Cervical cancer is the fourth most common cancer among women worldwide, accounting for significant morbidity and mortality annually [1,2]. Radiotherapy is a cornerstone in the treatment of locally advanced cervical cancer, and recent advancements, such as intensity-modulated radiotherapy (IMRT), have improved target conformity while minimizing exposure to surrounding organs at risk (OARs) [3,4]. Proper patient positioning during radiotherapy plays a critical role in optimizing dose delivery, ensuring better outcomes, and reducing treatment-related toxicities [5].

The supine position is traditionally used for radiotherapy, offering ease of setup and patient comfort. However, the prone position, particularly with the use of a belly board, has been reported to reduce radiation exposure to the small bowel and other critical structures [6]. Studies have shown that prone positioning can decrease acute and late gastrointestinal toxicities while maintaining comparable target volume coverage [7,8]. This is particularly important as the small bowel and rectum are highly sensitive to radiation and their sparing is crucial for minimizing adverse effects [9].

Advancements in radiotherapy techniques, such as IMRT, have significantly improved the therapeutic ratio in treating gynecologic cancers by delivering high doses to target volumes while sparing adjacent normal tissues [10]. However, the success of IMRT is highly dependent on accurate patient positioning and reproducibility throughout treatment. Prone positioning, aided by a belly board, has shown potential to minimize small bowel exposure by displacing it from the treatment field [11]. Despite these advantages, the prone position can pose challenges, including patient discomfort and increased setup time, which may impact treatment accuracy and compliance [12]. Therefore, it is essential to systematically evaluate the dosimetric benefits and limitations of both supine and prone positions to establish evidence-based guidelines for positioning during IMRT in cervical cancer patients.

Several dosimetric studies have compared supine and prone positions in pelvic malignancies, but there is limited literature specifically evaluating these parameters in carcinoma cervix patients undergoing IMRT [13]. This study aims to address this gap by performing a detailed dosimetric comparison of supine and prone positions in a cohort of carcinoma cervix patients, focusing on target volume coverage and dose to OARs, such as the bladder, rectum, and small bowel.

Study Design:  This prospective study was conducted at the MNJ Institute of Oncology and Regional Cancer Centre, Hyderabad, over 24 months, with a sample size of 25 carcinoma cervix patients.

Inclusion Criteria:  Patients aged 30–65 years with histopathologically proven carcinoma cervix in FIGO stages IB-IIIB were included. They had performance status 1–3 per the Eastern Cooperative Oncology Group (ECOG) criteria, normal complete blood counts, and normal liver and kidney function tests.

Exclusion Criteria:  Patients with distant metastases, FIGO stages IA, IIIC, or IV, poor performance status, immunocompromised conditions (including HIV positivity), or synchronous multiple malignancies were excluded from the study.

Patient Selection: A total of 25 eligible patients who presented to the Department of Radiation Oncology at MNJ Institute of Oncology were enrolled. The patients were selected based on the defined inclusion criteria.

Investigations: Diagnostic evaluations included

• Histopathological examination of cervical biopsy
• Complete blood count (CBC), liver and kidney function tests, and viral markers
• Chest X-ray
• Ultrasound scan of the abdomen and pelvis

Radiotherapy Planning

Imaging and Simulation

• Patients were immobilized using pelvic ray casts in both supine and prone positions.
• CT simulation scans from the diaphragm to the trochanter were performed for each position.
• A belly board was used for prone positioning, and intravenous contrast was administered for better delineation.
• A bladder filling protocol was followed, but no instructions were given for rectal filling.

Fig 1:  Prone

Fig 2:  Supine

Target Volumes and Organs at Risk

Target volumes and organs at risk were delineated on all axial CT slices with 3 mm thickness, following International Commission on Radiation Units and Measurements (ICRU) recommendations.

• Gross Tumor Volume (GTV): Macroscopic tumor, cervix, and corpus uteri.
• CTV1: Involved nodes and draining regional nodal groups (common iliac, internal iliac, external iliac, obturator, and presacral).
• CTV Primary (CTV2 and CTV3): Gross tumor volume, uterine corpus, parametrium, vagina, and ovaries.
• CTV2 (Uterus): Includes uterine corpus, cervix, and vagina based on clinical findings and MRI.
• CTV3 (Parametrium): Extends from the cervix to the pelvic wall, covering connective tissue, vessels, nerves, and fibrous structures.
• PTV: Combined CTV1 and CTV primary, with a 10 mm margin to account for setup errors.

Organs at Risk (OAR):

• Anorectum: Contoured from the anal verge to the sigmoid flexure.
• Bowel Bag: Small and large bowel contoured together, ending 1 cm above the PTV.
• Bladder: Contoured from the base to the dome.
• Femoral Heads: Contoured from the femoral head to the level of the lesser trochanter.

