C. Brooks

Organ-sparing Intensity-modulated Radiotherapy for Anal Cancer using the ACTII Schedule: A Comparison of Conventional and Intensity-modulated Radiotherapy Plans

AIMSnConventional external beam radiotherapy for anal cancer is associated with a high rate of treatment-related morbidity. The purpose of this retrospective study was to compare the dosimetric advantages of three intensity-modulated radiotherapy (IMRT) plans with the conventional plan with regards to organs at risk avoidance delivering the ACTII schedule of 50.4xa0Gy in 1.8xa0Gy/fraction: 17 fractions for phase 1 and 11 fractions for phase 2.nnnMATERIALS AND METHODSnTen anal cancer patients (T1-3 N0-3) treated with the conventional plan using four fields and conformal boost were identified. The phase 1 planning target volume (PTV) included tumour, anal canal and inguinal, peri-rectal and internal/external iliac nodes. Phase 2 included identifiable disease only. Three step-and-shoot IMRT plans were generated: IMRT1: phase 1 inverse-planned IMRT with two- to four-field conformal phase 2; IMRT2: both phase 1 and phase 2 inverse-planned IMRT; IMRT3: phase 1 IMRT and phase 2 forward-planned IMRT. All IMRT plans were then compared against the conventional plan on PTV coverage, small bowel, genitalia, femoral heads, bladder and healthy tissue dose volume information.nnnRESULTSnWhile achieving similar PTV coverage compared with the conventional plan, significant dose reductions were observed for IMRT plans in external genitalia, small bowel and healthy tissue. Reductions were also observed in the femoral heads and bladder.nnnCONCLUSIONSnIMRT significantly reduces the dose to organs at risk while maintaining excellent PTV coverage in anal cancer radiotherapy.

Cone Beam Computed Tomography-Derived Adaptive Radiotherapy for Radical Treatment of Esophageal Cancer

PURPOSEnTo investigate the potential for reduction in normal tissue irradiation by creating a patient specific planning target volume (PTV) using cone beam computed tomography (CBCT) imaging acquired in the first week of radiotherapy for patients receiving radical radiotherapy.nnnMETHODS AND MATERIALSnPatients receiving radical RT for carcinoma of the esophagus were investigated. The PTV is defined as CTV(tumor, nodes) plus esophagus outlined 3 to 5 cm cranio-caudally and a 1.5-cm circumferential margin is added (clinical plan). Prefraction CBCT are acquired on Days 1 to 4, then weekly. No correction for setup error made. The images are imported into the planning system. The tumor and esophagus for the length of the PTV are contoured on each CBCT and 5 mm margin is added. A composite volume (PTV1) is created using Week 1 composite CBCT volumes. The same process is repeated using CBCT Week 2 to 6 (PTV2). A new plan is created using PTV1 (adaptive plan). The coverage of the 95% isodose of PTV1 is evaluated on PTV2. Dose-volume histograms (DVH) for lungs, heart, and cord for two plans are compared.nnnRESULTSnA total of 139 CBCT for 14 cases were analyzed. For the adaptive plan the coverage of the 95% prescription isodose for PTV1 = 95.6% +/- 4% and the PTV2 = 96.8% +/- 4.1% (t test, 0.19). Lungs V20 (15.6 Gy vs. 10.2 Gy) and heart mean dose (26.9 Gy vs. 20.7 Gy) were significantly smaller for the adaptive plan.nnnCONCLUSIONSnA reduced planning volume can be constructed within the first week of treatment using CBCT. A single plan modification can be performed within the second week of treatment with considerable reduction in organ at risk dose.

Proposed genitalia contouring guidelines in anal cancer intensity-modulated radiotherapy

OBJECTIVEnIntensity-modulated radiotherapy (IMRT) for anal canal carcinoma (ACC) is associated with favourable toxicity outcomes. Side effects include sexual dysfunction, skin desquamation, pain and fibrosis to perineum and genitalia region. The genitalia are situated anterior to the primary ACC between two inguinal regions providing a challenging structure to avoid. Techniques improving outcomes require robust, consistent genitalia contouring to ensure standardization and production of fully optimized IMRT plans. Official recommendations for genitalia contouring are lacking. We describe a potential genitalia contouring atlas for ACC radiotherapy.nnnMETHODSnFollowing a review of genitalia CT anatomy, a contouring atlas was generated for male and female patients positioned prone and supine. Particular attention was paid to the reproducibility of the genitalia contour in all planes.nnnRESULTSnMale and female genitalia positioned prone and supine are described and represented visually through a contouring atlas. Contoured areas in males include penis and scrotum, and in females include clitoris, labia majora and minora. The muscles, bone, prostate, vagina, cervix and uterus should be excluded. The genitalia contour extends laterally to inguinal creases and includes areas of fat and skin anterior to the symphysis pubis for both genders.nnnCONCLUSIONnThis atlas provides descriptive and visual guidance enabling more consistent genitalia delineation for both genders when prone and supine. The atlas can be used for other sites requiring radiotherapy planning.nnnADVANCES IN KNOWLEDGEnThis atlas presents visual contouring guidance for genitalia in ACC radiotherapy for the first time. Contouring methods provide reproducible genitalia contours that allow the provision of accurate dose toxicity data in future studies.

