy) and 1.82 Gy (range, 0.19-2.12 Gy), respectively. In comparison to the planned doses all IC TLD dose measurements differed by a median dose of 0.02 Gy (range, -0.11/+0.19 Gy, p=0.102) (median difference of 1.1%, range -6.1%/+10.6%). Overall, 95% of IC measurements were within ±7.7% of the expected percentage doses and only 1 value was above +10%. For PS measurements, only one was not within ±7.7% of expected values (i.e., -8.9%).


CONCLUSIONS
Image guidance using CBCT for IVD with TLDs is helpful to validate the delivered doses in patients treated with VMAT for ano-rectal tumors.
Department of Radiation Oncology, Geneva University Hospital, Switzerland. Electronic address: Giovanna.Dipasquale@hcuge.ch.
Giovanna
G
Dipasquale
Department of Radiation Oncology, Geneva University Hospital, Switzerland.
Philippe
P
Nouet
Department of Radiation Oncology, Geneva University Hospital, Switzerland.
Michel
M
Rouzaud
Department of Radiation Oncology, Geneva University Hospital, Switzerland.
Angèle
A
Dubouloz
Department of Radiation Oncology, Geneva University Hospital, Switzerland.
Raymond
R
Miralbell
Department of Radiation Oncology, Geneva University Hospital, Switzerland.
Thomas
T
Zilli
D000368:Aged; D000369:Aged, 80 and over; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D001005:Anus Neoplasms / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D011785:Quality Assurance, Health Care; D011854:Radiochemistry; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D012004:Rectal Neoplasms / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy*; D013819:Thermoluminescent Dosimetry / Q000379:methods*
Anal cancer; CBCT; In vivo dosimetry; Rectal cancer; VMAT