Radiotherapy Technique

Treatment planning and dose-volume histogram (DVH) analysis were performed using Varian software. IMRT plans were generated for supine and prone positions using a seven-beam arrangement (angles: 180°, 30°, 330°, 80°, 280°, 130°, 230°). Dose prescription:

• Target Dose: 50.4 Gy delivered in 1.8 Gy fractions, five days a week.
• Planning Constraints: Priority was given to minimizing the dose to OARs while maintaining >95% PTV coverage.

Starting dose constraints for OARs included:

• Small bowel: V50.4Gy = 0%, V43Gy ≤ 10%, V33Gy ≤ 20%
• Bladder: V50Gy ≤ 30%
• Rectum: V50Gy ≤ 20%

Dose-Volume Histogram Analysis

The DVH parameters analyzed included:

• Target volumes: Total volume, PTV95%, PTV100%, PTV105%
• Organs at Risk: Relative volumes at V10Gy, V20Gy, V30Gy, V40Gy, V45Gy, and V50Gy.
  Average volume (cc) and mean dose (Dmean) for PTV and OARs were compared between supine and prone positions.

Table 1:  Descriptive statistic analysis for combined Prone and Supine

25% - First Quartile Q1, 50% - Second Quartile Q2, 75% - Third Quartile Q3

The data in the Table 1 summarizes key metrics across 50 observations. The average age is 45 years, ranging from 25 to 58. For the Planning Target Volume (PTV), the average volume is 1566.55, with a mean dose (Dmean) of 50.15 and consistent dose coverage at PTV 95% (0.96783). The Spinal Cord (SB) volume averages 1569.73, with dose metrics decreasing from V10 (0.91288) to V50 (0.03727). The Bladder (B) volume averages 139.774, with high coverage at V10 and V20, while lower doses (V30 to V50) progressively decrease. The Rectum (R) volume averages 41.31, with consistent dose coverage at V10 and V20 but minimal exposure at V50 (0.05974). Percentiles (Q1, Q2, Q3) highlight the spread and variability across parameters, illustrating dose-volume relationships for each region.

Table 2:  Supine Analysis

The data in the Table 2 summarizes metrics for 25 supine cases. The average age is 45 years, with a PTV (Planning Target Volume) mean volume of 1516.42 and a Dmean of 50.28. PTV95% coverage averages 0.9767, while PTV100% shows variability with a mean of 2.078. The SB (Spinal Cord) volume averages 1630.5, with dose metrics decreasing from SB V10 (0.8912) to SB V50 (0.0571). The bladder (B) volume averages 134.21, with high coverage at V10 (1) and V20 (0.9952), while lower doses (V30 to V50) decrease progressively. The rectum (R) volume averages 36.7, with full dose coverage at V10 and V20, and minimal exposure at V50 (0.0742). The data shows consistent dose-volume relationships with some variability across metrics.

Table 3:  Prone Analysis

The data in Table 3 summarizes metrics for 25 prone cases. The average age is 45 years, with a mean PTV (Planning Target Volume) of 1616.68 and a Dmean of 50.02. PTV95% coverage averages 0.959, while PTV100% has a mean of 0.519. The SB (Spinal Cord) volume averages 1508.96, with decreasing dose metrics from SB V10 (0.935) to SB V50 (0.017). Rectum (R) volume averages 44.34, showing high dose coverage at V10 (0.999) and V20 (0.998), with lower doses at V50 (0.045). Bladder (B) volume averages 145.34, with full coverage at V10 (1) and V20 (0.984), decreasing across higher dose levels. The data demonstrates consistent dose-volume relationships with some variability across metrics.

Study results

TARGET VOLUME: The mean volume of the PTV was1616.68 +_ 172.8504 in prone position and in supine position it is 1561 +_186.50, Demean was 50.02302 in prone and 50.282 in supine , PTV 95% Was 95.896 % in prone and in supine it is 97.669% , PTV 100% was 51.9% in prone and 20.7 % in supine , PTV 105% WAS 0.5 % in prone and 0.53% in Supine

INTERPRETATION: The volume of PTV is more in prone position and volume receiving 100 % of dose is high in prone position, but Dmean, PTV 95% , PTV 105% are            almost equal in prone and supine position.

SMALL BOWEL : The mean volume of small bowel involved in our radiation field is 1508+_178.65 cc in prone position and 1630+_168.5 cc in supine position ,mean V10 is 93% and 89% in pp and sp respectively , V20 is 69% (pp) 76% (sp) , V30 40% (Pp) 48% (Sp) , V40% is 16%(pp) 28% (sp) ,V45% 9.6% (pp) 21% (sp)          ,V50% 1.7% (pp) 5.7%(sp).

INTERPRETATION

The volume of small bowel included in radiation fields was significantly low almost 120 cc lower in prone position , the mean volume receiving 10 GY , 20 GY, 30 GY , 40 GY, 45 GY, 50 GY was significantly low in prone position significant reduction is seen at higher doses that is at 40 GY , 45 GY , 50 GY.