Cardiac volume effects during chemoradiotherapy for esophageal cancer (Regarding Lutkenhaus et al. Reduction in cardiac volume during chemoradiotherapy for patients with esophageal cancer).

To the Editor Lutkenhaus et al. [1] recently reported a reduction in cardiac volume for esophageal patients treated with conformal radiotherapy (CRT). They observed a median reduction of 8% assessed on cone beam CTs (CBCTs) between week 1 and 4 of treatment. 26 patients were eligible for inclusion; 20 received 41.4 Gy in 1.8 Gy fractions; and 6 received 50.4 Gy. No correlation was found between mean heart dose, initial tumor volume and change in heart volume. We found the Lutkenhaus paper interesting and were inspired to evaluate our esophagus patients to see if we saw a similar effect. At our center we treat approximately 50 patients a year with radical radiotherapy for esophageal cancer, of which 29 are VMAT and the rest are CRT. To assess whether an observable change in heart volume occurs during treatment, CBCTs were collected for 10 patients (8 VMAT and 2 CRT; all treated to 54 Gy in 30 fractions). Only mid or lower esophageal carcinoma patients were included to enable heart visualization on CBCT. The heart was outlined on each available CBCT and the volume compared to the first available CBCT and the planning CT heart volume. The superior border was outlined similarly for all CBCTs to avoid discrepancy. Outlining

Target volume motion during anal cancer image guided radiotherapy using cone-beam computed tomography

OBJECTIVEnLiterature regarding image-guidance and interfractional motion of the anal canal (AC) during anal cancer radiotherapy is sparse. This study investigates interfractional AC motion during anal cancer radiotherapy.nnnMETHODSnBone matched conexa0beam CT (CBCT) images were acquired for 20 patients receiving anal cancer radiotherapy allowing population systematic and random error calculations. 12 were selected to investigate interfractional AC motion. Primary anal gross tumour volume and clinical target volume (CTVa) were contoured on each CBCT. CBCT CTVa volumes were compared to planning CTVa. CBCT CTVa volumes were combined into a CBCT-CTVa envelope for each patient. Maximum distortion between each orthogonal border of the planning CTVa and CBCT-CTVa envelope was measured. Frequency, volume and location of CBCT-CTVa envelope beyond the planning target volume (PTVa) was analysed.nnnRESULTSnPopulation systematic and random errors were 1 and 3u2009mm respectively. 112 CBCTs were analysed in the interfractional motion study. CTVa varied between each imaging session particularly T location patients of anorectal origin. CTVa border expansions ≥ 1u2009cm were seen inferiorly, anteriorly, posteriorly and left direction. The CBCT-CTVa envelope fell beyond the PTVaxa0≥xa050%u2009imaging sessions (n = 5). Of these CBCT CTVa distortions beyond PTVa, 44% and 32%xa0were in the upper and lower thirds of PTVa respectively.nnnCONCLUSIONnThe AC is susceptible to volume changes and shape deformations. Care must be taken when calculating or considering reducing the PTV margin to the anus. Advances in knowledge: Within a limited field of research, this study provides further knowledge of how the AC deforms during anal cancer radiotherapy.

OC-0469: Genitalia contouring in anal cancer IMRT; comparisons of volumes with and without a genitalia atlas

ESTRO 35 2016 _____________________________________________________________________________________________________ Purpose or Objective: Online CBCT pre-treatment registration (Elekta, XVI) for locally advanced cervix carcinoma (LACC) is performed by RTT’s, using a cubic Clipbox-based Volume of Interest (C-VOI) algorithm. Consecutive manual adaptation in order to fulfill the predefined criteria for LACC-registration, implies large shifts. This is suboptimal regarding setup reproducibility, challenges PTV margins and strongly depends on RTT’s experience. The objective is to determine whether the use of a Mask-based VOI (M-VOI) reduces the magnitude of manual shifts and thus is a better starting point.