BLADDER : The mean volume of bladder in our radiation field in prone is 145.34+_79 and supine position is 134+_88 cc , the mean V10 100%(Pp) 100%(Sp) , V20 98.4%(Pp) 99.5%(Sp)         , V30 85.8% (Pp) 85.6%(Sp) , V40 58.5%(Pp) 68%(Sp) , V45 43%(Pp) 50%(Sp), V50 58%(Pp) 8.9% (Sp)

INTERPRETATION

The volume of bladder included in radiation fields was equal in both supine and prone positions , volume receiving 10 GY ,20 GY , 30 GY , 40 GY , 45 GY was almost same in both positions , but volume receiving 50 GY is low in supine compared to prone position.

RECTUM: The mean volume of rectum included in radiation fields is 44.336 +_14.92 cc in prone position and36.7 +_10.6cc in supine position , the mean V10 99.8%(Pp) 100% (Sp) , V20 99.7%(Pp) 100 ( Sp), V30 98%(Pp) 85% (Sp) , V40 83.3%(Pp) 93.5%(Sp) , V 45 73 % (Pp) 83% (Sp), V50 4.5 %(Pp) 7.4 %(Sp)

INTERPRETATION

The volume of rectum included in radiation fields was significantly low in supine position which was almost 10cc low in supine position , the mean volume receiving 10 GY , 20 GY ,30 GY Was almost same in both positions , where as volume receiving 40 GY , 45 GY , 50 GY was low in prone position , due to movement of rectum away from treatment volume in prone position.

Carcinoma cervix remains a significant health concern, particularly in developing countries, where it ranks as the fourth most common malignancy in women. Despite its high prevalence, it is one of the most curable gynecological cancers when detected early and treated appropriately. The disease primarily affects the quality of life in women due to its associated morbidities, but advancements in therapeutic strategies, particularly radiotherapy, have significantly improved outcomes. Combining radiotherapy with concurrent platinum-based chemotherapy forms the cornerstone of treatment for stages IB to IVA carcinoma cervix.

The primary objective of radiotherapy is to ensure adequate coverage of the tumor volume while minimizing radiation exposure to adjacent organs, thereby reducing treatment-related toxicities and improving patient outcomes. IMRT is a cutting-edge technique for external beam radiation therapy in carcinoma cervix patients. However, due to the anatomical overlap between target structures such as regional lymph nodes, parametrium, and uterus with surrounding organs at risk, pelvic irradiation often results in gastrointestinal and genitourinary morbidity [14]. Concurrent radiotherapy with platinum-based chemotherapy can further exacerbate these effects, with severe cases leading to total necrosis of the uterus [15]. The likelihood of treatment-related side effects is influenced by factors such as the radiation dose, the volume irradiated, and the patient’s surgical history [16].

The use of the prone position, aided by bowel displacement devices, has demonstrated a reduction in the radiation dose received by the small bowel, potentially mitigating treatment-related toxicity [14-19]. Roeske et al. highlighted the ability of IMRT to lower small bowel volumes irradiated to ≥45 Gy (V45 < 250 cc) in both prone and supine positions, significantly reducing acute bowel morbidity [20]. Similarly, Portelance et al. found that IMRT significantly reduced the small bowel volume receiving ≥45 Gy when compared to conventional 2-field and 4-field techniques, further supporting its effectiveness in reducing bowel toxicity [21]. Heron et al. demonstrated a 52% reduction in small bowel volume irradiation in the supine position using IMRT, further emphasizing its role in minimizing bowel exposure and associated toxicities [22].

Based on these findings, our study aimed to evaluate the effectiveness of IMRT in both prone and supine positions. By exploring the differences in radiation exposure to the small bowel in these positions, we sought to identify strategies to further reduce treatment-related bowel toxicity and improve the overall therapeutic ratio for patients with carcinoma cervix.

In this prospective study titled “A Dosimetric Analysis on Supine and Prone Positions in Carcinoma Cervix Patients Using Intensity-Modulated Radiotherapy at a Tertiary Cancer Centre”,  we demonstrated that pelvic IMRT in the prone position, utilizing a belly board, effectively reduces the small bowel volume receiving doses greater than 30 Gy. This approach also achieves better planning target volume (PTV) coverage, enhanced dose distribution, and improved homogeneity compared to the supine position in cervical cancer patients.

Additionally, the target volume receiving 100% of the prescribed dose was higher in the prone position. If this technique were implemented clinically across separate patient groups treated in either position, treatment-related toxicities could be more accurately assessed. However, daily reproducibility in the prone position poses challenges, and patient comfort must be a key consideration during radiotherapy. The prone position may be less comfortable for patients during daily treatments. Therefore, it is recommended that patients be treated in both supine and prone positions to comprehensively evaluate quality of life, treatment tolerability, and associated difficulties.

ETHICAL CLEARANCE: Ethical Clearance Certificate was obtained from the Institutional Ethics Committee (IEC) prior to commencement of study

CONFLICT OF INTEREST: Nil - No conflict of interest

SOURCE OF FUNDING: Self

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